New Pet Peeve- CAD drawing not in Proportion.

SIM · May 8, 2018

New Pet Peeve- CAD drawing not in Proportion.

Its like going back to the old hand drawn sketches on a napkin. The width may be a little longer then the length, a large circle could be a small hole, a 1" boss 1/2" high could just barely fit in a 4" square and look as tall as the 2" plate is sits on...but it was a hand drawn sketch and it usually came with a person who went over each detail with you. I understood, made my own drawing to a semi proportionate scale and we made part.

CAD came into play and life became easier in that no longer could you draw a 1" circle inside a 3/4"dia boss, a 1/4" keyway just looked wrong inside a 4" shaft, tapers machined matched tapers drawn...you could look at a CAD drawing and knew what the part was going to look like. You knew you could pre-drill a feature and had room to clean up later as the hole just looked bigger...so it was. I saw all through features where far from the edge, so didn't worry about parallel placement.

So the peeve is this...I am now getting drawings in CAD that are not proportionally correct. I didn't even know this was possible. Simple rectangular part dimensioned 2" wide x 3" tall has proportions were it is drawn wider then tall. Do you know how many times you need to verify the part is correct when that happens. Each time you go to another op...the part just looks wrong. Yes, I can and did redraw...but is was supposed to be a simple do at the machine job. Plus redrawing opens a new place to make errors.
Simple plug in a bunch of drilled hole locations from datum, parts a 1/2" thick...all holes situated way more then that thickness from edge...1/4" parallels will be fine...nope holes hit the parallels. Yes, we need to watch a bit more carefully...but again simple job that can, should have been done at machine.

Part with tapered feature turns out making part wider then drawn...My fault...I didn't layout the dimensions to verify stock size..just went off the dimensioned width,everything fell within. But now plug in the angles and material needs to be a quarter inch wider to fit that feature.

I have encountered this before from college students making prints in Power Point??? But those drawings just looked wrong in every conceivable way...so the Red flags had already gone up. But lately I am getting drawings from customers "engineering departments" Drawings look good, no flags go up till its a bit on the late side.

Rant over...lesson learned, assume nothing and verify everything. So much for the added edge of getting a CAD file...the big drawback used to be the happy zeros...the more the merrier. 1.0000 Clearance hole for 7/8 bolt...ahh those were the days.

DDoug · May 8, 2018

I ran into this before.

Worst one was a garbage packer.

The salesman was their "Drafsman" as they had fired everyone else.

He simply glommed various shaped pieces together, and then fudged all the dims.

HuFlungDung · May 8, 2018

Yes, that sucks big time. In fact, the reason I draw stuff with CAD is to properly proportion it to how it will really look and save myself the trouble of starting to make something that hits the 'impossible wall' and has to be scrapped.

Dimensioning a drawing that is not in proportion is actually lying, because there is no way in hell that the dimensions could add up. Warning should be written on the drawing, by the drafter, that scale and proportions are not necessarily correct. I don't know what the hell good that does to produce a sketch like that, but then you'd know what work you have to do before you start.

homanfab · May 8, 2018

Probably overriding displayed dimensions in the drawing without changing the model.

Mike1974 · May 8, 2018

homanfab said:
Probably overriding displayed dimensions in the drawing without changing the model.

I do this for tolerance, ie part is drawn/modeled at nominal, but need to add + or minus to assemble, etc. But it sounds like this is not what the OP is talking about...

DDoug · May 8, 2018

Mike1974 said:
I do this for tolerance, ie part is drawn/modeled at nominal, but need to add + or minus to assemble, etc. But it sounds like this is not what the OP is talking about...

Yup, and when I have done this (and it is used sparingly at best), I change the color of the dimension (I usually use light blue for dimensions) to yellow, so I know that the dim has been typed in.

And will not change value when the part is stretched either.

adamm · May 8, 2018

HuFlungDung said:
Dimensioning a drawing that is not in proportion is actually lying, because there is no way in hell that the dimensions could add up. Warning should be written on the drawing, by the drafter, that scale and proportions are not necessarily correct. I don't know what the hell good that does to produce a sketch like that, but then you'd know what work you have to do before you start.

It's funny you say that. Many of the CAD drawing templates that I see have a note that says something to the effect of "Not to scale", and "Do not scale drawing". It has been a while since I've seen some truly out of proportion drawing, but I have had some lately where there are two close elements, and the dimension extension lines don't point at either of them.

Back when I was working at place where the engineers did engineering, and the drafting department did the CAD, it was standard practice for engineers to use old drawings, white out the dimensions, and write the new dimensions. Though in that case, the company was fully product based, and there were only a few difference overall arrangements. Typically the drawings went to the CAD guys to show what is needed for the new part number, but sometimes they would go to the sample shop if timing required the parts be made before the official drawings could be made.

Joe Miranda · May 8, 2018

We have begun to add to our quotes that if we have to re-draw the 2D or 3D drawings that we add $100 per hour and our typical charge is 2-4 hours. Re-drawing is not free and besides that we become liable for the outcome which is a situation that we prefer to avoid.

The "threat" of an additional fee typically gets the customer to make drawings that don't need re-work - or at least - very little.

706jim · May 8, 2018

Maybe a little off topic, but for the past several years, drawings I have made were generated buy the CAD system from the solid model. If the model was modified for some reason, the drawing could be updated by the system. Also, CNC programs were linked to the solid and could similarly be updated.
This is using Catia which doesn't seem to be mentioned very often in this forum.
But if the machine shop did not have access to the solid (quite likely?) then none of this really applies.

G00 Proto · May 8, 2018

About the only way to get out of proportion dimensions with any modern CAD system is by over-ridding dimensions when you make the print. It is considered very bad form. The model is the control document and must reflect the finished part. Most competent shops will program directly off the model and only use the print for QC. Most of our prints also state to not scale the drawing. If a vendor is holding the part up to the print to make sure it is right, we are probably going to have some questions about your quality system

This is even more pronounced when we use a drawing size other than 8.5" by 11".

I also prefer that our drafters do not use bilateral tolerances (i.e. +0, -.005). Again, the part model should reflect the finished part, not be modeled at one of the extremes. This is somewhat negotiable, more of a strong preference.

Joe Miranda · May 8, 2018

I also prefer that our drafters do not use bilateral tolerances (i.e. +0, -.005). Again, the part model should reflect the finished part, not be modeled at one of the extremes. This is somewhat negotiable, more of a strong preference.[/QUOTE]

Man - I like your thinking!

DMF_TomB · May 8, 2018

SIM said:
New Pet Peeve- CAD drawing not in Proportion.

Its like going back to the old hand drawn sketches on a napkin. The width may be a little longer then the length, a large circle could be a small hole, a 1" boss 1/2" high could just barely fit in a 4" square and look as tall as the 2" plate is sits on...but it was a hand drawn sketch and it usually came with a person who went over each detail with you. I understood, made my own drawing to a semi proportionate scale and we made part.

CAD came into play and life became easier in that no longer could you draw a 1" circle inside a 3/4"dia boss, a 1/4" keyway just looked wrong inside a 4" shaft, tapers machined matched tapers drawn...you could look at a CAD drawing and knew what the part was going to look like. You knew you could pre-drill a feature and had room to clean up later as the hole just looked bigger...so it was. I saw all through features where far from the edge, so didn't worry about parallel placement.

So the peeve is this...I am now getting drawings in CAD that are not proportionally correct. I didn't even know this was possible. Simple rectangular part dimensioned 2" wide x 3" tall has proportions were it is drawn wider then tall. Do you know how many times you need to verify the part is correct when that happens. Each time you go to another op...the part just looks wrong. Yes, I can and did redraw...but is was supposed to be a simple do at the machine job. Plus redrawing opens a new place to make errors.
Simple plug in a bunch of drilled hole locations from datum, parts a 1/2" thick...all holes situated way more then that thickness from edge...1/4" parallels will be fine...nope holes hit the parallels. Yes, we need to watch a bit more carefully...but again simple job that can, should have been done at machine.

Part with tapered feature turns out making part wider then drawn...My fault...I didn't layout the dimensions to verify stock size..just went off the dimensioned width,everything fell within. But now plug in the angles and material needs to be a quarter inch wider to fit that feature.

I have encountered this before from college students making prints in Power Point??? But those drawings just looked wrong in every conceivable way...so the Red flags had already gone up. But lately I am getting drawings from customers "engineering departments" Drawings look good, no flags go up till its a bit on the late side.

Rant over...lesson learned, assume nothing and verify everything. So much for the added edge of getting a CAD file...the big drawback used to be the happy zeros...the more the merrier. 1.0000 Clearance hole for 7/8 bolt...ahh those were the days.

.
yes i have gotten plenty of drawings done in Visio or Powerpoint or Word which are not made for precision CAD. better than no drawing
.
sure electronic version of napkin drawing. but i have found some Engineers do not do CAD they pay someone to draw and consider CAD work beneath their engineering degree. so if technician or somebody not a degreed Engineer gives me any drawing even if poorly made its better than no drawing.
.
i have been at places Engineer showed you big machine and something he wanted changed or improved. i as a maintenance machinist made drawings and Engineer would approve for parts to be made installed aligned and equipment performance debugged. all without Engineer making any drawings himself. literally Engineer would just verbally ask he wants machine to do something different and please figure out a way or something to try
....it actually made for interesting job cause you had to think or invent stuff

SIM · May 8, 2018

G00 Proto said:
Most competent shops will program directly off the model and only use the print for QC.

Sounds great...although kind of tough to do when only provided with a print to work from.

G00 Proto said:
Most of our prints also state to not scale the drawing. If a vendor is holding the part up to the print to make sure it is right, we are probably going to have some questions about your quality system

I'd love to hear those questions...

The point of using a print to verify a part is right, can be likened to looking at the picture on the box of the JigSaw puzzle. A rough reference.

G00 Proto said:
I also prefer that our drafters do not use bilateral tolerances (i.e. +0, -.005). Again, the part model should reflect the finished part, not be modeled at one of the extremes. This is somewhat negotiable, more of a strong preference.

I too have preferences... one would be if your looking for a round part, don't give me a drawing that shows a square one.

DMF_TomB · May 8, 2018

yeah right going off 3D model. like every CNC has tool wear, temperature changes and part and tool deflection. you cannot just program from theoretical model you need to measure. so you need drawing with dimensions usually GD&T tolerances which model does not show how much bigger or smaller features can be
.
99.999999999% of my work is confirming, adjusting tool comp, boring bars etc so i get part in dimensioned tolerances stated on drawing.
.
ISO guy insists on drawing with name of who made drawing, revision level and who approved drawing for manufacturing, date, etc. you tell iso you went off 3D model without critical info like that you loose your iso certification

adamm · May 8, 2018

DMF_TomB said:
ISO guy insists on drawing with name of who made drawing, revision level and who approved drawing for manufacturing, date, etc. you tell iso you went off 3D model without critical info like that you loose your iso certification

It's possible to have 3D model with the information you give above. In a properly controlled system, the model already will have all that information. I've worked for ISO certified places where all dimensioning was to be taken from the 3D models in production. No dimensions on drawing. Fully ISO compliant. The GD&T, however, was on a drawing to accompany the model file.

adamm · May 8, 2018

G00 Proto said:
I also prefer that our drafters do not use bilateral tolerances (i.e. +0, -.005). Again, the part model should reflect the finished part, not be modeled at one of the extremes. This is somewhat negotiable, more of a strong preference.

I disagree. The standard fits and limits system is great. The only problem with asymmetric tolerance is that, for some reason, the CAD/CAM packages don't handle it. It's been standardized for longer than CAD has been around, but CAM doesn't deal with it properly.

SeymourDumore · May 8, 2018

adamm said:
I disagree. The standard fits and limits system is great. The only problem with asymmetric tolerance is that, for some reason, the CAD/CAM packages don't handle it. It's been standardized for longer than CAD has been around, but CAM doesn't deal with it properly.

Yeah? Well if they DID handle it, then HOW would they handle it?
My guess would be to find the middle and program accordingly....

Which BTW is why they should just draft to the middle and forget about it.
Or, better yet, CAD should handle it right out of the gate, period.
You define the feature, then define feature size by fits and limits and CAD should just put the damned thing in the middle.
I believe Inventor can do it ( though I've never checked it ), perhaps others as well, but once the file becomes non-native, all that info is lost and without a dimensioned blueprint
you're looking at a garbage model.

adamm · May 8, 2018

SeymourDumore said:
Yeah? Well if they DID handle it, then HOW would they handle it?
My guess would be to find the middle and program accordingly....

Which BTW is why they should just draft to the middle and forget about it.
Or, better yet, CAD should handle it right out of the gate, period.
You define the feature, then define feature size by fits and limits and CAD should just put the damned thing in the middle.
I believe Inventor can do it ( though I've never checked it ), perhaps others as well, but once the file becomes non-native, all that info is lost and without a dimensioned blueprint
you're looking at a garbage model.

That's a good question. How would they handle it? The CNC program should target the middle. Which means the CAM program should take into account the tolerance and shift the nominal. But to draft the model showing the tolerance? If the component is part of a large assembly, there is a really good chance that it will cause problems in the assemblies when shifting off nominal by half the tolerance range. I used to design equipment using a mixture of nominal inch units, as well as purchased components with nominal mm sizes. They would end up with surface heights stacking up to weird numbers, and things that should line up were out by 0.0001, or maybe 0.000001, and then things would get flakey and crash prone in Solidworks. It would be the same deal with a bunch of parts where the functional surfaces (which are the things that get used to create the mates) all have a bunch of trailing decimals. From a design of the overall mechanism, it doesn't really matter, but stuff like that can cause hours and hours of fighting crashing CAD.

Either way, things are not handled will in CAD and/or CAM software. Having done both ways, dialing in a fit by a few thou during manufacturing is, in my opinion, the easiest and least difficult way to do it.

Vancbiker · May 8, 2018

G00 Proto said:
About the only way to get out of proportion dimensions with any modern CAD system is by over-ridding dimensions when you make the print. It is considered very bad form. The model is the control document and must reflect the finished part.

This is only true for customers that state the model is the manufacturing authority. Many companies, including some of the biggest, often use the drawing as the manufacturing authority. Large companies sometimes find it faster to incorporate ECNs directly to the drawing than to change the model.

G00 Proto said:
Most competent shops will program directly off the model and only use the print for QC.

Again, if the customer states the drawing is the manufacturing authority, then programming from a supplied model can lead to discrepant parts. Many times a manufacturing model is built from the drawing to use for programming.

G00 Proto said:
If a vendor is holding the part up to the print to make sure it is right, we are probably going to have some questions about your quality system

You've never made parts that were inspected to a PCM? Never made parts on a tracer mill? Almost always inspected for contour compliance by comparing the part to a clear or translucent sheet with the part profile drawn, printed, or engraved on it.

There is a pretty wide world of manufacturing techniques out there. Not everyone does everything the same way.

Conrad Hoffman · May 8, 2018

I think I'd rather have a hand drawing on a napkin by somebody that understood what they wanted, than an incompetent CAD drawing.

New Pet Peeve- CAD drawing not in Proportion.

Titanium

Diamond

Diamond

Aluminum

Diamond

Diamond

Cast Iron

Titanium

Titanium

Hot Rolled

Titanium

Diamond

Titanium

Diamond

Cast Iron

Cast Iron

Diamond

Cast Iron

Diamond

Diamond

Similar threads