Tolerances in 3D

Puck

I am thinking of a feature that I don't think exist in any CAD software : full integration of tolerances at 3D level. Currently, tolerances are only added in the drawing and only as a display note (no actual implication on parts). Having all the tolerances defined during 3D modeling would considerably ease the process to create drawings. And the main feature I would want to emerge from this change of paradigm is to be able to actually visualize extreme cases considering entered tolerances. This would be a huge help in collision detection for precision parts.

gábor_kiczenko

Agreed. Decisions on tolerances come from the logical structure of the assembly. I'd love this feature too, simply to input information at the time and place where the decision is made. Not afterwards. Not to mention how much easier it would be to delegate the actual drawing for machining. Designers lose a lot of workhours doing menial tasks of drawing for production floor, which also creates tension between design dept. and machining dept. If tolerances could be included in 3D, most of the drawing work could be done by a member of the machining team, who already knows and OBSERVES the nitpicks of machinists standing at the CNC machines. This way the (lead)designer could be the person who approves the drawing. Which should be the case anyway. Is there an IR on this? 

Steve_Spanjers

Agreed.  I think NX has something similar (PMI)...  However, imagine how easy a tolerance stackup analysis would be if all the holes were dimensioned and toleranced properly in 3D.

tim_hess427

What you're describing sounds like what is generically called "model based definition" or MBD (different companies may have their own names for it). If you search for those terms you'll see more information about it.

I think there's a lot of interest in it, but I think it'll take a lot of time for people to move away from their reliance on paper drawings. There is an improvement request here: https://forum.onshape.com/discussion/comment/51049#Comment_51049

S1mon

Last I knew this costs about $30k, but CETOL does full 3D simulation of tolerance loops.

https://www.sigmetrix.com/products/cetol-tolerance-analysis-software/

michael_zeagler

Sorry for grave robbing the post, but I was hoping to find this in the Onshape feature set with no luck.

Inventor has tolerance analysis:
https://knowledge.autodesk.com/support/inventor-tolerance-analysis/learn-explore/caas/CloudHelp/cloudhelp/2019/ENU/INVTOL/files/GUID-38E025E4-D5C1-46CC-B5CC-67F52CB39139-htm.html

Solidworks has TolAnalyst and DimXpert:
https://help.solidworks.com/2022/english/SolidWorks/sldworks/c_tolerancing_overview.htm?id=f534e416795940bab793412d3bc162ec#Pg0

Honestly it's one of Onshape's greatest deficiencies, especially considering how easy it would be on the user with all the dependencies you could screw up in file-based systems.

Adrian_Marshall

Coming from a environment of Creo with MBD and looking at 3D tol-stack CTEOL , Onshape is missing a great deal, it needs detailed tolerancing in the model and an application that will work Could-native too.  It would be great if PTC could share a roadmap to this futur 

michael_zeagler

I put in an improvement request for this a while ago if you want to star it:

https://forum.onshape.com/discussion/18212/model-based-definition-and-tolerance-analysis#latest