Underdimensioned prints referring to the model with a generic profile callout

Hi All,

I'm checking some prints and coming across a batch that is using something that I've only ever seen with complex shaped mold cavities.

These are milled parts and have most, but not all of the dimensions there. There is a note to "check the solid model for any missing dimensions" and that "all dimensions from CAD are Basic". and also a callout for "all surfaces are PROFILE x.xx to ABC"


I'm just making a process check that the world has not changed on me while I am stuck in old ways. Are shops wanting to take in the solid model now and program toolpaths off the solid - and only see dimensions on a print for critical features? These are milled parts, not for EDM sinkers.

My initial reaction was that this was lazy, but maybe there is some merit to keep a print cleaner and just highlight the criticals

that seems to be the way things are headed. The result of laziness? Absolutely.

I work a lot from solid model assemblies. The designer gives me a step or parasolid file and I dimension each part myself. I can then make it manually, program off the wire frame, or program off the model for 3d surfacing. Very rarely do I get actual prints these days. I do like it better as I can control what dimensions I use and I no longer have to worry about missing dims.

At work we have the “lazy note” for flat parts which is basically a .060 profile call out. The parts are cut on either a plasma or laser in-house. The print really only matters if it has bends on it or has other secondary work like tapped holes. The design has to work using whatever falls off the cutting machine. The only thing a fully dimensioned print gets is better revision control.

Larry Dickman said:

that seems to be the way things are headed. The result of laziness? Absolutely.

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Overworked, and understaffed, try walking in some one else's shoes for once.

digger doug said:

Overworked, and understaffed, try walking in some one else's shoes for once.

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Amen, there are 4 of us providing manufacturing engineering support for 90 machines and 102 robots. If I can save an hour by creating a 2D print with only critical dimensions on it and send you a model for the rest, I really do not have much choice. I need that hour for something else that is so hot it is scorching my butt cheeks.

With the vast majority of manufacturing now produced by CNC via CAM software, there's little point fully dimensioning drawings anymore. In fact, dimensions are just another thing for inspection to reject it on, I've seen far too many parts scrapped because a clearance feature was out of tolerance, I'll actually ask engineers to remove dimensions before signing it off unless it's critical. As usual though, it's horses for courses, simple turned parts for example get fully dimensioned since it will likely be punched straight into the machine.

gregoryd said:

Hi All,

I'm checking some prints and coming across a batch that is using something that I've only ever seen with complex shaped mold cavitied.

These are milled parts and have most, but not all of the dimensions there. There is a note to "check the solid model for any missing dimensions" and that "all dimensions from CAD are Basic". and also a callout for "all surfaces are PROFILE x.xx to ABC"


I'm just making a process check that the world has not changed on me while I am stuck in old ways. Are shops wanting to take in the solid model now and program toolpaths off the solid - and only see dimensions on a print for critical features? These are milled parts, not for EDM sinkers.

My initial reaction was that this was lazy, but maybe there is some merit to keep a print cleaner and just highlight the criticals

Click to expand...

Typically in the aerospace r&d/prototype companies I worked at complex parts that were being cnc'd didn't warrant complex fully dimensioned prints,

1) because most machinists were too lazy to check the dimensions of parts, other than cursory checks. So a fully dimensioned print was a waste of time
2) about all the dimensions the machinists wanted was a few overall dimensions to make sure faces/lapjoints/overall lengths etc looked to be correct.
3) the most important dimensions/notes the machinist wanted was for clearance/tapped and reamed holes. as a check to make sure the programmer wasn't trying to tap a hole 10-32 when the print called out 8-32 etc etc.

I get prints from one vendor that has almost no usefull information, I concluded eventyally it was because they weren't capable/too lazy/incompetant to make decent prints. So as a result I decide what's important, and don't waste any time trying to figure out if they knew what was important.

Tonytn36 said:

Amen, there are 4 of us providing manufacturing engineering support for 90 machines and 102 robots. If I can save an hour by creating a 2D print with only critical dimensions on it and send you a model for the rest, I really do not have much choice. I need that hour for something else that is so hot it is scorching my butt cheeks.

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As I said above, I enjoy working from solid models. If I have a dimensional question I have all the answers right there, no need to track down the engineer or designer. As far as tolerance goes, we in the tool room work to near zero tolerance...meaning we go for as close to nominal as we can get.

I'll echo the time savings. A lot of times I am the one designing, programming, and building stuff for in house work. No need to dimension and tolerance everything, just the critical features will suffice. It does spill over into parts made by others, programmed by me. Same thing though, worry about the critical dimensions and the rest either don't matter or will fall into place with the critical features.

Thanks for the replies

I've been searching this a little more - and it turns out that there is a name for this: Partially Defined Drawing (PDD).

I was taught a long time ago by a strict Russian Engineer. This was when referring to the model was very rarely used and most CNC was done by hand (My first work computer was a 486 and we would do CAD on a UNIX box). Seeing what can be done today with CAM making auto generated toolpaths is amazing to me, and I can see where lots of time can be wasted by making a perfect physical print that is full of information that is never used and makes finding the critical features difficult.

So it looks like it is acceptable . . . . and is complimented if there is an accompanying CMM setup and software to inspect and report.

If shops are taking paper prints and making their own CAD model to feed into a CAM package I see how this is the way of the future.


Everything below I found online and did a cut and paste:
_________________________________

A Partially Defined Drawing (PDD) is a drawing that has been simplified in that it does not
contain a complete set of dimensions. For complete product definition the dimensional
information is queried from the model geometry contained in the CAD digital data file.

PERTINENT REQUIREMENTS FROM THE ASME STANDARDS

ASME Y14.5-2009 Dimensioning and Tolerancing

1.4 (b) Dimensioning and tolerancing shall be complete so there is full understanding of
the characteristics of each feature. Values may be expressed in an engineering drawing or
in a CAD product definition data set. See ASME Y14.41.

ASME Y14.41-2003 Digital Product Definition Data Practices

7.2.1 Basic Dimensions. Queried model values shall be interpreted as basic dimensions
unless superseded by a toleranced dimension or defined as a reference dimension.

7.3 Drawing Requirements
Basic dimensions not displayed on a drawing shall be obtained by querying of the model.

bigjon61 said:

I'll echo the time savings. A lot of times I am the one designing, programming, and building stuff for in house work. No need to dimension and tolerance everything, just the critical features will suffice. It does spill over into parts made by others, programmed by me. Same thing though, worry about the critical dimensions and the rest either don't matter or will fall into place with the critical features.

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I work in the toolroom at an aerospace foundry. 90% of what we do is one off fixtures. Some are as easy as plates with tfg points all the way up to contoured nests with locating pins. Some for wax and some for cast parts. The key is accuracy, ease of use,, and repeatability. I'm working on one now for assembling critical wax parts together for single crystal casting. Everything except the base is delrin and almost everything will get machined once attached to the base.

Moral of the story is, I couldn't do it with just 2d drawings. Everything has to line up just right or the castings will be garbage.

Here's the caveat, this model was made by engineering not our designer, he has looked at it and fixed some stuff but minor details like holes are out of wack, this is where I'm able to make the changes to put the right stuff together...like a .230 clearance for a 10-24 screw and then .136 clearance for a 10-24 screw.

My favorite is when I get a model and a print and neither had units...

gregoryd said:

There is a note to "check the solid model for any missing dimensions" and that "all dimensions from CAD are Basic". and also a callout for "all surfaces are PROFILE x.xx to ABC"


I'm just making a process check that the world has not changed on me while I am stuck in old ways. Are shops wanting to take in the solid model now and program toolpaths off the solid - and only see dimensions on a print for critical features?

Click to expand...

Yes. The world is changing.

You nailed the process for the majority of incoming parts we get. They send a CAD a model, then provide a super minimal print that only has callouts for the critical things.

For the vast majority of parts, we can post code driven from the model and hit a .010in profile without needing to check a damn thing. So really, I feel like these "lazy" prints just make everybody's life easier. We only feel compelled to check a couple reference dimensions pulled from the CAD, and anything the designer felt was important enough to put on the drawing.

boosted said:

Yes. The world is changing.

You nailed the process for the majority of incoming parts we get. They send a CAD a model, then provide a super minimal print that only has callouts for the critical things.

For the vast majority of parts, we can post code driven from the model and hit a .010in profile without needing to check a damn thing. So really, I feel like these "lazy" prints just make everybody's life easier. We only feel compelled to check a couple reference dimensions pulled from the CAD, and anything the designer felt was important enough to put on the drawing.

Click to expand...

Whenever I am designing parts internally, I model them exactly how I want the final part to be, then I use PMI to apply symmetric tolerances and use model to manufacture, maybe a print with inspection details. This way the model geometry can be used directly without fucking around with offsets and workarounds.

Unfortunately, pretty much ALL of our customers model to basic dims, then cover the print with asymmetric tolerances, which makes their models largely useless for manufacturing without a lot of additional work, so our workflow is to build a new model (modelled to mean tolerance dimensions) from the print and use that for manufacture. If any one of them sent me a model and a bare print I would be seriously anxious about it, because I don't trust them to model for manufacture.

digger doug said:

Overworked, and understaffed, try walking in some one else's shoes for once.

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Jesus Dougie, you took a break from scolding spammers for this?
Get back to work you lazy fuck.

Larry Dickman said:

Jesus Dougie, you took a break from scolding spammers for this?
Get back to work you lazy fuck.

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Ya know...when you walk a mile in someone else's shoes you end up a mile away from them and with a pair of shoes that aren't yours.

gregormarwick said:

Unfortunately, pretty much ALL of our customers model to basic dims, then cover the print with asymmetric tolerances, which makes their models largely useless for manufacturing without a lot of additional work, so our workflow is to build a new model (modelled to mean tolerance dimensions) from the print and use that for manufacture. If any one of them sent me a model and a bare print I would be seriously anxious about it, because I don't trust them to model for manufacture.

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Yes - everyone models to benefit their function. When we moved to the SI/ISO systems we designed and modeled parts to nominal and then added the Fits and Tolerances. It made it real easy to check and convey function on H7/g6 combination. Way easier than putting unilateral tolerances around designed clearances and always having to do the math between two separate prints.

Larry Dickman said:

Jesus Dougie, you took a break from scolding spammers for this?
Get back to work you lazy fuck.

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Try some compassion for your fellow man eh ?

digger doug said:

Try some compassion for your fellow man eh ?

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On this site? What are you going soft...