Jim Wilkins wrote:
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.
Worth a 1000 words. Very nice. Maybe down the road. Right now it is outside
the realm of the superglue-and-doublesided-sticky-tape technology in
operation here.
Your 3-jaw shims can be rings cut from plywood or discarded plates
with a scroll saw.
I was thinking bits of washers cut into three pie wedges.
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.
This is the plan for the face-plate and the holding plug. I found that
unless you actually finish them on some sort of lathe they never turn
concentrically, however nice the work appears to be when you cut them with a
router.
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.
In my case I let the piece overlap the face-plate by a little. That way (at
least in the improvised conditions) I was able to do the face and OD without
changing clamping arrangement.
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.
That is the current arrangement with a slight modification: The centre
wooden block is slightly tapered and is screwed down onto the shaft by a
screw and a big washer. with everything tight there has been no slippage so
far. I hope for even better result when
a) the face plate is running true
b) the centre block is turned more accurately
c) The whole assembly will be held on the 1"-8 tpi spindle with a single nut
I hope I can get the taper right so I can sneak right up to the central
block when facing (it seems possible even with rather awkward "tools". The
finish the ID on my mill using the boring bar sideways. That is the theory,
anyway.
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.
Either way, this is going all in my library for future reference. Thanks.
Hals und beinbruch,
I nearly did. But Gott sei dank, so far so good.
Dreimal Hoch!
--
Michael Koblic,
Campbell River, BC