4 Jaw Chuck Issues - Help!

[rwm]

I need help getting a quality 4 jaw independent chuck set up on my SouthBend (Grizzly) 10K lathe. There are a lot of issues. Let me start with the chuck I have.
This is a new model SB chuck that is of high quality made in Taiwan.




The jaws are very tight with no slop. The grind appears to be of high quality. It came with a factory D1-3 back plate that fits perfectly and runs true.

It seems whenever I clamp a round workpiece in this chuck the work is crooked with respect to the axis of the spindle. Obviously the radial runout is adjustable but shouldn't this align the stock to the axis? I can bang it around with a mallet and an indicator and eventually get it straight but this inevitably damages the work piece. Yes, brass shims and all that but I never have this issue with 3 jaws on this machine or with other 4 jaws I have used in the past. It seems like the grind of the jaw teeth is very sharp and too sharp to allow the stock to move straight when clamped. It just digs into the work. Am I confused about this? It also occurs to me that the jaws could be ground wrong with a conical or reverse conical grind?
Should I try to regrind the jaws?
I wanted to get a Bison but the 6" has a 2.75" bolt hole circle which cannot be used (easily) with a D1-3 back plate. I know that Monarchs have a D1-3 setup. What 4 jaw do they use?
I am willing to entertain all suggestions from operator error to regrinding the jaws to buying a new chuck if I can find a good one that fits.
Have you experienced this problem?

 

[rwm]

Let me ask a dumb follow up question. I have seen 4 jaws that have a flat face where they contact the work (tangential to the work surface.) This chuck has a convex surface on the teeth. Since that convexity would only really fit one specific diameter, why would you want it? Why is flat not the standard? It seems like the sharp edge of the convexity would cut in to the work especially if it was eccentrically placed? A flat surface is more forgiving.

 

[Nutfarmer]

Like what rwm said. I have only seen the jaws ground flat , never concave. Unless you are chucking something up that is that particular diameter it won’t hold the part properly.

 

[mksj]

The jaws should not skew the work, if they do then I would return the chuck if you bought it new. I would remove the jaws and back plate from the chuck. Check for any burs or high points. Clock the back plate on the spindle to see if the run-out changes in one of the 3 mounting positions, also try to sequentially torque the D1-3 pins in 2-3increments. First mount the back plate to the lathe and using a 0.0001' on its face check that it runs true while turning the spindle, then mount up the chuck and put an indicator on its face and check it. It is not uncommon that there are very slight mounting difference between the spindle nose and the backing plate, which can show up as skew, the backing plate run-out should be within 0.0001-2". You can also use some dye/marker to look at if the mounting interface is even.

Jaws should clamp the axis true, you should not be banging on them to true up stock, also not good for the bearings. They are typically not ground with a taper, but in some chucks, the headstock end may be ground slightly more (like 0.00005"), this very slight taper toward the back allows more even pressure from the tip of the jaw to the back, my understanding is that PBA chucks have this (at least that was what I had heard). I do not expect to see this on a 4J independent. Most of my chucks the axial skew is very small at 4-6" out, a 2-3 ten thousandths. some people have reground the chuck jaws using a Dremel grinder mounted to the cross slide, lots of videos on this.

 

[DavidR8]

Can you put a piece of stock in the chuck and shoot a picture of the resulting issue?

 

[rabler]

The only suggest I would make is to check the D1 mounting studs and make sure they are all seating at about the same point (that you're getting about 120 degrees of rotation on the lock from "free" to locked). I have had to adjust those studs by a turn on some chucks to get good tension.

 

[rwm]

I think I'm onto the problem. I clamped a small dowel pin between opposing jaws. It should be held straight and tight right?
See video:

0 new items by Robert Miller

photos.app.goo.gl

WTF?! These jaws are ground wrong. They are closer together at the tip than at the chuck face (conical grind.) This is carp. I paid a lot for this piece of junk. Its subtle but I think you can actually see it in this pic:

The teeth look slightly wider at the bottom than the top?
I bought this chuck new but it was back in 2017! I have been struggling with it and using it very little due to this. I cannot return it so if you all agree I'm going to need to regrind this.
Comments?

 

[pontiac428]

I have seen that bias grind before, as well as half round instead of flat teeth. The half round will support round work pieces coaxially. The bias I think is meant to compensate for deflection or large clearances on Asia chucks, and the cone should become cylindrical under clamping force. or at least that's my guess. Replacing my beginner 4-jaw on my Atlas was one of my first purchases- I had a chuck that wouldn't center due to wear, so I got a Yama. Then I got a Pratt-Burnerd. When I replaced my lathe, I fitted the new machine with four Bison chucks. You can trace the trajectory. I didn't just start buying $2000 chucks, I bought $2000 worth of progressively better chucks first before I woke the F up and realized where my money should go if I wanted these headaches to go away. And they have. Now I think it's quaint that I can watch others suffer! Now, I can share my experience and help others.

 

[rwm]

These jaws are so tight in the chuck that they have no slop at all. The jaw slots seem like a really good grind. Nothing to compensate for.
I have confirmed the error several ways. For example, the side of a 1-2-3 block placed on the chuck face is not parallel to the face of the jaw! That about says it.
I think I have a plan to regrind these with the jaw facing out so I can access the whole face. I'm just not sure its worth it. I may just call this a $500 paper weight and try to buy something good. I don't know what will fit. Doesn't look like Bison is an option.
I am open to suggestions on grinding as well as possible replacements. It also seems like these could be surface ground if you could use the slots on the sides of the jaws as a datum plane? Yes? how about setting the chuck on its side clamped to a 90 deg angle plate?

 

[talvare]

I posted a while back about grinding my 4-jaw chuck. You can check it out here:

Replacement 3 jaw lathe chucks

Greetings folks, I am having to replace my Atlas 12 inch Pedestal Lathe mod 3996 3 jaw chuck.....The chuck will not keep the work piece tight in the jaws.....I am wondering where you folks have gone to buy tooling or would go to find a good (hobby style) chuck that will not brake the...

www.hobby-machinist.com

Ted