On 12/24/2017 12:49 PM, Bob La Londe wrote:
On 12/23/2017 7:50 PM, Bob La Londe wrote:
I've been roaching out and regrinding twist drills all afternoon.Â* I do
a typical 3 facet grind on each cutting edge and then thin the web.
Works for most things.Â* In stainless it produces long stringy chips.Â* 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.Â* 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.Â* It might have even take a little less force.Â* Was that a fluke
or is there a different grind that works better in stainless?Â* 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!Â* 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.Â* It
seemed to grind easily enough, but man it sure is tough in operation.Â* I
hate to spend the money, but it would be awfully tempting to replace all
my drill sets with these.Â* 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.Â* We are talking atleast 5:1, and it just barely
starting to show signs of edge wear in the chips.Â* I could probably
punch several more holes with it.


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??

https://www.dormerpramet.com/Downloa...NAFTA_2017.pdf

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

Thanks,

Les