controlling bow of part in one direction
controlling bow of part in one direction
(OP)
I have a plastic injection molded part that is .120" with +/-.004 and flatness call out on the bottom surface of .010". To me this doesn't make sense. Anyway, what I'm trying to do is to control the thickness and the direction of the bowing. I would rather bow in one direction so that it will be flush to the mating surface when assembled. the length is 6 inches and width is say .25". what would be the best way to dimension this and how to measure it. I know that I can't use the part that bows .010" from theoretical straight line at MMC (.124) at assembly.
Thanks
Thanks





RE: controlling bow of part in one direction
Any chance of a drawing or sketch?
regards
desertfox
RE: controlling bow of part in one direction
You may be able to use profile of a surface on the surface that sits flush against whatever it assembles to and unilaterally dispose the tolerance zone to the outside. This will create up to a convex surface when the tolerance zone is used.
Anything I've said really depends on whether I've understood the original question. I'm envisioning a rectangular piece that is 6" long, .25" wide and .124" thick and there may be a counterbored hole on each end. The direction of the bow decides whether it comes out during assembly.
Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: controlling bow of part in one direction
In any case you can use a modifier like "NOT CONCAVE" if it is only permissible do deform in one direction.
RE: controlling bow of part in one direction
Kinsrow - what standards are you working to as this is a case where it may make a difference.
How about specifiying it in the restrained position and giving the 'clamping' info on the drawing? See section 6.8 of the current ASME standard & fig 6-54.
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at http://eng-tips.com/market.cfm?
RE: controlling bow of part in one direction
Insterad of flatness, try a bilateral profile tolerance.
RE: controlling bow of part in one direction
I might try Profile tolerance like Tick and Powerhound and see if we have the tools and set up to measure it.
Powerhound,
You understood the part I discribed except I've got many lighting holes between and 2 controlled mounting holes ( one rivet and the other is clearance for screw).
Thanks
RE: controlling bow of part in one direction
When interpreting a print to ASME Y14.5M-1994, thickness tolerance and flatness tolerance are related via general rule #1. Saying that the thickness can be uniform but the part can be warped is not correct. If the thickness is at MMC then the part cannot be warped at all nor can there be any flatness error. General rule #1, in a nutshell, states perfect form at MMC. Straightness and flatness are form controls and thus must be perfect if the feature is produced at MMC.
You started out describing a cylindrical tube then finished off talking about a plate so I'm not sure I really understood what you were trying to say. Maybe I'm addressing a non-issue.
Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: controlling bow of part in one direction
thanks
RE: controlling bow of part in one direction
Does this work for you Kinsrow?
http://www.tec-ease.com/tips/july-99.htm
Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion
RE: controlling bow of part in one direction
Have you tryed looking in the Dimensioning & Tolerancing standard, ASME Y14.5M-1994?
Specifically 6.4.2. deals with flatness.
6.4.2.1 states:
I don't know what standard your QC guys are working to but the above sounds pretty definitive to me, unless I'm missing something.
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at http://eng-tips.com/market.cfm?
RE: controlling bow of part in one direction
What you describe is sadly an all-too-familiar scenario in the industry that I work in. People running around professing to know GD&T when they have never opened a standard nor have they made the full understanding of it a priority in their discipline. Holding a QM title means nothing in the way of GD&T although it does mean a lot in the world of quality. Likewise, holding a certification in GD&T means nothing in the way of ISO 900* certification but then I never claim to know a thing about it.
General rule #1 is what you're after here. There's no symbol for it so those that think GD&T is all about memorizing symbols don't have a clue that it even exists.
Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: controlling bow of part in one direction
Drstrole
RE: controlling bow of part in one direction
If allowable distortion is greater than thickness tolerance at MMC, then flatness would not be appropriate.
RE: controlling bow of part in one direction
Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion
RE: controlling bow of part in one direction
Drstrole
RE: controlling bow of part in one direction
Thanks guys.
RE: controlling bow of part in one direction
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at http://eng-tips.com/market.cfm?
RE: controlling bow of part in one direction
Drstrole