New 6 Jaw Buck Chuck Backplate

[Woodenspoke]

I managed to pick up a lightly rusted, never used, 6 jaw, Adj-Tru, Buck Chuck with non reversible jaws. I cannot buy a factory ready back plate for the chuck since the mounting I need is 1 1/2 x 8TPI, they don't make those. So I ordered a pre-tapped blank Iron back plate.

I know how my non adjusting back plate fits in my current 3 jaw chuck, super tight. What would be the spacing needed between the shoulder and the plate for this adjust true chuck?

The new chuck is 6" and has 3 mounting holes, it came without the cap head mounting screws. Does anyone know the screw size, or how much play should be in the screw slot?

Any help or support machining the back plate would be appreciated.

Woodenspoke

[Adobe Machine]

Rutland tool (rutlandtool.com) has a Bison back plate ( same as "buckchuck)part # 2420 8132.this is a 1 1/2 " 8 TPI.Does this look like your prethreaded plate ? If not, it should.

The way I set up a Tru Set Chuck back plate is:
1)Install the plate on the lathe and tighten to the lathe specifications.

2) machine the face of the plate to 0 run out.

3) machine the boss to 0.05 undersize of the chuck recess.This will give you about 0.002 "play" to adjust TIR to 0. You may need more, but minimum is best to get the chuck to 0 TIR.

4)The 3 verticle special fasters are NOT mount bolts. The are the adjusting
special allen pads. Mine are a 3/4 18, the ends are ground and only move the chuck around the plate boss to zero in.

5)Usually these chucks will have 6 ,3/8-16 allen bolts that are horizantle with the machine shaft, these really are the mount bolts. The only way I would know how to drill and tap the plate correctly ( they must be spot on, absolute) would be with a CNC that keeps good tolerance. There is a small amount of oversize in the 6 chuck holes, that allow the chuck to be adjusted with the special adjustment allens with the ground pads. (above).



If I have you completley confused, I will post pictures of my plate and 6 jaw scroll chuck to clarify.

Adobe (old as dirt)

[Woodenspoke]

Adobe

That was the information I was looking for. .05 gap for the adjust true back Plate and 3/8-16 mounting screws.

I was planning on facing the back and front of the plate, in that order. Then mount the chuck and get it adjusted true to center. Then I would use a tight center punch to mark the mounting holes and drill and tap the back plate on my small x2 mill.

My assumption is that there is some play in the chucks mounting screw hole or how would you be able to adjust the chuck true?

I have seen the Bison Back Plates but unless I have an absolute yes it will fit A Buck Adj-Tru chuck the difference in price is $100 over a blank plate and I don't want to take that chance. Besides its good practical making a back plate to fit.

Woodenspoke

[Adobe Machine]

Well, understand where you at..The problem is, if your off say even .001 on punching one hole, then your outer chuck will not move around correctly,and the possibility of punching all the holes with out a shift in one or more of the holes is really pretty slim ( at least, in doing this for 35 years, I have learned its like a crap shoot) .If there is a CNC Machine shop in you area, they should be able to do the bolt circle real economical, just give them the bolt pattern circle measurements, and with maching the plate as you described, should give a spot on 6 jaw chuck.

One other consideration: You must be able to come back to the same mount thread distance if you should remove the chuck and plate, as that is where the mount plate was machined at..If not , when reassembled there possibly would be run out to exceed the adjustability, so mark the plate and the threads at the location you did the surfacing..

You will lilke that adjust True..They are super accurate, but if your turnin tuff stuff, check TIR regular...

Adobe (old as dirt)

[Woodenspoke]

Followup

Finally got everything turned, milled, drilled and tapped. I found the play using 3/8-16 cap screws to be substantial so I went ahead and used my own resources to do the bolt hole pattern. Sorry Adobe (old as dirt), I figured if I screwed up I would just have six holes instead of 3 and be a little wiser.

Well I guess I am lucky because everything worked out just fine.

I marked the lathe and backplate position after final turning for later removal and reassembly. I found the hash marks do realign when I remove the chuck. The hardest part was working through the procedure of adjusting true center on the chuck. I got it two within 1/2 tick on a .0005 indicator.

I wound up using a 3/8" spotting drill shaft as a surface to true from. Is there some other more precise surface you would use to help setup an adjust-true chuck? Any advise to making the adjustments?

Woodenspoke

[Adobe Machine]

Wow, Kool...I've tried that on a Set-Tru with 6 holes, and wound up with less than .002 radial play.., found the one that was off, did what I had to do and that was hone the one hole in the plate..Worked ok, just took a lot of time.
( this was all before cnc..) then I had a German National that was a very top notch machinest working for me. He could trig faster than I could. ( His education after their high school was ten years of engineering, machining and university study, actually he was a Mechanical Engineer, but no one in the US would recconize his credentials, really too bad.I did after a couple of years, designate him as a " Machinest Engineer" and paid him more than hourley wages, except he could not certify some of the documents for the weapons lab and other US Gov work).Any way, I let him do the next one as he kinda prodded me about the one I did..The new one was 8 holes, took him all day to lay it out and punch. Guess what, one was off just maybe high tenths, but we still had to hone some out..I was glad to see CNC..It has made jobs like you just did a lot quicker..I certinly do congragulate you on doing it the 1st time..shows determination and skill..

We always used drill rod or or a good 1/2" carbide endmill ( long type),both of which have been ground and polished. You are down to the point where even a speck of dust will show a bump..

You will really like the 6 jaw, requires less clamping pressure , always accurate..But do not be disappointed if after some use, when you check it, there will be some run out..Usually takes 2-3 times before everything seats in real good. Did you disassemble and clean ? You stated there was some rust, so would imagine there is some inside, which can affect holding and TIR. Now you get to buy a ring set so you can bore new jaws when needed, as they can not be done anyplace else except on your lathe !

Advise on procedure: Lots of patience,walk away for awhile when you start to get mad, Keep the kids and significant other away ( shop dogs are ok) and no noisy neighbors.

Adobe (old as dirt)

[Woodenspoke]

The chuck was an EBay find "never used with light rust". Well on the outside it was lightly rusted on the inside the rust was heavy but not bad enough to cause pitting. The model is an AT-6", 6 jaw fixed (whatever that means in the buck chuck archives). No noticeable wear or marks from use I could see.

The chuck had no oil or grease on anything. The smell when I took it apart made me think of waste water contact. I used electrolysis to remove the rust(car battery and baking soda solution) which allowed me to get into all unreachable areas. I buffed off the rust, now black (rust-less) spots, with some 3M pads. Everything was oiled down with some penetrating oil and finally the inside gearing was throughly greased (i just realized I should try the grease fitting to make sure it's good to go). The chuck looks good and works like a charm (so far). I realigned the lathe's tail stock and I'm good to go.

The whole cleaning/plate project took about two days and cost $360 including the $65 Bison plate. I think I lucked out all around.

I looked through my MSC catalog and noticed a 1/2 drill blank as a solution for an accurate measuring surface, it's 6" long and is at a price I can live with.

Thanks for the help Adobe

Woodenspoke