Better Grind for Deep Drilling Stainless ???

On 12/23/2017 7:50 PM, Bob La Londe wrote: > I've been roaching out and regrinding twist drills all afternoon. I do > a typical 3 facet grind on each cutting edge and then thin the web. > Works for most things. In stainless it produces long stringy chips. So > I didn't have to stop every time I roached a bit I gather up 4 that were > the right size and set them on my tool cart. When I got to one from > Precision Twist Drill it drilled about the same as the others, but the > chips came out in little pieces, Almost a turning insert with a chip > breaker. It might have even take a little less force. Was that a fluke > or is there a different grind that works better in stainless? Of > course, I paused to long on a peck and roached the tip so I had to > regrind it. Amazingly with my regular 3 facet grind the tip has been > outlasting the other bits including my Chicago Latrobe about 3 to 1. > > I've been drilling fairly deep holes (2.75inches) in 304 with either an > F drill or a 6.5mm drill for the last couple hours making last minute > Christmas presents.

Holy Crap! I never did figure out how it was producing chips instead of strings, but after I resharpened the Precision Twist Drill it finished all the rest of my deep drilling without being resharpened one time. It seemed to grind easily enough, but man it sure is tough in operation. I hate to spend the money, but it would be awfully tempting to replace all my drill sets with these. When I said 3:1 yesterday it was just how many more holes I had drilled with it over previous resharpened bits when I called it a day. We are talking atleast 5:1, and it just barely starting to show signs of edge wear in the chips. I could probably punch several more holes with it.

Does it have parabolic flutes?

I'm not sure what that means, but it does have a slightly faster helix than all my other drills.

Well Bob you got my curiosity up because in a past life I did a medium amount of machining and stuff.

So the drill bit you are talking about should be on pages 008 - 219 somewhere. Would you mind give a old phart a hint or two??

BTW If you didn't know "Precision Twist Drill" and "Dormer" have merged and it is now Precision Dormer.

Thanks,

Les

Its a 6.5mm out of my C252ASET. I just looked at a couple other drills in the set and they look like an ordinary factory grind. Rounded trailing rake with a chisel point. Not even web thinned particularly. Other than the slightly faster helix (and how well this one drill performed) nothing appears to set them apart. I use a 3 facet grind with slight web thinning because its fast, easy, and works in most materials. Looks like 099987 in bright finish.

Thanks Bob, I found it. Maybe it is just a 1 in a million special keeper!!

Thanks!!

Les