New Chuck, excessive runout

[AR1911]

Dumb question. Do you have acceptable runout with your previous chuck and what does it show under the same circumstances using the same test bars?

I never had the original chuck. I did mount a NOS Atlas 3-jaw, which had .006" runout. I sold the Atlas chuck to get a "better" chuck.

 

[AR1911]

With a 3 jaw, the jaws must be inserted in the correct order (1, 2, 3) but you can also rotate their relative position in different slots to see if that helps. I have a 3 J that is very true but one day, I remove the jaws and didn't put them in the same slots and RO was terrible. Put them back in their preferred slots and it was back to normal.

I considered this but did not try it.
I will try it next time at the shop.

 

[AR1911]

You might want to check-out Gary's thread here: http://www.hobby-machinist.com/showthread.php/11504-Truing-up-a-chuck?p=94306&posted=1#post94306

That's an interesting setup. I will consider trying that using the collet chuck on my Enco.
I'm wondering how straight the chuck body is when it's hanging out there like that. I'd sure check it before doing any cutting

 

[Ray C]

Give it a shot, you got nothing to lose. Rotate through all the position and see what combo looks best. If you find a good match, make a witness mark on one of the jaws and it's slot. Jaws are pretty darn hard so if you don't have a diamond tip punch, a roto-dremel tool will do nicely.


Ray

I considered this but did not try it.
I will try it next time at the shop.

 

[AR1911]

Actually, I already numbered them. The jaws were not that hard.
I wish now that I had not. If swapping them reduces the runout, I'll have to punch over the numbers.

 

[Chipper5783]

I trued up the shoulder on the backing plate. that is the outer 1/2" of diameter that bears against the chuck body.
Running the backing plate alone now shows zero runout, and that is repeatable

There is a stepped center portion, but it does not touch the chuck body except at the sides.
It may be worth trying to reduce that diameter and see if there is enough slack in the screw holes to get it aligned.

Sounds like you have done the initial starting steps. I've seen other posts suggesting over trimming the register on the chuck backing plate (the one between the chuck and the back plate), then shift it a bit on the bolt holes (you only need to go ~0.004"). That makes it your own version of a "Set Tru". If you are really fussy, once you have it where you want it, you could then pop a couple dowels in.

Strongly caution against trimming the jaws - only reason for that is if the jaws are worn/sprung to a "bell mouth".

Soft jaws are wonderful - Shars has them too.

 

[Smithdoor]

This is a good to use.
I have purchase a lot new chucks over years some had to grind the jaws others work right out of the box.
I do use Shars chucks they do work great I machine my own backs on the lathe I am using the chuck on.
FYI My lathe is 9A South Bend

Dave

Sounds like you have done the initial starting steps. I've seen other posts suggesting over trimming the register on the chuck backing plate (the one between the chuck and the back plate), then shift it a bit on the bolt holes (you only need to go ~0.004"). That makes it your own version of a "Set Tru". If you are really fussy, once you have it where you want it, you could then pop a couple dowels in.

Strongly caution against trimming the jaws - only reason for that is if the jaws are worn/sprung to a "bell mouth".

Soft jaws are wonderful - Shars has them too.

 

[autonoz]

If the chuck body has runout, I would remove it from the backing plate and check the shoulder on the backing plate where the chuck registers. See if that is true.

A step at a time when problem solving.

Charlie W.

This was the problem I had. Once I trued the shoulder my run out was much improved.

 

[Smithdoor]

This is expanding on Chipper5783
Just use adjusting screw if you ever have run out just adjust the set screws see drawing note: This is drawing for 4" shars chuck


Dave

Sounds like you have done the initial starting steps. I've seen other posts suggesting over trimming the register on the chuck backing plate (the one between the chuck and the back plate), then shift it a bit on the bolt holes (you only need to go ~0.004"). That makes it your own version of a "Set Tru". If you are really fussy, once you have it where you want it, you could then pop a couple dowels in.

Strongly caution against trimming the jaws - only reason for that is if the jaws are worn/sprung to a "bell mouth".

Soft jaws are wonderful - Shars has them too.

 

[P.K.]

I experienced a similar runout problem with a brand new 125mm Fuerda chuck I bought for my rotary table. I had to make my own base plate for the chuck and I was planning to center the chuck on the rotary table using the MT3 hole in the middle of the table. The idea was to not have to indicate every time I wanted to mount the chuck to the table.

I checked the hole in the table and it had a little less than 0.01mm (0.0004’’) runout with regards to the rotation axis so things were looking good. The chuck was a “plain back” type so I made the base plate with a tight slip fit into the register of the chuck. Then a 26mm dia. hole was bored in the center of the base plate for centering. Finally I made a tapered plug for the MT3 hole with a cylindrical end that has a tight slip fit into the base plate hole.

After setting the whole thing up, I put a piece of round stock in the chuck an indicated off of it. To my horror I realized the runout was 0.13mm (0.005’’). I checked everything; the hole, the plug, the base plate, the chuck body and register. Everything was fine so it had to be the jaws.

To check this I put a piece of round stock in my lathe, skimmed it to make it true, and then chucked the small chuck onto the round stock again. Indicated off the chuck body and found 0.12mm runout. Then I indicated off the register on the back of the chuck and found the exact same runout, so at least the register was perfectly true to the chuck body.

I removed the jaws from the chuck to see if the slots were numbered and if the numbers matched the jaws, and they did. I figured it couldn’t get any worse that this so I shifted the jaws one position counter clockwise and indicated again. I was very surprised to see that the runout was now just shy of 0.02mm.

I mounted it all together again on the rotary table and indicated in all three rotational positions on the table (my rotary table has 3 T-slots). In one of the positions the runout of the MT3 hole partially cancelled out the remaining chuck runout and so it was down to 0.01mm (0.0004’’). It also repeats every time I mount the chuck to the table so I’m very happy with that. I marked the position by stamping a 0 on both the chuck body and the base plate adjacent to 0 degrees on the table.

I guess it’s time to stamp some new numbers at the jaw slots to match the new jaw positions.