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#11
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aluminum rib, aluminum spar, holes drilled but screws broken off
jls wrote: I'm rebuilding a Super Cub wing and the flanges on the ribs and the blahblahblah. Larry, you damn long-winded thing, you. OK, guys, here's what the friendly engineer says. Use a 3/32 cobalt drill bit. Drill at 28k rpm or better and use cutting oil, ie, kerosene and lard. Hit it and back it off; hit it and back it off. Will let you know how it works, although I bought a lot of that other recommended stuff and a diamond burr the dentists use. |
#12
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aluminum rib, aluminum spar, holes drilled but screws broken off
Lots of good advice given but there's one problem that hasn't been addressed. That's keeping the drill bit in the broken screw and not letting it wander off into the spar. if the screw has been broken off under flush there's not an easy way of dressing up the surface for a good start. To keep from really messing up the job you may want to make a drill guide to keep the bit aligned and going straight into the broken screw. A piece of 1/2" square steel stock about 8" long from any hardware store will do. Set it up in a drill ress and drill a hole the size of the bit you want to use through one side directly through. Set the bar on the spar and line up the hole over the broken screw and then clamp the bar down securely to the spar flange. Now you can drill through the bar into the broken screw with far less chance of needing one of those special figure eight shaped screws to cover the mess you made. Any good quality SHARP drill bit will do the job with the correct technique. For drilling out steel screws, use a slower RPM and more pressure than for drilling aluminum. Start with a couple of light taps at high RPM to ensure the drill gets a good center on the broken screw shank or use a small center punch that will fit through the guide. Using cutting oil is a good idea. I don't think the Craftsman extractors are small enough for a #4 screw. I would go with a left handed bit, mouse milk, and take my time. |
#13
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aluminum rib, aluminum spar, holes drilled but screws broken off
On 2 Jan 2007 03:34:14 -0800, "Charles" wrote:
Lots of good advice given but there's one problem that hasn't been addressed. That's keeping the drill bit in the broken screw and not letting it wander off into the spar. if the screw has been broken off under flush there's not an easy way of dressing up the surface for a good start. To keep from really messing up the job you may want to make a drill guide to keep the bit aligned and going straight into the broken screw. A piece of 1/2" square steel stock about 8" long from any hardware store will do. Set it up in a drill ress and drill a hole the size of the bit you want to use through one side directly through. Set the bar on the spar and line up the hole over the broken screw and then clamp the bar down securely to the spar flange. Now you can drill through the I would suggest using a "center drill" that just nicely fits the hole in the steel plate at this point. It won't wander and will create a nice cone shaped indentation in the screw shank. Then switch to a drill and metal plate with a hole that fits the drill. A good sharp drill *should*follow the screw bar into the broken screw with far less chance of needing one of those special figure eight shaped screws to cover the mess you made. Any good quality SHARP drill bit will do the job with the correct technique. For drilling out steel screws, use a slower RPM and more pressure than for drilling aluminum. Start with a couple of light taps at high RPM to ensure the drill gets a good center on the broken screw shank or use a small center punch that will fit through the guide. Using cutting oil is a good idea. I don't think the Craftsman extractors are small enough for a #4 screw. I would go with a left handed bit, mouse milk, and take my time. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com |
#14
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aluminum rib, aluminum spar, holes drilled but screws broken off
I just looked, and the Craftsman extractors I referenced go down to a #
5 screw. It had a reference for a size smaller than #6, and I thought it was a #4, but alas. Bud Charles wrote: Lots of good advice given but there's one problem that hasn't been addressed. That's keeping the drill bit in the broken screw and not letting it wander off into the spar. if the screw has been broken off under flush there's not an easy way of dressing up the surface for a good start. To keep from really messing up the job you may want to make a drill guide to keep the bit aligned and going straight into the broken screw. A piece of 1/2" square steel stock about 8" long from any hardware store will do. Set it up in a drill ress and drill a hole the size of the bit you want to use through one side directly through. Set the bar on the spar and line up the hole over the broken screw and then clamp the bar down securely to the spar flange. Now you can drill through the bar into the broken screw with far less chance of needing one of those special figure eight shaped screws to cover the mess you made. Any good quality SHARP drill bit will do the job with the correct technique. For drilling out steel screws, use a slower RPM and more pressure than for drilling aluminum. Start with a couple of light taps at high RPM to ensure the drill gets a good center on the broken screw shank or use a small center punch that will fit through the guide. Using cutting oil is a good idea. I don't think the Craftsman extractors are small enough for a #4 screw. I would go with a left handed bit, mouse milk, and take my time. |
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