Hi,

If one has a piece of aluminum plate that one would like to make round using
a rotary table on a mill, how does one clamp it down so that one can use an
uninterrupted cut?

I can put a small (.200-ish) hole in the center, but that doesn't seem to be
enough to hold a clamp decently. I can clamp it from the outside, but I'd
have to move the clamps as I milled around the piece. I'm assuming that
this wouldn't allow for an uninterrupted cut which I wanted for the best
finish. Is this newbie missing anything? Suggestions?

Regards,

Peter

Subject: Milling round piece on rotary table
From: "Peter Grey"
Date: 31/07/04 16:43 GMT Daylight Time
Message-id: et

Hi,

If one has a piece of aluminum plate that one would like to make round using
a rotary table on a mill, how does one clamp it down so that one can use an
uninterrupted cut?

I can put a small (.200-ish) hole in the center, but that doesn't seem to be
enough to hold a clamp decently. I can clamp it from the outside, but I'd
have to move the clamps as I milled around the piece. I'm assuming that
this wouldn't allow for an uninterrupted cut which I wanted for the best
finish. Is this newbie missing anything? Suggestions?

Simple. Imagine the rotary table is to the left of the headstock so you're
milling on the right edge of the piece. You arrange a clamp from the bed on the
left side of the piece, bearing down on the centre of the piece, but this must
act through a ball bearing so it can rotate as the rotary table rotates. If you
have a lathe don't even bother though because on a lathe it's easy...

With the same principle, on a lathe you can grip a plate between two bungs
using tailstock pressure and a revolving centre without needing a chuck or
clamp, as long as you take light cuts. Making things round is a lathe job not a
milling job.


--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)

If you take light cuts and make multiple revolutions, double-stick tape like
carpet tape will usually hold well enough.

Super glue or epoxy the plate to the table. Heating the plate will release
it when finished. Take light cuts.

If you use a nut and a big washer on a stud through the center hole, put a
piece of sandpaper between the plate and rotary table top. Take light cuts.

Randy

"Peter Grey" wrote in message
nk.net...
Hi,

If one has a piece of aluminum plate that one would like to make round
using
a rotary table on a mill, how does one clamp it down so that one can use
an
uninterrupted cut?

I can put a small (.200-ish) hole in the center, but that doesn't seem to
be
enough to hold a clamp decently. I can clamp it from the outside, but I'd
have to move the clamps as I milled around the piece. I'm assuming that
this wouldn't allow for an uninterrupted cut which I wanted for the best
finish. Is this newbie missing anything? Suggestions?

Regards,

Peter

I like Dave's bearing clamp idea, I doubt that I'd have thought of that.
When I want a round cut out of a square, I bolt the corners to the table
T-nuts with a a sheet of scrap underneath the workpiece. When you near the
full depth, there will be a foil-thin amount holding the disc in place
(that's a good time to stop). The disc will separate easily as it's gently
pried up.
The other method I use is to utilize a 4-jaw chuck on the rotary table. The
same applies to the stop depth.
When you get bored/tired of cranking the RT, motorize it.
http://www.tcis.net/%7Ekwag98/shop/p2rt.html

WB
...................

"Peter Grey" wrote in message
nk.net...
Hi,

If one has a piece of aluminum plate that one would like to make round
using
a rotary table on a mill, how does one clamp it down so that one can use
an
uninterrupted cut?

I can put a small (.200-ish) hole in the center, but that doesn't seem to
be
enough to hold a clamp decently. I can clamp it from the outside, but I'd
have to move the clamps as I milled around the piece. I'm assuming that
this wouldn't allow for an uninterrupted cut which I wanted for the best
finish. Is this newbie missing anything? Suggestions?

Regards,

Peter

"Wild Bill" wrote in message
...
When you get bored/tired of cranking the RT, motorize it.
http://www.tcis.net/%7Ekwag98/shop/p2rt.html

Thanks. I've been thinking the same thing. I have a variable speed
(something small like 1/6HP?) motor and controller that I thought would be a
perfect compliment for my RT.. or the spindle on my mill...

Peter

Peter Grey wrote:

If one has a piece of aluminum plate that one would like to make round using
a rotary table on a mill, how does one clamp it down so that one can use an
uninterrupted cut?

I can put a small (.200-ish) hole in the center, but that doesn't seem to be
enough to hold a clamp decently. I can clamp it from the outside, but I'd
have to move the clamps as I milled around the piece. I'm assuming that
this wouldn't allow for an uninterrupted cut which I wanted for the best
finish. Is this newbie missing anything? Suggestions?

Easiest way if you have a lathe and start out with a suare work piece is
to drill four holes in the corner, screw the stock to a piece of 3/4"
thick MDF (medium density fibreboard aka Medite). Mount in 4-jaw chuck
or on a faceplate and cut out your circle. If the radius is large
enough, the work thin enough and you have a not-too-high parting tool,
you can use it otherwise you need a trepaning tool. A trepaning tool
looks like a parting/groving tool except that it's curved so the sides
don't rub.

Alternately, you can clamp the work piece to the MDF with a large washer
and an a draw bar through the headstock. This is the best if the stock
is rather thick. Rough it out with a band saw then machine it round.

If you really want to do it on the mill, here's how: My RT has a hole
in the middle to take a MT-2 center. This hole extends right through at
the smaller diameter of the taper. I made a special nut that is longish
and hex at one end and steped down to a round that fits into the hole in
the RT. This nut is threaded for 3/8-16 but could be 1/4 or even 3/16.
The work piece has a hole drilled in what will be the center to take the
bolt and a fairly large washer. The RT needs to be aligned with the
mill. You can see my procedure for this in
http://www.metalworking.com/DropBox/Prop_speed_reducer.pdf
The RT is set up on two parallels so a thin wrench can get under it to
hold the nut while the bolt is tightened. The workpiece is set on a
piece of MDF so I can cut right through the work piece without hurting
the RT. Offset by the desired radius and mill away. Contact me off
list if you need a picture.

Ted

maybe mit-tee-bite clamps. They are clamps that press on the od via a
camming action.

Tony

"Peter Grey" wrote in message
nk.net...
Hi,

If one has a piece of aluminum plate that one would like to make round
using
a rotary table on a mill, how does one clamp it down so that one can use
an
uninterrupted cut?

I can put a small (.200-ish) hole in the center, but that doesn't seem to
be
enough to hold a clamp decently. I can clamp it from the outside, but I'd
have to move the clamps as I milled around the piece. I'm assuming that
this wouldn't allow for an uninterrupted cut which I wanted for the best
finish. Is this newbie missing anything? Suggestions?

Regards,

Peter