Lathe chuck indexing?

Afternoon everyone,

I am trying to work out how I can direct index a lathe spindle to allow me to cut 18 internal splines with a single tooth cutter (it's only brass) using a 40 tooth spindle gear.

I can do the indexing on the mill and rotary table but it's really awkward getting the small cutter lined up and the mill has no spindle lock to prevent the cutter from rotating

My working-out so far is:

360 / 18 = 20° ...rotate the lathe chuck every 20° and make a cut.

I need to figure out how many teeth I should count so that I get a multiple of 20° yes?

I initially thought it could be 9 teeth, 360 / 40 = 9 ...but trying a test piece and drawing it out in CorelDraw confirms that is wrong.

So is this going to be like an indexing head where it uses one full rotation plus a number of teeth? or is it just not possible?

As always I appreciate any help.

Kind regards,
Ed.

Hi Ed,
You will not be able to cut 18 splines by directly indexing a 40 tooth gear as 18 does not divide into 40 an integer number of times. You would need an 18, 36, 54, 72, 90, 108, etc tooth gear. You may be able to use your screw cutting gears if you can get the correct ratio. If you use this method you will have to be careful to take up the backlash in the same direction for every cut. If you give a list of the change wheels you have I will see if I can work out a combination that would work. For indexing on my lathe I have made an indexing plate with 48 holes. (Using the rotary table and milling machine.) 48 holes would not work for your 18 splines. You would have to make one with 18, 36, etc holes.

Les.

Ed,

You haven't quite grasped the geometry there I'm afraid. Having no worm drive it has no similarities with a div head.

To do direct indexing you would need 40/18 = 2.22 teeth per slot. Not only does that clearly not work out but a lathe spindle doesn't lock either.

I once worked a lathe, possibly an Edgewick or Holbrook that had an oversize spindle gear which was graduated for multi-start threads but let's not go there.

With such limited kit the closest way is to put the stopped mill into low range and hope while plunging. If it's a vee spline you'll have to line up with a scribed line once centred. I will be an approximation.

How about a piece of paper taped to the outside of the chuck body. with 18 intervals marked. 100mm chuck should give you about 17mm between the marks so it's reasonable. Wrap a strip of paper round the chuck and mark off the overlap. cut to size and divide up into 18 gaps. double sided tape to fix back to the chuck and mount a pointer to indicate position. You could try engaging the clutch with the motor off to create a brake.

regards Martin

Hi Les,

Thank you very much. I'll probably go ahead and make a plate as you suggest. I must admit I had thought about that but I didn't think I had anywhere to fix it. Checking again I think there may be a way to attach it to the spindle drive pulley. It's the Warco WM-180 lathe (not mushroom inside).

If you wanted to work out the change gear method I'd still be interested to understand how to do that and it would be here as a reference for other folks too. My change gears are 20, 24, 25, 30, 35, 40, 45, 50, 52, 60, 66, 72, 80.

Thanks again,

Ed

Hi Capstan, to be honest maths was never a great subject for me at school and we seemed to do all the stuff that would never be any use in the real world. Matrices and the like! what was that all about. In physics class we had to calculate the thickness of a film of oil if a drop of oil were dripped onto a tray of water etc etc.

Hi Martin, I thought of that too, but I prefer to have something mechanical to ensure position I'm going to be doing a lot of knurling as well which requires loads of thin spray oil which covers the chuck and I think would unstick tapes and such like. Thanks for the suggestion though.

Cheers,
Ed.

Stick a suitable change gear on a mandrel in the rear of the spindle. You can use 45 teeth if you arrange to index both on and between teeth.

Here's my slightly more sophisticated setup;

Neil

Matrices are ubiquitous in real engineering.

Andrew

Got an angle box? if so stick it to a chuck jaw and just move to 20, 40, 60, etc

I used a change gear to index the dials on my Dore Westbury mill, made a mandrel to take the gear wheel and dial the used a simple stop to index round and used a slim tool on its side to scribe the line on each division.

Ed, your 72 tooth gear should give you 18 divisions.

Bob

Hi Ed,
If you mount an 80 tooth and the 72 tooth gear on the same spindle on the banjo with the 80 tooth meshed with the 40 tooth spindle gear that should work. This is the reasoning. For every revolution of the spindle the 80 tooth gear will rotate 1/2 of a revolution (40/80) As the 72 tooth gear is on the same spindle it will also rotate 1/2 a revolution which will be 36 teeth. So if you index on every other tooth you will get 18 divisions on the lathe spindle. I hope that makes sense. Making an index plate will be more accurate. I fixed my indexing plate to the aluminium pulley on the spindle with three 6BA or 3mm screws. You also have to be sure the index plate is concentric with the spindle.

Les.

A question here, if I were to drill index holes in the back plate of my lathe chuck what are the preferred number of holes for general engineering use? This would also mean making a bracket to fix a stop that would have a pin to go into the index holes. I only have a horizontal indexer.

Clive

I'd go for 12. Then you get 2,3,4,6,12.

.

I would raise that to 24 ... gives you 8 and 24 as well.

MichaelG.

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P.S. ... Don't forget this little gem of a divided-circle generator.

Edited By Michael Gilligan on 08/05/2015 19:38:37

Raise you to 60

I'd drill two sets of holes, one of 56 and one of 60.

Andrew

.

Thank you Les for the gear ratios and everyone for all the additional ideas and input. I'm in the process of making a small mandrel to take an indexing plate, had to stop as the old back is a bit dodgy. Will hopefully resume tomorrow.

Jason's angle finder got me thinking. I have a spare satellite dish motor which can index to degrees and minutes, maybe I could adapt that (in the future perhaps) to make an electronic indexer. I think I could use the Diseqc command set which can send a specific angle to it, although it might require a PC to do it. The nice thing about it is, it's powered and controlled through one coax cable.

Thanks all,
Ed.

Ha ha, it's easy to spend someone else's time and labour

My indexing fixture ,English made a long time ago, has 24 internal slots which are located with a plunger, this is a manageable number,the periphery of the fixture has 24 numbered divisions and degrees marked. an index plate with a lot of holes can lead to errors through mis indexing unless an index guide similar to a dividing head is used.Going back to the original question,the reader states that he has a rotary table for the mill,so why not make a circular plate and then drill a circle on the mill, and then fix the plate to the left hand end of the lathe mandrel with an index plunger attached to the headstock, the plunger will allow the lathe spindle to indexed and also stop the spindle rotating when machining the splines.