Best "Value" Lathe Chuck, & Backplate Interchange?

[Nesse1]

I cut the plate to fit my chuck, and other than the dents, protrusions, actually, on the spindle side, the damage cleaned up nicely.

Next is to drill the holes though the plate to mount up to the chuck. I bought some transfer screws of appropriate size and they worked great in terms of marking the drill spots.

Do most of you use a countersink or endmill to create recess pockets for the screw heads, so they sit below the plate surface? I don't think it matters functionally, but it would look better cosmetically.

I messaged the seller, asking him to contact me outside eBay. I want to pay him something. Waiting to hear back...

 

[mikey]

I messaged the seller, asking him to contact me outside eBay. I want to pay him something. Waiting to hear back...

This says a great deal about the man you are - good for you!

 

[Nesse1]

Got the chuck mounted up and there is about .004-.005" of runout when testing with a ground bar. Putting the indicator on the backplate register edge I cut shows no measurable runout, so the error seems to be in the chuck itself. I loosened up the mounting bolts a little, put the indicator on the bar, and tried to tap it to center, but it doesn't move. I think the register is too tight to allow the chuck to move, which means I did my job on that.

Is this amount of runout to be expected with a used chuck? Kitagawa has a good name, so I'm assuming it was better than this when new?

 

[Nesse1]

Update: I removed the "two piece" jaw sections, clamping the ground bar in the base jaws, and that reduced runout to under .002", which seems more like it. I'm going to have to study the jaws to see if any are not mounting properly. The jaw sections are super tight on the lower jaws. so I can imagine there is something keeping them from mounting properly. Fingers crossed anyway.

 

[mikey]

Nesse1, let me try to clarify a few things so that you have a more realistic grasp of what you have. Kitagawa makes some of the finest industrial quality lathe chucks on the market. Your chuck has a max rpm rating of around 4K, which suggests it is a more expensive forged steel model. It also has 2-piece jaws usually found on higher end models of Kitagawa chucks. These jaws are also precision ground and hardened. SO, you have a very high end model chuck there. Kitagawa is on the top tier level of lathe chuck makers, along with Samchully of Korea, Rohm of Germany and maybe SCA of Sweden. The fit and finish of the jaws is very accurate and they will remain accurate for far longer than most hobby guys will live. Period.

Now, there has been a lot of misunderstanding about run out and lathe chucks so let's try to be clear about one single thing: you cannot put a precision ground pin in a scroll chuck, measure the run out on that pin and gain any useful information from that experience. Doing so only tells you that you have such and such run on that pin in that position of the scroll - that's all. It tells you absolutely nothing about the quality or accuracy of the chuck.

A 3 jaw chuck is used for first operations work only. That means it is used to hold work that is being turned on the lathe for the first time. Once you turn the work piece but before removing it from the chuck, the work piece will be precisely concentric with the spindle axis of your lathe. That is, there will be ZERO run out. Try it and see. Once you finish turning the work and remove it from the chuck, you cannot put that work piece back in a 3 jaw chuck and expect it to have zero run out ever again UNLESS you use a set-tru/adjust-tru chuck and dial it in or use a 4 jaw chuck. Even accurate collet chucks will not be able to get you back to zero again unless they are also adjustable. Putting a work piece back in a chuck for further turning after the initial turning is called a second operation and requires a 4 jaw independent chuck, an accurate collet chuck or a chuck with an adjustable faceplate mechanism.

Edit: the fit of the top jaws on the bottom jaws is supposed to be very tight, almost an interference fit. Don't go lapping or filing or messing with them. Get them in the right position and gently pull them down with the cap screws, then leave them alone unless you need to change their position.

 

[Nesse1]

Hi mikey,

I understand most of what you say, and agree, mostly.

I bought the Kitagawa knowing their reputation. What I don't know is if the chuck has been abused in ways that are not visible.

When I first mounted up the chuck on the backplate, the mounting screws were binding, resulting in the backplate/chuck not seating fully, leading to more than .010" of runout. Opening up the holes a few thousands, and grinding the heads of the mounting screws a smig (my counter bore is a little too small) reduced the interference, reducing the runout to .004-.005". I measured to make sure the chuck is mounted up correctly, and not damaged in some way.

The fact that the reversible jaws add runout suggests they are not seating correctly. I don't expect perfection, but I do want the best possible outcome.

 

[mikey]

Okay, understood. However, if the backplate fits snugly into the rear of the chuck then the fit of the screws matters little. The fit of the jaws is another thing. Unless there is some evidence of damage to the jaws, it is unlikely for them to be causing a lot of run out. If there are no burrs or debris on them and you pull each jaw down and tighten them snugly then they should be pretty accurate. I would encourage you to do a turning test with the chuck to check it's accuracy.

 

[Nesse1]

Sorry, mikey, but I can't get out of the rabbit hole...

I removed the jaws, made sure there were no burrs, there wasn't any, put everything back together, and now I get .007" runout. Worse than before. WTF. So, I borrowed two 6" chucks from where I work and mounted them up to do the same test. One is a steel Bison, with integrated D1-4 pins, and that thing shows .020" runout on my machine! Unbelievable. Next, an older Kitagawa, I think, "made in Japan" and B728 is stamped. This unit also has an integrated backplate, and this unit has about .015" of runout. Maybe my Kitagawa ain't so bad after all?

Last test, an indicator on the lathes chuck adapter, both on the taper edge, and flat against the mounting face, and I see about .001" runout, or less, on my .001" indicator. Maybe I should have done this test first? Anyway, it's nice to see lathe spindle doesn't seem bent or anything.

I'm almost ready to give up. I'm going to fuss a little more to see if I can get this thing back to the .005" as before. After that, I'm going to stop fretting.

Edit: remounted the chuck, carefully measured runout, and I'm back to .004-.005". I'm calling it good. Sorry for my newbie nonsense.

 

[mikey]

If it was me, I would turn a piece of scrap stock with a properly ground HSS tool (to minimize deflection) and see if the turned part runs out. This is a first operation and is what a 3 jaw chuck is for. If there is no run out, and there shouldn't be, then the chuck is fine and you can move on.

You are not the first hobby guy to deal with this, trust me.

 

[Nesse1]

So, I bought a PM 5C collet chuck, and for the life of me, I can't get it to mount up flush with the spindle nose. I played around with different cam stud heights, but the chuck just doesn't want to snug town flat against the spindle nose; there is daylight between the chuck backplate and the spindle. This is the same problem I had with the Shars's backplate. I'm starting to wonder if the cam lock cams, are binding in some way. I'm not sure how the cam devices come out, but tomorrow I'm going to see if I can take them loose and look for someone wrong. Open to suggestions.