wrote in message
...
On Fri, 29 Jul 2011 13:50:15 -0400, "Existential Angst"
wrote:

"The Dougster" wrote in message
...
A 2- or 4- flute end mill makes a fine trepanning tool on the lathe.

Trepanning of a square blank held on an expaning arbor through a
smallish center hole leaves a square with a round hole, and a disc
with the smallish hole. If what one wants is the disc, trepanning
saves the wear, tear, and irritation of the interrupted cut, and save
turning all those square points into chips.

Assuming the blank is 1/2" thick, idnat why God invented hole saws?

I am struggling to find a good way of cutting out 2.5" disks out of
3/16" steel plate. I have not tried trepanning but it is on the list.

Would a hole saw be useful for this application? How many disks would
one be able to get out of one saw bit?

BTW if I farmed this out to a local shop for plasma cutting it would
cost me $6 per disc. Cutting the same disc with a jeweler's saw costs
1 hour, 2 blades and a sore shoulder.

Michael Koblic,
Campbell River, BC

I've not had good results with hole saws - neither cheap nor expensive.
They need slow feed and flood coolant. I keep them only for non-metal use
now.
Likewise, I've cut circles in steel with a (homemade) fly-cutter. It works,
but I find it tedious and marginal in terms of speed and finish.

How about rough cutting with a fine oxy torch, rough grind off the "bulbous"
dags, clamp together (between centres) and parallel turn to size on the
lathe?
Auto-feed and auto-switch-off and very fine feed means you can indulge in a
peaceful cup of coffee, or read a magazine, while the lathe patiently does
the dirty work.
Can you drill a central hole? That'd make it much easier to clamp.

Alternatively, hold the rough shape in a 4-jaw and attack it from the face.

(sorry if I've repeated earlier advice - only just jumped in now)
--
Jeff R.