Making a Rotary Table Spigot

[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. 



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..

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 )



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.....
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 

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   

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....



And here's the faceplate






A close-up of the thread



Just the MT2 taper to machine now....



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  )



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 







 

[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

 

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....

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  
I'll have to go and have a look......

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

[Darren]

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.


John

Ah, I see,

The 5C wouldn't be used on the RT, just on the lathe. The spigot could be held in the 5C collet on just the section behind the thread which is currently 30mm dia.
(The chuck register) This could be skimmed as it wears or becomes marked.

I will have to have a go at machining the Morse Taper so see exactly how and what I end up with. Start with it right back and maybe leave enough room to skim it too if necessary at a later date if it becomes marked/damaged.

One of the reasons for all this is to use the same spigot on the Smart and Brown lathe and the mini lathe as that has an MT taper in the headstock.

That way I get a four jaw and face plate for the mini lathe and a 3 jaw and faceplate for the S&B, oh and a driving plate too.
How well it will hold is another matter, but might turn out ok. Will just have to wait and see.

One thing I forgot to mention is that I had to modify the mini lathe as I couldn't get to gears to mesh properly. |But that was easily done by extending one of the slots in that gear holder plate thingy-bob, what's it called?

[bogstandard]

Banjo bracket.

[Darren]

That's the whatsamacallit....

Ta....

[Darren]

Well it's now "Taper Time"...

This is my first ever attempt at making a taper. I have read all sorts on the net, mostly saying you need a taper turning attachment.....coupled with complicated angle settings etc...

Well that all sounded a little too complicated and expensive for me..... I just set the cross slide over, I don't even know what angle I used and this is how I went about it......


To set the cross slide over to the desired angle I used this 2MT-1Mt adapter



The slide was set over and the angle gauged by running this little device up and down the taper. Adjustments were made until no clock movements could be discerned.



Now the angle was set it was time to fit the piece into the lathe



And a little while later we have a taper.



I did actually test the taper as I was going along just to be sure all was ok with this. Internal is 2MT.



Almost didn't have enough room at the small end....but just manage it....



The complementary tests with a Sharpie were carried out to check for high spots, all seemed ok.



Snug as a bug...with no wobblyness at all. Slap your hand on it and you need a tap from the underneith to get it out again....



Of course I could have fitted a chuck or backplate, but for now a single, allbeit grubby, bolt is all that is required.....



Almost ready for the next bit now....

Surprisingly this really didn't take very long at all, 40min max. But If I were to do it again I would assume it would be quicker than that.

[bogstandard]

Darren,

Now you are cooking on gas.

There are a few ways of making tapers, the one you have used is about the easiest to do, but the most limited. You can easily cut the length of stroke of your topslide, but to do any longer takes a bit of fiddling about, and hoping it blends in.

Spin did a little write up to show how he did his morse taper. Basically exactly the same way as you found out. Isn't it nice doing a bit of experimentation and it works out perfectly?

Maybe you need to make yourself one of those mini centres, but if you need something in a hurry, grind away at the side of a solid centre until you get clearance for your tool. You can in fact buy them ready done.

http://www.arceurotrade.co.uk/Catalogue/Centres

Second one down, MT half centres. But you must lubricate a solid centre while it is in use, otherwise they might friction weld themselves to your job.

Bogs

[Darren]

I thought I'd seen it somewhere?

But now that you mention it wasn't it John Hill, or have they both beat me to it 

I suppose my top slide has a long enough travel to get away with this at 4", are most lathes less than this?


I do have a half dead center John, but if I can I do like using the rotating type now that I've actually splashed out for one 
It was almost called upon...... But one of those teeny rotating types that I've seen on here somewhere might just be on the next list....