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Building Tips and technical articles. => Building techniques => Topic started by: Mike Scholtes on May 16, 2010, 11:52:24 AM
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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).
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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.
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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
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Brett,
I recently picked up some carbon steel drills. They seem to work fine. The TiN coated stuff tends to lose the coating pretty quickly with carbon fiber. I've used TiCN end mills to mill carbon fiber and it doesn't do well, but the TiAIN mills do pretty well and stay sharp. I haven't tried Cobalt coated stuff yet.
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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.
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Wow, it's a good thing I asked. So hammering a 6p nail through it would not be the best plan?
I will check out the site Howard suggests and see if I can obtain this part. I don't know any 11 p.m. drill sharpeners.
It is a little bit of technical overkill but what about laser or water jet cutting? I do actually know people (well, person) with that ability and equipment. Or should I just use the dural gear and go back to the 6p nail idea?
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If you're just drilling that one gear, I wouldn't think it would be worthwhile to get a high zoot bit.
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I agree with Howard (imagine that).
Just pick up a couple of cheap HSS drill bits and drill the holes. You will probably trash them but so what. And the job will be done.
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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.
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And no one tels you to watch out when you break through. Be carefull because the drill wants to grab and thread itself in like a screw. It also happends when you drill thin sheets of whatever.
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Good point. Make sure the gear is securely attached to something.
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I drilled a 3/8" hole in some .050" carbon cloth layup yesterday with a carbide Forstner bit. It worked dandy.
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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.
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Sometimes we get a job in from (of all people, Boeing), to drill some fairly good sized (~ 3/8"?) holes in carbon plate...that's somewhere around 1/2" thick. I've dodged that, so far, but I know they provide diamond drills; they don't last all that long, and they're buku bux. I would suggest getting stubby ("screw machine") cobalt drills. If you possibly can, always use stubby drills, at least for the pilot hole, even if you need to go deeper. I'll ask for more details tomorrow, if I don't....uh, forget. ??? Steve
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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...
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I asked today...since I never had to do the job myself. The drills Boeing provided are carbide, with a special coating of some sort...I was told it was diamond, but I wouldn't swear to it. Also was told high rpm, dry. Dust is a problem, but liquid coolant isn't the solution, because it'll make an abrasive slurry. A vacuum is a fine idea. I still think cobalt tool steel screw machine drills would be the practical way to go. Ask how much for a whole pack would be, just in case it's a screamin' deal. I don't think they like to take inventory of partial packages... LL~ Steve
Edit: Because cobalt drills aren't carbide, I'd lower the rpm considerably. Assuming somewhere around 1/8" drill (depending on the desired screw size), maybe 1,000r's. When the drill is obviously not as good as it once was, dispose of it in an environmentally safe manner (86 it anyway you wish!).
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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!
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The tapered drill reamer is the best drill to use on carbon, bar none. I built the b-2 with them and while management had an issue with boneheads whom would try usinging them in too laerge a step you could drill far more than 6 or seven holes with proper lubrication than you could with plain carbide bits.
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I never worried about drilling carbon fiber. 1/8 inch bits at Harbor Freight by the package. H^^