Chuck mechanism became tight?

[Geof]

I have an old HL1 dating back to 1995 with an 8" Kitagawa Chuck that is clamped by a large Belleville spring system and unclamped by an air cylinder; today the chuck would not open. After a bit of fiddling we got it off and dismantled it but getting the cam plate (wedge plate?), that connects to the drawtube and closes the jaws, out required significant persuasion with a big hammer and brass drift. There were a few burrs and dints around the jaw slides from chips so these were carefully filed off so the jaws would slide freely and the inside of the chuck and the OD of cam plate were nicely polished up clean.

The fun began when trying to put the cam plate back into the chuck. It seems to have developed an interference fit????? I know this sounds a bit ridiculous but we cleaned everything off with Scotchbrite which leaves fine scratch marks and after putting the cam plate back into the chuck and taking it out again it was possible to see abrasion marks on both the cam plate and inside the chuck. It was also necessary to tap the plate in and out because it would not slide freely.

Is it at all feasible that with age the chuck body has slightly distorted?? It sure seems like it.


Fortunately I just happened to have an 8" Kitagawa chuck kicking around in my office so the machine is back in operation but the old chuck is a bit puzzling.

[307startup]

Geof it almost sounds as if that plate and/or the chuck body had distorted together and that when you attempted to reassemble it, that slight bit of out of roundness conspired to give you those marks, due to not being reassembled to it's new ovality.
Seems odd that a chuck would suddenly distort that much, much less one that has been serving you for 13-14 years.
What were the indicators that this was happening?
Was today the first time you noticed the chuck not wanting to open properly?

[Geof]

....Was today the first time you noticed the chuck not wanting to open properly?

It always has been sluggish but in the past when we have taken it apart to remove accumulated chips it was possible to push the cam plate back and forth by hand. Now it is necessary to tap it lightly with a plastic hammer, it is completely impossible to operate by hand.

We did try assembling it in all three orientations to align with the jaw slots and there was not a noticeable difference. I find it a bit intriguing, (because I had a spare chuck I can say that...if the machine was still down I would be a bit more upset) because the simplest explanation I can come up with is that the body shrunk a fraction of a thou or the plate expanded. This is a simple explanation not necessarily a logical one.

[307startup]

Geof, being the intelligent guy I know you are and who's opinion I respect whenever I read your posts...I have to ask the obvious....

Have you measured your plate in several locations for out of roundness? Both across the diameter and from centerline?
Have you measured your chuck as well?

I'm beginning to think that the front of the chuck body has distorted and if you were to measure back to front from the through-hole you will notice a slight taper.

I also wonder how well those bellevilles are holding up and how many cycles they have been through...it would only take one spring failing to cause a domino effect.

Have you fully disassembled and inspected the draw works mechanism?

I just have this nagging feeling that there is more at work here than the symptoms you have described.

I'm wondering if the draw tube has slowly come out of alignment and is pulling at a very slight angle as to what it originally has and this helped contribute to the distortion of your chuck and/or plate.

[Geof]

Haven't done the measuring but have cleaned the drawtube and spindle. The drawtube slides perfectly free and operates the replacment chuck quite fine.

I agree there may be 'more at work here' but I don't think it is related to the draw mechanism or the springs.

Incidentally the new chuck is so free moving when it is off the machine the jaws open and close when the chuck is turned over; gravity is enough to move the cam plate. I presume the original chuck was this free when it was new.

As I say I find it intriguing and I wondered if anyone had encountered a chuck 'getting arthritis' and just seizing up.

It is probably going to end up in parts on my office floor for several months until I have the time and urge to see if it can be rehabilitated.

[307startup]

What's the static air pressure set at? Is there a baseline? Does it get adjusted according to any temperature/barometric shifts of the seasons, or is your shop so well maintained that there are no nasty temperature/humidity shifts?

Have you ever had a nasty knock with the tool turret close to the centerline of the jaws?

Has this been the only "tight" chuck you've experienced compared with your other Haas lathes?

[Geof]

What's the static air pressure set at? Is there a baseline? Does it get adjusted according to any temperature/barometric shifts of the seasons, or is your shop so well maintained that there are no nasty temperature/humidity shifts?

Have you ever had a nasty knock with the tool turret close to the centerline of the jaws?

Has this been the only "tight" chuck you've experienced compared with your other Haas lathes?

I don't think it is related to air pressure, etc because the replacement chuck works fine. Machine air pressure is around 85psi and where I am we don't get 'nasty' weather changes; actually the shop runs at about 65 to 70 F in the winter months.

This chuck did get a nasty knock about ten years ago so I don't think that can be related.

So far it is the only arthritic chuck but it is also the oldest and the only one operated by springs/air; all the others are hydraulic.

When I have time I will pursue it a bit further and make sure all the burrs that were thrown up by chips packed in the mechanism are thoroughly cleaned out and then see if it moves easier.

[307startup]

Sorry Geof, it's just that this one keeps nagging at me...like I'm looking directly at the problem, but not seeing it.

Usually my investigative skills are much sharper.

I'm sure when you find it, I'll have one of those "D'oh" forehead slapping moments.

What is most bizarre about the whole scenario is the seeming shrinkage of the chuck's machined orifices. Cast iron is such a stable material, it's almost unfathomable to see something like a chuck body "season" in place and distort to a noticeable amount.

[Geof]

....I'm sure when you find it, I'll have one of those "D'oh" forehead slapping moments...

Even if you don't, I have.

It was literally a case of shining a bright light on it. Under a bright light I could see little shiny spots on the ID and when I took my glasses off for a much closer look some where actually little rings with a dark center. Also a largish one was a shiny ring with a dark ring and a shiny center; this one still had the bit of chip embedded in it.

It seems that very tiny chips when they embedded in the steel body created a minuscule depression with a raised ring around it and even though we had scoured the chips out the ring was still there. Half an hour with a scraper made from a small file scraping away a couple of dozen shiny rings and the cam plate slides back and forthe under its own weight.

So it was very small scale distortion; and strangely enough very similar to the way arthritis starts so my flippant analogy was truer than I thought.

[307startup]

Yeah...definitely a head slapper.

I had some clue about the bore when you said chips, but you didn't seem to mention the "halos" before, so I kept going round&round in my head.

Good to finally know what it was though! I'm glad to hear she's right as rain again, or on her way!

[Geof]

What I find surprising is how much friction the halos caused. As I said there were a couple of dozen and they varied in size from maybe 10 thou up to 30 thou which calculates out to about 0.008 square inches but there was no way I could push the cam plate back and forth, I had to tap it with a plastic hammer. Certainly a learning experience.

EDIT: Popping parts out once more every 2minutes 12seconds

[307startup]

So you remounted her? Er...well, you know what I mean.

I'm actually not surprised at the amount of friction you mention, simply because it's enacted in a linear fashion...riding up the edge of the halo, over the center and such...over dozens of those little buggers.

Especially with such a close fit. I'm imagining somewhere on the order of .0005-.001" clearance. It went from an air-fit to a friction fit and even the steadiest of hands would be hard-pressed to push in a purely linear direction. Not to mention replicating the line pressure the closer uses (85 psi)(@27sq.in.)...@2000 lbs. of pressure!

That's alot of force that it was opening & closing with...no wonder it wasn't in-your-face noticeable! Depending on how big your plastic mallet is, I imagine even a HUGE guy would have trouble duplicating that effort!

Sure explains the dings & burrs you noticed on the closer plate/wedge you noticed upon disassembly.

I'm glad that you found the culprit...yet another lesson I didn't have to learn the hard way or through personal experience