"steamer" wrote in t...
--Having a little problem with same. I'm trying to bore 2-3/4" dia
holes thru 2-1/2" thick 304 stainless; gotta do 4 parts. I managed to get
the pilot holes up to about .875" with available drillbits, then I switched
to a boring head and, moving in increments of 0.1" on diameter I got the
holes enlarged to about 1.2" but then suddenly it got reeeeal hard to cut,
even with a carbide tipped boring bar. Shallower cuts seem my only option
but at this rate it'll be winter B4 I get the holes finished! I'm going to
go see a pal with a honkin' big lathe who can speed things up a little bit
and that will solve the predicament.
--But I'm thinking *next* time I'll want to do something different
like use an endmill and a rotary table to hog out that kind of material,
then do a cleanup pass on my wimpy little lathe. I'm curious to know what
others have done in similar situations. Any ideas?


On Aug 20, 6:38*am, "Steve Lusardi" wrote:
All stainless will work harden. Some alloys more than others. (304 is easy) The general rule is to use a fast feed, low RPM and a
broad nose on the tool. Of course this assumes the lathe is stiff enough to handle the increased load. Small lathes makes these
jobs very difficult. My suggestion is to use M42 cobalt tools (8% Cobalt) and more tool relief angle to reduce tool drag. Carbide
cannot support the amount of relief required. Normal HSS isn't hard enough and all tools must be SHARP. Please also consider using
a cool mister. Anything to resist temperature rise also helps.

Not tried boring stainless myself but I was chatting to my dad
yesterday about pillar drills and he said that when he was drilling
stainless they had to up the motor size as stainless needs something
like 50% more feed pressure than free machining steel or the drill
rubs and burns out in no time at all - even if you have re-ground it
to around 130º angle etc - and of course the higher feed pressure
translates into more motor power required.

Druid