3 jaw or 4 jaw chuck

[Fergie 307]

That's precisely the reason that I use soft jaws and machine them concentric with the lathe centre-line each time I mount the chuck. This is even better than using a collet chuck (I do also have an ER32 Collet set).

'Clocking' work in an independent chuck is an art and, unless you have had many many years experience, is unlikely to be more efficient (time wise) than using soft jaws.

If I need absolute end-on-end concentricity I turn between centres.

How do you tension the jaws for machining out of interest?

 

[Fergie 307]

That assumes your scroll is accurate all the way through it's range of motion

So true. I have a number of different sized Taylor dished face three jaw SC chucks. They are all very accurate, but the eight inch one is the best, runs out by less than a thou across the range. Beautifully made and designed, although very big and heavy for their capacity. Not sure how the modern, probably Chinese made chucks compare. All my others are old Pratt's, oldest about 1940, will no doubt still be giving good service to someone long after I'm gone.

 

[Fergie 307]

I would have thought that bit of knowledge was a given for any lathe user?

Collet chucks are definitely very useful, as I mentioned I have an ER40 which personally I think is the better choice for your average home DIY type lathe user for quite a few reasons.

As are most of the other points made.
And agreed a 5c chuck is only any use of you have a big enough machine, for most hobby machines it's going to be far too big. I love it because you can pick up used collets all over the place quite cheaply including square, hex etc, and tend to be top quality as mostly intended originally for industrial use. The modern set of metric collets I have are accurate enough, but nothing like the quality of the old imperial ones I have collected over the years.

 

[Inspector]

One other plus for the 5C collet system is they have depth stops you can add. Very handy when you have a lot of repetitive parting or facing cuts. Can't to my knowledge do that with any ER setup.

Pete

 

[Rorschach]

One other plus for the 5C collet system is they have depth stops you can add. Very handy when you have a lot of repetitive parting or facing cuts. Can't to my knowledge do that with any ER setup.

Pete

You could put a depth stop in your spindle if you want to, same as you would if you wanted a depth stop for a scroll chuck.

 

[Inspector]

True but with the 5C the depth stop is screwed into the collet itself and can stay with it when you remove it for another that can have its own stop for the next operation. The 5C (along with the others in the family) were designed for work holding where the ERs were for holding tools so the 5C have more options including being able to transfer to the milling machine into holders and spin indexes etc. There are many ways to skin a feline in the metal shop, especially in the home shop where one adapts rather than buying specialized tooling.

Pete

 

[Rorschach]

Exactly, that's why I said ER40 for the home shop DIY type machinist. If you are making money and buying in stock, get 5C or similar, but a DIYer might be using scrounged stock of odd sizes etc.

 

[J-G]

How do you tension the jaws for machining out of interest?

Astute of you to appreciate that there could be an issue

Generally I grip a small pre-machined billet at the back of the jaw carriers but it would depend on the job in hand. If the intention were to hold the work by expansion then I would use a larger 'Ring' on the outside.

 

[Sandyn]

I have read all the various advantages/disadvantages of my options. The Collet chuck sounds very good, but for the type of work I do just now, it's more than I need at the moment, but on the wish list. I'm back to favouring 4 jaw self centering chuck and if the out of round material causes real problems. I'll just buy better stock
Thanks for all the info.

 

[Fergie 307]

Astute of you to appreciate that there could be an issue

Generally I grip a small pre-machined billet at the back of the jaw carriers but it would depend on the job in hand. If the intention were to hold the work by expansion then I would use a larger 'Ring' on the outside.

Similar method here. I find old bearing races are good, big ones for the outside of the jaws, little ones for inside. Another method I have used if there is no easy way to mount something inside the base of the jaws is to use 3 lengths cut from a square bar and laid flat on the face of the chuck so that as you close the jaws they are gripped between the outer edges. For soft grip I picked up a job lot of thin copper sheets years ago and have rolled various different sized tubes out of it. Just pick one slightly smaller than the work and slip it over then position so the gap in the tube is between the jaws. Not as convenient as proper soft jaws, but you use what you have.

 

[J-G]

...I'll just buy better stock

Not always an easy option. The only steel that is usually supplied 'ground' - and therefore accurately 'round' - is Silver Steel which may not be suitable as stock where En1a, En8 or some other specific steel is specified, though, to be honest, the amount of out-of-round of any Bright Drawn Mild Steel is likely to be irrelevant in a home workshop environment.

I can't recall ever considering the OD of steel stock (or any material for that matter) to be the finished size of the component. I might take a small skim or even a polish with emery where the OD is not material to the function of the work but I usually expect to take at least a mm off so standard BDMS is perfectly good enough.

 

[Sandyn]

Thanks, I have just been using the material I have for welding, S275JR re-rolled steel, but I'll get some BDMS. for turning.

 

[J-G]

Ah... One of the problems of trying to give advice without really considering the basic knowledge of those asking for it !

I'd assumed that you were already using (at least) BDMS. 'Black Bar' is a different animal altogether, I would expect to take off at least 3mm before I got to a finished surface.

 

[J-G]

For soft grip I picked up a job lot of thin copper sheets years ago and have rolled various different sized tubes out of it. Just pick one slightly smaller than the work and slip it over then position so the gap in the tube is between the jaws. Not as convenient as proper soft jaws, but you use what you have.

That could be a useful ploy and I have done something similar - not with tubes made from sheet, but by making 'collets' from Brass, Alum or even steel - particularly useful when needing to hold very small dia. components.

 

[Fergie 307]

Ah the joys of really small stuff. I am very much into watches, but one thing I don't have the kit for is repairing broken pivots. I have to take them to a friend. Problem is scale, having to drill a hole maybe 0.2mm in a balance staff 0.7mm in diameter, and that's a big one! He has the proper watch making collets and a gadget that looks a bit like a dividing wheel, so you place the relevant sized hole over the end of the staff to act as a fixed steady. Then square the broken end and drill into it for a new pin to be inserted. I was surprised to learn that the standard technique is to use a graving tool to make a centre in the end of the shaft to start the drill, then use a spade bit to actually drill the hole. In many cases you have the added complication that the pinion was hardened, and this obviously tends to spread to the very end of the shaft below it. In this case the shaft has to be annealed before you start. It's surprisingly easy to do with the correct tools, and very satisfying. So far I have done some clock ones, much bigger, but really do need to get the kit to do my own watch sized ones. Unfortunately I think the boss lady would need some persuading to see it as a worthwhile expense.

 

[J-G]

The graving tool 'trick' is somewhat counter-intuitive until you've actually tried (and mastered) it.

I don't get quite down to watch pivots though I do build clocks. Even so I do have solid carbide drills down to 0.3mm Ø. The last 'collet' I made was to hold a 12T MOD 0.5 brass gear - 7mm OD 1.5mm thick which needed a 5mm x 0.5 recess and a 0.7mm drive pin fitted.

If I did have to get down to 'watch' sizes I'd be looking for a Lorch or Pultra. There was one on the [Home Workshop] site last week but it seems to have disappeared.

 

[Fergie 307]

The surprise to me was the use of spade bits. I have some very small drills for carburettor jets, these are essentially miniature versions of your regular twist drill with an identical twin flute angled tip. I had never really thought about it, but would have assumed watchmakers would have used something similar.
It's certainly an interesting subject, and I find it very satisfying repairing them.
You can also pick up some really nice old Watch making tools quite cheaply, and we all like to collect tools !

 

[Rorschach]

Spade bits are very stiff for their size and the cutting geometry works really well on brass, silver and gold.

 

[Fergie 307]

Absolutely, makes perfect sense. They also frequently use bits with a very slight taper, so the replacement pin is driven home into the taper to secure it. Much easier to make a tapered spade, especially in such small sizes. I particularly admire the balance staff on the old duplex escapement watches. They have a slot machined into the staff, typically about 0.1mm wide in a 0.5mm diameter steel staff. When you look at them through a microscope the machining is superb, and this in the mid 19th century. Would be fascinating to be able to go back and have a look around their machine shop.

 

[Sandyn]

One of the problems of trying to give advice without really considering the basic knowledge of those asking for it !

I'd assumed that you were already using (at least) BDMS. 'Black Bar' is a different animal altogether, I would expect to take off at least 3mm before I got to a finished surface.

Thanks for your advice. I will get some bright bar next time I order, I have to make do with the steel I have in stock. It's all part of the challenge. I turned some 40cm x 20mm 'black bar' for the sliding guard for my table saw and it worked really well. I used my 4 jaw independent chuck to turn it. I don't really worry about things being a few thou off for an old cast iron saw.

The clamp on the vertical bar is machined from an old cast iron window weight, they can be a few mm off circle for a 40mm diameter weight

I also used a window weight for the bearing housing for a windmill I'm building. The main shaft was machined from a length of 12mm black bar down to about 8mm, That also worked really well. Bearings are ABEC 7's from my son's skateboarding days.

I just rely on common sense when I don't know what I'm doing.