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TJ_50094833-Newcomer
3-Newcomer
September 5, 2025
Question

GD&T advisor Hole Pair

  • September 5, 2025
  • 1 reply
  • 533 views

HI,

 

First time user of the GD&T advisor, trying to add a position tolerance to one half of a hole pair (for a shaft) and a second position tolerance to the second hole of the pair, A simplified version of my part is shown in the attached image.

 

Currently running Creo 11.0.2.0

 

Hole was modelled as a single hole for both pairs. With the model setup like this I am unable to select either the right or left hole to assign a tolerance. Am I missing something here or is the only way to get this working by modelling this as 2 separate holes?

 

Thanks

 

1 reply

tbraxton
22-Sapphire II
tbraxton22-Sapphire II
22-Sapphire II
September 5, 2025

If the design intent is to support a shaft passing through the part, then you would want to make the holes in the same setup when milling. In practice I would expect that any competent machinist would line bore the workpiece as the design intent is for the bores to be on center. This is consistent with how you modeled it as a single hole. I think that the preferred GD&T controls would apply to the axis defined by each bore center in the part. If this is the case, then it would not make sense to put position controls on each hole separately. Control the position and orientation of the line bore axis relative to your established datum reference frame.

T
TJ_50094833-NewcomerAuthor
3-Newcomer
September 8, 2025

Tbraxton,

 

That is absolutely how its manufactured. This is a design that I have inherited. Probably poorly explained previously (and wasnt really the point of the question). The first hole is is a "rough" tolerance to locate the bores WRT the part features, the tolerance on the second bore is to tie it to the datums established from the first bore (first bore diameter and perpendicular face).

 

  I guess my question is why Creo limits the selection to half cylinder hole surfaces, it seems that is the worst implementation for tolerancing a hole be it a split bore or a continuous bore, I mean who is going to tolerance half a cylinder? Given this odd implementation I asked the question on the off chance that I was missing something WRT the Creo side of the equation.

tbraxton
22-Sapphire II
tbraxton22-Sapphire II
22-Sapphire II
September 8, 2025

Creo has always split circles and cylinders in half. It is hard coded in the geometry kernel and has been there since the first release. I have not heard an explanation of why this was done but we are stuck with it.

This can cause issues in some models. I am not clear on why this would cause a problem with GD&T advisor, but I am not knowledgeable about that module.

 

I doubt the selection of a cylinder wall of a hole feature would be problematic for GD&T application but if you think it is doing something wrong then you should open a call with PTC.

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