On 12/24/2017 2:58 PM, ABLE1 wrote:
On 12/24/2017 12:49 PM, Bob La Londe wrote:
On 12/23/2017 7:50 PM, Bob La Londe wrote:
Â* I've been roaching out and regrinding twist drills all afternoon.
I do
Â* a typical 3 facet grind on each cutting edge and then thin the web.
Â* Works for most things.Â* In stainless it produces long stringy
chips.Â* So
Â* I didn't have to stop every time I roached a bit I gather up 4 that
were
Â* the right size and set them on my tool cart.Â* When I got to one from
Â* Precision Twist Drill it drilled about the same as the others, but the
Â* chips came out in little pieces, Almost a turning insert with a chip
Â* breaker.Â* It might have even take a little less force.Â* Was that a
fluke
Â* or is there a different grind that works better in stainless?Â* Of
Â* course, I paused to long on a peck and roached the tip so I had to
Â* regrind it. Amazingly with my regular 3 facet grind the tip has been
Â* outlasting the other bits including my Chicago Latrobe about 3 to 1.
Â*
Â* I've been drilling fairly deep holes (2.75inches) in 304 with
either an
Â* F drill or a 6.5mm drill for the last couple hours making last minute
Â* 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.Â* 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


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.