Dividing head - Is this a silly idea?

[RussellT]

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.

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.  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

[chipenter]

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 .

[RussellT]

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

[chipenter]

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 .

[RussellT]

Thanks Jeff.  I've taken your advice. 3/4 bore with 1/2 split clamp.

Still needs a keyway, plunger and base.

Russell

[RussellT]

This should probably be a project log now, but I'll carry on anyway.

I made the plunger - I decided I wanted to make it index on top of teeth as well as between teeth - and I also decided I wanted to be able to latch it.  This is what I came up with.

Russell

[RussellT]

I finished the dividing head and tried using it to make gears using the method described in the thread on Cutting Spur Gears http://madmodder.net/index.php/topic,11964.msg141922.html.

The method wasn't quite as easy as the web page suggested because I wanted to make gears that would match my lathe change gears so I had something to compare them to.  I had to do the calculations for 14.5 degree pressure angle.    The next snag was that to make the tool using a pointed lathe tool required a depth of cut of about 0.23".  The largest silver steel I have is 9/16.    So I measured the lathe tool, ground a bit off the tip and measured again and adjusted the depth of cut accordingly.  I made a bit of a cock up here as I thought I had a collet that would take 9/16 but I didn't and the tool wasn't as concentric as I would have liked.

I made the gears from some bits of POM.  They seem to mesh with the lathe gears OK - a bit better than they do with each other.  I think perhaps they could have done with a little more depth of cut.

This was just a trial - a first attempt at making gears - and I'm pleased with the outcome.

Here are some pictures.

Russell

[chipenter]

Hears a program for making single point cutters , but will give you depth of cut and blank dia , runs in dos window on C++  .