[Schulze]

I got a deal on some new carbon rims that were made for internal nipples. These have a 2.1mm spoke hole. I'm going to drill them out to 4.2mm so I can use external nipples.

Let's think about this. Do I want to just drill? Or should I drill then ream? Should I drill in steps or just go all the way the first time?

My main concern is flaking. I want a clean hole.

The tragedy here is that I had an old set of carbon rims that I threw away last year. Mistake. Should have kept them to practice on.

Flame suit on. Don't hold back. Remember, verbally abusing anonymous internet posters keeps the thread bumped, so don't be shy.

 

[Schulze]

So far I have a drill press and all the materials for a wooden jig. So jigging for the proper angle isn't going to be a problem.

 

[Lone Rager]

Are the holes angled alternately toward the DS and NDS hub flanges? Is the thickness of the rim at the spoke holes thin enough to allow the square part of the nipple to protrude? Might need longer nipples? Other than that it should work.

I'd drill it in one shot at pretty high rpm and a slow feed with a nice sharp bit. It will dull pretty quickly so solid carbide or a diamond bit would be best.

 

[mikesee]

Occasionally I have a customer that wants to run schrader valves, so I need to ream out the valve hole. It is amazing how quickly and easily material is shed doing this.

Point simply being I doubt you'll have flaking, but ream the first few to get a feel for it.

 

[Schulze]

Are the holes angled alternately toward the DS and NDS hub flanges? Is the thickness of the rim at the spoke holes thin enough to allow the square part of the nipple to protrude? Might need longer nipples? Other than that it should work.

I'd drill it in one shot at pretty high rpm and a slow feed with a nice sharp bit. It will dull pretty quickly so solid carbide or a diamond bit would be best.

Rim thickness is 2.6mm at the spoke hole, so it will be good to go. Yes, holes are angled. This is the main reason I'm building a jig. I'll do every other hole, flip it, then do the rest.

Occasionally I have a customer that wants to run schrader valves, so I need to ream out the valve hole. It is amazing how quickly and easily material is shed doing this.

Point simply being I doubt you'll have flaking, but ream the first few to get a feel for it.

Thank you! I'll order a ream from McMaster.

 

[mikesee]

I'd drill it in one shot at pretty high rpm and a slow feed with a nice sharp bit. It will dull pretty quickly so solid carbide or a diamond bit would be best.

Sounds like you have machining experience, which I do not.

That said, I don't think even the cheapest bit will dull during this project -- the carbon is like room-temp butter. Hardest part will be alignment, followed by ensuring one doesn't inhale any dust.

 

[Jayem]

A possible issue is that this will destroy any clear coat applied to the holes (if it was applied in the first place), this will greatly enable galvanic corrosion if using alloy nipples, making whatever barrier compound you choose that much more important.

 

[Lone Rager]

Yeah, I have a fair amount of machining experience, even machining CF composite. It quickly dulls tools and dull tools can fray and crack CF. They'll also heat up and melt the epoxy. 64 holes will definitely dull a common tool steel bit. An alternative to carbide or diamond bits is just buy a half dozen tool steel bits and change them out after ten holes.

I haven't yet seen a CF rim that has any coating or barrier applied to the nipple seats or holes. Keep sealant out of the rim and the nips won't get eaten. I always grease the spoke threads and nipple heads, mainly to make it easier to get to 120 kgf tension without stripping the nips, but so far I haven't experienced rotting nipples on my own bikes, though I've seen plenty on other bikes.

 

[Schulze]

I just ordered a 4.2mm full carbide bit. Very convenient for me that that size is common and only $12 for the tool. I also have some acrylic clearcoat to touch up the hole after I drill.

 

[Schulze]

Update: I finally drilled and built the wheel. The drilling caused small flakes and fibers to still impinge on the hole. I used a round file to smooth them out. But it worked out nicely.

One thing I noticed is that the nipples on this wheel are straight in line with the spoke. On other factory carbon rims, even though the drilling says 6 degree in the specs, there is a slight bend to the spoke.

 

[PuddleDuck]

Update: I finally drilled and built the wheel. The drilling caused small flakes and fibers to still impinge on the hole. I used a round file to smooth them out. But it worked out nicely.

One thing I noticed is that the nipples on this wheel are straight in line with the spoke. On other factory carbon rims, even though the drilling says 6 degree in the specs, there is a slight bend to the spoke.

Awesome! Glad to hear that it worked out for you. I've an 2013 LB rim that I'd like to drill to 6 degrees. Would you post pics of the set-up you used, jig etc. Thanks