On 31 Jul 2011 04:33:00 GMT, "DoN. Nichols"
wrote:

On 2011-07-31, wrote:
On Fri, 29 Jul 2011 13:50:15 -0400, "Existential Angst"
wrote:

[ ... ]

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?

Hole saws tend to give really rough finish, and are best used in
a vertical position with a drilled hole intersecting the cut line to
drain away chips. And, given the number of cutters (teeth), and the
radius, it would probably be too much load for your fairly small lathe.

A trepanning bit for a lathe should be ground curved, so its
centerline matches the curve of the cut being made. There should be
clearance on both the inside and outside of the cut. It sort of should
look like this -- end on:

--((--

except that the curve and height of the tool should really stop at the
center of the height shown -- as indicated by the "-- --" lines.

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.

So -- you can figure the price of two blades. Do you have a
figure of what your time is worth? After a week or so of doing this the
arm should become accustomed to this, and the soreness of the shoulder
be reduced.

However -- I presume that the $6.00 is for cutting out a single
disc. What happens if you stack three or four sheets, so you get
multiple discs at a pass? The thicker it gets, the less precise the cut
line is I believe, but there should be some tradeoff value to determine
where to stop stacking them.

And have you checked what waterjet cutting or laser cutting
would cost instead of plasma cutting? Both of those do a cleaner cut
when stacked.

Good Luck,
DoN.

And water jet would be fairly cheap.

Though..I do have a nice small plasma cutter Id sell pretty cheaply to
someone here.......its good for 1/8" and will sever 3/16" Ive cut
1/4"..but it was slow...and nasty.

But its pretty good for sheet metal

Gunner

--
Maxim 12: A soft answer turneth away wrath.
Once wrath is looking the other way, shoot it in the head.