On Oct 28, 6:15*pm, John Weeks wrote:
I've been trying to construct and indexing disk for my lathe. It has
24 hole indexing built in, but I want 48 and 96 as well. I'm trying to
come up with the best way to lay out the holes and dril them on the
drill press. My first thought was to use a pin guide, something like
cutting box joints on a table saw, to avoid having to position the
drill bit by eye.
I carefully drilled the first two 3/16th inch holes the correct
distance apart, carefully positioning the disk with a 1/16th inch
drill in the chuck, clamping thedisk down, then switching to a 3/16th
inch bit and drilling the hole. The center of the disk is revolving on
a pin at the radius I wanted. Then, with the bit in the 2nd hole, I
pressed a pin through a guide block *into the first hole and clamped
the guide block in place.
I should be able to remove the pin, rotate the second hole under under
the guide, position it with the pin, drill the third hole, etc.
It's not working. When I get around the diameter I have lost or gained
a third to a half the distance between the holes. The drill press
table is locked down tight, the pin is a good tight fit. But there is
slop creeping in someplace.
This time I'm going to print a compass template with 48 radii and
position the bit by eye. The individual holes may be off slightly but
they should each be within a certain degree of error from the right
point.
Anybody have any better way of doing this?
I thought about using the index on the lathe, drilling the 24 holes,
then slipping the disk half the distance and going around again. But
I'd have to build a positioning jig for lathe drilling first.
JW.
I think the best tool for the job is the one your using right now.
Your computer as it is incredibly accurate. Find a drawing program
that will allow you to draw a pie graph with as many segments as you
need or even a segmenting program like woodturner pro which will let
you print out a picture of a finished ring. Make your inside dimension
0 and your outside dimension whatever diameter you want. Set it for as
many segments as you need and print it out. You could then glue it to
a piece of plywood. You could get all the corresponding perpendicular
points with a compass. Of course this is where human error would begin
if your compass wasn't exactly in the center but I would guess
negligible. With a very sharp awl mark all the perpendicular points
and drill them on the drill press with an accurate drill like a
forstner. To mount it to a faceplate turn a dowel the exact diameter
as the hole in the face of your faceplate and drill a hole in the
template the same size and it should be well centered. You could
actually find your perpendicular points once the disc was mounted to
the lathe by holding a pencil on the spinning disc at whatever
diameter you wanted. I don't know if this is what your looking for or
if it pertains to your project but it certainly would make an
extremely accurate indexing disc. Bob
http://www.outofcontrol-woodturning.com