Before long you'll want to chuck a bit of bar longer than an MT2 finger drawbar collet will take – remember that the standard drawbar is 3/8 too so that's the max size of the hole. Myford pattern collets are better but very hard to find and expensive, though you can make them (see recent thread on here somewhere). They use a closing nut that pushes them into the taper socket, they are bored to nominal size right through. Any finger collet of this sort only works on a very small range of stock diameters near the nominal size.

The same limitation on diameter/lengthapplies to ER (what are ERC?) collets on a taper shank. Save those for milling. They also stick out a lot for turning in my experience.

Easy to make a backplate for a front-mounted ER collet chuck – actually you can make the whole chuck in situ yourself for precision, only have to buy a closing nut.

If you go for ER40 it'll take bigger stock, but except for short bits you'll be limited by your spindle bore. Which is more useful for you – length or diameter?

I have a set of Myford pattern collets built up over the years; a full set of imperial and metric MT2 finger collets I bought rather mistakenly but sometimes are useful; and an ER40 chuck I bought from the old Myford (I have a large bore S7 so the larger diameter is useful, and for smaller stock I have the MT2 collets.  I probably use the ER40 more than the MT2 Myford collets, and more than the 3 jaw chuck.

Edited By John Haine on 05/06/2020 17:32:10

Hi Luke,

I would recommend an ER chuck that mounts on a backplate – something like this. I made an ER 32 chuck that mounts on the spindle of my small lathe, ER 32 because I already had some ER 32 collets. The chuck can take long bars up to 20mm dia. and has good repeatability. With an ER chuck that mounts on a backplate you can easily move the chuck to another lather if you decide to upgrade the ML4.

Thor

Not answering the actual question, but I'd put purchase of a decent 4" SC 3 jaw chuck as a far higher priority than collets. Much more versatile for general work IMHO and avoids the hassle of changing collets at frequent intervals. Accuracy for 2nd. ops. should be good enough for most work and there's always the 4-jaw as a fall-back.

If I did eventually go for collets, I'd not be keen on 2MT with drawbar, as being too restrictive in workpiece length.

A 3 jaw self centering chuck is unlikely to provide concentricity much better than 0.005"

It will probably hold a wider range of round or hexagonal material, reasonably concentric, than an expensive range ER collets.

A 4 jaw independent chuck will allow you to centre work (or to deliberately run it eccentrically if you so wish ) as accurately as you are your DTi can measure.

This will hold square, octagonal or irregular material concentrically, if that is your wish. Again the maximum size that can be held will be greater than ER40 collets.

No matter what chuck you fit, the 2MT bore will limit the maximum size of material that will pass through the Mandrel to about 1/2".

Buying both a 3 and a 4 jaw chuck is likely to be less costly than a full range of ER 40 collets.and a Backplate.

A conventional chuck will allow you to hold larger work than you can in an ER 40 collet chuck.

ER collets will allow you to hold Metric, or |Imperial material, as long as the difference in diameter does not exceed 1 mm (0.5 mm for the smallest collets )

The choice is yours, dependent on the budget. All three types have their uses, and so are present in my shop, The ER collets are used in the Mandrel, and the Tailstock of the lathe, as well as on the Mill, for work or toll holding, when the need arises.

HTH

Howard

You could do a lot better than 5thou but not if you buy cheap chucks, I get less than half a thou runout on my 3-jaw, less if I use the soft jaws.

I would get a decent 3-jaw SC before looking at collets.

I run a 125mm Bison 3274, Another member tipped me off a couple of years ago for some NOS selling for £100 which was a bit of a bargain, Rotagrip will want £500 for one at the moment, I did get the soft jaws from them. It is mounted on the original Warco backplate that the supplied 3-jaw came on with no modification and the dti shows just over one division of a 0.01mm dti.

Also have a 160mm Bison slim bodied 4-jaw that was second hand.

When I do use collets on the lathe I use 5C mostly unless I don't have the size then use a 5C to ER32 adaptor.

Like most things you get what you pay for, very cheap can be pot luck, mid range should be OK and top shelf stuff should be good.

2MT collets – in a small milling machine these provide lots more headspace compared to an ER collet chuck, but this may not be such a good thing on your ML4 – a classic British gap bed lathe.

Small work may not project far enough from the nose of the spindle to be machined without the saddle hanging in mid air over the gap.

ER collets of either size will project more in their chuck and be more useful, and they also allow a (limited) range of sizes to be held in each collet unlike a MT2

Edited By Nick Clarke 3 on 05/06/2020 20:59:41