Handlebar Assembly Tolerance
The following report is an analysis of the hole position tolerance for a handlebar weldment. We have further studied our manufacturing and inspection practices, and have determined that 100% of our parts meet the drawing requirements. We understand that there is an issue fitting the handlebars to the mating “pod” assembly, so you will find our suggestion near the end of this report.
The pods don’t have dimensions corresponding to 492.4 and 547.6 mm. As drawn, the four tapped holes are not controlled as a pattern. As such, the tolerance for their locations is unknown.
The pod – handlebar assembly uses countersunk head screws, which serve an aligning function. This restricts any relative motion between the parts when as screws are tightened, and takes up some of the fit tolerance.
An M4 screw has a max OD of 4 mm. The nominal hole size in the base is only 4.5 mm. This allows for .5mm of misalignment between the pod holes and handlebar base holes. As each screw is tightened, the allowance is becomes even smaller for the remaining holes. This clearance is not sufficient to ensure all of the parts assemble together.
Tightening the hole position requirements on the handlebar will make manufacturing more difficult, and will add to cost. As it is, about 10% of the production parts would have to be reworked or scrapped in order to ensure each part will fit the test gauge. It would be more cost effective to ensure the parts fit by enlarging the hole size in the handlebar bases.
We suggest that the customer determines the value of T2 by capability study of the pods or some other means. The client can then calculate the required size for the handlebar base holes, and give this number to the The Federal Group.
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