Bison 5 inch chuck

[hdwrench1]

Hello Everyone,
I have just recently bought a used plain back 5 inch Bison 3 jaw chuck with 2 piece reversable jaws and machined a backing plate for my 9 x 20 mini lathe.
The backing plate was machined as per instructions from the Little Machine shop and indicates .0002 on all surfaces using a Starrett Last Word indicator. The registration boss measures .150 (the boss on the chuck measures .162)
My problem is that I have .003 runout using a .500 hardened test piece.
I thought I had the runout problem licked when I removed the jaws to check the positions on the indicated jaws (1,2 &3) which were in the wrong location when I received the chuck. After putting them in the proper location I am still getting .003 runout.
Can anyone give me any direction as to get this as close to zero as possible as I am out of ideas.

Thank you
Wayne

 

[gbritnell]

Wayne,
I don't know what the specs. are on your chuck but I suspect that .002 would be a very good number, so you're only .001 off. Anything below that number and you're getting into collet territory. Why don't you try different diameter test bars? It's possible that the readings would be a little better, or worse, at different spots on the chuck.
What kind of accuracy were you hoping for?
gbritnell

 

[hdwrench1]

Hello Gbritnell,
I've tried a few different test bars yesterday towards the end of the day but I'll try a few different OD bars right now.
I was hoping for .001 accuracy.

thanks for the reply
Wayne

 

[portlandron]

The job of a three jaw chuck is quickly mount a piece, that has a larger diameter then you finished piece will have,and turn it in one operation to the desired diameter. If you can get it within a few thousands then you are doing good.
That being said if you want to spend some big bucks you can get three jaw chucks that have repeatable accuracies.

 

[hdwrench1]

So far ,same results .003 thousands. I've just received a 4 jaw plain back and some mounting plates. I'll do the mount plate for the 4 jaw for more accurate turning and start saving some beans for a collet chuck (after I buy my new Grizzley mill)

Thanks for everyone's help
Cheers
Wayne

 

[Mainer]

0.003" for a used 3-jaw is probably about as good as you can expect. As noted, different diameters may be better or worse depending on how the chuck is worn.

You could grind the jaws, but that would give you accuracy only at the diameter they were ground at. (n.b. to grind chuck jaws, they need to be preloaded so any looseness in fit is taken up. If you decide to grind them, read up on how to do it first.)

Another option is to take a few thou off the o.d. of the backplate so it's a loose fit in the chuck, then leave the mounting bolts slightly loose when you mount the chuck so you can tap it around while testing the runout until it's minimal, then tighten the mounting bolts securely. From what I've read, the chuck won't shift in use.

Personally, I think I'd leave it alone.

 

[hdwrench1]

Thanks Mainer,
I'll take the word of experience over doing something to damage the chuck. The 5 inch Bison is really nice and I can probably live with the .003 TIR using this chuck.
Please excuse my inexperience in this matter. I know the collet chucks are dead on however its not in the budget until the fall

Thanks for everyones input, MUCH appreciated.

Cheers
Wayne

 

[cfellows]

I had a .003" run-out on my harbor freight 7x10 3" chuck which was unacceptable to me because changing chucks on these little lathes is a pain in the you-know-what. So I made it into an adjust-tru chuck. I did this by pressing a ring over the outside of the chuck which extends out over the mounting plate. The ring had 4 tapped holes in it which allowed me to insert set screws which beared against the mounting plate. I also turned the recess in the back of the chuck about .030" larger than the lip on the mounting plate to allow a small amount of radial movement. Now I can adjust the chuck to be dead on with less than .001" run-out.

Here are some pictures of the chuck before I drilled the setscrew holes.

And here you can see the chuck mounted on the lathe showing one of the 4 setscrews.

Chuck

 

[Stan]

I know the collet chucks are dead on however its not in the budget until the fall

Not true! Just better than your three jaw. In machining, nothing is absolute. You work with tools and your ability to get the results you require. It is nice to have high quality, very precise equipment but they are not necessary for the work most of us are capable of doing.

 

[hdwrench1]

Wow Chuck,
Outstanding idea!!
This may be a far better idea than anything I've thought of so far.
Bison listed the spec at .003 TIR for the 5 inch chuck which is where it is however I would like .001 or less.
This seems to be the most practical idea so far.
Now to dig up some steel the size I need
Thank you
Wayne

 

[MachineTom]

Owning a couple of Bison chucks purchased new. They are good chucks but not up there with the very best, but priced affordable. First it matters what you are using as a test piece, a piece of random round, apiece of Ground and Polished, a piece Ground polished and hardened, or a real test bar quailty piece.

Dowel pins are the easiest round, hard and polished pieces to buy. 1/2" an larger. The two piece jaws on the bison are something to look at. The removable jaw should be bearing on the work, without contact on the Master or inner jaw, on my 3 jaw that was not the case, so a piece chucked in the outer jaws ran truer, than a longer piece shallowed in both jaws. The solution was to remove the outer jaws, grind the inner jaws, and reassemble. To test this, coat your test bar with bluing, tighten the jaws so that both jaw sets might bear on the piece, if there are marks from one or two inner jaws , and three outer jaws, thats part of the problem. Its best if there are no marks from the inner jaws, and three even marks from the outerjaws.

Do you have one or three jaw pinions, if three one will be marked with a "0" that is what the factory says is the master pinion, used to tighten the chuck for best accuarcy. Try the same test piece by grabbing in the outer jaws, and repeatly tighten, loosen and redo using each of the pinions, one will be better than the others, if it isn't the factory mark, just remark it yourself.

To grind the jaws is time consuming, but not difficult. You MUST have a internal Toolpost grinder, or an inline diegrinder. A Dremel or anything like it is not the tool to use, regardless of all the post that say differently, a tiny bushing in a plastic case with a .125 shaft is useless for precison grinding.

Grinding the jaws, first remove the outer and inner jaws, degrease, at the innermost portion of the inner jaws, you need to shorten the last jaw hump, about .050, on each jaw get them about even. Then using a piece of delrin or the like, you need a round disk just smaller than the bore of the chuck body. When you reassemble the chuck you will Grab the disk in the area where you ground down the jaws. tighten the chuck jaw using the MASTER pinion snuggly, it is plastic so not too much. Add the outer jaws and your ready to grind. I marked the jaws with a black marker to see how the cutting is going. Its best to grind from the inside out. a BIG cut would be .0005" it takes a while about 100-200rpm on the spindle, feed .002 your can hear it touch each jaw, and when it doesn't. After the ink is gone, you now have to disassemble the entire chuck and clean out the grinding dust, grind that small area next to the plastic disk to remove the tit that remains, grease everything up, and reassemble. It will take 4-6 hours for the whole thing.

Your runout now will be within tenths at about the diameter of that disk, it is as good as it gets.

Look at the inner and outer jaw bearing first before cranking up the grinder.

 

[maverick]

Wayne,
If your Mind isn't spinning yet and you'd like another option, the outer jaws can be replaced with soft jaws
made from AL. These can be bored to a specific size to hold a matching diameter. Before boring,
the master jaws should clamped on a disc or bar to take up the slack.

Mike

 

[hdwrench1]

Wow,
So many fixes, thanks everyone.
I'll have to tackle this next week as its a long weekend here in Canada and I've got a couple bikes that "have to be finished" before the weekend.

Keep the tips coming. I'll refer to everything this coming week and post my results.

Thank you to everyone that helped me out.
I really enjoy this board

Cheers
Wayne