Setting up a Bison Set Tru

[Sshire]

I got a new Bison Set Tru 5C chuck a few months ago. UPS will deliver the 1-3/4 x 8 backplate today (don't ask)
Any tips, suggestions, etc for aligning the Set Tru. My thought is to put the BestTest DTI on the ID (where the collets insert) and doing pretty much what I do when setting up a part in the 4jaw. (zero the indicator, rotate the chuck 180, adjust 1/2 of the difference, rinse and repeat until the error is within whatever)
The Set Tru doesn't not have the adjustment screws 180 apart. Any help is appreciated.
Best
Stan

 

[gbritnell]

Hi Stan,
Just to let you know a set-true chuck isn't necessarily any more accurate than a conventional chuck. The idea behind it is for repeatability. By that I mean if you are doing multiple pieces of say .75 diameter you would put your initial piece in and indicate it true by adjusting the position of the chuck relative to the spindle axis. Now every piece that you put in will be dead on. Most chucks will repeat exactly, what they won't do is center exactly over the entire range of the chuck. The even make set-true collet holders for the same reason, repeatability. The set-true chuck should have either 3 or 4 adjusting screws. You center it just like you would do with a piece in a 4 jaw chuck, loosen one and tighten the other.
gbritnell

 

[rkepler]

You want the mount the backplate on your lathe and take a skimming cut on the face so that it's perpendicular to the spindle axis before mounting the 5C chuck on it's face. As you say you use the inside 5C taper, working the pairs of screws until you don't see movement. I usually rough in on one pair and go to the second right away as they interact slightly. It's about the same as adjust true chucks with the screws at 90 deg from each other but with a little more interaction.

But the adjustment for a collet chuck should have to be repeated if you lock it down. If the collet taper moves you'll want to check the interface between the chuck and the backplate. If you see a centering error it's likely going to be the collet and long term it might be better to replace the collet than to have to tweak the chuck's mount out then back in again.

 

[MachineTom]

The bison setup does not have the screws at 90° to each they are in two sets of two, which are about 60° from each other and 180° from the other set, why they don't say.

What I have done is loosen all adjusting screws, hold down bolts snug, tap it close, I think a dowel in a collet will be easier than using the taper of the chuck, that angle itself will be moving the indicator, and you snug up the bolts it will keep running you around. Pick two adjusting screws 180° apart, If you need to thighten the screw at 9:00, be sure to first back off but don't let loose the screw at 3:00 position. Remember that you do not want to load the screws, you want to use them to move the around. When within .002 now measure the position 90° to the first screws line. Now with the first screws at 9, 3, the loose set screws are at 10 and 4, what is the reading of the DI at 12:00, Lets say the number is 15, and you had been around 10 at the 9-3 positions, You want to tighten the screw at 4:00 position assuming that would decrease the reading. You will get the hang of it after doing it a few times.

Its an odd way but that is the best procedure I've come up with on my Bisons.

 

[Sshire]

Thanks for the tips and procedures.
After reading I went down to the shop and did the facing cut.
Mounted the chuck and first used a DI on the outside to get close. Then used the BestTest on the ID and did the adjusting screw dance. After about 30 minutes, I've got it to "half a half a thou". Plenty good enough.
Then I used one of the Hardinge collets and chucked up a piece of 3/8" drill rod. Runout at an inch from the collet was less than .0005. I'm going to test some of the cheap collets on Saturday. I'm not expecting them to be as good as the Hardinge but I may be surprised. I'll replace any with unacceptable runout with good collets as I need them. All of the squares and hexes (used on eBay) are Hardinge but they'll get QC'd in any case.
George, I understand what you're saying but I just got tired of taking a piece out of the 4 jaw to do something to it and then having to recenter if it had to go back on the lathe.
The Bison is a beautiful piece of tooling and was a great gift to receive over the holidays.
I'll report on the collet QC after the weekend.
Best and thanks again
Stan

 

[Swede]

What these things are fabulous for is RE-mounting work.

The idea behind a normal 3 jaw chuck is to mount raw stock which will be machined all over, then parted off. Where it goes wrong is when someone attempts to re-mount a turned part in the chuck, and then they wonder why it is no longer turning concentric.

With a set-tru design, you can remount it and then indicate it to zero. Think of them as having 4-jaw tendencies when needed. And when you don't need zero, you can treat them as any other 3 or 6 jaw chuck. Simply skip the adjustment part of mounting.

I took an old AXA toolholder and mounted an indicator in it. That gets dropped onto my toolpost when I need to adjust the chuck. One thing - don't forget that the screws which enter the chuck face are there for rigidity. These must be partially relieved, the chuck adjusted, then re-tightened from the front once more.

These are WONDERFUL chucks.

 

[Sshire]

Another thing that makes life a whole lot easier is a collet block. I turned a piece to diameter today, left it in the collet and put it in a square 5c collet block. Moved the block to the mill and milled two flats 180 degrees apart on the piece, then put the collet back in the chuck. I checked with the DTI and it was a hair over 1/2 thou off. A happy guy.
I'm also liking the ability to turn right up to the collet.
Best
Stan