Dialing in Set Tru Chucks??

[J Tiers]

This raises one point that I haven't seem mentioned here before. The Bison set-tru chucks don't really use the greatest design. I don't know if this is a patent issue with Buck/Forkhardt or what... What Bison does is take a minimally shortened, plain back chuck and mount an adapter ring to it that has the fine adjustment screws around the OD. Now you use a backplate with a raised inner flange which the set screws contact for adjustment. There is nothing integral to their design. It adds length and weight that is unnecessary comparing to the Buck/Forkhardt standard. I don't know why Bison chose to follow this "adapter plate" design. It makes little sense to me. As mentioned earlier in this thread, that design used to be reserved for taking a plain back chuck and "makeshifting" it into a set-tru chuck. I'll stick by the "if it works, use it" for the OP, but not for Bison.

Well, Mr Marks.....

I have a Buck which is substantially the same as the Bison, except that the setscrews are at 0,90,180,270.

I do not believe you have correctly described the system.....

The chuck body has 4 setscrews in it for the Bison and for the Buck. The backplate has a "spigot" which the screws engage, and the backplate mates with the selected spindle nose type.

I really don't see how else they could do it, except to make it somewhat skinnier.....

I made a backplate for my Buck, doesn't add much if any length to the stickout.

I don't see where Bison "added" any extra at ALL to the chuck in the OPs pictures.... the seam you see is needed for the collet pinion.

In the case of the six jaw, I again fail to see the added portion...... unless you suppose the spigot could extend further into the chuck body........ probably it could, a small amount, but.......

[Charles P]

For Newbies, there is another very good English chuck made by Pratt Bernard called adjust tru, if I am not mistaken.
They only have 3 adjusting screws I believe. The screws are like taper pins, and the side of the pins impinge on the backplate, making fine adjusting very accurate and non-sensitive to torque

Rich

Almost.
It's the Griptru
Details http://rotagriponline.com/index.php?...mart&Itemid=29

I've got a 160mm version on my CVA

Charles

[JCHannum]

I don't see any major difference in the backplate between the Bison and Buck chucks either. My Bucks don't have metric adjusring screws either. As I recall, in the Buck, the screws do not bear directly on the spud, but have flat slugs between the screw and spud.

Is it possible that the screws have that odd arrangement to avoid the D mount pins?

[Arthur.Marks]

I think I'm full of #$*! too on this one I was seeing three sections bolted together for some reason with the Bison's. I don't think my brain had enough coffee yesterday. I think I was mis-remembering a "switcheroo" from eBay a couple years back to be honest... seller advertised and pictured genuine set-tru and a plain back with adapter ring/boss-plate showed up.

Forgive me. Unintentional Troll.

[JoeLee]

Well there are three sections bolted togather...... so your not really cazy. The chuck body, back of the chuck, and the back plate......... 3 sections.

JL.......................

[spope14]

I have three of the "off spaced" bison chucks, three jaw, 6 inch. After a few times, they are not hard to get indicated. My question for this is always "what type of mount?". If a D type, mark an index line on the chuck and spindle for mounting and be sure your D1 screws are set properly. This is a normal start. Keep back surfaces clean, stoned and tapers clean - you all know the spiel by now I am sure. Work on consistent clamping pressure when tightening on the workpiece. One thing oft overlooked in chuck indicating is to check the tightness of the master jaws to hard jaws, I can't count how many times I have gone to other peoples shops to show indicating methids and found some moderately loose (not unsafe, but enough to allow for more than normal flex) master/hard jaw fastening

All of this usually keeps my work within .003 or better repeatability when doing just normal work, mounting,unmounting.

There really is no tried and true short cut to indicating a chuck in all said and done, patience becomes a virtue and practice is a requirement.

I like the bolt and washer set-up, and would possibly try this in my shop, but in a setting like my shop where the three chucks are, any modifications bring out liability issues.

The problem faced with these chucks is overtightening (or gawd forbid undertightening,) work and the indicating screws. The indicating set screws are flat ended.

[JoeLee]

Since we are on the subject of Bison chucks, here is something I've wondered about for quite some time. As someone else mentioned I also have 5 Bison chucks. A few years ago I bought two new 5" chucks for my T & C grinder, a 3 jaw and a 4, both with 5C back plates as to adapt them to the KO Lee motorized workhead.
I bought the unfinished ones as I think that was the only way they were offered at the time with 5C mounts. The 3 jaw chuck measures 4 7/8" in dia. and so do both back plates. The 4 jaw however measures a bit more at 5 3/32" in dia.
Don't ask me why.......... both are still considered 5" chucks.
I didn't know this at the time, I thought they would both be the same OD.
The back plate offered for the 4 jaw was 2 3/4" in dia. as it was designed to fit in the center recess of the chuck. I thought it would be best if I got the full back plate instead. I don't see the reasoning in a small dia. mount for the 4 jaw as opposed to the full mount for the 3 jaw. I suppose I could now turn all that away to fit the inside recess of the 4 jaw or just mount it as is......... smaller than the OD of the 4 jaw. Any thoughts??????
Also somneone mentioned something about stacking all these adapter plates and back plates, as you can see in the picture my 8" 3 jaw mounted to the rotory table is quite tall becaause of this.

JL..................

[ulav8r]

The problem with the adjustment screws not being at 90 degrees has been around a long time. However, they work just the same as any other adjust tru or a four jaw chuck. Just be sure when making adjustments the the screw being adjusted is lined up with your indicator. If you do that it adjusts the same as ony other chuck.

[hwingo]

The problem with the adjustment screws not being at 90 degrees has been around a long time. However, they work just the same as any other adjust tru or a four jaw chuck. Just be sure when making adjustments the the screw being adjusted is lined up with your indicator. If you do that it adjusts the same as ony other chuck.

Well, not really. It's been my experience that the chuck actually moves in the opposite direction. One would think that if you screw the set-screw in, then the chuck would move that direction but it doesn't. Another poster pointed this out in a much earlier post.

Harold

[J Tiers]

it moves the opposite direction because the screw pushes the chuck body and not the jaw....... but it is just a matter of which way to turn the screw, a relativley trivial adjustment to technique.

The problem with the adjustment screws not being at 90 degrees has been around a long time. However, they work just the same as any other adjust tru or a four jaw chuck. Just be sure when making adjustments the the screw being adjusted is lined up with your indicator. If you do that it adjusts the same as ony other chuck.

Fundamentally it CAN'T adjust the same......

the problem is that with the standard 90 deg setscrews, the two axes are independent..... Adjusting one does not affect the other.

now, with a round or irregular-shaped workpiece, this may not be true in a 4 jaw, but in general it is true whenever the adjustments are at 90 deg.

And in this case, with the round "spigot", it is also not true.... for the same reason as with the 4 jaw.... In order for the "spigot" to move towards one of the two closer-spaced screws, it has to "slide past" the other one.

if the other one is at 90 deg, or close to it, that works. But when one is substantially off-90 towards the adjusted screw, the spigot cannot move directly towards the screw, unless the second screw is adjusted simultaneously.

Any attempt to move closer is obstructed by the second screw.... either forcing the spigot off line, or requiring both to be adjusted.

This violates rule #1 of the 4 jaw or "normal adjust-tru" setup, which is that you can adjust one direction and then the other, with "NO" interaction, or just the very slightest amount, which is cleared up in another pass.

With the 60 to 75 degree angle between, it flat doesn't work independently, and you will need to make several passes through, or develop a scheme for doing both together.

[Edwin Dirnbeck]

6 3 Jaws ''perfect'' Concentricity

I have 6 different 3 jaw chucks that I use on my lathe .I only have ONE backing plate.The front of my backing plate is flat and doesnt have a locating nose on it.My threejaws are located only by their mounting screws.I snug the mounting screws then chuck up my part I indicate the part by tapping the chuck body around .Then I tighten the chuck mount screws and machine my part.I have been using this method on the job every day for 20 years and NEVER had the chuck move on me.Also I have a front mount 5C collet chuck mounted like this and can get most any collet running dead true.PS another advantage is I that I can use any 3jaw that I can buy cheap because I dont have to have the correct backplate.