solidworks modelling tolerances

Does anyone know if it’s possible to change the modelling accuracy tolerances in Solidworks? can’t find the settings anywhere.

as with all solid modelers, Solidworks computes to 10 or 11 decimals. No one needs to change this unless you’re doing atomic scale design.

Do you mean other interpretation of tolerance?

All user customizable aspects are under tools-options, or locally by chosing dimension and modifying in feature window pane.

maybe this issue is less relevant now than it used to be?.. I’m starting to use CAD seriously again but been out of the surface modelling picture for a couple of years.
3d apps are usually tuned to what the software vendor thinks is the best compromise between performance and accuracy (too accurate and the software’s slower than its competitors, too fast and the data’s garbage). I think Pro/E and NX used to have a default of 0.01mm for edge alignments… but this was modifiable. It’s surprising if SW doesn’t allow you that option.

Solidworks does not allow you to do this.

I can understand why you might want to do this, starting out with a very tight tolerance and loosing it up a little bit as your model gets more complex. You know what, I suggest you register and make a topic at the official solidworks forums:

Those guys are very responsive to user input, if enough people want it, they’ll consider putting functionality in new versions.

Maybe you could tell us a little bit more as to why you want higher (or lower) tolerance in SW? I’d be interested to know. The accuracy of the parasolid kernel is set by SW, but we are considering some user control in a few areas. One of the biggest is literally one of the biggest: and that is the 1000M limit, which we freed up in Assemblies in 2009. In SW2010 we’ve introduced user specificed knit tolerance.



I guess the root issue is problematic data transfer between SW and Alias (both directions) … I’d like to find out any best practice for this as I’ll be needing to do it a lot more in future. Beyond this, I need the data I send downstream to be as bulletproof as possible.
From past experience with other apps <-> Alias, this has come down to choosing the best and compatible modelling tolerances before modelling (from the Alias end this usually meant cranking them up pretty high as the software defaults were dangerously low) and hoping for the best.
From SW into Alias is the biggest mystery to me - many models import fine, and it’s nice to see alias now supports direct import of SLDPRT models, but some models come in unstitched. Changing the import tolerance settings seems to work ok, but still not foolproof… it was interesting to see that Alias reports the following tolerances from imported files (in other words the original modelling tolerances used by SW) :

curve fit distance tolerance : 0.0005mm
curve fit checkpoints : 5 (if I remember rightly, this means the # of points along meeting edges where the above tolerance is checked - so if the two surfaces are 1mm long, this isn’t an issue, but if you have a styling line running the length of a yacht, this should be a high number to minimise the effect of curves doing their own thing between checkpoints)
continuity max gap distance : 0.0005mm
trim curve fit : 0.0002mm
curve on surface max gap between curves : 1mm !
topology distance : 0.2mm

I don’t know if these are genuine SW settings or Alias’ interpretation of them, however it does worry me that poor edge continuity might be hidden until the surfaces can be seen naked and unvarnished in Alias/Catia/etc. by which time it’s a problem.
It would be great to control settings like these - and it sounds like 2010 has some options already (I’m stuck with 2009 for the moment due to budget)
In the short term, can you recommend any way of working or existing settings to improve data transfer?


I usually only go one way. Alias forms into SW for fine detailing.

In Alias, I have the Construction Options set for “Solidworks” and usually export as iges into SW. If you set the Significant Digits in the Alias iges export window to 15, everything usually stitches into a solid body in SW. Occasionally it won’t, but that’s usually due to duplicate surfaces. I’ve found this to be a pretty reliable way to go into SW.

I don’t usually go back into Alias, but I do remember big headaches when I did. Using Rhino as an intermediary step usually kept everything tight. In school, I think I had Rhino just for this sole purpose…

thanks brett

btw you can open sw parts directly in recent alias versions but i think you need to have sw licensed on your machine. there’s no indication in the import options but you can do this with the direct connect software installed. for my money step format works well enough to take tooling surfaces back and forth between sw and aliasdesk.

for pro-e you can export to granite format then reimport the granite file (one gotcha: i needrf to change alias’s granite import options from the default in order to get anything to import from the granite file, otherwise i always get no surfaces on import). granite rebuilds everything to degree 3 surfs and fools with the trim edges so i used this round trip method to fix my granite exports and then export to granite a second time to get the best possible surfaces importing to pro-e.