# Thread: In search of index plate ideas for lathe chuck

1. Member
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Dec 2018
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## In search of index plate ideas for lathe chuck

Hello all,
I am in search of ideas to utilize lathe headstock as a indexer to layout/start bolt patterns while still mounted in the lathe chuck/faceplate.
My first thought was to count teeth on my headstock spindle, but that is a odd number of teeth, and won't divide evenly to any bolt pattern.
The next thing I saw was a youtube where a guy mounted a skillsaw blade on back end of spindle and indexed off the teeth.
I have tried to go around the chuck with a dividers and do a layout, I dont like this, can't get it right.
I am not dividing for gear cutting here, only good looking bolt patterns.
So, what is a easy breezy way to get some sort of decent indexer out of lathe chuck?

2. Senior Member
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Hi,

Since you aren't looking to make high speed gearing, checkout something like this :https://www.blocklayer.com/timing-tape.aspx may help you.

I have used this myself and it worked well enough for my needs.

3. Senior Member
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Aug 2005
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One additional useful piece of information to get good suggestions is how many bolt patterns you expect to use. If 3, 4, and 6 for instance, 12 marks would be a good pattern and you can lay it out with dividers by trial and error, or do a little math computation. If you need 5 holes as well it gets more complicated.

You've said that you tried dividers and it didn't work well. Hearing more about how or why it didn't work might also lead to a solution. There's the well know technique of dividing a circle with a compass using the radius (original circle size) stepped around the circumference. It's not exact since pi isn't an even number and you're stepping off chords but it can be tweaked to come pretty close.

Alternatively, if you measure the diameter of your chuck accurately, you can calculate the chord length of the dividers for any number of division, set the dividers, scratch the layout you've painted round the chuck, and center punch a small dimple you'll use later.

4. Member
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Dec 2018
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i put a piece of tape around the chuck, and stepped it off with dividers. it was frustrating to play with it.
I am wanting some kind of indexable plate or circle that I can drop a pin into, or something similar, something I can come back to without starting all over with the dividers thing.
12, 24, or 36 is a good number to give varied bolt patterns.

5. Senior Member
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Google image search-lathe dividing plate hundreds of examples pop up,but basically it involves attaching a dividing plate to the back of the chuck,or drilling the index holes right into the chuck backing plate.

Orphan dividing head plates pop up on ebay,you could also use old gears,probably the easiest thing to come up with though are bicycle sprockets.

30 and 36 tooth would give you a good range of options as well as 40 and 48

It's also possible to make an expanding arbor to fit the end of the lathe shindle bore,to that you can make whatever you want and hang it back there.

Still another option is to salvage a worm and wormwheel from an old right angle gearbox.Mount the worm wheel to the back of the chuck and the worm on a swinging arm that engages the worm wheel for indexing.

6. Senior Member
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Aug 2008
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spider for left end of spindle, mount degree wheel on spider, use a stationary pointer.

7. Senior Member
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The direct answer to your question is that accurate division in the lathe will take some doing, there have a been numerous clever lathe dividing attachments made over the years that will work work when accuracy is needed. For example when cutting a gear.

But you need a bolt circle layout, which needs a lot less accuracy. So I'd go go back to what you're trying to actually make than how to divide in the lathe (if a gear doesn't work, and besides, since you have a mill, you'd be better off putting energies in to something that divides on the mill, than in the lathe.)

Bolt hole circles are readily done in the mill. Machinery's handbook gives the coordinates for any bolt pattern, i.e. # of holes. There will be some error, the error of your feed screws over the distance, but unless them machine is complete clapped out, it will be more than accurate enough for bolt hole circles.

If you like, you could make a rough dividing plate on the mill using bolt hole circle coordinates and attach to the outboard side of the spindle. Or even lay the bolt circle out by hand - set the divers with a caliper and loupe carefully using the distance for the side of a polygon (https://www.mathopenref.com/polygonsides.html). Then, where you can, layout its mate with transfer punches.

I a perfect world we'd make the bolt holes with live tooling in our Hardinge cnc lathes.....but in the real world, especially when starting, you've got to go what you got - bolt hole circles can be done with nothing more than drill, dividers and a scale.

Last edited by Mcgyver; 01-01-2019 at 03:39 PM.

8. Senior Member
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Make a combination spider and index plate mount for the outboard side of your spindle.

Mount a pin on the head.

9. Member
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Dec 2018
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The bicycle sprocket sounds like a great idea.
My lathe spindle is #3morse taper, and I have a drawbar.
A bicycle sprocket bolted in with drawbar sounds easy.

10. Senior Member
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Ringo, do you do CAD at all? A LARGE degree wheel with an expansion locking hub that goes into the hole on the outboard side along with an intexing finger that runs from a spot anchored to the adjustable arm under the outboard cover would not be too hard to make. And with a few holes at strategic degree splits you'd have your rapid layout points but also any other angle from eyeballing any special needs.

To make it easy to see each degree and even split them in half and eyeball quarter degrees the degree divisions should be about 1/8" wide. 360 x 1/8= 45 inches. 45/pi=14.324". Make a disc like that out of 1/8 or 1/4 plate. mount to an expanding mandrel that locks into the outboard end of your shaft, rig up a spring arm with index pin. CAD the degree wheel in paper and after cleaning the disc glue and seal the paper degree wheel to the disc. Or if you have a rotary table you could cut the markings directly into the metal. If you go with the paper degree wheel clearly it would need to be done on some large format printer. Or go for two halves done on legal size paper that mate together. With 1/8" wide divisions you should not have any trouble lining up two halves.

If you do this don't use a water based glue. I'd stick with epoxy to bond the paper to the disc and then to overcoat the paper to seal it. And there's some other little tricks to use to check that your printer does not stretch or foreshorten the print and to compensate if it does. Cad is a wonderful thing

Really though while it sounds a bit odd the saw blade idea is not a bad option at all. And all you need then is a stub mandrel to lock into the outboard end and the sprung indexing finger attached to something inside the outboard gearing array or to the back cover. So much so that I'd suggest you consider making the expansion mandrel with a 5/8 stub to take the saw blades and if you're worried about slipping that you use an indexing pin(s) to pin the blade rotationally. It takes a special drill bit to drill the saw plates but it can be done. And later on you could add a proper degree wheel if you prefer.

If you'd rather have the index holes on the chuck end it would mean setting up and drilling holes in your backing plates and the edge of your faceplate. If you would rather do that get some long paper tape for an adding machine. Wrap it around the chuck or plate and mark were it overlaps. Or better yet cut through both pieces at that point. You might also have good luck with using wider masking tape for this. Just try not to pull too hard and cause it to stretch.

Now lay out the paper or tape and accurately measure and mark the length to split it into your divisions. For the size of this a sharp tipped pencil or very fine pen is fine. Before you re-wrap the paper or tape around your chuck rig up a long extension arm or rig up a temporary support and with a suitable cutter put a good strong scratch or shallow groove around the edge of the backing plate. Then with a center punch feel through the paper or tape at the marks and CP the plate right in the scratch line. Finally rig up some way to support and drill all the holes.

When you make up the indexing pin take note that it should be tapered so it wedges into the indexing holes.

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