On Feb 14, 3:54*pm, "DoN. Nichols" wrote:
On 2009-02-14, Michael Koblic wrote:
"DoN. Nichols" wrote in message
Of course -- there are also pie wedge soft jaws, which form an
nearly complete circle when the chuck jaws are at the tightest setting,
and those can be turned for your workpieces. You can even turn several
diameters working as steps from shallow at the OD to deep at the ID, so
progressively smaller discs can be gripped.
Pie jaws:
http://picasaweb.google.com/KB1DAL/T...90941151914594
That chuck opens and closes only about 0.050" total, so the jaw steps
have to be quite close to the size of the work. It's nice for lens
rings etc but not for general work. The internal mechanism is slanted
bar cams as shown in an early Holtzapffel drawing.
Your 3-jaw shims can be rings cut from plywood or discarded plates
with a scroll saw.
I make pulley and other wheels on a plywood-covered faceplate. First I
drill a small center hole for a locating & centering pin. Then I
attach the blank to the plywood with screws in the waste areas and
turn the friction-reducing recess between the rim and the hub on both
sides, using the pin to recenter the blank. This is equivalent to you
facing both sides, BEFORE turning the OD and ID.
If you want a bevel around the inner hole you could cut a shallow
recess where the hole will be and bevel its edge, leaving the center
to support the disk.
Next space the disk out from the plywood with collars on the screws,
in your case probably the inner ones, and turn the OD.
Add a ring of screws and collars around the OD, with washers under the
heads to spread the grip and protect the finish. Cut the center loose
by wiggling the bit sideways slightly for clearance as you run it
toward the headstock. This should work on the OD as well, with the
benefit that the outer screws support the blank better. The bit I use
for this plunge cut is rounded on the end with parallel sides, both
relieved to cut. I use it for the cable groove too.
Or reverse it, bore the center first and clamp the disk to the plywood
with a plate larger than the hole and again the spacers on the screws
to support the disk. This way will be harder to assemble but safer.
The best way might be to attach a temporary wooden block to the center
and turn it to fit the bored ID snugly, then screw another clamping
plate over it to sandwich the disk. Then the disk could slip without
causing a problem when you turn the OD. The lathe's tailstock does a
fair job of clamping the outer plate.
Use brass or soft steel screws, NOT sheetrock screws which are
hardened.
You could make clamps out of small short bars drilled through the
center for the clamp screw and tapped through the outer end for a
stand-off screw to make them sit flat on the disk. Be careful, they
grab clothing.
The spacer collars are easier to mill than turn to identical length.
They don't have to be cylindrical, cross-drilled bar stock is fine.
My lathe will take collets and a faceplate simultaneously, so I center
the blank with the locating pin in a collet and then attach it to the
faceplate. Unscrewing the faceplate pops out the collet adapter.
Hals und beinbruch,
Jim Wilkins