4-Jaw chuck for rotary table

[PStechPaul]

At Cabin Fever Expo on Saturday I bought a 4-jaw 6" chuck with the idea of using it on my rotary table. I paid $50 for it and it seems to be in good shape, although one adjusting screw and jaw seems rather loose, while the others are very tight. My rotab is also 6" and I should be able to mount this chuck with four bolts in the T-slots. This is how it looks with the jaws fully tightened:







Here it is with the jaws opened to as far as they will go easily. The #2 jaw can be loosened all the way quite easily and the jaw can be removed:

[craigd]

So one jaw is somewhat sloppy. I'm not sure that would be a problem - generally when you use the chuck to hold a work piece, the jaws are tight - so everything stays solid (sort of what a chuck is for). Afterall, the jaws have to always have a bit of clearance, or else they won't move - so you have one jaw that has a little extra room. It looks like you are intending to use the back face of the chuck for mounting, instead of the original mounting surface and register? You may want to recut that back surface. Just grip a good sized bar in your existing chuck (long enough to go through and be supported on the tailstock), take a skim cut, then grip the "new" 6 inch chuck backwards. You'll have to decide what to use for center (the OD of the chuck? the bore of the chuck? the existing register?) - then skim the back face and skim the register. It would be up to you whether you ever use the chuck register when mounting the chuck onto your rotary table - afterall it is a 4 jaw. Making up some sort of a registering plug/sleeve would make it quick to remove and reinstall, and not lose center on a job that you want to move to some other machine and back again.?

[PStechPaul]

I am used to my other 4-jaw chuck on my lathe having a rather loose fit, but it had been damaged at some point and I made new screws which are not precisely machined.

As I look closer at this chuck, I notice a few things that indicate it may have been repaired. On the back, the yoke pins have small tapped holes with set screws in them, and there are punch marks corresponding to 1, 2, 3, and 4. But the single punch mark corresponds to a "4" on the outer surface of the chuck, while the face is marked "3" which matches the number stamped in the jaw's slot. Two punch marks are for "1" on the outer surface and "4" on the face, matching the #4 jaw. Three punch marks are for "2" on the outer surface and "1" on the face and matching the jaw. Four punch marks are for "3" on the outer surface and "2" on the face and jaw.

Also, the entire chuck is very clean and the machined surfaces look as if they may have been bead blasted or otherwise treated. Yet the bore has some caked-on substance like old grease and rust. I can't find any manufacturer markings - just a 160 (mm), 0779, and 85. One of the outer mounting holes seems to have been drilled through part of those stamped numbers, and there is an off-center shallow counterbore on another hole, where I have seen manufacturer insignia on other chucks.

[Paul Alciatore]

Pale. Mineral Spirits. Add a bit of oil. Soak it for a few days. Then disassemble and clean with a brass brush.

Considering that it is a four jaw, I do not think there is any need to keep the pins in their original holes, but also there is no harm in doing so. Do check to see that those punch marks do not protrude above the back surface as you want the chuck to lay flat on the RT table. If they do, a light filing or stoning should take care of it.

I too have a four jaw (6") for my RT(10"). My table has six slots so I had to carefully locate three holes for mounting bolts. For most work you do not have to be concerned about keeping the chuck precisely centered on the table as the work is centered in the combination with a DI anyway. I just roughly center it with an adjustable square.

[RWO]

If the chuck is larger than the rotab, turn a recess about 1/8" deep in the back of the chuck to a snug fit on the rotab OD. This automatically centers the chuck on the rotab.

RWO

[Daveb]

A chuck with tight jaws is not pleasant to use. I usually strip the chucks when I buy a new (old) Machines. Dismantle the chuck, soak the parts in solvent and give it a good clean. Check the jaws for bruising or damage, correct with small slip stone as necessary and fit the jaws in the correct slots, if they are tight, remove burrs from the chuck slots (not the slots in the jaw) with a smooth file until jaw until each jaw moves smoothly for it's full travel (without the screw). Ensure screws are clean and no debris is stuck in the threads, refit jaws with the screws and retainers and check for full travel. Screws may need burrs removed. Lubricate as preferred. Screws may have been replaced, new ones can be very tight, I have dressed the tops and flanks with a knife file with much improvement. Most of the problems I've had with 3 and four jaw chucks have been due to debris and/or distortion in the jaw slots of the chuck body. Purists are welcome to post their old stiff chucks to me and buy new ones.
Dave

[PStechPaul]

I think the chuck was repaired or remanufactured. Everything appears to be very clean, except the caked-on crud in the bore. I don't know how to remove the retainers. Maybe if I remove the set screw the cap will pull out (or maybe push in to pop the screw). On my other 4-jaw the screws came right out, and the retainer just seemed to be a U-shaped cradle for the neck in the middle of the threads.

The chuck seems to be 160 mm, a bit larger than 6", so it might be a little bigger than my rotab. But if I face off part of the back surface it will cut into the retainers. I can probably make a MT2 shaft that centers in the rotab and also fits the chuck bore for centering. But being a four jaw independent that is not really necessary.

[CCWKen]

Check the back of the jaws to see if they all have the same serial number. The serial number(s) may be located in the slot instead.

[craigd]

I think the chuck was repaired or remanufactured. Everything appears to be very clean, except the caked-on crud in the bore. I don't know how to remove the retainers. Maybe if I remove the set screw the cap will pull out (or maybe push in to pop the screw). On my other 4-jaw the screws came right out, and the retainer just seemed to be a U-shaped cradle for the neck in the middle of the threads.

The chuck seems to be 160 mm, a bit larger than 6", so it might be a little bigger than my rotab. But if I face off part of the back surface it will cut into the retainers. I can probably make a MT2 shaft that centers in the rotab and also fits the chuck bore for centering. But being a four jaw independent that is not really necessary.

The 4 outer holes have been added (the original did not drill through the brand tag). To remove the retainers, first remove that set screw, then remove the jaws. You should be able to reach a small punch in along the side and get at the ends of the yoke (which is the other end of that plug) and tap it out enough to extract the jaw screw. Once the jaw screw is out, then you can get at the plug and tap it all the way out. For a punch, grind up a piece of scrap so it fits (covers as much of the tip of the yoke as possible). Don't force it, the tip of the yoke is fragile. Cutting into the back of the retainers should not be a problem, they are pretty thick.

[old mart]

The screw retainers are marked because the grub screw threads would not align if they were mixed up. Someone has removed them at some time and had the good sense to mark them. I removed the retainers on a Chinese chuck, they were very tight and did not have the grub screws. Best not to remove them unless one of the screws breaks, getting them aligned for the grub screws would be a pain. That odd hole may be to balance the bare chuck body.

[PStechPaul]

I think I will pretty much leave the chuck alone. It is clean and everything works, and the tight jaws will probably loosen up with some use. I will have to try mounting it on my rotab to see if there is any problem with alignment or flatness. Thanks for the ideas and discussion.

[PStechPaul]

Here is the chuck on the RT. It is somewhat larger, probably 6.299" (160mm) on the 6" table. It seems to clear the handles on the RT, so it should be good. I used two 3/8" carriage bolts with flats filed on the heads for mounting. The nut is a fairly tight fit in the counterbore, so I might need a thin wall socket or perhaps mill the flats of the nut for the next smaller size. Another option would be to drill two holes and use a pin wrench. Maybe the best solution would be to make T-nuts and use SHCS. It's a bit tricky to align the holes on two bolts, especially since the round head makes them lie at an angle rather than straight up. Four bolts would be trickier, unless I made flats on the heads.

[mattthemuppet]

just make some t-nuts for your rotary table and thread them for whatever socket head screws you have that are long enough and fit through the body. It's going to be a) quicker to make and b) quicker to take the chuck off if and when you need to do so.

[old mart]

I also use a four jaw on a rotary table, I use the front mounting holes. I had never considered the mounting face before the number 2 reply by Craigd. Probably, the error, caused would be small, but I have just refaced the lathe backplate for this chuck so that it registers in the inner part and leaves a couple of thou gap outboard. I will do something about the back of the chuck before mounting it back on the rotary table.