On 2010-02-13, Michael Koblic wrote:
"Jim Wilkins" wrote in message
...
[ ... ]
All you need is a chunk of steel or iron the right size. I've made
adapters out of scrap hydraulic cylinder rod, a cast-iron pipe coupler
and a locating pin from an old Segway fender mold.
Barbell weights are the right shape, though the iron may be difficult
to cut. A few days of cooking inside the wood stove might soften then
up enough, it works well with flame-cut hot rolled steel.
Fitting an adapter to the spindle is easier if the adapter is on a
mandrel between centers so you can check the fit and replace the
adapter exactly concentric, to remove another half thousandths all the
way around. You could bolt it to the flange to cut it almost to size
quickly.
[ ... ]
BTW
can you part the piece out by having the parting tool at 90 degrees to the
usual direction? Cutting into the piece at the right angles with the tool
lined up along the lathe bed? I have seen it done with a wood lathe.
No! The blade of the parting tool would need to be curved like
a parenthesis on a radius to match the cut to be made. This is called a
trepaning tool. A standard parting tool would bind on the outside
below the cut.
[ ... ]
5" is a reasonable size for the chuck on a 10" lathe. You don't want
it to hit the carriage. I have a 5" 3 jaw and a 6" 4 jaw and have to
be very careful with the larger one, or set a stop.
Here is a question then: Say you have a 9" swing lathe and a 8" diameter,
0.25" thick plate of mild steel than needs a 6.5" hole bored in the centre.
You cannot hold it on the outside in a chuck. You cannot clamp it outside on
a face plate, even a wooden one. Not enough space for the clamps. What do
you do? Would making an 8" sacrificial face plate and super gluing the work
piece to it work? Would you cut the hole with a mill on a rotary table? None
of the above?
What I would do is to mount the faceplate (which is probably
larger in diameter than the chucks), coat the surface with double-sided
tape, approximately center the workpiece, and using a live center with a
flat pusher in it -- or a turned piece of aluminum with a large center
hole drilled not all the way through, and use the tailstock and this to
press the workpiece against the faceplate. Better if your pusher is
turned to press near the OD and relieved a bit inside that.
This is used to press the (slightly oversized) workpiece firmly
against the plate to get the tape to grip firmly. Then (using very slow
speeds) drill through the center with a bit which fits your lathe --
perhaps a 1/2" one unless you can find a Morse taper shank drill to fit
the tailstock taper.
Then, using a boring bar, bore through the workpiece slowly
increasing the size until it is the right ID.
Then -- put on the 3-jaw chuck (assuming that you don't need the
OD to be truly concentric with the bored hole) expand the jaws inside th
bored hole to grip the workpiece so you can turn the OD to something
close to concentric.
If you need the two to be truly concentric, turn the OD while
still holding the workpiece against the faceplate with the live enter
and pusher adaptor. Then shift to boring the OD.
Yes -- the super glue (or a bearing mount Loctite) would work in
place of the double-sided tape. You will need to use heat to release
it.
And -- while boring, it would probably help to have an extra
sacrificial aluminum plate between the workpiece and the faceplate so you
don't cut the faceplate.
Of course if the plate which you are machining can tolerate some
holes in its surface -- perhaps in places which would be machined larger
later -- drill and tap for bolts to hold it to the faceplate..
And yes -- you could use a rotary table and the double-stick
tape or glue again on the mill to do the same thing. The finish of the
bore will probably not be as nice, however.
Note that you can probably use a larger diameter 4-jaw on the
lathe than the 3-jaw because the jaws are easier to adapt to not stick
out as far. My 12x24" Clausing has a 6-1/4" 3-jaw, and a 10" 4-jaw.
In your particular described situation, a 9" swing lathe, and an
8" diameter workpiece, *if* your jaws for an 8" 4-jaw chuck have the
last step only 1/2" thick, you could just barely grip the 8" diameter
workpiece with the jaws extending only partially beyond the OD of the
chuck. Be very careful when doing this:
1) Make sure that it does not hit the bed or the wings of the carriage,
and that the tool can reach fully through the workpiece without
bringing a part of the carriage into contact with the jaws.
2) Don't crank down too tight on the jaws. Extended even a single
step beyond the OD of the body puts an extra stress on them.
Or -- you could perhaps make extended soft jaws for the 3-jaw
chuck if it has two-piece jaws. You can extend them far enough to grip
the OD of the workpiece, and make them of aluminum so you are less
likely to damage the bed if you don't adjust things quite right.
Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. |
http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---