Concentricity vs. wall thickness
Concentricity vs. wall thickness
(OP)
Hello All,
I have a small cylindrical part that has a hole drilled into it. I am trying to decide if the OD and the ID (really the diameter of the hole) should be called out as a wall thickness or a concentricity tolerance.
The part is molded out of plastic. I'm leaning towards wall thickness because the fixturing to measure it would be much easier to make.
Thanks for any help in advance!
I have a small cylindrical part that has a hole drilled into it. I am trying to decide if the OD and the ID (really the diameter of the hole) should be called out as a wall thickness or a concentricity tolerance.
The part is molded out of plastic. I'm leaning towards wall thickness because the fixturing to measure it would be much easier to make.
Thanks for any help in advance!





RE: Concentricity vs. wall thickness
Your dimensioning and tolerance scheme should be based on functionality, not ease of making inspection fixtures.
RE: Concentricity vs. wall thickness
RE: Concentricity vs. wall thickness
At least with ASME concentricity is rarely the right control except for things like long prop shafts etc. Consider if Position or one of the runouts is appropriate based on function.
Position may allow even easier gauging, especially if you can use MMC on both the hole & OD datum feature.
KENAT, probably the least qualified checker you'll ever meet...
RE: Concentricity vs. wall thickness
KENAT, probably the least qualified checker you'll ever meet...
RE: Concentricity vs. wall thickness
I would suggest that you reflect the hole in either circular or total runout using the OD as the datum. This will control the wall thickness a little bit easier than positonal.
Both will achieve the same results.
Dave D.
www.qmsi.ca
RE: Concentricity vs. wall thickness
RE: Concentricity vs. wall thickness
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Concentricity vs. wall thickness
Go ahead and use wall thickness if you want! If the part is not rigid then its form may vary to some degree. Using the controls for position, profile, or runout will penalize that deformed part even if it has acceptable wall thickness. As others have said "consider the function in specifying the control".
Concentricity is definately not what you want because concentricity does not control size or form... only location. For instance... the OD and ID could be perfectly straight and perfectly concentric yet have elliptical shapes where the max ID and min OD are 90 degrees "out of phase" naturally wall thickness would exhibit the extremes resulting from size for each.
If there was a wall thickness requirement one of the sizes would not be required.
Paul
RE: Concentricity vs. wall thickness
http://www.tec-ease.com/tips/february-98.htm
Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion
RE: Concentricity vs. wall thickness
Maybe I shouldn't be answering your question... forgive me but for rigid parts I would Yes! However for ME2QE's original question... with a plastic part and his leaning to specify "wall thickness" and his assertion that gaging would be easier... I would say it doesn't explain the size and "wall thickness" option.
Paul
RE: Concentricity vs. wall thickness
I understand. There are some good suggestions above and I was just adding some additional info for ME2QE to use (future reference).
Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion
RE: Concentricity vs. wall thickness
He also talks about a hole being drilled, which would suggest reasonably stiff/rigid part, unless they just mean a hole co-axial to the OD, not specifically created by drilling.
KENAT, probably the least qualified checker you'll ever meet...
RE: Concentricity vs. wall thickness
Sorry if I wasn't clear. The plastic part is molded with the hold in it. Its a pretty compliant part (soft plastic).
The hole mates to a shaft. At its smallest, the hole is already .001 larger than the OD of the shaft.
I'm not designing the part, just trying to fix the drawing so that we keep a specific wall thickness intact.
I haven't used GD&T in a while so I'm taking a long time to understand what you are all saying. Anyone know where I can get a refresher of sorts? I'd even take a class all over again if I could.
RE: Concentricity vs. wall thickness
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Concentricity vs. wall thickness
RE: Concentricity vs. wall thickness
Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion
RE: Concentricity vs. wall thickness
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Concentricity vs. wall thickness
you mention to hold the OD as a datum for a runout tolerance on the ID. Is it the same if i hold the ID as the datum and runout the OD?
RE: Concentricity vs. wall thickness
The results would be the same but I caution that both total and circular runout are appropriately applied on small cylindrical parts. Your part is cylindrical so it would work.
Sometimes it is easier to have the ID as the datum (place in chuck)and perform the runout on the OD. That is from a measuring perspective.
Dave D.
www.qmsi.ca
RE: Concentricity vs. wall thickness
What my inspectors would do is put a pin gauge into the hole, zero off the pin gage, and then runout the OD.
Thats why I just wanted to make sure that the opposite works.
RE: Concentricity vs. wall thickness
assuming i dont want the wall thickness to fall below .0085, does this tolerance make sense? I don't want to submit this to a vendor and have them laugh in my face.
Thanks for all the help! You are all teaching me a lot.
RE: Concentricity vs. wall thickness
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com