Mounting a chuck on a Rotary table

Ok, so I want to fit a 100mm 4-jaw (as used on minilathes, 20mm central bore) with mounting holes in the back, to a SOBA 4" rotary table with 3 x 120degree t-slots and an MT2 central taper.

One option would be a backplate screwed to a MT2 arbor. I suppose with the table horizontal this wouldnt need a retaining bolt on the rear of the table (otherwise that would prevent the table being bolted down to the milling table without some spacers in between), but might need one when the table was vertical?

I looked at the way RDGTools/Chronos do it but they fit a 80mm chuck to a 100mm plate and therefore there is room to have bolts round the outside, or they use a front-mounting chuck and I want to use what I already have..

Thoughts?

To use 4 inch onto 100mm you could use a back plate that has a fixed 2mt spigot and 3 equal spaced spigots that fit the T-slots it should fit tight enough to resist lifting.

Phill

Thanks Phil

I have thought of another option. Since this is an independent 4-jaw theres no scroll.... so no reason (at least I can't see one) why I cant drill right through from front and counterbore for some allen cap screws and use t-nuts in the slots...

Of course getting the holes in the right place needs a rotary table...lol

John Stevenson came up with an idea to fix the chuck using tappered screws screwed into t-nuts fitted to the back.
Not sure if anyone tried it but it should be worth a try!
Not sure where I saw this idea perhaps sit John will be along soon.

peter

They say talking to oneself is the first sign of madness :mad:

anyway, that last thought nearly works... for accuracy I could drill through the three 120deg mounting holes on the back, but then it occured to me that I wont be able to use the chuck on the minilathe afterwards as there wont be any threads left, although there's no reason why I can't front mount on the lathe - is there?

Quote:

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Originally Posted by ptjw7uk

John Stevenson came up with an idea to fix the chuck using tappered screws screwed into t-nuts fitted to the back.
Not sure if anyone tried it but it should be worth a try!
Not sure where I saw this idea perhaps sit John will be along soon.

peter

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Yes, I was thinking of nuts that could be expanded from the ends of the tslots, but it seems a lot of work...

I'd drill through but a smaller size and preserve lathe mount threads (stick some centre marked studs in the thread first and drill through them)? Not sure what size the mounting bolts would be then? If too small for the job...... drill out any way to fit rotary table, then carefully make a back plate with six holes, three to take the new bolts to hold the chuck and three to mount the chuck on the lathe? Or, drill and tap three new mount lathe mount holes in the chuck.
Or, can you get long (1 1/2 inch) bits of t nut profile to fit? Drill and tap the ends. Take the chuck apart and turn a groove 1/8 to 1/4 from the mount end, only needs to be shallow. Make 3 L shaped clamps with a hole in the midle of one side, the other the same length as the groove from the back of the chuck. That end goes in the groove and clamp it down using the t nut overhang?

Tom

Tom,

I'm trying to visualise your suggestion and failing badly, can you expand on it...

Attachment 2337
Art is not my strong point! I hope this comes out! I have looked at the pic of the table at Chronos and this will foul the locking nut preventing full rotation? Another thought. Why not make a round plate that fits the top of the table but bigger diameter, counter sunk short bolts for the t nuts so the front is flush and it doesnt foul that nut (you could turn a recess so it doesnt). Now you will have a table with a surface that is a bigger diameter than the chuck? Make (or buy) another plate like the chrnos mount plate and bolt straight to it?

Wow, I can see my rubbish drawing!

Attachment 2338
A drawing (of sorts) of the other idea. Make the plates, drill tap etc and put a hole in the middle of each. If your not confident of the accuracy of the plate, make a mandrel, bit of bar faced off, drill and tap centre and bolt (counter sunk) on each plate in turn and very gently face off all 4 surfaces so chuck will be dead parallel to face of table?? Apologies for the crude scribble! I have no idea of your skill on the lathe or your.. if you're like me, incredible scrounging skills and alergic to buying things when you can spend 6 months making one! But just to add, 120 deg holes are very easy. Again, 3 jaw chuck and mandrel you just made with a plate bolted to it through the centre in lathe, get a bit of scrap bar (or a snapped off pencil) that just fits between a flat conveinient surface like the bench and the chuck (lathe) jaw. Turn the lathe off! Hold the jaw down on the scrap so its wedged between jaw and bench and using the crossslide and a sharp turning tool, scribe a line with the lathe tool. Turn the chuck till the next jaw rests on the scrap, hold and scibe again, then do again with the final jaw = 3 x very accurate lines at 120 degress apart. Decide where the bolt centres will be, set the lathe tool to the right diameter (PCD) and rotate the chuck by hand marking the hole centres?
Hope this is of some help.

Tom, Thanks for those thoughts. I have a feeling there's not enough clearance between table and locking arm etc. to do that but I'll go measure over the weekend. the pictures were fine, as they say, worth a 1000 words! I've seen works of art such as these decribed as CoC elsewhere on the web... CoC = "Crap O' CAD" :heehee:, works for me!

CoC... like it!

Attachment 2339

I'll try to explain the drawing above.

One back plate screwed to rear of chuck. studs and grub screws to match the number of Tee slots.
The grub screw fit into tapped holes in the side and need a taper on them.
The studs have a matching tapered hole BUT it's drill slightly lower than the centre of the grub screw hole.

The idea is that as you tighten to grub screw up it pulls the backplate and table together.

Nice thing about this is that it's not size related to the table. You could fit an 8" chuck to a 6" table using this method.

Don't get trapped in 2D. Bolts can go through a backplate and still be accessable from the side. All you need is one Allen key clearance :naughty:

Quote:

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Originally Posted by John S

Attachment 2339

I'll try to explain the drawing above.

One back plate screwed to rear of chuck. studs and grub screws to match the number of Tee slots.
The grub screw fit into tapped holes in the side and need a taper on them.
The studs have a matching tapered hole BUT it's drill slightly lower than the centre of the grub screw hole.

The idea is that as you tighten to grub screw up it pulls the backplate and table together.

Nice thing about this is that it's not size related to the table. You could fit an 8" chuck to a 6" table using this method.

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Great idea John :)

My Haighton mill uses a similar mechanism for the swivel table lock:(albeit the other way up)

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Attachment 2341

Hi Bill,

Those pictures were really helpful in concreting JohnS' thinking. That doesnt look so hard to make either, though how do you make a small (say 5mm dia max) tapered hole. A 3 - 14mm HSS taper drill is about a tenner on Amazon (although these are supposedly only for drilling sheet). Machining a taper on a bit of 6mm silver steel rod shouldnt be hard - tho I'd imagine these might need hardening after?. The T-slot in the table is 6mm wide I think, so some 12mm silver steel rod would do for the pins (again do I need to harden after)? Then I need a 100mm cast iron plain backplate, or a 12mm thick bit of 100mm dia mild steel?? I suppose it has to be steel?

Wish i had joined earlier.
I have had a 5 1/4" 3 jaw on a vertex 8" rotary table with 4 slots for 11 years. Its done a lot of work.
http://pic20.picturetrail.com/VOL15/...2/14584660.jpg
Take chuck apart and you will find an area you can drill straight through. I used 6 M5 cap heads going in to self made T slot nut, 4 or 5 direct in to table tapped M5.
Did originally make a boss to centralise the chuck in to MT3 taper but would easilly go out of true.