+/+ tolerances?
+/+ tolerances?
(OP)
Bearing seat dimension is nominally 4.7244" diameter. The model is constructed that way. Now I'm tolerancing the drawing.
I want to show limit dimensions as 4.7251/4.7245.
SW was having none of it. When I put a negative value in the (-) deviation, SW seemed to take the absolute value. Sorry, I'm used to another package that interprets a negative value for a minus deviation to mean plus.
I was able to force what I want by giving SW an override primary value of 4.7245 (which it insisted on displaying as 4.725 within its dialog box), and specifying deviations of -0/+.0006.
Is there a better way to get SW to deal with press fits?
I want to show limit dimensions as 4.7251/4.7245.
SW was having none of it. When I put a negative value in the (-) deviation, SW seemed to take the absolute value. Sorry, I'm used to another package that interprets a negative value for a minus deviation to mean plus.
I was able to force what I want by giving SW an override primary value of 4.7245 (which it insisted on displaying as 4.725 within its dialog box), and specifying deviations of -0/+.0006.
Is there a better way to get SW to deal with press fits?
Mike Halloran
Pembroke Pines, FL, USA






RE: +/+ tolerances?
RE: +/+ tolerances?
RE: +/+ tolerances?
Dan
www.eltronresearch.com
RE: +/+ tolerances?
RE: +/+ tolerances?
If it were nominal, it would be 4.7248 +/- .0003.
Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 04-21-07)
RE: +/+ tolerances?
Mike Halloran
Pembroke Pines, FL, USA
RE: +/+ tolerances?
Mike Halloran
Pembroke Pines, FL, USA
RE: +/+ tolerances?
Check out the options in the Tolerance / Precison section of the Dimension Manager. It has selections for the type of fit required along with the corresponding alpha-numeric designations.
IMO, the Override option should never ever be used. In fact, SW should never have made that an option.
RE: +/+ tolerances?
Dan
www.eltronresearch.com
RE: +/+ tolerances?
Thanks again.
Mike Halloran
Pembroke Pines, FL, USA
RE: +/+ tolerances?
RE: +/+ tolerances?
The other option is to use the override, as also mentioned. I use this method more commonly these days, but it wasn't available on older versions of SW.
Matt
CAD Engineer/ECN Analyst
Silicon Valley, CA
sw.fcsuper.com
Co-moderator of Solidworks Yahoo! Group
RE: +/+ tolerances?
RE: +/+ tolerances?
+/+ tolerances are not explicitly shown in ASME Y14.5M-1994, but they are not explicitly banned either. In ISO406, Figures_12 and_13 show +/+ and -/- dimensions. Strictly speaking, the diagrams show assembled components with nominal dimensions and tolerances slopping the same way.
ISO406 is sort of more permissive about this.
Sometimes it is useful to show the actual modeled CAD dimension in addition to the permitted variation. Think about the machine shop that asks for a DXF of your fabrication drawing so that they can program their CAM machine.
JHG
RE: +/+ tolerances?
Personally, I would still never allow this on a part drawing.
RE: +/+ tolerances?
Which still leaves the problem of using DXFs. Too bad that their native world, architecture, doesn't use tolerances, so they're not in the standard.
Mike Halloran
Pembroke Pines, FL, USA
RE: +/+ tolerances?
RE: +/+ tolerances?
The limit dimension seems to be the lesser of two evils. I would still model to actual size. I've had mold makers build right off the model without even looking at prints, only to find that molds were not "steel safe" as a result.
Ask for what you want, on the drawing and in the model.
RE: +/+ tolerances?
Sure, I'd trust a real machinist to do a little math, or figure out a fit, but inspectors often enough seem to be pulled from the casual labor pool.
Mike Halloran
Pembroke Pines, FL, USA
RE: +/+ tolerances?
Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 04-21-07)
RE: +/+ tolerances?
I met machinists who couldn't understand +/+ and -/- tolerances. They didn't last long.
RE: +/+ tolerances?
I model at the nominal and apply tolerances. I use the SolidWorks bilateral tolerances on my drawings. When I finalize them, usyally, I change them to limit dimensions. Sometimes, I forget.
I have not had a phone call from the shop about this. I have had people in-house discuss how to convert them to "correct" dimensions. This can get dangerous.
JHG