Which drill bits?

[plain ol Bill]

For small holes (up to 3/16 - mostly 1/16 & 1/8) in high carbon steel I have been using good quality HSS bits. The "feel" of these bits going thru high carbon is - crunch, thump, crackle --------. Would cobalt or carbide work better in these diameters in HC?
I run the bits slowly (260 RPM or thereabouts) w/ rapid tap as a lube - should these bits be run at a high RPM?

[Webster]

Yes, run them at a higher rpm. It does depend on the material being drilled; I drilled 1/8 holes today in A2 tool steel at 2000 rpm and had no problems. If you have a good HSS drill bits you shouldn?t have to use anything else. I would recommend using 135 degree split point drill bits.

There maybe several reason for that crunchy feeling. Running your bits at that slow speed you may be case hardening the steel you are trying to drill thru (thus you are always drilling thru hardened steel). Make sure when you drill your holes you give constant pressure and don?t keep pulling the bit out of the hole.
Hope this helps.

Bob Cannon

[Ray Rogers]

I'm not sure what that crunching is all about. What I can say is that I also drill everything at 260 rpms, with lubricant, and I've never noticed a problem like that. But, all my drill bits are cobalt steel. I know that what Webster is saying is what I usually see recommended, but it's never worked well for me.

Maybe your drill bits are flexing and drilling a hole at an angle. Using a spotting bit first should help with that if you think that's what is happening......

[samf]

POB
kelly johm and i get are drill bits from west coast repointers they work great you have to have the drill press going as fast as you can
sam fogler

[Ed Caffrey]

Cobalt is my choice for the "middle ground" between the cost of carbide, and the economy (read short usage life) of HSS bits. The worst thing about making folders is that when you get a package of folder making tools from MSC or where ever, the package is the size of a matchbox and it costs $200+!

If your getting the "crackle/crunch" when drilling, try a little cutting fluid, and slow down your feed a little. If you working on Titanium, I tend to "tap" the bit up and down on the material and seem to have good luck.

[Bill Vining]

I have experienced the crunch and crackle myself. It always ended up with a trashed drill bit. I have since increased my drilling speed and it's much better now. The holes are much cleaner too.

[Bob Warner]

I have had that creacking sound before and I just sharpen the bit and then finish the hole. It seems to me that crackling happens right before the dull bit screetch.

Try sharpening the drill bit and see what happens.

[Don Cowles]

I use the cobalt bits in screw-machine (instead of jobber) length. Because they are shorter, they are stiffer and drill truer holes.

[Ray Rogers]

What Don said. I'm so used to it that I didn't think to mention it but my cobalt drills are always screw machine length too ......