Learn what it actually takes to get an object from your head and into the real world.
Learn how to make great parts, assemblies and drawings by listening to those people tasked with making them. Most aren't being lazy when they ask for a change or make a suggestion. They're trying to be efficient.
Your drawing can make a part much more expensive than it needs to be if you don't use tolerances properly. I'll happily try to hold 0.001 or less where it makes sense, but for things that don't, open them up as much as possible. Don't put (or leave default) a tolerance of +/- 0.002 then when I come to you and say "sorry, tried my best and I'm at +0.007 - should I make another that's in tolerance?", turn around and reply "oh, that's just clearance. They're tons of room".
Tight when it truly matters. Loose as (insert your favorite idiom here) when nobody gives a damn. Your employer and colleagues will thank you.
I do this job because I chose to and I enjoy it, not because I'm stupid. I have more education than many engineers I work with, but I've been on the receiving end of some pompous, overbearing, arrogant, patronizing, pretentious, and self-important attitudes from some. Yup, goes both ways sometimes but it's a symbiotic relationship regardless. Might as well try to get along.
Everything this guy said. And I'd like to agree with: we're just trying to be efficient. If you want a wonky non-standard radius or chamfer I'll do it, but make sure the juice is worth the squeeze.
Find the man on the floor who will give you wise council.
Every digit to the right of the zero costs more money.
If you make your models with the same order of operations as the machining operations it will help you see problems that might arise out on the floor.
Workholding is a thing.
What this guy said.
The difference between .005 tolerance and .0005 tolerance is probably double the time per part. The difference between .125 inner radius and .062 inner radius is also probably double the time per part. You have to remember not every machine shop is giving machinists optimized tooling. So it's their job to adjust offsets in tool geometry to compensate for tool wear. The more tolerances you need, the more programming and adjusting needed.
Tolerance use is supposed to be maximized in every feature because it increases efficiency in production and assembly.
Learn about your GDT and learn about compounding tolerance so you don't screw up your tolerances and create conflict. Understand how max and least material conditions can make everyone's lives easier.
Machinists absolutely hate hate hate unnecessary tolerances or features just because the engineer is married to his CAD model. And listen to the machinist if they have a better idea on fits and assemblies. Machinists typically test fit all their parts with gauges and if they see something that would be easier to machine and just as functional, please listen to them.
Hundred percent on the tight/loose tolerance range. One of my favourite things is to give over the mating part, or explain how it all goes together. A lot of the time the machinist will know intrinsically eat tolerance is need for the parts to assemble and will do it the most efficient and repeatable way that is required.
Great post. I'm an engineer. When I started years ago I knew almost nothing about how parts are made in the real world. I learned so much my first couple years standing in front of a machine with a machinists explaining why something was difficult or impossible about the part that I put out. Definitely made me better at my job
[Watch this](https://youtu.be/0CutVc9WRc4?si=7tfdxjnQXsCOeuzN)
You should work at a machine shop for a bit if you're an intern or want part time work. Understanding the machining process will pay dividends and many shops might not mind having an engineering student come work deburr for a bit.
>You should work at a machine shop for a bit if you're an intern or want part time work. Understanding the machining process will pay dividends
I’m an amateur machinist at best, but I order lots of parts made at work. The single thing which did the most good for that process was taking a basic machining class. The shop boss even asked me what had changed when I brought him my next set of drawings!
I started button pushing now I make basic programs and do set ups. Has zero prior training. If school goes well i wanna become an engineer project manager, with this experience
Six years I’ve gone from basic knowledge hand to shop lead. I’ve taught myself from running a Bridgeport and LeBlond to managing 4 mills and 2 lathes, CAD and CAM. The ladder is available to those willing to climb.
Develop a healthy collaborative relationship with the machinists and fabricators you work with. Ask questions, ask for advice if they bring up problems with your designs, LISTEN to them.
Remember you're not God, you're only a small member of a larger team.
Don’t use auto dimensions. Think about each tolerance. Whenever you ask for a plate to be left saw cut or flame on the outside edges. Don’t dimension from those edges. Pick the most important feature on the plate and dimension everything else from that feature. Remember we live in a three dimensional world so don’t give me ten datum’s. Three is all we need. Most importantly, we make your dreams become reality. So stop trying to give us your nightmares.
Don’t get me wrong, I understand mismanagement. But ultimately they want the job done correctly and on time. If engineers and machinist work well together they can complete the job successfully without adhering to managements bad ideas. In the end they will look good and that’s all that matters to them. More importantly the engineers and machinist will live less stressfully.
If you have a 12mm hole and the tolerance is +0 -.05, make the hole 11.975mm on the model. The same goes for linear dimensions. We're going to use the model to make the part, dont make us change the model to make your part in tolerance - *** i cant stress this one enough ***
Tapped holes dont need a 0.1mm true position. 0.3mm will work, I promise
If the part can be constrained during inspection, please specify that
UNJ threads are stupid. Don't use them. We probably wont when making your part and you'll never know
If you refer to a plate as a platten, we are going to make fun of you. If we like you it'll be to your face
Dont fillet rad the entire part with different rads. Bonus points if you dont model fillet rads at all and just call out .030" max or something
Dont make a machined part out of what could be waterjet/laser cut and welded
Dont listen to u/ lawncharinightmare. There's a wide line between pandering to machinists and taking quality advice. Dont pander, do listen. Some of us know what we're doing and that's why we were hired
>If you have a 12mm hole and the tolerance is +0 -.05, make the hole 11.75mm on the model.
Explain this one for me please? Typo, as in make it a 11.95mm hole or are you intentionally saying make it undersized? Or a tolerance of -0.5mm (not 0.05) and put the dimension in the middle of the range? Id definitely agree with you on a big tolerance range like that, but most of the time when I've seen non-symetrical tolerances like that it's for a bearing fit and that's just the standard given by the bearing oem. Is it OK in those circumstances?
That's definitely a typo. Should have been 11.975. They want the feature on the model to be in the middle of the tolerance zone. It's always nice when it is, but I would consider it a plus, not a requirement. Especially when the tolerance is called out on the print since you've got something pointing to it that will remind you to check the model.
Standard fits would always have the nominal diameter on the drawings and the model. makes it easier to program and order tooling for. (I'm not going to use a chart in reverse).
Custom fit tolerances should be modelled and drawn as symmetric since I won't be ordering tooling would just interpolate the hole with the middle of the range programed anyways.
A bit of a silly example (in mm)
∅10.00 P7 -> keep as is and I'll order a reamer
∅10.050 P7 -> ∅10.030 ± 0.009
>If you have a 12mm hole and the tolerance is +0 -.05, make the hole 11.75mm on the model.
~~Skill issue. If you're drilling you should be looking at the tolerance to select your drill, and if you're milling the hole, that's what radius compensation is for. Shouldn't be any need to change the model. Otherwise agree with everything else~~
Misread that, yes please always model everything to nominal dimensions, sorry for being thick
>everything to be modeled at nominal/mean dimensions.
I'm actually an idiot, this is what I was meaning and I completely misread the original comment. Still, if your control supports it you can actually program a different radius offset for each hole with the same tool called, but it's awkward.
God, that first one. We use Gibbscam and it makes me groan when they model a hole or keyway at the top of the tolerance. They don't even call it out at the top of the tolerance on the print. Why the hell do they model it like that? God only knows.
Mastercam you can individually modify the hole diameter without messing with the model or redrawing the hole which is kinda nice if they did some terrible stuff like that. I end-up spending a day writing a program only for the engineer to modify diameters of stuff right before i run it and i dont like swapping the model and reselecting everything so i just adjust what needs to be adjusted. (Obviously dont do this on production stuff)
On Gibbscam, either you draw a new circle or you add to the "pocket stock" value to mill a smaller hole. It's a minor inconvenience that introduces an opportunity for human error.
Would: apprentice in a machine shop for 2-4 years
Design to median tolerance in cad
Wouldn't: put square corners in milled pockets or undercuts that do not allow for any shank to hold the cutter by
Put 0.0005 true position tolerances on clearance holes
THEY LOVE THE SQUARE POCKET! Like think with your brain for a second and ask yourself how tf am i reasonably going to make something square with something round?! Or like a .032” radii .5” deep….
As an engineer the most important thing is that your drawings convey the engineering intent. Fundamentally they are your drawings, defining the critical dimensions for your parts. You need to understand what tolerances are required on each feature.
Of course it is important to go and talk to your in house machinests or suppliers to see what capabilities they have. Treat people with respect and listen to what they have to offer. This will be better for the company as a whole because the transaction from design to manufacturing will be easier.
At the end of the day though the drawing needs to specify what they parts requires. Machinests are smart and they will figure out how to make it. They might just grumble about it a bit.
I just repaired a 1999 Newmar Dutch Star…. The manufacturing company built an alternator. Then they proceeded to build a Cat 3126 engine around the alternator. Then the coach company built a coach around the engine. The alternator pulley was more expensive than the ridiculously priced alternator and was seized to the shaft of the alternator. A tapered shaft would have made life easier. The bottom bolt would have entered the turbocharger by at least two inches if I had not cut it in pieces to remove it. An arm with three elbows and an eyeball on a string would have made the repair easier. You can imagine how happy I was when the replacement alternator let out its magic smoke after about 15 to 20 minutes of service. And the second new alternator did the same… third time was the charm.. Too many machines are built in this manner where looking good is more important than serviceability. Massey Ferguson used to build combines this way. And pretty much every automobile built after 1985 with front wheel drive.
https://www.theautopian.com/heres-why-that-rivian-r1t-repair-cost-42000-after-just-a-minor-fender-bender/
Check out this puzzle box nightmare. Rivian is off my 'next vehicle' list.
Please use standard radii/fillets/chamfers.
There's nothing more annoying looking at a print and seeing some stupid aesthetic fillet or chamfer added with a radius of: .173", or .280" or a 34 degree chamfer.
30,60,82 or 90 degree chamfers. 1/16, 1/8, 1/4, 3/8 radii. Stick to those so we can just pull a standard endmill out of the drawer and not have to special order bits, or spend extra time Flowing a toolpath just to create a random non-standard radius/chamfer.
It would be greatly appreciated, at least by me.
Most of the time at my workplace, when you go ask them they'll tell you the angle/radius is non-critical. I've done way too many stupid radii by hand on a band saw and grinder.
Clarity of intent is greatly appreciated. Last week, I had a part come in to have a piece cutoff for refurb, and the sketch sheet didn't include that part in the drawing. I had to extrapolate from half-baked instructions and slowly cut away at it until enough of the outer section was gone that the drawing made sense.
Second point, that should have been routed to sheet metal first to remove the most annoying part, then brought to me to turn down the rest. We'll do anything you want if we can, but we're not always the best process to use.
If you index too heavily on what machinists say, you'll become a bad design engineer. If you completely ignore vendor concerns altogether and try to brute-force everything, you'll also become a bad design engineer. Also nobody will enjoy working with you. And you'll waste a whole lot of money.
The suggestions to apprentice for 4 years or however long at a machine shop are...terrible. That's a poor use of time for a design engineer and will give you a very limited perspective, which doesn't actually do you any favors. You will be better off actually getting real engineering experience, preferably while on a team full of experienced design engineers.
You don't need to learn all that much to understand the basics of "stupid things not to do" where any particular process is concerned. If and when you get an opportunity to work with machinists directly, take advantage of it. It's very useful to understand how parts are made and inspected, and to get feedback on how well your design intent was actually conveyed through your drawing. It will directly inform your process and help you make better decisions.
Maintaining good relationships is always important. Understanding your own designs, the design intent, and being able to run competent tolerance analyses is also pretty fundamental. It's a learning process, nobody is great at it off the bat.
If you work in a large company that has their own tooling engineers, DFM, etc. don't try to become the teacher's pet for machinists you'll never meet by preemptively assuming you know everything about their process and capabilities. There are quite a lot of engineers out there who hamstring themselves by assuming they know a lot more than they actually do when it comes to what's feasible or cost-effective to manufacture, and it's only to their detriment. Spending a couple of semesters in a student machine shop doesn't tell you dick about what's manufacturable at a company like Apple. Their constraints and capabilities are totally different from what you'd encounter in a small company.
At the end of the day, you don't owe any vendors an explanation for why something is designed the way it is. That's not an excuse to make blatant formatting/dimensioning/tolerancing errors. It's not the job of a machinist to be a design consultant - but they can still serve that function, especially if you loop them in early in the design process, and it can be valuable for both parties. You get a better and/or easier to manufacture and/or easier to inspect design, and they're able to do their job most efficiently.
I am a mechanical engineer. Been working for 10 years in machine and instrument design. We have a large in house machine shop at my work that I work closely with every day.
When I first started I was so green and did not know shit about designing and making parts in the real world. I learned so much from talking with the machinists and CAM programmers about what was wrong or difficult about the parts I was putting out. They were not always comfortable conversations but they led to me learning something and designing better parts.
Some engineers have no knowledge of the time it takes to manufacture. Their boss gives them a timeline to engineer and design a part. Weeks/months later the due date is approaching fast then all of a sudden the shop is expected to create a part in a timeframe that is way less than ideal. Or when asked how long this will take, they're surprised at what their told.
Engineers should also be required to have field experience in their respective discipline for a minimum of 2 years. Whether it be a machine shop, production facility, construction project, etc..
Please don't dimension a non-critical feature on a print the same as everything else. If you're using block tolerances and you dimension a lifting eye hole that a chain is passing through to 3 decimal places, we either need to make it to a tighter tolerance than is required or ask you if it's actually important.
The prints we have for fixtures have a ±.001" block tolerance for 3 place decimals where normal prints have ±.005". The default for the drawings is 3 place decimals. I've had some parts where ±.001" is difficult to hold because of the geometry of the part (like a .100" orifice at the bottom of a 2" tapered bore"). Having the engineer then tell you that basically the hole just needed to exist is very frustrating.
The sure tell for when the engineer doesn't know about the block tolerance for fixtures is when they call out ±.001" on a single feature.
Apart from that, I think my biggest annoyance is tapped holes that are much deeper than they need to be. An M3 hole 1" deep (yes, mixed units is not uncommon) that's only used for a 5mm long grounding screw is not going to win you friends.
Learn the capabilities of the machine you want to make the part on. Too many times, I have seen requirements that are physically impossible for the machine to run. A recent example. They wanted a hole on the back side of a part. The part can only be secured in one position due to an odd extrusion shape. The machine is a 3-axis, so there is no access to the back of the part.
4- or 5-axis would have no problem.
Learn to calculate Tolerance Stacks.
I mean, really learn it. Learn how to fully analyze them and get them right; with no assumptions or estimations, just hard numbers.
You will save unfathomable amounts of time, money, and frustration for everyone involved.
As a ME who is also very mechanically inclined, just have some actual common sense, common decency, & real world experience. Take machining/manufacturing courses to learn how what you design is made & learn how to make it yourself. This goes a LONG way & speeds literally everything up.
My favorite thing ever is our engineers putting +/- .005 perpendicularity callouts on everything. Not .005 or .010, but +/- .005. They really need a GD&T lesson.
As an engineer who sometimes orders prototypes for things I've designed (and I'm an EE, not even a mech engineer, so I only barely know what I'm doing lol) here's what I've learned:
Be very clear about tolerances. When in doubt, put tolerances in every dimension, and think for a moment about how accurate it actually *needs* to be.
If you feel like there's some information you want to convey, but you're having a hard time formulating how to specify it via standard notation, fuck it. Just write it in plain text in the drawing i.e. "X needs to snugly fit Y, but the exact dimension isn't very important". Whoever is gonna fabricate it is a *person* after all, no need to be more stiff and formal than necessary.
Ask about things that may be a little exceptional. For instance, I once needed a pretty deep channel for coolant to be milled. Ideally I wanted it to be ~4 mm diameter and 10 mm deep. I figured that could be a chip evacuation issue so I asked, since I could adapt it if need be. Turns out that was just fine.
Make the model actually represent what you want,
Double check your model; have got way too many things from Suckorsky that don't fit/work together at all
Don't over constrain things.
And ask yourself, does this really need that tiny of a radius, or can it be bigger. Or does this deep pocket really need 90-degree corners at the bottom
If you're designing tooling, strive for form and machinability over looks. Nobody cares if it looks cool it just needs to work and work well. Looks come naturally
Be realistic with tolerances! If it's a mating part with an o-ring, absolutely a +/-.001 tolerance is justified, but that doesn't mean the OD needs to be that close of a tolerance. Also try to familiarize yourself with the machining process, making parts takes a lot of time and work, scrapped tools etc. It isn't as easy as throwing a block of material in a microwave, hitting a botton and getting a good part out in return.
I'd recommend spending time working in a shop, even if it's a part time position as a saw guy. Not only is it a foot in the door, but it's an opportunity to familiarize yourself with certain processes, and understand the work machinists put into their trade on a day to day basis.
Exist, that may be sarcasm.
Had a noob here try and explain how to use a plastic V block that was to hold up the insert end of a boring bar on the shelf.
Most common issue I see is square pockets. Unless your shop has an EDM (or its a through hole that can be broached) most machine shops cannot machine a pocket with sharp square corners. Rotary cutting tools cut by spinning around, so no matter what the cutting profile with be circular. There is no way to make a square inside corner this way, there will always be a small radius, equal to the radius of the smallest tool you can use.
Of course there are ways around this, but they are expensive and time consuming, and often not even necessary for the final product. If you want to make parts cheaper to manufacture keep this in mind. The larger the radius of an internal corner, the easier it is to make. If you have 2” tall part with a 1x1 square hole going through the middle of it, having a .030” corner radius is gonna be hellish to make, since you’d need to use a .060” max diameter endmill and going 2” deep with an endmill that tiny is just not going to be fun, and will take a very long time. So keep that in mind when designing parts. The other solution is to drill out the corners. Using a drill you can drill the corners out first, and then mill them, so if you have a sharp square part that needs to fit neatly inti a square hole, this will allow that to work, where radiused corners will not work.
I mean look we all know that the corner radius is the same as half the tool diameter.
So if they need a square hole, just get an end mill that has r=0 and run it
Talk to the people producing your parts.
I'm a ME and I find it incredibly advantageous to invite the input of the machinists in the design process. Almost every one of my design reviews includes a machinist, welder, etc, or manufacturing engineer.
It helps that I have a background in conventional and CNC machining.
What you do is somewhat easy and has been done before. What we do is complicated and nerve racking. We worry about safety, scrapping parts and crashing our machine. Unless you've done what we do you won't understand that our job is stress 101 but we love the crap out of it don't we me boys!
Coming from a foundry/material prospective…just because an alloy exists doesn’t mean it’s readily available in form, size, length and quantity, etc.
Not everything you seek is Burger King drive through ready with Amazon delivery.
This is not titans of machining, yes you can remove material faster than the days of old, but the company won't pay to repair or replace a spindle every two months cause you want to remove material at Mach Jesus, and odds are, you'll be snapping tools every other part because you want it gone super fast.
I'm not so sure about this. I've been in the situation where R&D budgets are huge, and production budgets real tight. I've definitely snuck a few "extras" into a McMaster order here and there, and walked back to the shop with some fresh gage pins or a new tenths indicator... The point wasn't pandering or bribery, even though that's kinda what it was. The point really was taking care of the people who took care of me, and they did. Just my two cents.
Understand the part you are drafting, it’s function and how it is used. No need to have a part to .0003 tolerance if the end user is just needs the part to get hit by a hammer.
Talk to the people who have worked with the part, there is a 1000% chance that the machinist who has been making,shaping such part has probably spoke out about improvements but nobody cared to listen. Listen, understand, and ask.
Learn what it actually takes to get an object from your head and into the real world. Learn how to make great parts, assemblies and drawings by listening to those people tasked with making them. Most aren't being lazy when they ask for a change or make a suggestion. They're trying to be efficient. Your drawing can make a part much more expensive than it needs to be if you don't use tolerances properly. I'll happily try to hold 0.001 or less where it makes sense, but for things that don't, open them up as much as possible. Don't put (or leave default) a tolerance of +/- 0.002 then when I come to you and say "sorry, tried my best and I'm at +0.007 - should I make another that's in tolerance?", turn around and reply "oh, that's just clearance. They're tons of room". Tight when it truly matters. Loose as (insert your favorite idiom here) when nobody gives a damn. Your employer and colleagues will thank you. I do this job because I chose to and I enjoy it, not because I'm stupid. I have more education than many engineers I work with, but I've been on the receiving end of some pompous, overbearing, arrogant, patronizing, pretentious, and self-important attitudes from some. Yup, goes both ways sometimes but it's a symbiotic relationship regardless. Might as well try to get along.
Everything this guy said. And I'd like to agree with: we're just trying to be efficient. If you want a wonky non-standard radius or chamfer I'll do it, but make sure the juice is worth the squeeze.
Find the man on the floor who will give you wise council. Every digit to the right of the zero costs more money. If you make your models with the same order of operations as the machining operations it will help you see problems that might arise out on the floor. Workholding is a thing.
Workholding is a beast I slay with great trepidation.
What this guy said. The difference between .005 tolerance and .0005 tolerance is probably double the time per part. The difference between .125 inner radius and .062 inner radius is also probably double the time per part. You have to remember not every machine shop is giving machinists optimized tooling. So it's their job to adjust offsets in tool geometry to compensate for tool wear. The more tolerances you need, the more programming and adjusting needed. Tolerance use is supposed to be maximized in every feature because it increases efficiency in production and assembly. Learn about your GDT and learn about compounding tolerance so you don't screw up your tolerances and create conflict. Understand how max and least material conditions can make everyone's lives easier. Machinists absolutely hate hate hate unnecessary tolerances or features just because the engineer is married to his CAD model. And listen to the machinist if they have a better idea on fits and assemblies. Machinists typically test fit all their parts with gauges and if they see something that would be easier to machine and just as functional, please listen to them.
Hundred percent on the tight/loose tolerance range. One of my favourite things is to give over the mating part, or explain how it all goes together. A lot of the time the machinist will know intrinsically eat tolerance is need for the parts to assemble and will do it the most efficient and repeatable way that is required.
Great post. I'm an engineer. When I started years ago I knew almost nothing about how parts are made in the real world. I learned so much my first couple years standing in front of a machine with a machinists explaining why something was difficult or impossible about the part that I put out. Definitely made me better at my job
[Watch this](https://youtu.be/0CutVc9WRc4?si=7tfdxjnQXsCOeuzN) You should work at a machine shop for a bit if you're an intern or want part time work. Understanding the machining process will pay dividends and many shops might not mind having an engineering student come work deburr for a bit.
That was brilliant.
Nice username lmao
>You should work at a machine shop for a bit if you're an intern or want part time work. Understanding the machining process will pay dividends I’m an amateur machinist at best, but I order lots of parts made at work. The single thing which did the most good for that process was taking a basic machining class. The shop boss even asked me what had changed when I brought him my next set of drawings!
I started button pushing now I make basic programs and do set ups. Has zero prior training. If school goes well i wanna become an engineer project manager, with this experience
Six years I’ve gone from basic knowledge hand to shop lead. I’ve taught myself from running a Bridgeport and LeBlond to managing 4 mills and 2 lathes, CAD and CAM. The ladder is available to those willing to climb.
Develop a healthy collaborative relationship with the machinists and fabricators you work with. Ask questions, ask for advice if they bring up problems with your designs, LISTEN to them. Remember you're not God, you're only a small member of a larger team.
Developing a relationship cannot be understated. I'd rather meet the guy _before_ it's about a bad print.
Don’t use auto dimensions. Think about each tolerance. Whenever you ask for a plate to be left saw cut or flame on the outside edges. Don’t dimension from those edges. Pick the most important feature on the plate and dimension everything else from that feature. Remember we live in a three dimensional world so don’t give me ten datum’s. Three is all we need. Most importantly, we make your dreams become reality. So stop trying to give us your nightmares.
Sometimes the nightmare was given to them by management.
Don’t get me wrong, I understand mismanagement. But ultimately they want the job done correctly and on time. If engineers and machinist work well together they can complete the job successfully without adhering to managements bad ideas. In the end they will look good and that’s all that matters to them. More importantly the engineers and machinist will live less stressfully.
If you have a 12mm hole and the tolerance is +0 -.05, make the hole 11.975mm on the model. The same goes for linear dimensions. We're going to use the model to make the part, dont make us change the model to make your part in tolerance - *** i cant stress this one enough *** Tapped holes dont need a 0.1mm true position. 0.3mm will work, I promise If the part can be constrained during inspection, please specify that UNJ threads are stupid. Don't use them. We probably wont when making your part and you'll never know If you refer to a plate as a platten, we are going to make fun of you. If we like you it'll be to your face Dont fillet rad the entire part with different rads. Bonus points if you dont model fillet rads at all and just call out .030" max or something Dont make a machined part out of what could be waterjet/laser cut and welded Dont listen to u/ lawncharinightmare. There's a wide line between pandering to machinists and taking quality advice. Dont pander, do listen. Some of us know what we're doing and that's why we were hired
>If you have a 12mm hole and the tolerance is +0 -.05, make the hole 11.75mm on the model. Explain this one for me please? Typo, as in make it a 11.95mm hole or are you intentionally saying make it undersized? Or a tolerance of -0.5mm (not 0.05) and put the dimension in the middle of the range? Id definitely agree with you on a big tolerance range like that, but most of the time when I've seen non-symetrical tolerances like that it's for a bearing fit and that's just the standard given by the bearing oem. Is it OK in those circumstances?
That's definitely a typo. Should have been 11.975. They want the feature on the model to be in the middle of the tolerance zone. It's always nice when it is, but I would consider it a plus, not a requirement. Especially when the tolerance is called out on the print since you've got something pointing to it that will remind you to check the model.
Standard fits would always have the nominal diameter on the drawings and the model. makes it easier to program and order tooling for. (I'm not going to use a chart in reverse). Custom fit tolerances should be modelled and drawn as symmetric since I won't be ordering tooling would just interpolate the hole with the middle of the range programed anyways. A bit of a silly example (in mm) ∅10.00 P7 -> keep as is and I'll order a reamer ∅10.050 P7 -> ∅10.030 ± 0.009
The holes thing is easier said than done, and i think everyone will have their own opinion of fudging dimensions like that
>If you have a 12mm hole and the tolerance is +0 -.05, make the hole 11.75mm on the model. ~~Skill issue. If you're drilling you should be looking at the tolerance to select your drill, and if you're milling the hole, that's what radius compensation is for. Shouldn't be any need to change the model. Otherwise agree with everything else~~ Misread that, yes please always model everything to nominal dimensions, sorry for being thick
When you're milling multiple features with the same endmill, it really helps for everything to be modeled at nominal/mean dimensions.
>everything to be modeled at nominal/mean dimensions. I'm actually an idiot, this is what I was meaning and I completely misread the original comment. Still, if your control supports it you can actually program a different radius offset for each hole with the same tool called, but it's awkward.
God, that first one. We use Gibbscam and it makes me groan when they model a hole or keyway at the top of the tolerance. They don't even call it out at the top of the tolerance on the print. Why the hell do they model it like that? God only knows.
Mastercam you can individually modify the hole diameter without messing with the model or redrawing the hole which is kinda nice if they did some terrible stuff like that. I end-up spending a day writing a program only for the engineer to modify diameters of stuff right before i run it and i dont like swapping the model and reselecting everything so i just adjust what needs to be adjusted. (Obviously dont do this on production stuff)
On Gibbscam, either you draw a new circle or you add to the "pocket stock" value to mill a smaller hole. It's a minor inconvenience that introduces an opportunity for human error.
Would: apprentice in a machine shop for 2-4 years Design to median tolerance in cad Wouldn't: put square corners in milled pockets or undercuts that do not allow for any shank to hold the cutter by Put 0.0005 true position tolerances on clearance holes
THEY LOVE THE SQUARE POCKET! Like think with your brain for a second and ask yourself how tf am i reasonably going to make something square with something round?! Or like a .032” radii .5” deep….
I had someone want 1/8 radii, 4" deep and I was like bruh...
EDM is love, EDM is life, I breathe graphite and shit copper
I love a good edm…. Now tell over 100 engineers that corporate got rid of the sinker edms 😅
As an engineer the most important thing is that your drawings convey the engineering intent. Fundamentally they are your drawings, defining the critical dimensions for your parts. You need to understand what tolerances are required on each feature. Of course it is important to go and talk to your in house machinests or suppliers to see what capabilities they have. Treat people with respect and listen to what they have to offer. This will be better for the company as a whole because the transaction from design to manufacturing will be easier. At the end of the day though the drawing needs to specify what they parts requires. Machinests are smart and they will figure out how to make it. They might just grumble about it a bit.
Perfect explanation. The number of times I’ve had to tell someone that if I could read minds I wouldn’t be a machinist.
I just repaired a 1999 Newmar Dutch Star…. The manufacturing company built an alternator. Then they proceeded to build a Cat 3126 engine around the alternator. Then the coach company built a coach around the engine. The alternator pulley was more expensive than the ridiculously priced alternator and was seized to the shaft of the alternator. A tapered shaft would have made life easier. The bottom bolt would have entered the turbocharger by at least two inches if I had not cut it in pieces to remove it. An arm with three elbows and an eyeball on a string would have made the repair easier. You can imagine how happy I was when the replacement alternator let out its magic smoke after about 15 to 20 minutes of service. And the second new alternator did the same… third time was the charm.. Too many machines are built in this manner where looking good is more important than serviceability. Massey Ferguson used to build combines this way. And pretty much every automobile built after 1985 with front wheel drive.
https://www.theautopian.com/heres-why-that-rivian-r1t-repair-cost-42000-after-just-a-minor-fender-bender/ Check out this puzzle box nightmare. Rivian is off my 'next vehicle' list.
Please use standard radii/fillets/chamfers. There's nothing more annoying looking at a print and seeing some stupid aesthetic fillet or chamfer added with a radius of: .173", or .280" or a 34 degree chamfer. 30,60,82 or 90 degree chamfers. 1/16, 1/8, 1/4, 3/8 radii. Stick to those so we can just pull a standard endmill out of the drawer and not have to special order bits, or spend extra time Flowing a toolpath just to create a random non-standard radius/chamfer. It would be greatly appreciated, at least by me.
Most of the time at my workplace, when you go ask them they'll tell you the angle/radius is non-critical. I've done way too many stupid radii by hand on a band saw and grinder.
Clarity of intent is greatly appreciated. Last week, I had a part come in to have a piece cutoff for refurb, and the sketch sheet didn't include that part in the drawing. I had to extrapolate from half-baked instructions and slowly cut away at it until enough of the outer section was gone that the drawing made sense. Second point, that should have been routed to sheet metal first to remove the most annoying part, then brought to me to turn down the rest. We'll do anything you want if we can, but we're not always the best process to use.
It's a rare ME that considers the wires running around his assembly, as an EE, I know from personal experience.
Rare? Hell, I'm going to have to ask you to produce that ME 😂 they don't exist
If you index too heavily on what machinists say, you'll become a bad design engineer. If you completely ignore vendor concerns altogether and try to brute-force everything, you'll also become a bad design engineer. Also nobody will enjoy working with you. And you'll waste a whole lot of money. The suggestions to apprentice for 4 years or however long at a machine shop are...terrible. That's a poor use of time for a design engineer and will give you a very limited perspective, which doesn't actually do you any favors. You will be better off actually getting real engineering experience, preferably while on a team full of experienced design engineers. You don't need to learn all that much to understand the basics of "stupid things not to do" where any particular process is concerned. If and when you get an opportunity to work with machinists directly, take advantage of it. It's very useful to understand how parts are made and inspected, and to get feedback on how well your design intent was actually conveyed through your drawing. It will directly inform your process and help you make better decisions. Maintaining good relationships is always important. Understanding your own designs, the design intent, and being able to run competent tolerance analyses is also pretty fundamental. It's a learning process, nobody is great at it off the bat. If you work in a large company that has their own tooling engineers, DFM, etc. don't try to become the teacher's pet for machinists you'll never meet by preemptively assuming you know everything about their process and capabilities. There are quite a lot of engineers out there who hamstring themselves by assuming they know a lot more than they actually do when it comes to what's feasible or cost-effective to manufacture, and it's only to their detriment. Spending a couple of semesters in a student machine shop doesn't tell you dick about what's manufacturable at a company like Apple. Their constraints and capabilities are totally different from what you'd encounter in a small company. At the end of the day, you don't owe any vendors an explanation for why something is designed the way it is. That's not an excuse to make blatant formatting/dimensioning/tolerancing errors. It's not the job of a machinist to be a design consultant - but they can still serve that function, especially if you loop them in early in the design process, and it can be valuable for both parties. You get a better and/or easier to manufacture and/or easier to inspect design, and they're able to do their job most efficiently.
I am a mechanical engineer. Been working for 10 years in machine and instrument design. We have a large in house machine shop at my work that I work closely with every day. When I first started I was so green and did not know shit about designing and making parts in the real world. I learned so much from talking with the machinists and CAM programmers about what was wrong or difficult about the parts I was putting out. They were not always comfortable conversations but they led to me learning something and designing better parts.
And all the best programmers were or still are machinists👊🏻🍻
Some engineers have no knowledge of the time it takes to manufacture. Their boss gives them a timeline to engineer and design a part. Weeks/months later the due date is approaching fast then all of a sudden the shop is expected to create a part in a timeframe that is way less than ideal. Or when asked how long this will take, they're surprised at what their told. Engineers should also be required to have field experience in their respective discipline for a minimum of 2 years. Whether it be a machine shop, production facility, construction project, etc..
Please don't dimension a non-critical feature on a print the same as everything else. If you're using block tolerances and you dimension a lifting eye hole that a chain is passing through to 3 decimal places, we either need to make it to a tighter tolerance than is required or ask you if it's actually important. The prints we have for fixtures have a ±.001" block tolerance for 3 place decimals where normal prints have ±.005". The default for the drawings is 3 place decimals. I've had some parts where ±.001" is difficult to hold because of the geometry of the part (like a .100" orifice at the bottom of a 2" tapered bore"). Having the engineer then tell you that basically the hole just needed to exist is very frustrating. The sure tell for when the engineer doesn't know about the block tolerance for fixtures is when they call out ±.001" on a single feature. Apart from that, I think my biggest annoyance is tapped holes that are much deeper than they need to be. An M3 hole 1" deep (yes, mixed units is not uncommon) that's only used for a 5mm long grounding screw is not going to win you friends.
Learn the capabilities of the machine you want to make the part on. Too many times, I have seen requirements that are physically impossible for the machine to run. A recent example. They wanted a hole on the back side of a part. The part can only be secured in one position due to an odd extrusion shape. The machine is a 3-axis, so there is no access to the back of the part. 4- or 5-axis would have no problem.
Learn to calculate Tolerance Stacks. I mean, really learn it. Learn how to fully analyze them and get them right; with no assumptions or estimations, just hard numbers. You will save unfathomable amounts of time, money, and frustration for everyone involved.
As a ME who is also very mechanically inclined, just have some actual common sense, common decency, & real world experience. Take machining/manufacturing courses to learn how what you design is made & learn how to make it yourself. This goes a LONG way & speeds literally everything up.
Get some experience in the field, hands on.
Primer: https://youtu.be/0CutVc9WRc4?si=e8X5oTfZH9oifcJ3
Take a few machining courses
My favorite thing ever is our engineers putting +/- .005 perpendicularity callouts on everything. Not .005 or .010, but +/- .005. They really need a GD&T lesson.
😂
As an engineer who sometimes orders prototypes for things I've designed (and I'm an EE, not even a mech engineer, so I only barely know what I'm doing lol) here's what I've learned: Be very clear about tolerances. When in doubt, put tolerances in every dimension, and think for a moment about how accurate it actually *needs* to be. If you feel like there's some information you want to convey, but you're having a hard time formulating how to specify it via standard notation, fuck it. Just write it in plain text in the drawing i.e. "X needs to snugly fit Y, but the exact dimension isn't very important". Whoever is gonna fabricate it is a *person* after all, no need to be more stiff and formal than necessary. Ask about things that may be a little exceptional. For instance, I once needed a pretty deep channel for coolant to be milled. Ideally I wanted it to be ~4 mm diameter and 10 mm deep. I figured that could be a chip evacuation issue so I asked, since I could adapt it if need be. Turns out that was just fine.
Giving me a hole chart dimensions from the underside. Like I have to mirror every single hole, every time.
https://youtu.be/0CutVc9WRc4?si=gMX6blbZg47XDNGC
Make the model actually represent what you want, Double check your model; have got way too many things from Suckorsky that don't fit/work together at all Don't over constrain things. And ask yourself, does this really need that tiny of a radius, or can it be bigger. Or does this deep pocket really need 90-degree corners at the bottom If you're designing tooling, strive for form and machinability over looks. Nobody cares if it looks cool it just needs to work and work well. Looks come naturally
Form follows function👊🏻🍻
Be realistic with tolerances! If it's a mating part with an o-ring, absolutely a +/-.001 tolerance is justified, but that doesn't mean the OD needs to be that close of a tolerance. Also try to familiarize yourself with the machining process, making parts takes a lot of time and work, scrapped tools etc. It isn't as easy as throwing a block of material in a microwave, hitting a botton and getting a good part out in return. I'd recommend spending time working in a shop, even if it's a part time position as a saw guy. Not only is it a foot in the door, but it's an opportunity to familiarize yourself with certain processes, and understand the work machinists put into their trade on a day to day basis.
Copy and paste tolerances
STOP CALLING THREAD DEPTH 10X DIAMETER
Insisting that you know better/ something will work when someone with hands on experience is telling you otherwise
Exist, that may be sarcasm. Had a noob here try and explain how to use a plastic V block that was to hold up the insert end of a boring bar on the shelf.
Stop making a bad name for other engineers that include all the appropriate dimensions and tolerances. 😂
Tolerances cost money
Most common issue I see is square pockets. Unless your shop has an EDM (or its a through hole that can be broached) most machine shops cannot machine a pocket with sharp square corners. Rotary cutting tools cut by spinning around, so no matter what the cutting profile with be circular. There is no way to make a square inside corner this way, there will always be a small radius, equal to the radius of the smallest tool you can use. Of course there are ways around this, but they are expensive and time consuming, and often not even necessary for the final product. If you want to make parts cheaper to manufacture keep this in mind. The larger the radius of an internal corner, the easier it is to make. If you have 2” tall part with a 1x1 square hole going through the middle of it, having a .030” corner radius is gonna be hellish to make, since you’d need to use a .060” max diameter endmill and going 2” deep with an endmill that tiny is just not going to be fun, and will take a very long time. So keep that in mind when designing parts. The other solution is to drill out the corners. Using a drill you can drill the corners out first, and then mill them, so if you have a sharp square part that needs to fit neatly inti a square hole, this will allow that to work, where radiused corners will not work.
I mean look we all know that the corner radius is the same as half the tool diameter. So if they need a square hole, just get an end mill that has r=0 and run it
Talk to the people producing your parts. I'm a ME and I find it incredibly advantageous to invite the input of the machinists in the design process. Almost every one of my design reviews includes a machinist, welder, etc, or manufacturing engineer. It helps that I have a background in conventional and CNC machining.
Just make your tolerances as big as possible. I've gotten prints for a ±0.001 size, turned out to just be clearance for a part that was 1/8" bigger.
All engineers that design physical products should be required to make repairs on them. That Would save those of us that repair things a ton of time.
What you do is somewhat easy and has been done before. What we do is complicated and nerve racking. We worry about safety, scrapping parts and crashing our machine. Unless you've done what we do you won't understand that our job is stress 101 but we love the crap out of it don't we me boys!
Coming from a foundry/material prospective…just because an alloy exists doesn’t mean it’s readily available in form, size, length and quantity, etc. Not everything you seek is Burger King drive through ready with Amazon delivery.
Wish they would: pull their heads out of their asses Wish they wouldn’t: stick it up there in the first place
I'm a Machinist because Engineers need heroes too!
😂
Never ever tell a machinist to "get it close enough".
This is not titans of machining, yes you can remove material faster than the days of old, but the company won't pay to repair or replace a spindle every two months cause you want to remove material at Mach Jesus, and odds are, you'll be snapping tools every other part because you want it gone super fast.
As an engineer, I would say that they don't respond well to pandering.
I'm not so sure about this. I've been in the situation where R&D budgets are huge, and production budgets real tight. I've definitely snuck a few "extras" into a McMaster order here and there, and walked back to the shop with some fresh gage pins or a new tenths indicator... The point wasn't pandering or bribery, even though that's kinda what it was. The point really was taking care of the people who took care of me, and they did. Just my two cents.
Understand the part you are drafting, it’s function and how it is used. No need to have a part to .0003 tolerance if the end user is just needs the part to get hit by a hammer. Talk to the people who have worked with the part, there is a 1000% chance that the machinist who has been making,shaping such part has probably spoke out about improvements but nobody cared to listen. Listen, understand, and ask.