Rejuvenating a Pratt Burnerd LC-15?

[mcdanlj]

I have been wanting a large collet chuck (larger than the ER40 I already have) for a while, and I finally bought a Pratt Burnerd LC-15 (lever closed) EC collet chuck and set of EC (mostly; one MC) collets. The 1.5" capacity is pretty close to the spindle bore on my G0709.

It has some surface corrosion, but the real problem is that it is frozen solid. I cannot turn the cap on the nose.

I have retaining compound curing now in a shop expedient 3" pin wrench to try to remove the cap from the nose and start disassembling it for deep cleaning. I have coated it inside and out with aviation corrosionX because that's supposed to work in and detach corrosion eventually, but with the tight tolerances on the PB chucks that might not be super quick.

The chuck was sold as functional, so if I can't get it working in the next two weeks, I guess I'll be sad and return it to the seller. But I'd rather get it working.

If there is anyone here with experience with any PB LC collet I'd love to get advice.

 

[matthewsx]

No experience with this particular chuck but why not contact the seller. They might know a trick that’s not obvious.

John

 

[mcdanlj]

The seller is an auction house. That's why I asked here if anyone here has experience.

 

[mcdanlj]

I put the chuck on my lathe and put it in low gear. My new 3" face pin wrench was a good fit, so I held it in place and tapped it gently with a hammer and got the cap turning. Once I got it off, it was clear that it was full of old chips. I worry a bit that there could be more chips jammed up deeper inside. We'll see.

Now I can't get the lock ring off to keep disassembling it and clean everything out nicely. I don't have a 120mm C pin spanner to remove it, and this one I'm going to buy instead of make, so as not to screw this up.

 

[Chipper5783]

I just picked up a KC-15 (same collets EC3 to EC13) - some corrosion, but it cleaned up well (didn’t try to get rid of all the stains). I think the main difference with yours is that mine uses a chuck key. I’ve been completely disassembling the collets for cleaning. The first one took some time to sort out a method of managing the springs and of removing the front steel ring, but pretty easy now. If you want some pointers on that aspect let me know. My set is missing two of the little “wing” springs and the stabilizer bushing on the EC13 (I can swap springs around as need be and can make the bushing, but would prefer to track down replacements).

Do you have a parts source?

 

[mcdanlj]

I don't have a parts source, no — though I thought I saw mention that PB still makes EC collets (for a pretty penny) — maybe that was old news. Rotagrip lists new collets for £150.00 (I wonder if I could replace VAT with shipping for sending them to the US?) but I don't know whether that's NOS or current manufacture. I haven't contacted Pratt Burnerd America to ask, either — have you?

I'd love any pointers; I haven't started with the collets at all. One of the collets that shipped with it was an MC instead of EC collet (has a screwed-on face on the front) and I'm hoping that I'll find that this particular chuck has a cap that is compatible with that MC collet (apparently many were). Once I get this unit otherwise operational I can find out whether the MC collet works...

I'd think that it wouldn't be too bad to make a custom mandrel to wind new springs?

This is the only parts diagram I have found so far, which is barely readable:




I'm guessing that the KC-15 doesn't have that lock ring because it's really part of the lever action. Does the key just screw the cap down like an ER nut, or does it still use ball bearings in the body and you tighten past a cam-over point to know when you have positive lock?

 

[mcdanlj]

I think I should be able to take this apart by operating the release key, but I can't get it to move. I don't quite understand from the drawing how it works, so I don't know how gently persuade it to move in the right way, and I definitely don't want to break it.

 

[Chipper5783]

The KC is similar to a large drill chuck (the next page of the manual from the LC image you posted). As you turn the outer ring (the “nut”), it pulls the inner ring closer to the lathe headstock, which in turn pushes the collet harder into the tapered cone - closing the jaws. Yes, there is a ring of balls (loaded one at a time through a small hole). The inner/outer groove for the bearing are ground directly into the chuck body.

To disassemble the collet, put a short stub of material (short enough to fit inside the collet) to fit the large range of that collet. It doesn’t have to be perfect - even a socket may fit close enough. The purpose is to keep the jaws from falling out once the springs are removed. Then I gripped it in the bench vise on some soft jaws (i.e. pad it with some gasket material - don’t want to chip the hardened jaws). Then I used two small screw drivers - one to push the tail of the spring in, the second to slide the spring all the way along - they all just roll out. The PB web site / manual says the jaws can go in any location (they are not specific to that slot). Once you have the 6 jaws out, you can squeeze in the collet a little bit - to slip the steel ring off the outer end. I used my 6 jaw chuck, it is only a 6” so I removed that lower centering bushing (remove the 3 very small set screws) to get a slightly better bite with the 6J - didn’t have to crank it in very hard.

There manual says that there are no parts available for the actual chuck (I think you and I are working off the same document). David

http://www.rotagriponline.com/datasheets/Pratt/PrattChuckSpares.pdf

 

[mcdanlj]

I had not seen that PDF yet, but finally I have a readable view of that image! All I had before was a fuzzy image of a scan of paper. Maybe I can use it to puzzle out how the release key is meant to work. Thank you very much!

 

[mcdanlj]

The sliding cone doesn't slide at all in my unit. The lock ring does not unscrew. There's a chance this is going back to the seller since it was listed as functional and it most definitely is not functional as provided.