On race cars the floor trays are often carbon composite flat panels and held to the main carbon tub by countersink Allen screws. Grounding or general butchery sometimes makes the female hex unusable, or they are rounded off. Drilling is often the only way to remove them, by taking their heads off and removing the rest with grips once the panel is out of the way. HOWEVER, I get through umpteen bits like this, good ones I might add. What am i doing wrong, a pistol drill is the only option. I start with maybe a 1/8 bit then go to something like a 5/16 or 3/8 bit. I now have a retirement home for knackered drill bits..... Is there some trick to this? :)
If you're using an airdrill the speed might be a bit high. Another trick that help you out is to use a Left Hand drill bit. They are commonly found in the better bolt extractor kits, but any good supplier should be able to get them for you. A lot of the time the bolt will thread itself right out while you are drilling.
^^^^^^^^^^^^^^^^^^^^^^^^^^ I take it from the OP that these Allen screws are on the underside of the race car, and by "grounding" he means they get damaged when the car bottoms out. I don't see how Bondo would do any good against forces like that, but it would make it almost impossible to insert an Allen wrench. Chris, could you tell me what I am missing?
I use carbide drill bits for allens. I can do it because I grab dull ones out of the carbide scrap recycling bucket, put a quick edge on them on a green wheel and when I chip one from the lack of rigidity, I either fix it up, or use another one from the recycle bucket.
There are a few bennies working in a manufacturing facility that has a lot of cnc stuff. In a perverse way, I like drilling the heads of allens because it is so much easier than when I worked in a place where HSS was all I had to work with.
As far as HSS, sharp, oil, slower speeds. Learn to touch up your drill bits, doesn't have to be perfect you are going to ruin the edge quickly.
Usually, the problem is that the drill chips the corners off because the edges of the drill catches in the head recess. Try starting with a drill about the diameter of the O.D. of the head. Drill deep enough to eliminate most of the screwdriver recess and then change to a drill about the diameter of the screw shank to get the head off.
Button head cap screws might make more sense if they are getting bashed up like that. Not that they WON'T get bashed up too, but they have a natural ramp around the head and a lot more material on the sides of the head and will be lower profile too. They're available in hex, Torx, etc.
I know this goes against what others have already advised but this way also works! - HSS TiN coated stub drills, preferably with 4 point geometry. Drill once using lots of speed (preferably with an air powered drill) use just enough pressure to locate the drill in the hex. Size the drill a couple of mm larger than the thread OD.
On Fri, 27 Mar 2009 22:11:37 +0700, the infamous Bruce In Bangkok scrawled the following:
I've used a grinder to take the head off, then drilled out the stud when necessary. A die grinder with a 3" cutoff blade can cut a nice slot in it if you want to try that angle, too. Cutoff blades are 50 cents ($4.99/10-pack) on sale at HF.
I had a treat yesterday. I installed a grab bar in an old coot's shower. To do the job properly, I finally broke down and bought a real glass/tile bit for $12. (I didn't think B&D -made- anything that expensive.) It went through the grout and ceramic tile like a charm, and without raising a single chip around any of the 6 holes.
I may purchase a set of those from HF and see how they differ in quality. Then I'll have smaller and larger bits, too.
Just a casual comment: If that is the version with the spiral cut on the shank and the small flat carbide insert brazed in the tip, they don't cut metal worth a damn. Needed to drill some holes in a HSS hacksaw blade and didn't have the correct size carbide drill so in desperation bought one of the smaller sized "cement drills". Didn't work :-(