|
I totally agree with Ray! Slow is the way to go.... and more importantly HOW (the method you use) drill makes a huge difference. If you try to "cram" a bit through steel as most would do with wood, you're going to dull or break bits, and/or you're going to end up with oblong holes, and many other possible problems.
I've trained myself over the years to use a method that I call "tap drilling".... bring the bit down until it touches the material, give it LIGHT downward pressure until you see a few chips, then bring the bit out of the material to allow the chips to clear the flutes....then do it again, again, and again, until you complete the hole. You should be able to "feel" when the bit is about to break through the material....that is where you can create problems if you're not careful....your instinct is going to be to "cram" the bit through in order to finish the hole....but you want to do just the opposite.....lighten up on the pressure and let the bit cut it's way through..... if you try to cram the bit through that last little web, it common for the flutes to grab the material and try to suck whatever you're drilling up the drill bit.
Many times when drilling steel or titanium, I will cut/drill all the holes with a smaller drill then needed, and then go through the hole again with the desired end size bit....this is more accurate, and gives truer round holes then if you drill the hole(s) with the final size bit. When I need very precise holes, as in building folders, I drill with an undersized bit, then use a solid carbide reamer to get the exact size finished hole I need.
If you ever get oblong/slightly oval shaped holes, it's generally because you are using too much pressure/force, and the bit is flexing as you drill....or the bit is dull, and you are having to apply too much pressure....and again, the bit is flexing as you drill.
They type and quality of drill bits used also make a huge difference. Stay away from most "hardware store" drill bits. Those are the usually the lowest quality bits you can get..... the only exception would be that if you MUST buy/use bits from a local store, I would recommend buying Irwin brand..... they are what I call "the best of the worst". I use very few HSS drill bits....most of mine are cobalt, and I also keep various sizes of solid carbide bits on hand for those instances where I goof up and miss drilling a hole prior to heat treating. Most of my drill bits come from either MSC or KBC Tools. I tend to buy/use "screw machine" drill bits because their shorter length help prevent the bit flexing as a hole is drilled.
|