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Setting up a rotary table with chuck

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Sam Longley 110/08/2016 10:26:22
742 forum posts
26 photos

i have the same rotary table as the one under the thread on "rotary table problems" post no 1

I am not sure if i am missing a trick here but i need to set up the 3 jaw chuck on it ( the table has 3 grooves) which needs to be central. I then need to get it central under the mill.

I have a half inch bar to place in a half inch collet so once the chuck is on the table i was hoping to use the bar to get the chuck & table into the right playing field before clamping into place to get it centrally placed about the mill prior to moving off to the required offset

First problem is getting the chuck central on the table

The whole thing is really a palaver & i suspect experienced modellers have a spare table & chuck permanently mounted- or do they- or is there a simple way to go about this as i want to get on with the machining operation but the set up puts me off. If i rush it the final outcome will be wrong

Can anyone tell me please is there a simple method for this?

Ajohnw10/08/2016 10:53:41
3631 forum posts
160 photos

One way is to make a back plate for the chuck with a spigot on the back and use that to locate it. The back plate needs to be a bit bigger than the chuck so that the table slots can be used to clamp it. Nice and simple if it's a plain hole. If morse I might be inclined to machine a bit of it away to create a plain hole but some are so thin it would leave no morse taper. One answer would be a morse sleeve with a plain hole - top lying under the surface of the table so that the back plate will really be clamped flat down and rigid.

Or one of those mores adapters with a chuck fitting on them. I feel they are of more use on a tailstock though.



Martin Kyte10/08/2016 10:57:43
1807 forum posts
33 photos

What size hole do you have in the rotary table.

Find a bar that fits the central hole which should be concentric with the rotary table. It will be either a taper or parallel.

You need one end that fits the table and a parallel portion you can grip in a collet or drill chuck in the mill spindle.

Fit the bar into the rotary table. Manouver the table under the spindle and grip the other end in the chuck/collet.

Clamp the rotary table.

Fit your 1/2" bar in your 1/2" collet and grip in the spindle drill chuck.

Lower on to the rotary table and clamp up.

Everything should now be correctly located.

regards Martin

Martin Connelly10/08/2016 11:02:11
1250 forum posts
152 photos

As Martin K says above centre the RT then mount the chuck. There are plenty of YouTube videos showing this.


Martin C

Ajohnw10/08/2016 11:55:30
3631 forum posts
160 photos

Well my way just the work has to be centred as I am assuming it might already be in the chuck.

Whoops - assuming the hole in the table is central.



Edited By Ajohnw on 10/08/2016 11:56:16

MW10/08/2016 12:03:27
2051 forum posts
51 photos

Ive had this problem before, you just need a plug that will fit both the chuck and RT center holes perfectly. Turn one out of anything other than jelly and it should be plain sailing setting er up.

Michael W

Tony Pratt 110/08/2016 12:15:46
1100 forum posts
3 photos

You can put a bar in the 3 jaw & then set it roughly concentric, apply a DTI to the bar & spin the rotary table. Adjust chuck position until you have no run out, tighten bolts & re check, the bar is then running concentrically to the table rotation.

Put a DTI & clocking arm adaptor in the chuck or collet, rotate the spindle with the DTI touching the bar & adjust the table until the spindle is concentric to the bar.

Hope that all makes sense


Ajohnw10/08/2016 12:31:53
3631 forum posts
160 photos
Posted by Michael Walters on 10/08/2016 12:03:27:

Ive had this problem before, you just need a plug that will fit both the chuck and RT center holes perfectly. Turn one out of anything other than jelly and it should be plain sailing setting er up.

Michael W

Yep. There are all sorts of variations on the same theme. Even a flange fitting for the table if the lathe uses that type of chuck. The same sort of thing can be done on a dividing head. I need 2 chucks for the lathe in that case as one is a bit too big.



Andrew Johnston10/08/2016 14:56:09
5411 forum posts
627 photos
Posted by Sam Longley 1 on 10/08/2016 10:26:22:

The whole thing is really a palaver & i suspect experienced modellers have a spare table & chuck permanently mounted- or do they...................

It's very simple; I don't have a chuck mounted on my manual rotary table, and never have. When I bought my (secondhand) rotary table I rushed out and bought a cheap 3-jaw chuck, but never got around to fitting it. I don't suppose I ever will now; in retrospect I don't have a need for it.


JasonB10/08/2016 15:04:13
17856 forum posts
1954 photos
1 articles

I just mount the R/T and use an edge finder in the hole to ctr R/T, then wind up the mill head, pop a bit of ground bar* into a collet and grip that with the chuck which will then ctr itself, then bolt chuck to table. This allows for any run out between back of chuck and its jaws.

If the chuck is still on teh table from teh last job then again ground bar in collet, tighten chuck jaws onto it and then bolt R/T to mill table, zero dials/DRO.


* tool shank will do as a ground bar.

Neil Wyatt10/08/2016 18:47:04
17729 forum posts
697 photos
77 articles

I made my RT with a 'bobbin' shape on top - the upper flange is a copy of the spindle flange of my lathe so it takes all my chucks & faceplate, the cut out allows me to fit the securing nuts.


Speedy Builder510/08/2016 18:51:25
1987 forum posts
139 photos

I find the worst problem is that when I mount the chuck onto the rotary table, using a Boxford spindle nose welded to a backplate, I loose headroom. In some respects, I should have a spare chuck, no backplate and bolt directly to the table.

John Haine10/08/2016 21:48:06
3013 forum posts
160 photos

3-jaw chucks on RTs are a snare and delusion. When did you have a dead accurate 3J chuck at all radii? A 4J chuck is a much better bet. At an MEX last year I was standing next to a gent about to buy a small RT and separate 3J chuck, and I asked him how he proposed to get the chuck (not of the highest quality) centralised? After a few moments thought he decided on a 4J instead!

I've a 6 inch RT with 4 tee slots and an MT2 socket. I have a shortened MT2 shank (it fractured!) with a true disc loctited on the end that snugly fits the bore of my 4J chuck (sans backplate). Drop in the taper, drop the chuck over it, bolt the chuck on using 4 threaded holes in the table surface (not the tee slots), job done. Centre the job using the normal procedure for a 4J chuck. Takes a bit longer but I don't have any worries. If I need the depth I fish the disc out with a magnet.

Having said that I almost never use the RT, most stuff that would otherwise need it gets done on the CNC.

David Taylor11/08/2016 07:08:59
128 forum posts
39 photos
Posted by Michael Walters on 10/08/2016 12:03:27:

Ive had this problem before, you just need a plug that will fit both the chuck and RT center holes perfectly. Turn one out of anything other than jelly and it should be plain sailing setting er up.

Michael W

I also do this. A 2MT arbor with a 25mm parallel end bought from the usual suppliers allows the RT to be centered easily.

I machined a sleeve that is a good fit over the 25mm straight part of the 2MT arbor and a good fit in the 3J chuck's hole, or can be gripped by the chuck jaws.

1. Center the RT using the arbor - I use a 3MT centre in the spindle to do this. Clamp the RT down and zero the dials.

2. Put the sleeve over the arbor.

3. Put the chuck over the sleeve and bolt it to the RT.

This is accurate enough for me.

not done it yet11/08/2016 08:24:14
4505 forum posts
16 photos

I fitted a self centring chuck to my rt, but in hindsight, an independent 4 jaw would have been better for accuracy. It is the part that needs centring, not the chuck. A dti should get you closer than a chuck with run out. More trouble, perhaps, to centre with an independant jawed chuck, but how often is it used? And odd shapes can be accommodated. Win, win for the independant chuck, I reckon.

Howi11/08/2016 09:01:04
273 forum posts
15 photos

I also use a 2 my arbor with a 25mm parallel, 25mm part reduced to fit hole in centre of 4 jaw chuck. Put arbor in RT centre, put chuck on centering on the parallel poart of the arbor, mark for chuck holding bolts. When fitting chuck use the arbor again, locate chuck and tighten centre the RT I have a very small hole <1mm in the end of the arbor.using a wobbler point in the mill, centre the RT then lock down to mill table.once the RT is centered it is simple to centre a part in the chuck jaws by adjusting the jaws as you would on back lathe.

Lots of ways to do the same thing, whatever works for you. 4 jaw preferable to 3 jaw even though more of a FAFF to get part central.

Edited By Howi on 11/08/2016 09:02:06

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