Measuring a drilled hole angle in a thin walled part

I am trying to figure out how to quickly and accurately measure the angle of a drilled hole on a thin walled part. The part is bicycle rim; the thickness of the wall is > 0.100. The basic geometry is an arc that is 0.100 thick and the holes are drilled at alternating angles slightly off center. We have a Micro-Vu, height gauges, gauge pins blocks etc. I cannot come up with a good way to measure the drilled angle. Gage pins move when you go to measure so it is not accurate. I am looking for any suggestions.
Thanks

nkeith said:

I am trying to figure out how to quickly and accurately measure the angle of a drilled hole on a thin walled part. The part is bicycle rim; the thickness of the wall is > 0.100. The basic geometry is an arc that is 0.100 thick and the holes are drilled at alternating angles slightly off center. We have a Micro-Vu, height gauges, gauge pins blocks etc. I cannot come up with a good way to measure the drilled angle. Gage pins move when you go to measure so it is not accurate. I am looking for any suggestions.
Thanks

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You should be able to come up with a reasonable approximation using gage pins. Is there any reason you're trying to measure this? What is the tolerance? Does it assemble with the mating component?

I am not sure if you have drilled the holes yet (or if someone else has) but I would put the time into setting up the machine accurately in the first place for this, the holes would need to be drilled with special drill/endmill and or bored as a normal drill would tend to push off centre.
Depending on the set up, if the center line and angle is set correctly a finger dial indicator could be substituted for the drill as a final check that the hole has gone in the right place ,do the first one undersize to check all is going to plan before opening out to final size to save scrapping the job.A similar setup could also be used to check existing holes.

Several years ago, I ran into a similar problem but we were making hubs for motocross bikes. We had over .250" of material to drill through so using a gage pin to check the angle was not a problem. That being said - the method was overkill. Rims and hubs are designed with a lot of 'wiggle' room on the orientation of the spoke. It actually helps during assembly and especially when adjusting or truing the rim to have room for the spoke to swivel around. The only problem we ever had with the spoke holes had nothing to do with alignment and everything to do with depth. If the depth was off, the spoke would either not reach the rim or it would go too far through. The customer simply provided us with a couple rims and a few sets of spokes and we would lace one up to ensure the rim was positioned correctly in relation to the hub.

Are you trying to QA a rim you are building? I would think the thing to do is make a segmented circle that fits into the rim walls where the catch for the tire bead goes - and has holes you can line up and get a gage pin to stay in.

In other words, make some kind of backing fixture which will also help you make sure the holes are aligned correctly with the rim side walls and the bead seat.

We are trying to check the drilled angle on a Carbon-fiber bicycle wheel. Very similar to what Old Nubbins said except carbon tends to be less forgiving then metals and we have much less material <0.100 . I think as Sable said verifying machine setup might be the best option for us.

Depending on your production volume, this sounds like a good application for a poke-yoke. Expanding on what Bryan suggested, an arc segment (say 45°) with pins installed per the geometry of the rim at MMC (pins at minimum hole size) can verify all holes are positioned correctly. If one of the holes is out of position, the gage will not fit (theoretically, of course).