rotary table as a poor man's lathe

Hi all.

I need to reduce a spindle diametre from 1 1/4" to 30mm (yes it's from a spindle moulder). I've got a rotary table and a chuck that I can mount vertically on a milling machine. The spindle itself is not very long (about 75mm). I've tried this setup to hold it and the measured run-out is 0.02 mm.

My question is: can I use this contraption and a milling cutter to do the work (revolving the rotary table when cutting)? Would it be better to mill from above or from the side? Can I expect a decent finish at the end?

thanks for any help

In principle it should be possible. I've done similar sort of thing to round the bottom of a model i.c. engine, albeit in aluminium rather than steel and using my dividing head as a rotary table. I cut most of the material away by setting the milling cutter over the centre of rotation and milling in the X direction at about 15 degree intervals to end up with a 24 sided polygon. (I also need to mill the slope for the upper part of the crankcase but that's not really relevant but you can see the set up)

In order to finish the curve I then rotated the job under the cutter. I had to move the cutter away from the centre line so that it was not trying to cut with the centre of the milling cutter, even though it was a centre cutting 2 flute slot drill

A milling cutter will rarely give you as nice a finish as the lathe but it should be dimensionally accurate even if you can see a lot of machining marks. Worth a try anyway.

HTH

Rod

As your cutter block won't be rotating on the shaft it should be OK if the finish is not totally smooth so long as its a good fit in the block. Just check the spindle is not hardened.

Trying to do it with the work on the same axis as the mill spindle will mean a lot of tool overhang if you are to reach along the full 75mm. Do it like Rod shows with the tool at 90deg to the work. This is a bit of 1.75" steel I did the other day at 1 degree increments. to make a "D" shape

Edited By JasonB on 13/11/2014 17:06:35

I have done something similar when machining a large diameter that would not fit in the lathe. I did add a motor to the rotary table via a toothed belt to save me winding the handle round but I did have a fair bit of metal to remove from a 300mm work piece taking about 3 x 3mm cuts and a final finishing cut.

Bob

Edited By jason udall on 13/11/2014 17:23:11

I think this is unwise. You should not underestimate the precision needed to ensure a good fit in the block and true concentricity. Any error will result in vibration which will show up on the finish on your wood. You would be better off getting a machine shop to do it and take along a block to make sure they got a perfect fit WHEN COLD. Better still have them make a duplicate spindle so you can switch back.

You should be able to get the shaft dead centre in a 4 jaw chuck on a rotary table, support the free end with a tail stock centre. Nothing is impossible, some things are just a bit more difficult.

Ian S C