6-jaw backplate install

[rabler]

As I've already posted, I went to an auction earlier this week, and picked up three six jaw chucks (two 8" Buck, and one 6" Bison). All three of these are of the set-tru variety. Of course none of them came with the backplates I need, D1-6 for two of the lathes, and a D1-3 for the smallest. New Bison/Buck set-tru backplates would rival the cost of all three chucks for one backplate, so I went with a Shars set-tru style backplate. I have no doubt that it's not at the same quality as the name brand backplates. For one thing the Buck backplate is steel, whereas the Shars model is cast-iron. Buck rates their 8" 6-jaw at 3000 RPM. But a cast iron backplate would make me nervous at those RPM. Of course the used chuck may be of different specs than a current chuck, any factory markings with such information are long gone.

The first target for the 6-jaw is my Monarch 12CK lathe. It is a worthy machine, but at 77 years old it does have some limitations. One of which is a maximum RPM (after some modifications) of about 1000RPM. More within the range that is comfortable with a Chinese cast iron backplate.

First step was to clean up the spindle mount on the lathe. Wipe it off, blow it out, repeat. I lightly stoned it smooth, did the same for the backlate mounting face, and put the backplate on the lathe. First thing I noticed was the camlock studs dragged going in/out on the spindle. So they got stoned too. I put an indicator on the face of the backplate. 0.009" runout! yikes. Shars claims it is "Finished Machined" in the title, but the fine print says The back plate is fully machined but still need secondary operation to fit with... The inner shoulder that the set-tru registers on was also visibly out of center. I didn't put and indicator on it since I new that needed to be turned down.

Being cast iron, and where I wanted minimal skim cuts, this was an ideal (in my mind) job for a HSS tool. Took a few minutes to grind up something that would cut into the corner and get both faces. Used the diamond lapping machine to finish honing it. Unfortunately the picture focused on the resulting mess not on the HSS tool I wasn't too particular about exact angles, cast iron just isn't that challenging. Just applied oil liberally while cutting.




Having squared up the backplate, I decided I really should service the chuck before putting it on. So I took it apart, thoroughly cleaned the old grease and chips out of it, lightly greased it and reassembled. The front and back of the chuck are held together with 6 SHCS bolts near the center hub. By loosening those up to be slightly proud, I was able to stand the chuck on its side and lightly tap each in turn to get the halves to separate. Best approach I could figure, if anyone has a better procedure I'd be interested.

I wish I would have gotten a picture of how set-tru adjustments on the back of the chuck. I'll grab a picture tomorrow of that angle on one of the other chucks.


The innards of the chuck looked good, scroll sat tight in the back part. Looks like a few chips had left scours in the front, trapped in the scroll threads? Picture looks worse than a fingernail indicates (note there are two minor shoulders in there too). Jaw bases (2-piece jaws) fit snuggly in their tracks.

Getting the chuck mounted on the backplate and trued up took some tinkering. Note that the shoulder of the backplate needs to be turned a few thousandths smaller than the chuck recess. This gives some clearance to center up the chuck. I had to take the chuck off and shave the shoulder once to get the appropriate fit.

I set up a dowel pin and indicator to center up the chuck. Centering up the chuck is really counter-intuitive after working with a 4-jaw, as you need to tighten on the lows and loosen on the high side. You're working 4 setscrews to center the chuck on the backplate, and 6 SHCSs to tighten up the chuck onto the backplate. I think a torque wrench, and slowly stepping up the torque on those SHCSs betweem centering with the 4 setscrews, will be my procedure for next time.

I was using a .0005" indicator. Got it centered to the point where I couldn't detect any needle movement beyond the slight deflection from friction when starting/stopping. Of course, it was either Stephan Gotteswinter or Robin Renzetti who said if you can't see any movement, you're not using a fine enough indicator. Reality is the bearings (when cold) on this old lathe will deflect about .0004 if I use a light lift with a hoist on the chuck. So I'm calling it centered.

I'd upload a video but my internet connectivity makes that painful.



Cleaning up the lathe of all the cast iron shavings took a while

 

[benmychree]

Cast iron is normally machined dry, that is without any cutting fluid; using cutting oil would make twice the mess that may be expected. I just use a chip brush to keep the chips from flying all over. If you get .0004 deflection, the spindle bearings likely need a bit of snugging up. I had a 12" model CK in my shop, hated to leave it behind.

 

[benmychree]

The chucks from the factory with backplates have much more than a few thousandths undersize on the diameter that the centering screw bear against.

 

[rabler]

The chucks from the factory with backplates have much more than a few thousandths undersize on the diameter that the centering screw bear against.

I figured it was easy enough to cut a bit more if needed, which I ended up doing once. But I lost track in the process of how much undersized I actually went, as I didn’t tkink it was critical. It worked out. Maybe more by luck than careful planning.

 

[rabler]

If you get .0004 deflection, the spindle bearings likely need a bit of snugging up. I had a 12" model CK in my shop, hated to leave it behind.

I have an oil leak from one of the headstock shafts that has a bearing cap on the clutch end of the headstock. My goal is to get my 612 lathe working well, and then move everything into the the shop being built in the next month or two, then tackle the next round of repairs on the CK. The clutch also has a bad rattle when disengaged, I believe the pressure plate under the springs (outboard end) has gotten sloppy. Any experience there? I’ve had it apart a couple times to degrease and replace the tiny springs that open the clutch up when disengaged. Anyway, those are all on the project list after rearranging deck chairs, erh, shops and machines.

I also need to work on the compound, cross slide, and carriage as there is pretty significant wear. Scraping and rulon/turcite/moglice. And the tailstock is badly galled and worn. So it’s a work in progress. But those will all get addressed over time. Just a few too many irons in the fire right now. But yes, I really like this lathe.

 

[Beckerkumm]

I've done a few Shars backplates ( not for Set Tru ) and they can be made to work fine as you did. I recently sucked it up and bought a Bison set tru backplate and the price became more evident and hurt less than I expected. You can find some deals and they are heavy, thick, and finished almost like jewelry. Either way, the set tru is worth it. Dave

 

[benmychree]

I figured it was easy enough to cut a bit more if needed, which I ended up doing once. But I lost track in the process of how much undersized I actually went, as I didn’t tkink it was critical. It worked out. Maybe more by luck than careful planning.

I'd guess that mine has about 1/16" of clearance on the diameter.

 

[rabler]

Here is what the back side of a adjust-tru/set-true chuck looks like:

You can see the large recessed adjustment setscrew on the near side of the chuck, and the flat of the setscrew on the inside of the recess on the opposing side. There are 4 of them total. (This happens to be the other 8" 6-jaw, it's in a little better shape actually).


Also, probably obvious, but the clocking of all this matters. I put witness marks on my backplate to match my #1 camlock (on the lathe spindle, all of the camlocks are numbered). Then a paint mark on the backplate and matching mark on the chuck. The backplate/chuck mark isn't really necessary since removing the chuck would mean loosening the adjustments and starting all over, but easier to keep track of things up front then realize after the fact that you don't know the right orientation.

Also if you take a close look at the last picture in the first post you'll see the outside face of the jaws are pretty beat up. They are two piece jaws so I'll probably look for replacements.

 

[rabler]

I've done a few Shars backplates ( not for Set Tru ) and they can be made to work fine as you did. I recently sucked it up and bought a Bison set tru backplate and the price became more evident and hurt less than I expected. You can find some deals and they are heavy, thick, and finished almost like jewelry. Either way, the set tru is worth it. Dave

If I ever get the 10EE rebuilt, I expect to use the 6" 6-jaw on it. I will probably spring for the name brand backplate at that point, especially since that lathe was designed for up to 4000 rpm (the Bison 6" is rated for 3200).

 

[Beckerkumm]

Here is the Bison backplate. I have a 6 jaw set tru as well as the 5c and they along with an old union combination three jaw get the most use. The Smart Brown has a 3000 rpm limit. Dave