Lathe work

Hi Pete, I'll PM later. At the moment SWMBO has got me clearing, painting and decorating the small bedroom. Had to go out this morning and buy some architrave ! Tomorrow she wants some paint and wallpaper. I'm sure you know how long that can take.

I can confirm that there is no twist in the lathe bed. The test bar in the soft jaws of the three jaw scroll chuck using the dial gauge showed just under a division 0.01 mm from one end to the other over 150 mm.

I will before I start doing an work on the jaws check using parallels in the slots on the jaws. I do know that there is a few thou difference in the hight of the slot on one of the jaws which can be seen in one of the pictures. But I doubt that that will make any difference.

I can tell you that the tailstock needs adjusting, its not quite point to point with a pair of centres. I would say a fraction high and slightly to the right. If I push the tailstock away from me it is just about spot on.

This is using the steel rule method. But the tailstock doesn't concern me at the moment, but at some point I will run a between centres check and adjust it.

Looking at the pictures of the jaws from the lightweight four jaw chuck, and having recently sold a set of new ones, I recon yours are in pristine condition, there are almost no signs of wear. The threads are ACME form, there is a variation with square threads. I have a set of worn jaws, they look very different both in the thread wear and the contact edges.

There is a method of grinding these independent chuck jaws, one at a time, in the chuck. That would ensure they are accurate when used.

Doubled up post yet again 

Edited By old mart on 18/05/2020 20:55:45

Yes I agree they should look pristine The chuck has not been used more than once !

But I do agree that they can be easily trued up insitu. I did try them turned around and with the 20 mm test bar they are virtually spot on. I discussed this with a friend, and how they could be trued up. I mentioned it in an earlier post.

If you grind them in situ you will neef to make a clover leaf plate or at least packing sttrips between adjoining jaws to push the jaws outwards while grinding.

Hi Hopper,

Yes I agree with you for a three jaw chuck ! With a four jaw you can grind each jaw independently. The technique that has been described to me is to lock the chuck so that the jaws are horizontal and then grind the face of the jaw so that it is square. To prevent the jaw moving whilst grinding, use a clamp across opposite jaws.

As long as each jaw has a true face then any work placed in them and trued up should be true at both ends.

Hi Guys,

To close this thread.

In my case all four of the jaws all had different amounts of taper to the back. I've simply reground mine parallel.

However I've also recently discovered that PB deliberately grind the jaws with a 2 to 3 thou backwards taper. Apparently to allow for grinding tolerances in the guides.

Anyway having reground them I can now set the test bar true at the chuck and it is still true within two tenths of a mm 150 mm away. So I'm very happy with that.

If I need to grind the compensation for guide wear back in all I have to do is reverse the jaw, clamp it against the inside so that it can't move and regrind the jaw face with the chuck locked so that the jaws are parallel to the bed and lock the chuck so it cannot move.

The general setup.

Ready to start grinding.