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Tolerancing Press Fit Thin Tubes

Tolerancing Press Fit Thin Tubes

(OP)
Hi all,

I am somewhat of a novice in GD&T and needed some guidance on the call outs in this thin walled tube drawing. This is an aluminum tube and there will be another thin wall tube that will press fit against the OD of it. Then there will be another tube that will press against the ID of the reference drawing which will make two separate press fit. The final goal is that I like to keep all these separate tube coaxial to each other as best as possible after the press fits.

My initial thought is to use concentricity to control the coaxiality but that doesn't really control form so I added a cylindricity to control the tapered and straightness. Straightness is important because I don't want the part to get cocked when pressing. I ,however, am hesistant about this callout because it seems there is a consensus online that concentricity is often misuse and hard to measure without a cmm.



My first question, however, is this callout reasonable and legal? My second question are there more appropriate alternatives that can achieve the design intent? It seems like a lot of people are fans of runout or total runout or perhaps maybe even a positional tolerance to control the ID could be suitable as well.

Also the tube will most likely be machined on a lathe and our company don't really use any particular drawings standards believe it or not but our group try to follow ASME Y14.5M standards as much as possible.

Let me know your guys thought.

Thank you

RE: Tolerancing Press Fit Thin Tubes

gotpho,

My first thought is that you should apply your cylindricity specification to the inside diameter, which is your datum feature. One problem with concentricity is that it only meaningful if you have a well defined cylinder. You have one. The other problem with concentricity is that it is being disparaged and may be phased out of the standard. How about specifying run-out on the OD?

--
JHG

RE: Tolerancing Press Fit Thin Tubes

My suggestions would be:

Regarding form and your design intent - I would let Rule #1 control the form of the ID and OD. This would be perfectly cylindrical at MMC and within .002 at LMC.

Regarding the coaxial relationship - I would use position at LMC for both the datum (ID) and the feature (OD). This would control minimum wall thickness while maintaining the coaxiality.

Certified Sr. GD&T Professional

RE: Tolerancing Press Fit Thin Tubes

Profile of a surface is also be an option.

What is the wall thickness of the tubes that will be pressed over/in the tube you show in the drawing? Also, how long is the press fit/length of engagement?

RE: Tolerancing Press Fit Thin Tubes

(OP)
Thank you all for your thoughts. I think I will go with runout on the OD and cylindricity on the inner ID as you suggested Drawoh.


Nescius,

The engagement is over the whole entire cylinder and the thickness of the press fit tubes are twice as thick as the one shown.

RE: Tolerancing Press Fit Thin Tubes

Interesting. Do you find the press fitting to be a challenging operation? 3 inches of engagement on that aluminum tube seems like quite a lot, unless you control the diameters very strictly or use heating/cooling or other tricks.

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