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Making a Rotary Table Spigot

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Darren:
During my recent project making a new crosslide screw and parts for my lathe http://madmodder.net/index.php?topic=460.msg12410#msg12410
I came to the point of needing the use of my Rotary Table (RT) which I have yet to play with.



Having a hunt around I came up with these items from my Union Lathe...they might not look much but they are at least mechanically sound. I also have a catch plate and dog, but I can't see these being very useful on the RT.  :scratch:



Now I could have simply fitted the four jaw and been done with it. Would have been a simple task with it being a front fitting type.
But oh no, I couldn't just do that could I, that would almost be like cheating, and what about the 3 jaw and faceplate. They really could be useful on the RT

This is what I came up with. A bit of a collection of ideas from other members ideas on this forum.. :thumbup:

Starting with a piece of free machining steel from a previously abandoned project (no, not Stainless or some bit of hard halfshaft for a change :lol:)



This is the back end of the fixture which has just been reduced to 22mm and will become an MT2 taper to fit the RT, The very end is reduced to fit into the mini lathes chuck to help reduce overhang later.
I have just machined an 8mm thread for a drawbolt.



Turned around to machine the front end to 22m. This will be threaded to 7/8th 12tpi to match the chucks backplates.
Again I have added an 8mm thread for simple fixture holding.



I looked up the changewheel requirements for 12tpi here http://littlemachineshop.com/Reference/change_gears.php
Imagine my horror at discovering I didn't have the required pair of 65T gears..... :bang: :bang: :bang:
They don't come with the metric version of the mini lathe.

I started to have a go at calculating what I could achieve with what gears I have, but the resultant headache got the better of me  :smart:

So time to go a hunting, Google hunting that is.....I found this....http://www.lathes.co.uk/latheparts/page14.html
I downloaded a small program called NthreadsP and it told me I could cut 12tpi with the gears I had with a 0.345% error.
If I had the two 65T gears I would have a 0.197% error

0.345% didn't sound too bad to me? So off I went to have a go.... :)

Then onto the mini lathe to machine the thread, I was a little apprehensive as this is my first real attempt at single point threading that needed to be accurate and was this large. 6 & 8mm is one thing, but this is almost an inch....huuuuge   :lol:

This is part way through



Now just need to bring it down to size. I took many light passes testing the fit each time. The result was a very nice snug fit.... :ddb:



And here's the faceplate






A close-up of the thread



Just the MT2 taper to machine now.... :ddb:



The culprit for all this effort, it will be fitted using the 8mm thread in the front of the spigot. Well, while I was at it I thought I might as well make it versatile....



Talking of versatility why not make it fit into a 5C collet at the same time? This way I could machine a part on the lathe and then transfer it to the RT ( or vice versa) without upsetting the centering. (thanks Bogs  :thumbup:)



And about that 0.345% accuracy?
It fits the backplates real snugly, and here it is with a thread gauge for comparison...looks good enough to me  :nrocks:







 

bogstandard:
Very nicely done Darren.

You are certainly putting that little mini lathe thru it's paces now, and getting some fine results.

Be careful with your thoughts though Darren.

A RT doesn't usually look all that high, but as soon as you have things growing out of it's face, you can soon run into major clearance problems under the mill tooling. My mill has something like 14" throat from quill to table, but by the time I put the RT with adapter, a chuck onto it, the piece into the chuck, a collet holder and the cutter, that 14" soon reduces down to very little. Also the higher you go, the less rigid is the setup.

So do all the length calculations first, and see just how high your setup will grow, before commiting your plan to metal. It could save you a lot of wasted time and precious materials.

John

sbwhart:
Well done that man

 :clap: :clap: :clap: :clap:

Johns got a point about losing head room building a tower on your RT, that was one concern with the chuck adaptor plate I did for my RT, up too now it hasn't been too much of a problem as the X3 has got quite a bit head space, but you have to be aware of it.


I'll be interested to see what method you use to set up for the M2 taper

Have fun


Stew

Darren:
Thanks guys,
I was really please with the way the thread came out. I mean, that finish and fit just ain't mine.... :lol:

I'm not sure where you think the height bit comes into it? I don't think it will end up quite as high as yours Stew  :scratch:
I'll have to go and have a look...... :thumbup:

John, surprisingly (for me) the mini lathe coped just fine cutting this thread in low gear.

bogstandard:
Darren,

I think it comes from you showing the 5c collet, giving the impression you would be making a holder for it to fit onto your RT.

I think everyone is getting rather obsessed with mounting all sorts onto their RT. I did it purely for production speed up.

The RT can be used for much more complicated machining than comes with just a chuck. Using a chuck is about the most simple use for the RT.

Normally you would use the bare RT faceplate. Using clamps, with a sacrificial plate underneath, almost anything can be mounted onto the face, and all sorts of rotary machining exercises can be carried out, even ones that you would use a chuck for. It just takes a little time to centralise the job to the table and the cutter to the job.

John

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