# 3 jaw or 4 jaw chuck



## Sandyn (29 Aug 2021)

I need to get a new chuck for my ML7 Lathe and favour a 4 jaw self centering chuck. I mainly turn round and square stock, never triangular or hex. I already have a 3 jaw self centering and 4 jaw independent, both are well past their best, but still usable. I'll probably get an HBM from RDG Tools, or Chronos.
Are there any disadvantage of the 4 jaw I haven't thought of?


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## Daniel2 (30 Aug 2021)

I can imagine two limitations, rather than disadvantages, with this chuck.
First, is not being able to set the workpiece off centre, for certain operations.
Second is the inability to grip irregular shaped pieces, which includes pieces
of rectangular section.


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## Rorschach (30 Aug 2021)

Daniel2 said:


> I can imagine two limitations, rather than disadvantages, with this chuck.
> First, is not being able to set the workpiece off centre, for certain operations.
> Second is the inability to grip irregular shaped pieces, which includes pieces
> of rectangular section.



He already has a 4jaw independent for those tasks. 

I use a 4 jaw self centring chuck a lot, works great. The only thing you need to watch for is if you are using round stock that isn't perfectly round, a 3 jaw handles this much better and you would probably never even notice it wasn't round but in a 4 jaw you can run into some problems if you are not careful. Otherwise though, go for it, a 4 jaw SC gives you machining options that are almost impossible on a 3 jaw and for regular stock much faster than the 4 jaw IND.


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## Daniel2 (30 Aug 2021)

Rorschach said:


> He already has a 4jaw independent for those tasks.
> 
> I use a 4 jaw self centring chuck a lot, works great. The only thing you need to watch for is if you are using round stock that isn't perfectly round, a 3 jaw handles this much better and you would probably never even notice it wasn't round but in a 4 jaw you can run into some problems if you are not careful. Otherwise though, go for it, a 4 jaw SC gives you machining options that are almost impossible on a 3 jaw and for regular stock much faster than the 4 jaw IND.



I think a 4 jaw sc chuck is probably a very handy accessory, but, in addition to an
independant.
The OP's question was if there were any disadvantages, so I was trying to
imagine some.  
It saves having to clock the work in, I suppose.


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## TFrench (30 Aug 2021)

I always find the more options you have, the better. Always having the right tool for the job saves a lot of struggle. If you turn a lot of square stock it makes perfect sense!


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## Sandyn (30 Aug 2021)

Rorschach said:


> The only thing you need to watch for is if you are using round stock that isn't perfectly round, a 3 jaw handles this much better and you would probably never even notice it wasn't round but in a 4 jaw you can run into some problems if you are not careful.


That's just the kind of info I was looking for! I do turn a lot of rolled steel which is never really round. What you say suggests there are ways round the problem. Is it a case of rotating the bar until it grips better?

Thanks everyone for replies


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## J-G (30 Aug 2021)

Sandyn said:


> Is it a case of rotating the bar until it grips better?


If your stock is out of round, rotating it in a four jaw SC chuck will have little effect since you will still be holding on only 3 of the jaws. It might be a different one that doesn't actually make contact. 

It would be possible (though you may have to be very precise with your positioning) to hold on only two jaws of course. With a three jaw, the out of round issue goes away completely.

As @TFrench has said, having more options is certainly good and (for me) the availability of 'Soft' jaws is of paramount importance. I have 4 jaw Independent, 4 Jaw SC and 3 jaw SC chucks and all get used as needed but the majority of my work is done using soft jaws (mild steel or hardwood) on the SC chucks. My 4J SC is ostensibly a wood-turning chuck and therefore has carriers to which I can screw Steel, Brass, Alum, Beech, Oak (or any hardwood) 'Jaws' which I can machine to suit whatever work-piece is in use. 

Using my CNC machine I can even accommodate 'off centre' or 'non-round' work.

The referenced chuck from RGD is unlikely to have either soft jaws or 'carriers' available.


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## Phil Pascoe (30 Aug 2021)

If your stock is out of round, rotating it in a four jaw SC chuck will have little effect since you will still be holding on only 3 of the jaws. It might be a different one that doesn't actually make contact. ...

It might, if you rotate only 45 degrees.


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## J-G (30 Aug 2021)

Phil Pascoe said:


> It might, if you rotate only 45 degrees.


It's a moot point Phil.

As I'm sure you'll appreciate (knowing my previous posts), I could go into great detail with drawings but I'll not bother


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## Sandyn (30 Aug 2021)

Thanks for all the replies and great information, I think a new 3 jaw would be more sensible to start with then get a new 4 Jaw independent if I find I still use the old one a lot.


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## Daniel2 (30 Aug 2021)




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## Rorschach (30 Aug 2021)

Sandyn said:


> That's just the kind of info I was looking for! I do turn a lot of rolled steel which is never really round. What you say suggests there are ways round the problem. Is it a case of rotating the bar until it grips better?
> 
> Thanks everyone for replies



Depends how out of round really. Usually turning it a little bit will help, a bit like the the old rotate your table if one of the legs wobble on uneven ground, you usually find a sweet spot that evens things up. A 3 jaw is definitely better for round stock that is a bit uneven but most round stock will be fine in the 4 jaw too. Really the 4jaw SC excels at holding square stock or self centring on odd stock be either gripping at 45deg or even just by taking out 2 jaws and using it as a 2 jaw chuck. 

Like I said, I like mine, I use it an awful lot, way more than my 3 jaw chucks and almost as much as my collet chuck. It's a nice thing to have for any lathe user but I think a 3 jaw is still pretty essential for most people as well as the 4 jaw independent. 

Collet chuck is really nice, you will want one of those too  (I recommend ER40).


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## Sandyn (30 Aug 2021)

Rorschach said:


> A 3 jaw is definitely better for round stock that is a bit uneven but most round stock will be fine in the 4 jaw too


Thanks. More good info, looks like it's time to get a coin out and make a decision!!


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## Inspector (31 Aug 2021)

If a 4 jaw is better than a 3 jaw then a 6 jaw has to be better than both of them. 

Pete


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## Fergie 307 (31 Aug 2021)

Surprised no one has mentioned the obvious problems with any SC chuck, namely that they don't hold a piece exactly on centre, there is always a degree of error. A real problem if you ever need to turn the work round and machine something concentric in the other end. With an independent you can do this, just down to how much trouble you are prepared to go to setting it accurately. And I would definitely go for a collet chuck. I have a 5c, use it all the time, and you can get square collets as well if you turn square stock a lot. Mine is only a cheap Chinese job, about £200. Pretty impressed with it though, accurate to about 0.001 inch which is plenty good enough for anything I do. Makes life very easy for anything that will fit in it.


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## Rorschach (31 Aug 2021)

Fergie 307 said:


> Surprised no one has mentioned the obvious problems with any SC chuck, namely that they don't hold a piece exactly on centre, there is always a degree of error. A real problem if you ever need to turn the work round and machine something concentric in the other end. With an independent you can do this, just down to how much trouble you are prepared to go to setting it accurately. And I would definitely go for a collet chuck. I have a 5c, use it all the time, and you can get square collets as well if you turn square stock a lot. Mine is only a cheap Chinese job, about £200. Pretty impressed with it though, accurate to about 0.001 inch which is plenty good enough for anything I do. Makes life very easy for anything that will fit in it.



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.


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## J-G (31 Aug 2021)

Fergie 307 said:


> ...the obvious problems with any SC chuck, namely that they don't hold a piece exactly on centre, there is always a degree of error. A real problem if you ever need to turn the work round and machine something concentric in the other end.


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.


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## Rorschach (31 Aug 2021)

J-G said:


> 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.



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


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## Daniel2 (31 Aug 2021)

.... and chasing that last elusive angstrom of precision.


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## J-G (31 Aug 2021)

Daniel2 said:


> .... and chasing that last elusive angstrom of precision.


For me that's a given 

If you don't aim for it you'll never achieve it.


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## Fergie 307 (31 Aug 2021)

J-G said:


> 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?


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## Fergie 307 (31 Aug 2021)

Rorschach said:


> 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.


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## Fergie 307 (31 Aug 2021)

Rorschach said:


> 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.


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## Inspector (31 Aug 2021)

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


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## Rorschach (31 Aug 2021)

Inspector said:


> 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.


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## Inspector (31 Aug 2021)

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


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## Rorschach (31 Aug 2021)

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.


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## J-G (31 Aug 2021)

Fergie 307 said:


> 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.


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## Sandyn (31 Aug 2021)

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.


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## Fergie 307 (31 Aug 2021)

J-G said:


> 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.


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## J-G (1 Sep 2021)

Sandyn said:


> ...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.


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## Sandyn (1 Sep 2021)

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


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## J-G (1 Sep 2021)

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.


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## J-G (1 Sep 2021)

Fergie 307 said:


> 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.


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## Fergie 307 (1 Sep 2021)

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.


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## J-G (1 Sep 2021)

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.


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## Fergie 307 (1 Sep 2021)

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 !


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## Rorschach (1 Sep 2021)

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


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## Fergie 307 (1 Sep 2021)

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.


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## Sandyn (1 Sep 2021)

J-G said:


> 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.


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## J-G (2 Sep 2021)

Sandyn said:


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


By far the best policy. If it 'feels' right it usually is.


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## Inspector (2 Sep 2021)

As long as you learned what common sense was a long time ago and built on it. Some people's common sense is closer to nonsense but it make sense to them. Often a frightning thing to be around. 

Pete


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## Sandyn (14 Sep 2021)

I sat on the decision for a while, but got a 4 jaw self centering chuck. I opted for the 125mm. My goodness!! what a monster compared to my old 100mm Pratt Burnerd.







I tried some out of round steel bar and it gripped it without any problem. The chuck is pretty good quality. I assume it is Chinese . No country of origin on the box or unit, but it carries the same number as the Sanou K12-125

My old Pratt chuck was a bit worn. I took it to bits and cleaned it out and examined the jaws. I found they were worn along the gripping face. I tried grinding them (nothing to lose). I re-assembled the chuck and using a circular grinding stone in the tailstock chuck, set the main chuck so it just gripped the grinding stone lightly and ran the stone in and out of the chuck a few times, then closed it down very slightly. It worked amazingly well, but the grinding stone wasn't really good enough to do more. A diamond grinding point would be perfect, but soooo expensive. When I took the chuck to bits,I could see what was causing the old chuck to be a bit sticky when operating. Each of the pinion wheels were worn at the shaft end. Would be easy to put a bush in to take up the wear. The gear surfaces were fine. 
Overall really happy with the new chuck.


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## Rorschach (14 Sep 2021)

Looks good, have fun with it. See if you can get yourself some soft jaws for it, 4 jaws are very versatile with soft jaws as you can use 2 for gripping unusual shape objects.

Also, get yourself a mt2 arbour with myford thread on it, then you can put the chuck in your tailstock and use it as a self centring/cross drill drill jig for stock that is too large to spin in the headstock.


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## Sandyn (14 Sep 2021)

Rorschach said:


> Looks good, have fun with it. See if you can get yourself some soft jaws for it, 4 jaws are very versatile with soft jaws as you can use 2 for gripping unusual shape objects.
> 
> Also, get yourself a mt2 arbour with myford thread on it, then you can put the chuck in your tailstock and use it as a self centring/cross drill drill jig for stock that is too large to spin in the headstock.


Thanks I'll have a look for soft jaws.
can you explain the second part more. I understand the MT2 arbor in the tailstock and fitting the chuck. The drill in another chuck in the headstock.
The centres of the tailstock and headstock are the same height from the bed, So that places a limit on the dimension in that plane, but no limit to size in other directions. I don't get how I can get a cross drill when the centres of the headstock and tailstock are always in line?


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## Inspector (15 Sep 2021)

The usual way of fixing the jaws is to put a small grinder in the tool post and with it and the lathe running kiss the stone to the jaws and advance it in. Repeat until all jaws are cleaned up. The jaws need to be held in such a fashion as to preload them so the slack is taken up.

Pete


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## Rorschach (15 Sep 2021)

Sandyn said:


> Thanks I'll have a look for soft jaws.
> can you explain the second part more. I understand the MT2 arbor in the tailstock and fitting the chuck. The drill in another chuck in the headstock.
> The centres of the tailstock and headstock are the same height from the bed, So that places a limit on the dimension in that plane, but no limit to size in other directions. I don't get how I can get a cross drill when the centres of the headstock and tailstock are always in line?



Maybe this pic will help. The 4 jaw chuck would be used in place of the cross drilling jig. It is also self centring on any stock and holds it secure so much safer than the picture.


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## Sandyn (15 Sep 2021)

Thanks! This morning when I woke, out of the blue, I thought of a metal bar in the tailstock chuck and understood what you meant. Makes perfect sense now and a great idea.


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## jonn (15 Sep 2021)

Inspector said:


> As long as you learned what common sense was a long time ago and built on it. Some people's common sense is closer to nonsense but it make sense to them. Often a frightning thing to be around.
> 
> Pete


Read up on *agnotology*, something much practised in USA, and seemingly coming to UK. As to common sense, it might be common, but often doesn't make much sense.


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## Rorschach (15 Sep 2021)

Sandyn said:


> Thanks! This morning when I woke, out of the blue, I thought of a metal bar in the tailstock chuck and understood what you meant. Makes perfect sense now and a great idea.



I had a small 4 jaw SC with no backplate that I was struggling to find a use for so I decided to mount it permanently to an MT2 arbour. I use it in the headstock (with drawbar) or in the tailstock pretty much only for cross drilling stock. I also have made a little adaptor that lets me put a MT2 in my drill press table again so I can mount a lathe chuck there for drilling items too awkward to do in the lathe. Very handy.


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## Sandyn (17 Sep 2021)

jonn said:


> Read up on *agnotology*, something much practised in USA, and seemingly coming to UK. As to common sense, it might be common, but often doesn't make much sense.


Very interesting. I had a conversation some time ago with a flat earther. It was an interesting conversation, but I soon realised the guy was quite insidious His aim was to try and plant seeds of doubt about any argument I put forward. I'm not sure what the aim of these people is?


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