Rotary table...with a thread on chuck?

[Jswain]

So I recently picked up a Craftex ct129n mill and it came with an STM 6" rotary table. Looking to make use of the 3/4 jaw + collet chuck I have for my Southbend which are 1-1/2" x 8tpi thread on.

My rotary table has a threaded center, and from what I've read using it to mount a chuck is less desirable. So I am thinking of cutting out a chunk of 3/4" plate for the mount, then I have some ~ 1-3/4" rod I could bore the center of the plate, press in & weld. Turn down and thread for 1-1/2 x 8tpi

Could probably use a clamp kit on the face of the chuck to keep it from turning if needed? Any of you guys make one of these for thread on chucks, or is there a better way? Thanks!

Basically looking to imitate this

 

[Susquatch]

Your rotary table has a threaded center? Can we see a nice photo of that? What model is it?

 

[Susquatch]

I'd be tempted to make a big backplate for it and then clamp the backplate to the table T-Slots. It wouldn't be too hard to dial that in.

 

[Jswain]

It does, all the documentation says mt2 but it is threaded and I'm weary of trying to pull the threaded portion out as it doesn't look to me that it would be mt2 behind it. Also has a threaded plate on the back. Pictures coming

 

[Jswain]

Unless that centre section pops out? It was missing one of the locking blocks& both handles so those were my first projects to replace them & add some 3d printed covers

 

[Jswain]

Versus a factory photo with mt2 centre...which leads me to believe someone either swapped it out or drilled/tapped the threads, or it previously came threaded

 

[Darren]

That piece on the back is definitely not factory

 

[DavidR8]

Is the back piece threaded into the insert thing?

 

[Jswain]

The rear plate unbolts and it appears everything would function as it should without, I believe previous owner made it for locating or some type of setup.

No it isn't threaded into the insert they are two seperate pieces

 

[Susquatch]

It is somewhat interesting to me that both top and bottom appear to be threaded the same. Might be for some specialized custom function.

Have you tried tapping out the top threaded piece using a bolt or bar with that thread? If not, maybe the table needs to be taken apart to remove it.

 

[Jswain]

I have not attempted to remove yet, and I don't know if I will unless I can find a reason to need a morse taper in the center?

 

[RobinHood]

That threaded center is not going to do you a whole of good. For example: how are you going to center the RT under your spindle? You can’t indicate off of the threads. I don’t see a shoulder that could be useful.

I would pull off the plate on the bottom first - it is just four bolts - and see what you discover.

It seems to me that that plate is only semi-useful anyway (probably was for a special setup as has been suggested). It does not rotate with the RT top. Anything screwed into those threads would either tighten up or back off, depending which way the RT top is turned. I think the plate may have been used as a “quick mount” of the RT to some appropriately threaded boss, the OD of the plate being used as a radial locating feature.

The plate also eats into the headroom on your mill.

 

[Jswain]

I've already had the plate off and like you said I believe it was to intended to quickly install/locate the rotary table. With the plate removed it should function like normal.

Indicating the rotary table in with the threads I didn't think about, perhaps I will need to remove it, or if the threads are centered then make a threaded plug to indicate off of?

I will remove the plate and take another pic from the backside

 

[Jswain]

Plate removed on backside. Looks normal minus the 4 threaded holes. I think eventually I will dismantle and see if I can press out the threaded plug, who knows maybe I'll be left with a morse taper hole with any luck?

 

[LenVW]

Looks like the previous owner tried to use the plate to raise the RT for a particular operation.
(The outer edge is too rough to use as a reference surface for positioning)

Take it apart and discover the components involved.

 

[thestelster]

Versus a factory photo with mt2 centre...which leads me to believe someone either swapped it out or drilled/tapped the threads, or it previously came threaded

In the factory description it says, "...MT2 center sleeve."

To me, sleeve implies that it is removeable.

 

[Susquatch]

who knows maybe I'll be left with a morse taper hole with any luck?

Exactly what I'm hoping for you too. But even if not almost anything is better than a threaded hole. I think it will be difficult to create a center on a threaded hole. But not impossible.

 

[Rauce]

I have an 8” stm rotary table, mine came to me with the MT center sleeve already removed by a previous owner. What’s there is a plain bore that runs true to the rotation of the table (less than .001” TIR).

I have been working on a plate that uses this bore to locate a chuck. It’s mostly done but still needs the features on the chuck side machined.

 

[Jswain]

Thanks for the photo. I wonder if a puller from the front would work better to remove.

 

[RobinHood]

or if the threads are centered then make a threaded plug to indicate off of?

Unless there is a registration surface (like there is on a threaded chuck), threads are not accurate enough to indicate off of - even with a threaded plug.