View Full Version : Changing chucks in lathe

07-14-2010, 08:30 PM
I'm a newbie to the machine world. I recently picked up a used Rockwell 10 X 36 lathe. I am getting 3 to 4 thou out of roundness with the 3 jaw chuck during setup. Is this normal? Anyway I want to put the 4 jaw chuck on, just to do it. The 3 jaw does not want to budge. What is the best way to remove the old chuck without breaking anything? It could of been on there for years.

07-14-2010, 10:04 PM
i dont know the 10",i have a 14". it has the L spindle nose. is the 4-jaw original to your machine? if it has female threads, it simply screws on like a nut on a bolt. if the chuck has a male thread with a tapered bore and a keyslot its an L spindle nose. that one has a lock ring that pulls the chuck tight onto the tapered spindle nose. both of these have the righty tighty,lefty loosey thread. put up a pic and someone can tell you real quick.

07-14-2010, 10:16 PM
Describe the back of the four jaw. Is it a female thread, a female taper with an outside large thread, or a short female taper with three or four pins sticking out of the back. Let us know and we will be able to assist. Peter

07-14-2010, 10:27 PM
If there's a lock ring with several large spanner wrench holes, it's a L00 spindle. If so, lock the spindle and loosen the lock ring (L/H thread), if you don't have a spanner, you can use a piece of drill rod.
If it's not the L00, here's a link that can help you:
Lots of good info there.

07-14-2010, 10:48 PM
The 10" should be a threaded spindle. I don't think they even offered L00 on that one, and I know they didn't offer D, A or DIN mounts.

As for getting it off, the general process is to set the "Lock" position on the headstock selector, and then break the chuck loose. Perhaps you can use a strap wrench, or some folks have resorted to putting a 2x4 in the jaws to get leverage. But don't try to use a key in the screws, more than one has been broken that way. May need to let sit with some penetrating oil, depending on condition. If reasonable efforts fail, some folks have even put the lathe in back gear with the board in the jaws. Then, with the board on the ways, use the drive (under power, or manually) to turn the spindle. If it's been "slammed" home or left to rust, getting it off can be a real bear...

Paul Alciatore
07-15-2010, 12:36 AM
One thing I noticed when I was searching for a lathe to purchase was that a very common problem with used lathes is gears (usually back gears) with missing teeth. I have come to realize that this is likely due to locking the gears to remove a chuck.

I would strongly recommend using the penetrating oil and avoiding too sharp of a pounding on the chuck when removing it. I personally prefer using something with some give to it on the chuck. A strap wrench is nice as the rubber strap does not allow too sharp of a blow. That is my preferred tool. I have never tried it, but the 2X4 may be OK also as the wood fibers will crush, providing some give. I am not so sure about using reverse power: that just plain scares me. If I had a stuck chuck I would try to use another method of locking the spindle instead of locking the gears in any manner. I have a hand crank that attaches directly to the spindle itself and could be pressed into service for this if needed.

What I am saying is just be careful.

07-15-2010, 01:05 AM
One thing I noticed when I was searching for a lathe to purchase was that a very common problem with used lathes is gears (usually back gears) with missing teeth. I have come to realize that this is likely due to locking the gears to remove a chuck.

I agree in the unfortunately frequency of such damage, but not with the suggested cause and effect. To damage these very beefy gears (at least on the 11) while fully engaged would be almost impossible.

I think the more likely cause is attempting to shift from direct to reduction without waiting for complete spindle stop. There is a safety interlock that, when working properly, prevents this possibility. But the Rockwell design was rather marginal and quite prone to wear, which if not adjusted, will render the lock-out ineffective. On my old 11", it was completely inoperable but was showing almost no wear and no damage, and worked perfectly when adjusted. Anyway, I've seen the same sort of damage (though far worse) on a Mori MS850 (over $2k in parts alone) that was due to an operator shifting without stopping the spindle.

07-15-2010, 01:07 AM
From what I've seen and read, three or four thousandths isn't that bad for an old chuck. I've seen newish ones with that much.

On an old chuck the amount of runout will vary for different work diameters, because the scroll wears unevenly. There are all sorts of tricks to compensate for chucking error, but it's good to learn how to use the 4-jaw.

07-15-2010, 07:55 AM
From what I've seen and read, three or four thousandths isn't that bad for an old chuck. I've seen newish ones with that much.

Oh, forgot I had intended to make that same comment too. With the exception of high end "adjust true" (type) chucks, 3 jaws are about convenience and speed, not accuracy. If you want all 3, and parts are suitable, get a collet system. Otherwise, a good 4 jaw. The key important part with a 3 jaw is that the part is held coaxial (so that run out near the chuck is similar to what is measured several inches out). As long as that is true, and the run out is within a 1-4 thou or so, not much point in worrying about it. After all, 3 jaws are really intended for rapid single setup production work. You can also use soft jaws to minimize (almost eliminate on a good chuck) run out for (semi/full) production runs. If you want the ability to keep the part coaxial with multiple setups, then a 4 jaw or between center turning is preferred.

But either way, you still have to get that chuck off first. Good luck...

07-15-2010, 10:26 AM
I finally got the old 3 jaw off. After locking the headstock I tried putting a piece of 1 inch round stock in the chuck and put a 12 inch pipe wrench on the stock. The stock slipped in the chuck after considerable pressure was applied. I found a piece of scrap hex bar, which was part of an axle or pto at one time. I put that in the chuck, and a socket over the end. Using an 18" breaker bar it finally came loose. Wow! The 4 jaw is now on.

Rich Carlstedt
07-15-2010, 10:27 AM
I agree with Paul, most of the small lathes I have seen have broken gears from trying to change the chuck. This occurs from the snapping of hitting the chuck when you have backlash in the gears.
You can do two things
Take a hardwood wedge and insert it between the bull gear closest to the chuck, and the pinion gear (small) on the back shaft...from the bottom
The hardwood will engage several teeth and lessen the forces when you loosen the chuck. Now put a 2x4 between the jaws and force downward, which causes the chuck to loosen. The 2x4 should be about 2 feet long and if still stuck, hit it with a mallet..downward.

The method I use when helping friends with this is similar.
Instead of wood, I engage the Backgear, and the Leadscrew drive (resistance directly)on the spindle, and place the 2x4 vertically (or even at 2 O'clock) (Move carraige and tailstock to the far right)
Taking the 2x4 in the left hand , I pull it down (CCW)as quickly as I can and when I am near the 10 or 9 O'clock position, strike the 2x4 with a heavy mallet blow (Not your hand !) WITHOUT STOPPING !
This approach keeps all backlash out of the gears, as you are manually loading them with your pull, and the mallet blow is the sudden acceleration needed to break the spindle/chuck engagement.
This approach has never failed me, nor have I ever broken a gear.

BUT if it does not work,OR you are afraid of breaking a tooth, you need to make an internal expanding mandrel and insert it into the spindle.
Find a 12" long pipe that fits inside, mill two flats for a wrench on one end, and then slice the pipe in several places at a 45 ~ degree angle.
Insert it with the wrench flat on the left and using a long bolt (& washers) tighten the heck out of it. The pipe will expand against the inside and give you a direct lock for loostening the chuck.