Lathe Maintenance

[Haynie]

In another thread, Skiprat said the following"

I have collets and know that they can be the most accurate method of holding properly round material, but a properly cleaned and tuned 3 jaw self centering chuck should be good enough for all but the very best of metal lathes.

This got me thinking that I have never done this and never even thought about it. How do you properly clean and tune a 3 jaw chuck?

Yep, I am still a rank novice.

 

[frank123]

Don't know about the total process of "tuning" a 3 jaw, but I periodically dissemble mine and thoroughly clean the scroll and dry lube it with a dry lube spray. Remove any burrs or rough spots you find.

Grind the jaws for as close to zero run out as possible at close to the diameter you will most commonly be using. Keep the jaws in the same slot every time you remove them and check for run out increasing that would indicate wear that needs them being ground again.

Even a cheap chuck can be kept to a few tenths (.0001) run out with care, and most of us can't really measure accurately to that tolerance anyway. (but cheaper ones won't be as consistent or hold tolerance as long as the better ones will)

There's instructions for doing this in a number of places on the internet.

 

[Haynie]

I have been looking and not really finding anything I understand. In fact I read something about grinding the jaws and can't figure out how taking the jaws out of the chuck and grinding will make them true.

How do you grind? In my world grinding something means whip out the angle grinder and smooth out the weld on the pontoon. It is my assumption that this is not what folks mean.

 

[frank123]

I have been looking and not really finding anything I understand. In fact I read something about grinding the jaws and can't figure out how taking the jaws out of the chuck and grinding will make them true.

How do you grind? In my world grinding something means whip out the angle grinder and smooth out the weld on the pontoon. It is my assumption that this is not what folks mean.

Essentially, you grind them with an improvised "tool post" type grinder while they are mounted and clamped down using a sort of spyder type of thing (home made. but I think there are actually commercial ones available) that allows the tips of the jaws to protrude but still holds them tightened in place. This results in close to a axis parallel cylinder resulting in the clamped object.
Here's one description I found quickly that is mostly similar to what I do but not exactly the same. It should convey the concept. Varmint Al's Mini Lathe Page

BTW, that site is pretty much oriented to the HF type mini lathe, but contains information that can be adapted and applied to about any metal lathe. IMO, constantly improving the precision and utility of the lathe is one of the more fun things about owning one. (but if you got enough money you can purchase one that is extremely precise without any more work on it being needed)

 

[Rich L]

You can also do it with a boring bar and a disk clamped at the back of the chuck. Bore enough to finish each jaw, take the disk out and knock off the small part at the back of each jaw that you couldn't bore with the disk in there. There are more complex disks that fit over the jaws instead of inside but this is a cheap and easy method to use tooling you probably already have.

Cheers,
Rich

 

[Haynie]

Thanks.

 

[jd99]

I have my 3 jaw chuck set up with set screws that push against the shoulder or step on the backing plate, there are 4 set screws.

I can make the chuck on perfect center (well as perfect as the bearings are) by tighting or loosing the set screws. Much like you would use a 4 jaw chuck.

I loosen the mounting bolts, adjust the four set screws untill i get the smallest amount of runout possible, then tighten the mounting screws.
Works great