Laying out and drilling an index disk

In message , John Weeks writes

Hi John, not exactly sure of the design of your indexing disk, ( A picture would help - but not here)

Have you considered a different approach

24 is half of 48 48 is half of 96

Rather than drill 96 holes, is there a way you can apply an offset to the indexing pin ?

I.e.

----------o

-----------------o

-----------------------o

On my chuck I have a number of holes which I can locate the indexing pin into.

The indexing arm is fixed to the lathe.

But supposing the arm is square section . Make a sliding attachment that has 3 pins in it.

Each pin offset from the index arm mount by say half inch the closest pin to the chuck being half inch long the middle one being 3/4 inch and the closest to the head stock being 1 inch. The reason for the length variations is to ensure the next pin is clear of obstructions on the chuck

If you have a round arm you could make a simple 4 way offset indexing guide which rotates on the arm and is located by a pin in through the shaft. Made from a square section with hole in middle to fit arm, you then fit a pin in each face at a suitable offset.

There may be a minor issue with the curvature of the indexing ring , but I am sure you can overcome it

How about drilling the 24 holes on the lathe and then making up a jig from plywood (or whatever) and affix two dowels that will fit into any two adjacent holes of the 24. Find the center and drill a guide hole for one halfway in between. Repeat with a new jig for 96.

John, What you are trying to do is, for all practical purposes, an impossible task. The cumulative error you build in when going from hole to hole is killing you. For an example, look at the 96 hole index disk. That's 360 deg. / 96 holes or 3.75 degrees per hole. But, if you are in error by only

0.05 degrees when you drill the first 2 holes, the cumulative error over 96 holes is approximately 1 degree - or about 1/4 the distance between two holes. .05 degrees is a very small error when drilling holes with even very high quality machine tools. Jim Seelye

I understand in your suggestion. My built in index is inside the headstock, there is a spring loaded pin that goes through the headstock to lock the shaft.

I've got index holes on my Vicmarc chuck, but I want to be able to index things on a faceplate.

Thanks for the idea, though.

JW

Yep. Pretty much what I've concluded.

"John Weeks" wrote: (clip) Anybody have any better way of doing this? ^^^^^^^^^^^^^^^^^ One of our club members had a large number of indexing disks with different spacings, which he did by using other devices to get the spacing. He would clamp a saw blade or a gear. etc. to the spindle, and use a positioning tab to drop into the notches (saw teeth, gear teeth, etc), and then make the new disk. His disks were not drilled--they were notched, but the idea is the same.

On Tue, 28 Oct 2008 17:15:46 -0500, John Weeks wrote (in message ):

I am thinking that using the built-in indexing capability would be the way to go. Instead of measuring and locating every hole, it would be much simpler to accurately locate just one hole, and then let the lathe do the rest. tom koehler

John - a couple of thoughts

first and most importantly - are you using a center drill for this? otherwise the drill itself will wander. second, drill opposites - e.g. drill hole 1, then drill the hole 180 deg opposite hole 1 so only 1/2 error can accumulate if possible, drill by bisecting angles always center punch first - use dykem and a sharp scribe to layout

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

All Right! Thanks to suggestions from Bill and others, I've got a nice index wheel, 15" in diameter, in 1/4" hardboard. The wheel will rotate in a slot in a piece of 2x2 clamped to the lathe bed, with a hole through the 2x2 for the pin.

I can't believe I was actually reaching around my brad point bits to get the set of ordinary drill bits! Using the brad point bit allowed be to get very good location by eye - I could just touch the surface then raise the bit to check and reposition if necessary.

I tried using a center punch, then realized I was having to locate the point in two dimensions by eye. Since the disk was going to rotate under the drill on a fixed pin, I decided this wasn't necessary. If I'd been drilling in metal that might have been required.

I'm laying out lines on wood for carving by hand - I don't need thousandths of an inch accuracy.

I have also found that local machine shops can do this for remarkablr reasonable prices (unless your working in some really odd dimension).

If that si not an option, a good drawing prgoram 9there are free versions of CAD that can do this) and any non-dot-matrix printer can get you a layout star that is with in pixel (print as high res as your printer allows)..

-JAmes

Why not buy one at

or on Ebay? Fits midi lathes and a new larger indexing system for 10 to 24 inch lathes!

Tim

Hello John,

I didn't see this message until today. Now, I'm sure that I need to get another way to read the newsgroup.

In relation to your question, I've made a number of indexing wheels over the years. The easiest way is to use Woodturner PRO or one of the other segmenting projects. Select a ring diameter that will print onto an 8-1/2 x 11 inch page. Set the center diameter to the diameter of your lathe spindle; i.e. 1", 1-1/4", etc. Then set the number of segments to 96. Drill a hole for the center point i\of a size to slip over your spindle. Print out the drawing, cut out the center hole for the spindle, and glue it to your indexing disk using the lathe spindle to center the drawing on the plate when gluing.

Now, turn the disk round to match the outside of your drawing that has been glued to it. Then take the disk to the bandsaw and make cuts on each of the 96 segment edges. Make a deeper cut on every other one to indicate what is the 48 position slots. If you don't have a bandsaw, use a hacksaw to saw the slots.

Again, mount the disk on your lathe and make up a mounting for a piece of a hacksaw blade to swing in and engage the slots in the disk. This will give you the option of 96 or 48 position indexing, plus a number of other positions less than 96.

This works much better than trying to get your drill to make a hole exactly on one of the lines that will always align with a pin arrangement. I've made them both ways, but found that the slot with a piece of hacksaw blade works best. For easy attachment of the hacksaw blade mounting to your lathe headstock, a magnetic base works very well.

I hope this helps. If you have questions, go to my web site to get my e-mail address and ask the questions that way.

Fred Holder

Thanks for the reply, Fred. I did get a wheel made on the drill press and it works fine for my purposes, but the next one I make I'll try this way!