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


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.

The rough finish would not be a problem as the whole thing gets
finished in he lathe anyway. Cost in terms of consumables (blades) is,
as well as the duration of the procedure.

I see some people make their own trepanning tools:

http://bbs.homeshopmachinist.net/showthread.php?t=45764

Although their skill is admirable I am not sure that I want to invest
the time etc. in a single purpose tool.

I looked at what was available commercially and came across this:

http://www.kbctools.com/can/Navigati...cfm?PDFPage=52

What I found interesting was that they seem to use the same cutter
over the whole range of radii which is quite wide.

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.

I asked for a quote on 10. $58 including the material. Looking at
other vendors on line the drop in price from 10 to 100 is not that
significant.

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.

I would be surprised in anyone within 100 km has either of those, but
one never knows.

Michael Koblic,
Campbell River, BC