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Multiple Tapered Parts all fitting together.

Multiple Tapered Parts all fitting together.

Multiple Tapered Parts all fitting together.

(OP)
We have a design situation that includes the use of 3 conical tapered parts that all fit together, and are metric parts.  We have an outer housing, a sleeve, and a part that fits into the sleeve.   I cannot get into specific materials, or why it is this way and not another, but suffice to say we have 3 20 degree basic included tapered parts that fit together, and we would like to maintain the top of the 3 tapered parts (top is perpendicular to the axis of the taper).     According to ASME Y14.5, the best way to dimension this is to basic the diameter of a gauge point at a toleranced distance from the top, and provide a basic taper or angle.  Our parts are all ~15 deep (tolerance not important for this feature at this point, and can vary widely), and going from outer to inner:
Housing:  7.5-0.2, 10.95 Dia basic  (tight tol as is)
Sleeve:  Housing mate 7.5+0.5, 10.95 dia basic  (all the mfg can hold, strange propritary process)
Center part mate 7.5-0.5, 10.3 basic dia
Center (conical) part: 7.5+0.1, 10.3 basic dia (tightest practical tol)

As you can see, this gives us flush or within 0.2 of flush some of the time, but some times it can be ~0.6 below at LMC.  We want all flush at the max, and at a min, we want the sleeve to support the center component.  

We do have sucessful prototypes, but from a mfg perspective, this is not ideal due to scrap.

We also dont know if our customer is agreeable to "matched parts" wherein we define several dash part numbers that would bin the tolerances for all the parts tigheter, and have 100% inspection to get us "binned" and on orders specify a % range or ratio of each dash number, for example for the sleeve outside, a -1 would be 7.5+0.199, -2 7.7+0.399.  

Has anyone had sucess with this method for a production run of ~1500 precision assemblies?  We're going for a low rejection rate.

Here's some other relvant information / ideas we have discussed:

-replace the housing with a "collet" style part that would be more forgiving to the taper and allow us to "push" the sleeve and the center cone upwards towards flush?
  However, due to the strength the material must have, this is most likely impractical.
-Replacing the sleeve with a poured in place material such as a hard solder.
-Parts cannot be ground down, that would cost more than scrapping 50% of the parts.
-sleeve  mfg is a propritary process, vendor will not provide insight as to why this tol is so hard to control.
-once parts are assembled, there are no servicible parts, if a part wears, the entire assembly is replaced.

The questions i realy need answers to are:
-is there a way to solve the tolerances (based on the available band) to give us flush to 0.2 below flush.
-Is "binning" the parts practical for production of this scale?

I dont have prints at home for this, but attached is a very basic & crude sketch

-LMH  

RE: Multiple Tapered Parts all fitting together.

What is the material of the sleeve? Can it be make from sheet formed into a cone with a gap of 2 to x mm? If so you could make a number of sleeves with different thicknesses. Your Housing and Center parts would have the size measured and stamped on the part. You would have a chart showing what thickness would be needed depending the size of the two parts.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net

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