1/8" thick 4" diameter steel circle.
has a 1" hole in center.

I want to stack many of these and drill
holes in them.

How can I get these disks to center on
the rotary index table?

Someone had this idea:

use lathe to taper 1" round stock to
a point. The point is center. Put
this in the center of the rotary
index table (it has a small indentation
at center). Drill a 1" hole in a
1/2" thick piece of steel. lay this
on top of the index table, with the
1" tapered round piece going through
the hole. The taper goes through
the clamp "ways" on the rotary index
table. The 1/2 " steel is to keep
the tapered 1" rod 90 degrees to
the table.


*****
#####*****###### -----1/2 " steel with 1" hole drilled in it
-----*****------ ---- top of index table
# *** #
# * # ------------ "clamping ways" on index table
O
\_____small indentation in center of index table.

There must be a better way?

Rich

What and where are the holes you need to drill?

wrote in message
oups.com...
1/8" thick 4" diameter steel circle.
has a 1" hole in center.

I want to stack many of these and drill
holes in them.

How can I get these disks to center on
the rotary index table?

Someone had this idea:

use lathe to taper 1" round stock to
a point. The point is center. Put
this in the center of the rotary
index table (it has a small indentation
at center). Drill a 1" hole in a
1/2" thick piece of steel. lay this
on top of the index table, with the
1" tapered round piece going through
the hole. The taper goes through
the clamp "ways" on the rotary index
table. The 1/2 " steel is to keep
the tapered 1" rod 90 degrees to
the table.


*****
#####*****###### -----1/2 " steel with 1" hole drilled in it
-----*****------ ---- top of index table
# *** #
# * # ------------ "clamping ways" on index table
O
\_____small indentation in center of index table.

There must be a better way?

Rich

Hi,

thanks for reply,

Holes need to be drilled on outer diameter of
the metal discs, 4 of them. They all need
to be 1.5" from the center of the discs, at
0,90,180,270 degrees (a square)

problem is the discs have a 1" hole in
their center, so a compass cannot be
used to locate the center of the holes
that need to be drilled.

I don't know what to measure off of.

I will go upload drawings to dropbox
now.

Thanks,
Rich

My thought would be to make a jig for drilling.
A piece of metal maybe 1/2 inch thick with a 1 inch shaft in the center
which would center the disc. Then four drill bushings in the right
places.

No rotary table required for use. Just drop the jig over the disc.
Drill the first hole. drop in pin so disc does not turn, Drill three
remaining holes.

Dan

If the discs are really round, and if the holes don't have to be super-precise,
then the way I'd do this is:

(trig moment)

chord length L inscribed in a circle of diameter D with an angle ALPHA:
L = D * SIN(ALPHA/2)

Disc is 4" diameter, angle is 90°, sin(45°) = 0.707: L = 2.828"

Set dividers to 2.828", ink discs, step off 3 times, check that 4th step exactly
returns to first mark (if not, adjust calipers slightly, reink and iterate)
until you've accurately divided the circumference into quarters. Then draw
diameters through your marks, lay out your holes, centerpunch, and punch out the
holes on an ironworker. Take lots longer to do the layout than to punch the
holes, but still MUCH faster than drilling on RT.

GWE


wrote:

Hi,

thanks for reply,

Holes need to be drilled on outer diameter of
the metal discs, 4 of them. They all need
to be 1.5" from the center of the discs, at
0,90,180,270 degrees (a square)

problem is the discs have a 1" hole in
their center, so a compass cannot be
used to locate the center of the holes
that need to be drilled.

I don't know what to measure off of.

I will go upload drawings to dropbox
now.

Thanks,
Rich

If your lathe is an Atlas, you could chuck a stack of washers in the
3-jaw and use the index pin in the bull gear to locate the hole
location. Mount drill on toolpost.
- -
Rex Burkheimer


wrote:
1/8" thick 4" diameter steel circle.
has a 1" hole in center.

I want to stack many of these and drill
holes in them.

How can I get these disks to center on
the rotary index table?

Someone had this idea:

use lathe to taper 1" round stock to
a point. The point is center. Put
this in the center of the rotary
index table (it has a small indentation
at center). Drill a 1" hole in a
1/2" thick piece of steel. lay this
on top of the index table, with the
1" tapered round piece going through
the hole. The taper goes through
the clamp "ways" on the rotary index
table. The 1/2 " steel is to keep
the tapered 1" rod 90 degrees to
the table.


*****
#####*****###### -----1/2 " steel with 1" hole drilled in it
-----*****------ ---- top of index table
# *** #
# * # ------------ "clamping ways" on index table
O
\_____small indentation in center of index table.

There must be a better way?

Rich

wrote in message
oups.com...
Hi,

thanks for reply,

Holes need to be drilled on outer diameter of
the metal discs, 4 of them. They all need
to be 1.5" from the center of the discs, at
0,90,180,270 degrees (a square)

problem is the discs have a 1" hole in
their center, so a compass cannot be
used to locate the center of the holes
that need to be drilled.

I don't know what to measure off of.

I will go upload drawings to dropbox
now.

Thanks,
Rich


A pic isn't necessary to solve this riddle. Make a simple aluminum holding
fixture that has a 1" pin that protrudes upwards, long enough to locate as
many pieces as you'd like to drill at one time. There should be enough
thickness of the fixture to allow you to drill through the bottom part
completely, but not drill into your table. SET A STOP so you can't drill
too deep. This setup will locate your parts on center with no setup time.
The pin in the fixture should also plug into the hole in the rotary table
(or index head), automatically centering itself with the table. All you
need do is locate the centerline of the table/index head as it relates to
the spindle (which you do by the use of a DTI, before inserting the fixture,
or by dialing the pin afterwards), then step off the radius. A couple
finger clamps will hold the parts while you're drilling them. By dialing
the table concentric with the spindle, you "measure" off the centerline of
the setup, which in turn relates to the centerline of the parts. Clear?
If not, ask questions.

Harold

If I had to do this:
Assumptions: 4 pieces, +/- 1/32" or better
*MIG tack weld the 4 together
*Use centering head on a scale and scribe a diameter line on top disk
*Prick the first and oposite hole at .5" from the OD on the diameter line.
*Set your divider/compass to 2.12132" swing the divider/compass from both
pricks to mark the other holes. Prick and follow with a bigger centerpunch.
*Use a combined drill/countersink or center drill then follow with drills up
to size.
*Grind open the weld to free the disks.


wrote in message
oups.com...
Hi,

thanks for reply,

Holes need to be drilled on outer diameter of
the metal discs, 4 of them. They all need
to be 1.5" from the center of the discs, at
0,90,180,270 degrees (a square)

problem is the discs have a 1" hole in
their center, so a compass cannot be
used to locate the center of the holes
that need to be drilled.

I don't know what to measure off of.

I will go upload drawings to dropbox
now.

Thanks,
Rich