Which chuck to buy for first lathe ?

A three-point hold will grip firmly at all three points.

A four point grip will only be the same at all four points if the material is perfectly square or round and the chuck is perfect.

In practice there's enough elasticity in the setup that a 4-jaw self-centring will hold round bar, but imperfect square bar may be out enough to cause a challenge for it.

Now would photographers be arguing a four legged camera stand with individually adjustable legs is easier to use than a fixed tripod on a flat floor...?

Neil

I'd like a little 3 jaw chuck for my Super Adept, the 4 jaw chuck is quite fiddly to work with at this size.

With Chinese, and Taiwanese lathes in NZ it is usual to get one of each 3 and 4 jaw, but when a friend got his lathe home, and opened the box he found 2 of each, and 2 face plates.

Ian S C

| "Now would photographers be arguing a four legged camera stand with individually adjustable legs is easier to use than a fixed tripod on a flat floor...? "

Great analogy Neil - I can see why they made you the "head - hitter" !

( Bloomin' "return to go" on carriage return still not fixed !!******!!)

Norman

PS Also over enthusiastic spellchecker changed my "carriage return" to "marriage return" - fraught with danger I fear!

Edited By NJH on 07/12/2014 10:27:03

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Michael,

I think Neil has probably answered most of this on my behalf, but here goes ...

• Brian has already ruled out the 4-jaw independent
• I was therefore talking explicitly about 3-jaw vs 4-jaw self-centering.
• For your homework, today read about kinematics ...
• why do photographers and surveyors use Tripods?, and why does a milking stool have three legs?
• Extrude that point contact in the Z-axis and you have three lines
• At the limiting condition; when real surfaces meet, there is only ever three point contact ... anything more will involve [perhaps microscopic] distortion of surface[s].

Now, translating all of this to the self-centering chuck question: The 4-jaw will grip round stock less reliably for the same reason that a four-legged chair might wobble on a floor [whereas the three-legged stool will never do so].

The independent 4-jaw is, of course, a different matter.

And, by the way; the 3-jaw self-centering will grip any shape ... provided that it has constant cross section along the length ... it's just that the centre will be wherever it falls naturally.

Hope that makes sense ... happy to discuss further, either here or by P.M.

MichaelG.

Hi Ian,

It will have to be lever scroll to be short enough to allow the jaws can expand into the gap.

Problem with small screw fit chucks is that a short screwed adaptor might be too thin, so an overhung design would be needed.

But, I've got a 2 5/8" lever scroll chuck that's a good fit with the adept. It has a three-screw fitting rather than being screw on. I've made a backplate, but I can't turn the front of it until the adept is up and running.

Neil

off topic but useful education:

If you put a 4 legged table on rough ground you find 2 legs' in the air'. Try again and the other 2 legs are now in the air. Bother . However a little thought reasons that somewhere beteween those two places is a transition point as it goes from one pair to the other pair and all 4 are firmly in contact . I never have a problem with getting a 4 legged table stable on rough ground.

Hi All Did anyone ever make a three jaw independant chuck?

Roy

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I bet you can stand a sharp pencil on its point, too

MichaelG.

Roy

"Did anyone ever make a three jaw independant chuck?"

Yes - after a fashion. This is the "Griptru" chuck which allows micro adjustment of the position of the chuck on its backplate. Another "nice to have" - I picked up a S/H one in good condition and it does have its uses - but I would have to think carefully about paying full price for one!

Norman

A Combination chuck is probably closer than a Grip-True as each of the 3 jaws can be independantly adjusted with the key but they then also have a scroll so that all three will then open equally and return to the same shape when tightened. Handy if you have a batch of eggs to hold or multiple parts that are eccentric

I'm genuinely surprised this even being debated to the degree it is. The three jaw self centring chuck is the obvious choice which again I reiterate is why all lathe manufacturers supply a three jaw as standard. If something needs holding to the nth degree of accuracy and someone feels their personal three jaw chuck is lacking, then you can always add cigarette paper or brass shims under the appropriate jaws to make it hold concentrically. Most three jaw chucks of reasonable quality hold acceptably well for the bulk of turning operations.

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Ian,

Have a look at the Bergeon set [third item on this page]

... Then get buying Lotto tickets !!

MichaelG.

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[Chris: Please feel free not to look.]

Considering the prices, the finish on a few of those accessories (tailstock and toolpost, for example) looks a bit less than perfect!

Neil

Judging by the prices this gear is made of platinum!

Is this a first?

John

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Agreed ... But unfortunately that appears to be the standard finish for the Model 50.

[from lathes.co.uk] ... "Unfortunately, the model 50 model not only looked rather prosaic but was finished in a "hammered" paint finish quite out of scale with the size of the machine. However, the superb Bergeon quality remained unchanged and the lathe was every bit as good as it predecessors."

Previous models did look much smarter !!

MichaelG.

Edited By Michael Gilligan on 07/12/2014 16:56:21

Good grief Michael !!

Many years ago I picked up, for not much money, a secondhand watchmakers lathe which came with a set of collets 0.4mm to 4.8mm in 0.2mm steps and, as I like the smaller end of things, this has been of use from time to time. I will certainly treat it with greater respect in future - indeed maybe a nice polished mahogany base and pride of place in the wife's display cabinet is more appropriate than the workshop!

Norman

( Sadly though it's not a Bergeon )

Edited By NJH on 07/12/2014 17:37:12

Hi MichaelG and Neil. Apologies to the OP.

Dan Gelbart was the name of the US guy I was thinking of, this links you to one of his youtube videos. **LINK**

About 3/4 of the way through he talks about using a self centering 4 jaw chuck. He has a bit of an accent so I may have miss heard him. Hearing gone south as well

I think I hear him say 4 jaw independant is a boon for R&D and precision work.

I shall cross him off my christmas card list and thanks for saving me £80

Mind you his lathe probably cost more than my house

Cheers Michael

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Michael,

Thanks for the reminder about Dan Gelbart's remark ... Very interesting !

I have just checked his video, and I think he's recommending a self-centering 4-jaw.

It's very brief, but he does appear to show a self-centering 4-jaw gripping a hexagon at four points [lines]. ... I must admit, that's counter-intuitive; but it's food for thought.

That said; I do stand by my opinion on the kinematics.

MichaelG.

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Edited, and hopefully clarified.

Edited By Michael Gilligan on 07/12/2014 19:53:46

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Well ... I thought, and I browsed and: Yes, it does work geometrically.

Look here, at the diagram for the largest square within the hexagon. The four intersection points prescribe the locations at which the external chuck jaws would need to act.

The practical usefulness may depend on the shape of the chuck jaws, but the theory is good.

The day is not wasted ... I have learned something.

MichaelG.