Will the results make a difference to your work or is it just out of interest?

Purely by the way, the certificate appears to have been completed by a French or other person of continental origin.

Unless our education system has changed which is possible UK students do not use a ‘bar’ on a 7 , but hey just for fun I occasionally do 😉

Tony

I use a barred 7. Why? Because when I was in secondary school my coursework had them.

Anyway, the 1 digit is typically continental on that test cert.

I started to use a barred 7 when I began scoring at darts in school to avoid confusion. But then a git of a history teacher (described as the ugliest man in England by an old boy speaker at speech day) corrected each date in a one page summary of the eighteenth century with each one as a spelling mistake – and yes 1777 was three spelling errors!!

Possibly refers to the outside jaws having the long end of the stepped jaws machined to a V whereas the inside jaws have the short end of the stepped jaw machined to a V. Hence Long V and Short V jaws refers to the length of the V.

Ignore the letters R and L in the pic, just some random pic off the net and not relevant. But Long V on the left, Short V on the right.

We'd all like to know the answer, but it seems no-one does! Hopper's is best suggestion so far, but it's too subtle for my taste. Not saying it's wrong, just not obviously right.

I spent yesterday's coffee-break touring a couple of jaw catalogues hoping to find an answer. No luck. Schunk  list about 40 different styles of jaw, but no sign of long or short V jaws. Nothing in Pratt-Burnerd's web info either.

Chasing the best is a hard sport. Having made sure the lathe spindle is good, one buys a chuck with a proper specification. Specifications are good, but worrying unless they're understood! Figures don't mean much unless the way they were measured is known. And having understood the spec, some forum smart-a*se (me) points out luxury chuck owners also have to choose the most suitable jaws for the job from a long list!

My take is the main advantage of posh tooling is saving time. For example, my ordinary 3-jaw is good enough for most turning unless the job has to be taken out of the chuck and replaced, perhaps after a bit of milling. Taking work out of my 3-jaw is a bad move, because chuck doesn't allow accurate resetting, although putting it back exactly as it came out and tweaking with a DTI helps. Trouble is tweaking takes time and doesn't always work because the chuck doesn't have high repeatability.

One answer is to buy a better made 3-jaw chuck, but even these struggle to reset work when high accuracy is required. Better for amateur purposes I think to fit a 4-jaw when reset is needed, because even an ordinary one will give a top-end 3-jaw a run for it's money! But 4-jaws have a major disadvantage when it matters, which is the time taken to adjust them. Not a problem in my slow-moving tinkering workshop, but slow working methods are bad news when a pro machinist has to work against the clock. Collets are often a good answer, but they have other limitations. Jigs and fixtures outperform ordinary workshop methods, but are only worthwhile for mass-production.

I suspect the best way for an amateur to do high-precision work is by sending CAD files to a professional CNC shop. There's no need to have an expensively equipped workshop at all.

Not seriously suggesting we should do everything from comfy chairs! I enjoy my workshop, hands-on making things is interesting fun.

Dave

Edited By SillyOldDuffer on 17/06/2022 09:51:53

Can I also second Hopper's suggestion. I came up with the same conclusion but couldn't think how best to describe it.

Peter

That's easy. The inside jaws are the ones you crash into with your left hand turning tool and the outside ones you crash into with the right hand turning tool. The ambiguity in the jaw and tool nomenclature is a form of magnetism – the more there is, the stronger the attraction.

..well, the ticket clearly has spaces below the 'Body No.' serial box for the recording of 'LV' & 'SV' Jaw Set serial numbers – what else might they refer to other than the sets of external & internal jaws supplied with the chuck?

On rereading the OP it seems Long V and Short V is an assumption by the OP. The chart itself only says LV and SV, which could be anything, even just randomly assigned model letters to identify different jaws. The OP should call Pratt Burnerd's UK HQ and enquire. But he has made his first and only post here and no return since so can't be too worried about it.

Or practice using the quick method of setting up the four jaw chuck. IE set the dial indicator on the back of the job in the horizontal plane. Rotate the job once and set the dial's zero to halfway between the highest and lowest reading on the indicator. Then go around and adjust each pair of jaws until each reads zero. A pair of "twiddlers",short chuck keys, makes this easier. Then go around again and final tighten and adjust that last thou or so. Two to maybe four revolutions of the chuck. It takes about a minute or two with a very little bit of practice.

If you just use the trial and error and hope for the best method, it can take all day.