Need help with Lathe chuck please.

[BaronJ]

Hello Eric,

My error, I miss read. A four jaw has to be in really bad shape to be unusable.

In order to answer your question, yes soft jaws is one way, and I've on occasions just knocked up a set to do a particular job.


Some 40 mm alloy bar cut into slices and drilled to suit chuck jaw. In this case 16 mm, 5 mm from the edge.

Marked on edge prior to drilling and threading for 2 Ba screws. The holes are centered on the chuck jaw.

Threading 2 Ba under power at 50 rpm.

I did have a picture of these fitted to the chuck jaws but can't find them at the moment.

The other method I use is to make a collet. Again I use anything convenient, alloy, brass, and plastic.


This is a collet that I made to drill and ream a 1/4" hole in a piece of 1/2" silver steel bar.
It is just a length of nylon rod the length of the chuck jaws, drilled 1/2" and the position of jaw 1 marked, and the steel bar pushed through it.

 

[SubtleHustle]

If you think you need a new independent four chuck, then the one you have must be in a really bad way !

I would be interested in what is wrong with it.

Yup, it's an old 3 jaw, that I'm having problems with. Looking to get a new, undamaged, chuck and read that 4 jaw independent ones are the most accurate. So I'm looking for one of those.

 

[SubtleHustle]

Thanks Hman and Eric. You all have no idea how helpful you've been. I am totally learning to machine on my own. My friends just look at me when I talk about it, which I find myself doing most of the time now. The hobby machinist is exactly what I needed. So again, thanks to all of you.

 

[BaronJ]

Hi Guys,

Adding to my previous post because things got a little weird last night. I suddenly found that the Internet connection stopped and it took a few minutes to recover and then I had to do an edit post to carry on. So I just posted as far as I got.

Right lets carry on:


These are the pictures I was looking for. At the time I only had a toothed belt pulley to make these soft jaws with.

Here I was precision boring a steel replacement gear for my mill in order to replace a plastic one that was defective from new and failed later whilst in use. I actually replaced all the plastic gears in the mill. It has made a terrific difference.

Now the last picture in my other post. Making a collet, plastic, aluminum or steel. It doesn't matter what material you use. I like nylon, A: because I have a lot of it, and B: you can compress it easily. Being able to squeeze the collet onto the work piece is important.

The technique is this. Cut a length of the material that you are going to use that is long enough to be gripped by the whole width of the chuck jaw and big enough in diameter to allow the work piece to pass through it with a reasonable wall thickness. In the case of the 1/2" diameter bar, that piece of nylon was 1" diameter.

Place the material that you are going to make the collet from into the three jaw and tighten the jaws. Now mark the material in some way so that you know where it goes. I use jaw 1. Now carefully center drill and then drill right through using a drill about half the diameter of the work piece, stepping up drill sizes until, in the case of nylon, and in this particular case where the material is a standard diameter, a 1/2" drill.

In nylon a 1/2" rod is a very good push fit in a 1/2" drilled hole. The plastic seems to shrink slightly. In this example, I had to take the collet out of the chuck and press the rod into it by hand. Then refit it in the chuck in exactly the same place. After I put it back I went through the center drilling and then drilling to 6 mm for reaming to 1/4" for the shaft.

If you are using a metal to make the collet the steps are the same except that you may need to bore out to suit your work, bore out just a half mm or so smaller than your work. Remove the collet and slit it lengthwise, so that you have a gap a few mm wide. Obviously avoiding where the jaws land. You may need to put relief slits between the other jaws depending upon how thick you have made the collect wall.

Once you have done this, return the collect to the lathe and bore out to final size which should be a good sliding fit. Be careful not to over tighten the jaws when boring to size because you will need to be able to tighten the chuck jaws down enough to grip your work firmly.

I hope that makes sense !