To be exact the rpm of the drill is calcualted as:
rpm = ( sfm * 3.8 ) / diameter
(sorry to those of you in metric countries, but this is all inches, etc)
For mild steel the sfm (surface feet per minute) can be 75 to 100. As the
material gets harder, either by alloy content or heat treating, you need to
drop the sfm. For example 4140 might be in the 60-70 range, tool steels
(annealed) might be in the 40-50 range, etc. So if we assume the plate has
some alloy content and/or has been heat treated & tempered then a 1/4" drill
shuld proabably live for some time if not turned faster than around 700 rpm.
Feed is also a big problem. A persons normal 'feeling' is that if the
material is hard that you should feed (in the case of a hand drill that
would be basically be the pressure that you put on the drill motor) lightly.
Many of these odd alloys of steel (including stainless) work harden, some do
it VERY readily. You MUST feed hard in these situations. When using a
machine tool, a normal feed for a drill might be something like 0.003 to
0.005 inches per revolution. On these types of materials I can run 0.006 to
as much as 0.010ipr. I realise that this is somewhat meaningless for a hand
drill but like you said, the chips should come out silver and curly.
That is all (or is that, that's enough!)
je
===
To unsubscribe from the mil-veh mailing list, send the single word
UNSUBSCRIBE in the body of a message to <mil-veh-request@skylee.com>.