I recently bought a 125mm vertex taiwanese 4 jaw for £115 if my memory serves me well, in my opinion, well worth the extra 30 quid or so.

p. s Forgot to say if your lathe came with a 80mm 3 jaw then it will have a 55mm spindle register but you can get a pre machined 55 to 72 back plate I think RDG do them. If your lathe came with a 100mm chuck then you should be fine?

I'd stick with Arc,

Jim

Here is the ARC 4 jaw and backplate just fitted onto my SC3 – it takes up some of the length between centres, but less of an issue on this lathe. The casting is a 7 1/4" Tich wheel – Just trying it for size!!

I just wanted to see what the capacity is – I only roughly centred it by eye but it ran smoothly enough with plenty of jaw engagement and plenty of clearance over the bed. I need to practice centring things in a 100mm four jaw!

I have access to a larger lathe with backgear at the club workshop, and at my rate of working all of our current troubles will hopefully be out of the way before I need to turn these wheels (actually at my rate of working probably the next two issues to face us as well! )

So unless we are still in lockdown this may not need to be resorted to – but I am confident it could be done should I need to.

The wheel by the way finishes to 4 1/2" over the flange so without measuring it, is probably about 4 3/4" as is.

Edited By Nick Clarke 3 on 25/04/2020 13:55:57

Nick Clarke 3:

Thanks for filling in the background. I suppose that you could rough turn at the club and finish off at home.

My sensitivity to jaw projection is due to having a three jaw with one broken tooth (not my doing); I think the four jaw may be more resistant to this kind of problem, however.

I didn't realise that Tich came in the large size!

So far as jaw projection is concerned rough rule of thumb with three jaws seems to be no further than the first inside step so largest size that can be held is chuck body diameter. Many chucks will have marks on the jaws to indicate exactly how far is OK but its not universal even on quality brands.

Four jaw chuck adjusting systems are much stronger that three jaw ones because the half thread on the back of the jaws engages properly with the thread on the adjuster. Three jaw scrolls are inherently much weaker because the contact between scroll and jaw tooth is pretty much line due to the need for clearance between the tooth and the varying radius of the scroll.

Rough rule of thumb with a four jaw seems to be up to about half way out if you are careful. In practice a four jaw properly sized to the lathe will start hitting the bed once it gets much more than one step outside.

Realistically, for chcks correctly sized to the lathe, its officially the same for both types. Maximum diameter to be held is same as chuck body diameter. As ever some wiggle room.

Clive

With a 80mm chuck the spindle register will be 55mm so you will need the back plate if you go with a 100mm 4 jaw. If you decide to get it from ARC then the chuck is part number 040-040-10600 £48 and the back plate 040-060-10100 £20.28. So a total of £68 and you won't have any machining to do and don't worry about losing rigidity it will be fine.

Also bear in mind that ARC also stock a 80mm 4 jaw for £44 and you wouldn't need the back plate it will be a straight fit. If all you intend to do is make small parts then the 80mm chucks may be fine.

From my experience with a mini lathe I would go with the 100mm 4 jaw chuck and at a later date you may find you need to go up to 100 for the 3 jaw also but that is your decision. Earlier a 125mm 4 jaw was mentioned but I would avoid that on a 300 watt mini lathe.

Ron

Edited By Ron Laden on 26/04/2020 06:25:20

I think that the Machine Mart mini lathe is made by Sieg, so Arc should be able to supply parts to fit.

Possibly a red herring.

If you feel the need to modify the register on the new 4 Jaw independent, you could try this. No doubt someone will ,object!

It assumes that the tappings for the retaining studs coincide with the holes in the flange on the Mandrel, and that the register needs to be enlarged..

Clamp a piece of bar in the 3 jaw chuck, and take a light skim, to just clean it up (i.e. the OD will, be truly concentric )

Clamp the 4 jaw to the turned bar, with the jaws toward those of the 3 Jaw..

using a DTI, adjust the jaws to set the body so that it runs true, within whatever limit you see fit to accept.

Machine the register to the size that you require yo be a good fit on the flange.

H T H

Howard

I believe that the Clarke Cl300 has a different register to the normal mini lathes.
i suppose this is so Machine Mart etc can charge their normal inflated price.
so anything will always have to be 'amended' 😛

I don't know why it's been said that the fixings of chucks on Machine Mart CL300 are different from other Seig machines. I have bought an ER25 chuck and a 4 jaw self centering chuck from Arc Euro and they fit without any modification. I also have the original 3 jaw that came with the machine as well as a 4 jaw independent which came from them. ( before I discovered the alternative suppliers )

Anthony