View Full Version : Fitting a chuck to a rotary table, - one answer.

John Stevenson
09-21-2006, 08:02 AM
Prompted by the reply I made to Baddog about fitting chucks to RT's as I went away working I realised that this is a very common question and one that I have never seen a satisfactory answer.

One answer is to fit the chuck to a backplate and mount the backplate using tee nuts and the Tee slot. This is fine if your chuck is smaller than the RT.
Next idea is to use front mounting chucks and drill and tap into the backplate or table.
Disadvantages of this method are that front mounted 3 jaws chucks are quite rare and often people won't drill and tap the table.

The real problem arises when the chuck is the same size as the RT or even bigger and the only two ways are to use front mounting chucks again or remove the table, drill thru from the back and reassemble which is a bit of a balls ache if you need to keep swapping over.

As I was working I gave this some though, knocked off, had a coffee and built a mock up.
Although it's a mock up it does work and function correctly.


Basically imagine that alloy block as a circular backplate that you can screw your chuck to either from underneath with counterbored cap screws or thru mounts if you are so lucky.

Now that block has three holes [ or 4 ] that match the tee slots on the RT. You then drill a tapping sized drill hole from the side to meet the vertical hole, don't tap at this point.

Next job is to machine 3 [ or 4 ] circular tee nuts as in the last photo and flat two side to sides [ actually thinking about this as I type that's not even needed, you can leave them circular but they have ] to fit the slot.

Number the tee nuts and holes. Then fit the tee nuts to the slots, drop the plate on and using a screwdriver or wedge raise the tee nuts up. Spot thru the side hole to LIGHTLY mark the tee nuts.

Strip and remove the tee nuts and about 1/32" LOWER down from the mark drill a hole same as the tapping drill size.

Last machining job is to tap the side holes in the backplate and get three allen grub screws and machine a 10 degree taper, [5 degree set over on the top slide ] to blend in.

To assemble, fit the chuck to the backplate, slide the tee nuts into the slots and drop the backplate over the tee nuts, get the number right.

Then fit the allen screws and tighten in turn a bit at a time.The wedging action of the screws will draw the tee nuts and the backplate firmly down to the table.


This block is very firmly fixed and a decent tap with a hammer won't move it.
With a spigot it will be a very secure method of fastening but also quick to swap over.
It's also possible to use this method to fit an 8" chuck to a 6" table, cleanly, neatly and firmly.

Oh BTW this is now under the El Stevo International Patent rights :D


09-21-2006, 01:45 PM
Very nice, and good thinking...

John Stevenson
09-21-2006, 04:45 PM
Forgot to mention that if you have a couple of RT's then the same plate can be used to fit provided you have tee nuts for each RT.

It's a bit like a poor man's camlock chuck :D


Peter N
09-21-2006, 04:47 PM
Clever idea. Nice one again John.


09-21-2006, 04:48 PM
[poor man's camlock chuck] Yeah John, I like simple quick fixes. Good suggestion.

09-21-2006, 09:32 PM
Bright idea John. I can also imagine those clamps could be put to use in many ways.


06-09-2007, 03:38 PM
Resurrecting an old thread: I have all the parts made for mounting a 6" 4-jaw chuck to a 6" rotab per the El Stevo patented method but am having a problem deciphering the tapered grub screws.

When Sir Stevo says "a 10 degree taper, [5 degree set over on the top slide]" does that mean 5 degrees 'off of zero'? When I cut at 5 degrees, it looks to be about half of the angle shown in his pic. His looks like it's 10 deg. 'off of zero' although it may be just the way the picture looks. I always have trouble with freakin' angles. :(

Also, if the hole in the tee-nuts is drilled at tapping size, wouldn't the mating surface between the screw's taper and edge of the hole in the tee-nut be into the beginning of the threads? I'm using 1/4-28 screws with a #3 (.213") tap drill and when I check where .213" is on the taper, it's into the start of the threads.

I know the 1/32" offset will affect this but it seems like the hole ought to be a tad smaller. (?)

John Stevenson
06-09-2007, 04:56 PM
Serves you right for nicking my patent ;)

Tapping size is right as you want it to go into the hole and lift up.
If the hole is too small the taper can wedge into the hole and still not pull up enough to be tight.

The only bit that counts is the taper on the top of the hole pulling up it doesn't need to touch the bottom of the hole.

Taper could be a bit shallow and you may have to turn a bit more lead on to get it to enter the hole.

It's a bit of a suck it and see method without knowing depths of the T slots etc.


06-09-2007, 05:09 PM
I successfully drilled through a (TOS) 10" chuck to fit it to a rotary table.
It did need a bit of careful planning, with the chuck in bits, to work out where best to drill.


06-09-2007, 06:30 PM
I took a three jaw chuck and drilled two holes oposite, counter sunk the head for allen screws and attached it to my rotary table with T nuts. Machined the sides off the nuts so I would have a little play to perfectly center the chuck. Did the same thing with a 4 jaw chuck but used 4 screws on it. Both chucks were D1-4 chucks with the lugs out. riceone.

06-09-2007, 08:34 PM
So....20 yrs. from now when my daughters are selling off my stuff on TelepathyBay, they're going to say "4 jaw chuck with 4 precision lightening holes included, blue paint is extra." Nah, not cool. ;)

I gotta try this first. If it don't work, maybe then and only then I'll think about swiss-cheesing my chuck.:D