Vary wall thickness relative to tube OD
Vary wall thickness relative to tube OD
(OP)
I wish to specify the OD of a tube with a tolerance, the wall thickness of the tube with a tolerance, but add +tolerance to the wall as the OD varies from LMC to MMC.
This large tube fits inside a tube, and another tube fits inside the tube in question.
I have reviewed Y14.5, but I am still stuck. Input is appreciated.
This large tube fits inside a tube, and another tube fits inside the tube in question.
I have reviewed Y14.5, but I am still stuck. Input is appreciated.





RE: Vary wall thickness relative to tube OD
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: Vary wall thickness relative to tube OD
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Vary wall thickness relative to tube OD
I wish I could let the wall thickness go and use only the ID and OD tolerances, but I need to tightly control the wall thickness as well.
The large diameter tube is custom made, it is extruded and then expanded to meet the spec. As such, concentricity is basically not an issue in this case.
The only options I envision so far:
A. Three overlapping tolerances (very ugly to achieve, probably flat-out wrong)
B. Specify only lower limit for the ID and upper limit only for the OD (is that even allowed?).
C. A wall thickness +tolerance bonus chart or table in the notes.
D. Some GD&T symbology that still escapes me.
Any further input is appreciated.
RE: Vary wall thickness relative to tube OD
RE: Vary wall thickness relative to tube OD
I would actually like to avoid any ID spec and rely on OD with tolerance as well as wall thickness with tolerance. This is because the OD and wall thickness are easy to measure.
RE: Vary wall thickness relative to tube OD
Since you're not using a process that removes material I don't see how they could apply.
I'm thinking profiles for both inner and outer surfaces should fully constrain everything.
RE: Vary wall thickness relative to tube OD
I need a lower ID constraint, an upper OD constraint, and +/- constraints on the wall thickness. I can add + bonus tolerance to the wall thickness as the OD goes form lower tolernace to upper tolerance. It is possible to meet both the ID/OD constraints and have the wall thickness too thin or too thick.
I have never used profile GD&T, but my materials seem to imply that I could not use it with a modifier for bonus tolerance.
RE: Vary wall thickness relative to tube OD
"Part must conform to ID and OD tolerances and at the same time at no point may the wall thickness be thicker than X or thinner than Y."
Maybe someone will be able to conjure up a set of GD&T symbols for it, but you'll get a phone call "What the heck are you asking for?" and you'll have to explain it anyway.
RE: Vary wall thickness relative to tube OD
I am reassured that I am not missing an ANSI method of achieving this, thanks.
Hoepfully they can also contend with an equation to calculate the added wall bonus tolerance as it relates to the OD.
RE: Vary wall thickness relative to tube OD
I thought I'd seen LMC used in similar applications but the details don't spring to mind right now.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Vary wall thickness relative to tube OD
This will allow the position of the inside hole to float as the hole moves away from LMC, which ensures that you maintain your minimum wall thickness.
You could also call the ID a datum and position the OD relative to it with an LMC modifier. Tomato-tomahto.
RE: Vary wall thickness relative to tube OD
BTW
Concentricity is used in high speed rotating part applications.
RE: Vary wall thickness relative to tube OD
RE: Vary wall thickness relative to tube OD
The allowable wall thickness varies with the OD. Maximum thickness is desirable for manufacturability, but is limited by the ID and OD constraints.
AliThePro,
I may end up taking the suggested approach, it is reassuring that it is not "wrong" to specify all three ranges.
In the mean time, I thought it best to specify the OD with tolerance, then calculate the wall thickness upper tolerance with a simple formula based on the measured OD. This would leave the ID open (no need to measure), though effectively constrained.
RE: Vary wall thickness relative to tube OD
Double dimensioning:
A feature shall not be located / defined by more than one toleranced dimension in any one direction"
Reference dimesion:
"A dimesion shall be enclosed in parentheses () when it is (a) repeated on the same drawing, (b) specified on a subordinate document, (c) an accumulation of other dimensions, or (d) shown for informational purposes."
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This is basic drafting / dimensioning regarding "double dimensioning" and when to use a reference dimension. I would strongly disagree that tolerancing all 3 features(ID, OD, wall) isn't "wrong". It definitely does not adhere to good basic drafting. I would argue that it is "wrong".
Always keep in mind that normally, many people will be involved with interpreting the drawing.
I would agree with your last posting to dimension OD and wall. Easy enough to interpret.
RE: Vary wall thickness relative to tube OD
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net