I have a nice Carbon gear from Mejzlik that is undrilled and needs holes for mounting bolts and for axles at the end of each gear leg. I have never had to drill carbon parts and don't want to ruin the part by cracking it. Does CF require a special type of drill (as does acrylic/plexi for instance) and/or technique to safely drill it? The part is about 3/16 thick at the mount and 1/8 at the gear leg ends. Thanks in advance to anyone with experience doing this (successfully).

I've drilled it a lot. Just have to be careful that the drill is square and you go slow. And understand that the stuff will dull your drill bit pretty quickly.

   What little I have had to do worked just dandy using TIN coated drill bits, and so far they haven't gone dull on me.

     Brett

This reminds me of a story (as so many things do).  Once long ago I was drilling carbon motor mounts for combat planes.  I was getting five holes per drill bit and running out of bits.  It was 11:00 PM.  I knew that Adrian Barraclough would: 1) know how to sharpen drill bits, and B) be awake at 11:00 PM, so I called him.  Not only did he come over and sharpen bits, but he brought along John Hart-Smith, the world authority on composite structures, who was visiting at the time. 

Although you could probably drill all the holes in a set of carbon gear with one new HSS bit, you might, depending on the material, damage the material around the hole.  This may not be a problem, because you should have lots of edge margin.  A carbide-tipped bit is probably better.  It would certainly last longer.  I use carbide tapered drill-reamers I got from the Boeing surplus store.  I think these are the same: http://www.starliteindustries.com/c00400/page27.shtml .  These last a long time, don't make a lot of heat, and make clean holes.  Note that Starlite says to operate them at 125-150 SFPM.  Assuming this is surface feet/minute, it works out to about 4,000 RPM for a 1/8" bit.  I remember hearing 5,000 RPM.  I use the fastest speed on my Sears drill press, which works OK.  I use isopropyl alcohol for a lubricant, but I don't remember where I got that notion.   



 

If you're just drilling that one gear, I wouldn't think it would be worthwhile to get a high zoot bit. 

Thanks guys, I will give it a go. Good luck at the NWR to all you soggy folks up in the Pac NorWest. Work and family obligations preclude me from making it but I will watch the results on the forum.

Good point. Make sure the gear is securely attached to something.

I don't think this stuff had been invented when I took junior high school metal shop. We just hit things with rocks until they were the right shape.

I now think I need to find a source of high quality tool pieces (IOW not Harbor Freight, Post Tool, Home Depot) and get some decent drills. I am not worried about the cost of the tool nearly as much as screwing up a $40 part. I am still recovering from cracking a custom formed plexiglass windshield for my Taylorcraft about 30 years ago with the wrong drill.

Steve,

The stuff you're getting is probably carbon/kevlar/osmium/unobtainium Boeing super-secret ceramic composite. While standard carbon fiber parts can be tricky to drill, it usually doesn't take billion dollar drill bits. But hey, if you got 'um...

I used to be a member of the Producibility Engineering group at Raytheon.  We determined that for production a polycrystalline diamond drill worked best but they are $$$.  For limited numbers of holes carbide works just fine but do not expect over 25- 50 holes.  We ran ~1/8 dia at 6K rpm (if I remember right).  HSS will work but do not plan on more than 1 or 2 holes per bit.  I once tried band sawing some 1/4 carbon for 1/2A motor mounts I got about 3" before there were no teeth left!

I never worried about drilling carbon fiber.  1/8 inch bits at Harbor Freight by the package.