Author Topic: Dividing head - Is this a silly idea?  (Read 404 times)

Offline RussellT

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Dividing head - Is this a silly idea?
« on: February 14, 2017, 01:48:50 PM »
I've been thinking of making a Sparey style dividing head but in true Madmodder spirit I don't feel tied to the drawings but the concept of using lathe change wheels for dividing will be used. :mmr:

One of the ideas that had occurred to me was  to use the lathe banjo for setting up gear trains rather than making a dedicated part.

Today's idea came to me when I was tidying up and came across the lathe leadscrew bracket which I took off when I fitted a gearbox.  It seems to me that this might do as the body of a dividing head.  :scratch: It would be really easy to fit the lathe banjo.  Locking a shaft in place would be more difficult.  What does anyone think? The leadscrew bracket is from a Boxford - from memory the bore is 3/4".  Pictures below.

Russell

Offline chipenter

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Re: Dividing head - Is this a silly idea?
« Reply #1 on: February 14, 2017, 01:58:57 PM »
Go for it Boxford gears are 18dp and 9/16" bore , or iff you want more numbers make a worm and angle the mount to fit .
Jeff

Offline RussellT

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Re: Dividing head - Is this a silly idea?
« Reply #2 on: February 15, 2017, 10:38:03 AM »
Thanks for the encouragement Jeff.

Here's a picture of a mockup using some bits.

This is what I'm thinking so far.  It would be sensible to make it so it would be on centre height on the lathe in case I wanted to use it there.  It would also be useful for it to be tall enough to get the lathe chucks on (centre height works for 3 jaw but not for 4 jaw).

It seems to me that the least rigid part will be the relatively small base to the casting so there won't be much benefit to having a larger base.  Should I drill the base or just rely on clamps to hold it down? If I extend the base back past the end of the casting the largest gear I could put on for direct division would be 80 teeth as opposed to 60 with a longer base (eg the bit of stock it's on in the picture but turned through 90 degrees).

For versatility and using on the lathe I think the dividing plunger should be mounted on the lathe banjo (which I didn't take off the lathe for the mockup).

To use the lathe banjo for compound gear setups the first gear has to be flush with the left end of the casting so it will need to be retained by a nut which will also set the end float in the shaft.

The difficult bit is how do I clamp the shaft in position while using the dividing head for machining.  I am thinking about two options at the moment.  One is to extend the shaft to the left and make something that clamps onto the shaft there.  The difficulty with that is that the base would need to be longer.

The other more traditional option would be to drill through the casting and make a split clamp.  There are two difficulties with this, one is that it would weaken the casting where it's already thinnest and the other is that the bore is wider in the centre to provide an oil reservoir so this sort of clamp would tend to bend the shaft.  I don't know whether this would be significant in practice.

What does anyone think?

Russell






Offline chipenter

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Re: Dividing head - Is this a silly idea?
« Reply #3 on: February 15, 2017, 01:51:53 PM »
I would put a split clamp between the bolts , you wont need more than 12mm with a 6mm cap head bolt , mine is 3/4" bore with a 1/2" split clamp and holds well .
Jeff

Offline RussellT

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Re: Dividing head - Is this a silly idea?
« Reply #4 on: February 19, 2017, 03:00:16 PM »
Thanks Jeff.  I've taken your advice. 3/4 bore with 1/2 split clamp.

Still needs a keyway, plunger and base.

Russell