GD&T question: Measuring basic dimensions

Stijloor

Staff member
Super Moderator
#31
I'd already responded before seeing Sep68's response. (if it "potentially" applies) I smell a scam. That's taking more than little liberty I'd say on their part.
That's why the supplier has the obligation to review all customer's documents (drawings, specs, whatever) before the order is accepted. We used to call this "contract review." Too many suppliers wait until problems occur, and then complain about unfairness, etc. Most questions should be asked before order acceptance, not afterwards.

Stijloor.
 
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J

JaxQC

#32
Yea, DCX (Chrysler) already has that on their prints but we never had that capability. In my mind it would be nicer to just trace the part in on the CMM, overlay to the model and be done. Anyone with actual exper on that?
 

Stijloor

Staff member
Super Moderator
#33
Yea, DCX (Chrysler) already has that on their prints but we never had that capability. In my mind it would be nicer to just trace the part in on the CMM, overlay to the model and be done. Anyone with actual expertise on that?
One of our Fellow Covers Mr. Mark Boucher is. You could send him a PM.

Stijloor.
 
S

sept68

#34
Wait 'till you see the new Standard where now tolerances are specified relative to the CAD model. Meaning that "the model" is the basic dimension.

Very common now in automotive, which means that the supplier is expected to acquire the appropriate (CMM) software to inspect the part.

Stijloor.
We do have the ability to check a profile will CMM. We even have the ability scan product with lasers. However doesn't tell you how to fix anything that falls outside the profile. Also you can run into problems relying on software if you did not start out with a valid set up. Most of our sub components were bid without fixtures.
 

Kingsld1

Involved In Discussions
#35
Another reason to report BASIC values is to aid the shop in making corrections. If a machinist just sees the diametrical value he is clueless in how to make adjustments.
 

Stijloor

Staff member
Super Moderator
#36
We do have the ability to check a profile will CMM. We even have the ability scan product with lasers. However doesn't tell you how to fix anything that falls outside the profile. Also you can run into problems relying on software if you did not start out with a valid set up. Most of our sub components were bid without fixtures.
Understood. Good points. Lessons learned should be taken in consideration when bidding the next job. And that does not always happen either. As a result, you're in the middle of it...no fun.

Stijloor.
 

Stijloor

Staff member
Super Moderator
#37
Another reason to report BASIC values is to aid the shop in making corrections. If a machinist just sees the diametrical value he is clueless in how to make adjustments.
Train the machinist! Ensure competency in understanding the meaning of call outs on prints.

Stijloor.
 
S

sept68

#38
Another reason to report BASIC values is to aid the shop in making corrections. If a machinist just sees the diametrical value he is clueless in how to make adjustments.
Its not always good to report everything. Reporting basic values could confuse jury if you know what I mean.
 

Kingsld1

Involved In Discussions
#39
Its not always good to report everything. Reporting basic values could confuse jury if you know what I mean.
If you are reporting to someone who does not need the details, I agree that the diametrical zone is adequate.

If you are trying to diagnose a machining problem, a diametrical zone will not give enough information to fix the problem. Fixing a hole pattern where the holes are all shifted the same way is different than one where the holes are shifted multiple ways.
Noone knows which way the holes are scattered unless the BASIC details are provided.
 
D

David DeLong

#40
If you are reporting to someone who does not need the details, I agree that the diametrical zone is adequate.

If you are trying to diagnose a machining problem, a diametrical zone will not give enough information to fix the problem. Fixing a hole pattern where the holes are all shifted the same way is different than one where the holes are shifted multiple ways.
Noone knows which way the holes are scattered unless the BASIC details are provided.
You are correct here but I hope that people in Quality do NOT tell manufacturing how to fix a problem (sometime it happens) since it will surely bite them later. I have seen in the past where someone in Quality would say "got to move it .040" left on the X axis and .035 up on the Y".

I would suggest that if more detail is needed on out of position holes, one could always report the actual location of the hole in X & Y co-ordinates, corresponding to basic dimensions, placing a bracket around the result showing that it is a reference value. It is the responsibility of Manufacturing to figure out how to move the tooling and not Quality. Do NOT place a tolerance on a basic dimension otherwise everyone will know that you have no clue in GD&T.
 
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