Thread: 4 jaw chucks?

The 3 jaw chuck is normally used to grip a round and within limits it doesn't matter how worn or battered the chuck is, the 3 jaws will always grip the round. The round may not be centred in the chuck but it will be tightly gripped. They work well in the real world.

You couldn't say the same for a self centring 4 jaw though, it would only be useful in an ideal world, ie where all stock is a perfect round or a perfect square.

An independent 4 jaw however is a very useful piece of kit.

3 jaws will grip a cylindrical object, even if it is not quite cylindrical. 4 jaw self centring chucks are available but if the object is slightly out of round, it will not grip securely. This could even apply when gripping a square section if it is not perfectly square.

Michael

Ausee Mchines list 4 jaw independent and self centring chucks for the C6. They also have the C6 backing plate.

3 jaw self centering (SC) chucks can grip round workpieces, and hexagonal workpieces which are the most common shape beside round.

But most importantly, each jaw of a 3-jaw chuck will be in contact with a slightly out of round workpiece such as a warm rolled steel bar. Not so an SC 4-jaw chuck. Think of a 3 legged stool on an irregular floor, versus a 4 legged stool on the same floor. The 4-legged stool is guaranteed to need a shim to stop it wobbling.

There are 6-jaw SC chucks, and these are preferable to 4-jaw SC chucks if the aim is to distribute clamping pressure, for example not to squash a thin walled tube whilst clamping.

4-jaw SC chucks do exist but are rare. About the only use I can think of, is to clamp square stock. One is much more likely to stumble on a 6-jaw SC chuck, than a 4-jaw SC chuck. In a home shop situation, the vast majority of people that own an SC 4-jaw chuck, usually find it hard to remember when they used it last.....

Do not confuse this with a 4-jaw chuck with independently adjustable jaws, which is more useful than any self centering chuck can ever be.

I have a 5" 4 jaw SC chuck. Haven't used it in over 15 years which gives an idea of how useful I think it is.

I'd rather have a really good 4 jaw independent chuck any day, in fact if I could only have 1 chuck it'd be a 4 jaw independent without question.

PDW

Thanks for your replies and explaining the differences, makes sense now.
I am used to 4 jaw self centering wood lathe chucks .

I did buy a 4 jaw independent chuck and backing plate from The little machine shop but it is so wonky it not funny.

That Aussee machine site has some interesting gear.

Is that the one that you adjust the jaws by moving a bolt,if so ask someone else to make or suggest your purchases.

Originally Posted by wm460

Why are metal lathes self centering chucks most commonly 3 jaw?
Wouldn't 4 self centering chucks be more use full than 3 jaw?
Do they make a 4 centering chuck for a Seig 6 style lathe?

Your 3 jaw vs 4 jaw question has already been answered, but if you are specifically wanting to buy a self centering chuck, what about a 6 jaw?

http://www.assetplant.com/epages/sho...ucts/12%2B0542

Backing plates

http://www.assetplant.com/epages/sho...ssories/Chucks


Ray

This is what I got, by memory it was recommended by Bigshed.

https://littlemachineshop.com/produc...1588&category=

https://littlemachineshop.com/produc...ProductID=1921

So 2 lessons learnt,
1) dont always except reccomendations from someone.
2) Is it the chuck or backplate or lathe spindle that is wonky or a mix of all 3.

Originally Posted by pipeclay

So 2 lessons learnt,

Originally Posted by pipeclay

1) dont always except reccomendations from someone.
2) Is it the chuck or backplate or lathe spindle that is wonky or a mix of all 3.

Measurements on backing plate taken inline with each jaw.

Measurements on chuck taken inline with each jaw.
both on this and backing plate the gauge returns to zero when I return to the first jaw.

Thread inside the backing plate.

The measurements you have taken on the chuck are roughly in proportion to the measurements you made with the DTI on the side of the mounting plate, so it looks like the chuck to backing plate part is alright,
The thread in the backing plate is sadly not untypical but should not matter. More important are the register surfaces.

A couple more tests. Using the DTI, remove the chuck and indicate on the inside surface of the spindle bore. Mark on the spindle approximately the jaw positions so if there is variation you can relate it to the other measurements.
Do this test but mount the taper adaptor and a centre in the headstock spindle. Indicate off the centre near the tip (you are trying to see whether the bore for the adaptor is in line with the point of the centre)
Mark your chuck and backing plate so you can put it back together in the same orientation and then separate it. Put the backing plate on the lathe and measure the face of the backing plate.
The first test will hopefully show that your spindle is alright (not bent). The last will see if the backing plate has been machined properly to take the chuck.
The fix may be to remachine the backing plate so that it is properly perpendicular to the axis of the lathe and remount the chuck, but if the spindle is bent (if the lathe is still under warranty) it may be better to get a new spindle - or send it back)

Michael

Michael