On Thu, 16 Dec 2010 05:26:26 -0800 (PST), Jim Wilkins
wrote:
On Dec 15, 11:38*pm, wrote:
...
Following the principles of the soft jaws and the step collet I
thought of attaching a 5/8"+ thick aluminum plate to one of my
faceplates, turn it true and face it. Then turn a recess in the face
of this plate with the ID=OD of my work piece (well, a slip fit).
Clean the inside of the recess as well as the work piece and attach
the work piece inside this recess with double sided sticky tape. This
should allow boring ID and facing of one side of the work piece. If
all my future pieces are turned to exactly the same OD and the face
plate-aluminum plate assembly is kept intact this setup should allow
repeat work....
Michael Koblic,
You may be remembering a similar custom wooden chuck from Holtzapfel.
There or somewhere I saw a variation with the outer lip slit and
undercut so a large sliding steel ring (hose clamp?) would wedge it
closed on the disk. I think he suggested a mix of pitch and wax,
available now as cross-country ski wax, to further hold the disk. I
use hot melt glue for such tasks, melted with a hot air gun or hair
dryer. So far it's held as long as the work doesn't become too hot to
touch.
Holztapfel would be the original reference. There have been at least a
dozen suggestions elsewhere for variations of the same: Many use wood
(MDF seemed particularly popular) and hold the piece variously with
wax, pitch, shellac, hot glue, double-sided sticky tape and superglue.
I have a problem with using wood: The sacrificial plate would have to
be turned on the metal lathe to get the centering just right and that
would create an unholy mess. I thought aluminum would be a reasonable
compromise. My concern with pitch, wax, hot glue etc. was that you
have to get a definite layer of the adhesive between the piece and the
plate. Making sure that it lies flat against it would be, I imagine,
difficult to achieve. How did you manage it yourself? I have tried the
double sided sticky tape in other applications and thought it an
advancement on an old idea.
My large thin disks are gear or pulley blanks which can tolerate extra
mounting holes, and I have 5C pot collets to hold them.
http://media.photobucket.com/image/p...chine/pot2.jpg
This (see?) second-hand pot collet had been pretty much used up for
custom jobs, so I refurbished it by boring the inside smooth and
turning a matching plug on the side of a thick aluminum disk. After
tapping the aluminum and screwing it to the collet I sawed it into
sections. The steps I've cut are as shallow as 0.020", to hold thin
spacer washers.
OK this would be what others called a "step collet"?
Some of the older pot collets have a solid shank and a tapered closer
ring at the OD like the wooden chucks. I'm trying to think of a way to
mount an inside-tapered ring on a face plate such that it would force
pie jaw plates inwards as you tightened them against the faceplate.
Perhaps a large tapered pipe thead like a drain pipe cleanout plug
would hold square while closing the jaws.
That is getting too clever for me. Which is where the double-sided
sticky tape comes it :-)
There seems no doubt that if one did a lot of this the pie jaw
solution is the best one. A better 4-jaw chuck follows some way behind
as, if I am correct in diagnosing the problem as flexing of the part,
it would not really solve the problem. I am told that my lather is too
small for 5C collets but looking at this it may not be strictly true:
http://www.youtube.com/watch?v=zHDa707aEBQ
Either way, not much change from $500 when all is said and done, pie
jaws or 5C collets.
Fortunately the issue is neither critical nor time-sensitive.
Michael Koblic,
Campbell River, BC