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Replacing a Clarkson 'autolock' chuck with a standard ER collet chuck?

Help please

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Dave Bullock MBE23/10/2019 16:02:12
6 forum posts
7 photos

autolock chuck arrowed.jpg

HI experts,

I have just inherited a very old C1903 horizontal milling machine with a vertical conversion.
The problem I have is that it has a Clarkson Engineering MT2 taper "Autolock" chuck (pictured). I would like to convert it to a standard ER collet chuck to be compatible with the collets used on my lathe.
However as you see the Clatkson chuck has two machined flats (arrowed) that mate with corresponding slots in the end of the milling machine's quill. The two 'lugs' on the end of the quill fit neatly over the flats on the chuck allowing the taper to tightly mate with the female taper in the quill.

I think therefore that the 'lugs' on the end of the quill will prevent a standard ER type collet chuck from fully entering the female taper?

So ..... has anyone found an ER type chuck (maybe ER25) that has the machined flats?
An ER collet chuck with enough material in the body that would allow the flats to be added without breaking through into the collet cavity?
Any bright ideas/advice please?
Thanks in anticipation ...

old mart23/10/2019 20:25:42
1519 forum posts
136 photos

Too much bother, you could sell the Clarkson and get a MT2 er25 which goes to 16mm. It should not need the locking flats. Only buying one and fitting it will allow you to find out if it is viable. It wouldn't cost much to prove it one way or the other:


 I have an er25 MT2 which I could measure to give some idea if adding those drive flats would be feasible, but it is difficult to judge exactly how deep the tool goes into the spindle. Hopefully, I will remember to measure it tomorrow (Thursday).                                                                                                                                                                          Your Autolock is a rare bird, and may have been made in this form just for that one make/ type of mill.

Edited By old mart on 23/10/2019 20:42:01

Edited By old mart on 23/10/2019 20:44:34

Neil Wyatt23/10/2019 20:44:31
17712 forum posts
697 photos
77 articles

If push comes to shove, make an ER25 holder from an MT2 with a blank on the end and machine the two flats.

I'm pretty sure you could machine the flats on a standard MT2 ER25 holder, they typically have spanner flats there already.

colin vercoe23/10/2019 21:11:31
32 forum posts

Hi I have a mill with MT3 spindle and driving flats also, which will still accept all other MT3 tooling. It is the collet chuck that has extended driving flats down the MT shank and not the spindle, Also worth considering the Clarkson is an industry standard with positive locking and will not slip in the spindle.

peak423/10/2019 22:38:09
1075 forum posts
124 photos

Your Clarkson Autolock looks different to my "C" Type one. I wonder if its been modified, particularly if the V. Head is home brewed.
Where yours is turned down from the main body size, and then further machined with the flats, mine is full diameter and sporting a left hand thread with a nut to act as an ejector.

I'm sure, as Neil mentioned above, you could duplicate the spanner flats on a cheap MT2 ER25 holder.

Quick edit as tea's ready;

See This Thread, which I've not fully read yet, and This One which show chucks with the same flats as yours.

Also, it looks like the particular Clarkson chuck you have, it appears to be a "C" Type, has the advantage that it will also hold plain shank cutters.



Edited By peak4 on 23/10/2019 23:14:16

David George 123/10/2019 22:40:29
1189 forum posts
405 photos

At a previous job we had a jig borer that had similar shank but the spindle had an English thread in the end you need to consider the whole fitment if you can get a drawbar to fit I believe that you can mill the flats on the ER chuck to suit.


Dave Bullock MBE24/10/2019 10:04:52
6 forum posts
7 photos

Hi everyone, many thanks for your super replies.

Yes my chuck is like the ones in your link, (Peak4) the collets have the two small 'lugs' on the opposite end to the tapered 'nose'. I am beginning to get a sense that the Clarkson chuck is quite an asset and that I should maybe try to persevere rather than swap to ER collets? Problem is that I don't have a great selection of collets.
Going back to my ER swap idea....
My MT2 taper matches exactly the true dimensions published for an MT2 taper so that's good. However if you look at the attached picture you will see that the end of the quill has slots (creating a pair of 'dogs' that fit the the flats on my chuck. This means that the female taper starts inside the quill beyond the length of those two 'dogs'. A standard MT2 ER chuck taper will be prevented from mating fully because the dogs will strike the back of a standard ER chuck. before the taper mates, requiring those flats to be added to the chuck.
Looking at the ER chucks available on line, the chuck body doesn't look long enough to machine the flats without breaking through into the collet cavity?

quill.jpgI look forward to your further comments....Thanks...Dave

P.S. does anyone recognise my milling head below?


IanT24/10/2019 10:13:45
1499 forum posts
142 photos

Looks like a Dore Westbury Dave


PS I'd keep the Clarkson too....

Edited By IanT on 24/10/2019 10:15:13

thaiguzzi24/10/2019 10:24:56
688 forum posts
131 photos
Posted by IanT on 24/10/2019 10:13:45:

Looks like a Dore Westbury Dave


PS I'd keep the Clarkson too....

Edited By IanT on 24/10/2019 10:15:13

+2. I'd keep the Clarkson too.

Dave Bullock MBE24/10/2019 10:45:48
6 forum posts
7 photos

p1080214.jpgHi IanT

Wow! it does.

I thought it was a homebrew device engineered by the previous owner who made several super steam locos.
The whole machine looked a bit Heath Robinson until I got it home and started reassembly. I then realised that both horizontal and vertical milling functions had been preserved making the machine really versatile.
It's an Alfred Herbert (Coventry) machine from around 1903 and still going strong


Dave Bullock MBE24/10/2019 11:21:20
6 forum posts
7 photos

Here's a picture from a different angle before the strip down and relocation.
You can see why I thought it seemed Heath Robinson...... an HSE's nightmare LOL!

I managed to strip it all down but was thwarted by the two items arrowed below.
There is a compound pulley 'lay-shaft (Orange arrow) feeding power to the main horizontal milling shaft (arrowed yellow).
I had to leave this in situ as I couldn't figure out how to release the Vee belt between the two?

The layshaft (blue assembly) has a rotating pulley assembly and tensions the belt to the main shaft with the lever with the red knob.
I couldn't see how this lay-shaft shaft is removed from the blue adjusting assembly
Similarly I cant see how the main shaft (yellow) is removed from the body of the milling machine.
I could do with knowing the answer to this secret just in case I ever need to replace the Vee belt?

Does anyone know how these disassemble please?

Thanks everyone for your interest and great advice.
I will persevere with my Clarkson chuck.


peak424/10/2019 14:57:00
1075 forum posts
124 photos

Dave, yes that's a Dore Westbury Mk1 head you have there. Quite a neat idea with the slot to save anything spinning in the MT2 bore.
I'm almost certain that the thread will be a Myford nose thread, the same as a Super 7 etc.

Whilst it will be more expensive than a cheap imported MT2 ER25 collet chuck, I'd consider one designed for a Myford, intended as a lathe collet chuck.

More rigid by quite a long way; It's what I fit, when I want to use ER25 collets in my DW Mill

Also has the advantage that no drawbar is required, so less chance of something stuck in the taper, if one is a bit over enthusiastic with a spanner.

There are other suppliers, but Here's an example. In the ideal word, it would help to have a friend with a Myford to fit the two parts together correctly on the register.

I'm off out now, but I'll try and come up with a photo later today or tomorrow when it's raining.




Edited By peak4 on 24/10/2019 15:06:14

Edited By peak4 on 24/10/2019 15:07:54

old mart24/10/2019 18:52:58
1519 forum posts
136 photos

I have some dimensions of the MT2 er25 collet holder that I have. It is one of the cheap Chinese ones from ebay. The 0.7" large end could be compared with that same diameter on your Clarkson to get a reasonable idea of how deep it will seat. There is some scope for adding flats, although the milling might require carbide cutters. I used solid carbide endmills to put spanner flats on both of the R8 er25 collet holders that I bought before it was common to include the flats from new.


Edited By old mart on 24/10/2019 19:00:03

Dave Bullock MBE24/10/2019 19:24:44
6 forum posts
7 photos

Hi Old Mart , my taper is 0.7" right at the point where it joins the chuck so would have to fully enter the quill. However the flats would have to be 0.2" wide and looking at your diagram would almost certainly break through into the collet 'cavity' in the chuck. Whether this would foul the collet or whether the straight section at the base of the cavity is 'free space' I am not sure?

Hi Peak4 I had not considered screwing something onto the end of the threaded end of the quill. I can check the thread compatibility as my lathe is a Myford 7. It would make an easy switch to try but I am not sure how true the chuck would run just screwed onto the thread? Maybe there is a referene face it can tighten up against. I will have to look.

Thanks chaps...

old mart24/10/2019 19:38:07
1519 forum posts
136 photos

That peak 4 suggestion sounds promising regarding the spindle nose threads.


As for the lack of enough metal in that collet holder, it is the only one I could measure. There may be others with greater lengths, but it would be a lottery whether they would work, I will see if my R8 ones have that 0.733" bore in them.

Edited By old mart on 24/10/2019 19:45:48

Vic24/10/2019 20:17:24
2489 forum posts
14 photos

I can’t help but would like to say it’s really nice to see an old machine like that still working, albeit modified for the modern world.

peak424/10/2019 21:04:07
1075 forum posts
124 photos

Dave, personally I'd go for the smaller ER25 collet chuck than the one Oldmart linked to, as it's just less cumbersome as well as being cheaper.
A less expensive one to that which I linked to earlier, is available from Chronos, but I've no idea of the quality; they also supply it in a kit with collets, if you don't have any already. This looks to be a one piece version with no machining to complete. Either would then fit onto an MT2 arbor with a pre cut Myford spindle nose. I have one of these as well as a parallel to Myford arbour. The latter might make tool sharpening easier too, should you ever obtain a tool cutter grinder.

If I was in your position, I wouldn't modify either the mill spindle, or your Clarkson Chuck. Since you've got a Myford, the ER chuck I linked to earlier would seem the best option, if finances allow.

Looking at your earlier photo, I'd say your spindle has both the Myford thread as well as the circular register behind/above it. Certainly that was the original design. I've even used a conventional, Myford fit, 3&4 jaw chuck on the mill to hold a large fly cutter.

I'd certainly look to getting one with a ball race closing nut, rather than a plain one, as shown in that link. Collets for the C Type do come up on ebay and at car boot sales/autojumbles. Note, they are not interchangeable with either the S Type or Osborn ones.

My chuck came with just imperial collets; so to start with, I made my own metric set, even those are 20TPI, so a 1/4", 3/8", and 1/2" imperial taps were used to cut the threads in the 6mm, 10mm and 12mm. I was struggling for something to use for a 16mm 20TPI, so in the short term I used a plain home made collet until a proper 16mm one turned up at a steam rally.

Apologies for the poor photos to follow, but they were just quick grab shots, as we're off out to Wetherspoons for a curry soon.

Here's my version of the Clarkson C type with the left handed nut at the top.

Note the little slug at the left hand end. It's 3/8" WW external to fit the drawbar hole in the taper, with a 6mm hole in it to fit the smaller draw bar in the DW mill spindle. I also have a 6mm/10mm one to allow the use of cheaper imported MT2 blanks, which come tapped M10, rather than 3/8.

collet chuck 01.jpg

And fitted to my DW mill, with the nut removed as it's just a bit too thick for this application.;

collet chuck 02.jpg

Next for a height comparison, the same 10mm threaded Clarkson cutter in an MT2 ER25 holder.

collet chuck 03.jpg

Followed up with the ER25 collet holder on a Myford nose; in this case a Warco 720 Super 7 copy.

collet chuck 05.jpg

And on the mill

collet chuck 04.jpg

Just for comparison, the same mill in an MT2 Clarkson S Type, the release nut just fits on this one.

collet chuck 07.jpg

And an MT2 Osborn Titanic

collet chuck 08.jpg

The ER chucks and the Clarkson C Type will hold plain shank cutters without modification, The S Type and the Osborn need a little slug making to enable the chuck to tighten up the collet on the shank of the mill.
All will hold threaded end mills, but only the ER type will easily hold double ended ones.



Edited By peak4 on 24/10/2019 21:25:55

old mart24/10/2019 21:04:11
1519 forum posts
136 photos

For potential fitting of a Myford backplate onto the spindle, there is a shoulder just below the spanner flats. You could make a tubular collar for the backplate to tighten onto. Unfortunately the backplate will have to be machined in situ on the mill for it to run true, an easy job if you think of a vertical lathe and hold a lathe tool in the milling vise. Expecting the backplate/ collet chuck to run true if you were to fit it on the lathe is very long odds against. The mill and the lathe would each have to have their own backplates, but could share the collet plate.

I bought a 9" faceplate on ebay very cheap, for the Smart & Brown model A. I knew what it was by the casting number on the rear. I cleaned everything and set up a tool to skim it on the lathe, and something got into my head that I should check it first. It ran 0.0005" tir, so the skim was cancelled.

The RDG collet chuck and backplate is a very good buy, and as mentioned, more compact than my link.

The Tom Senior Light Vertical mill which we have been working on has been converted from MT2 to R8, it came with their version of a Clarkson Autolock for screwed shank tooling, it has a threaded collar at the top which is tightened against the end of the spindle. This stiffens up the rather flexible MT2. I wasn't happy to use MT2 which was why I converted it to R8, also to use all the R8 tooling that we have.

Edited By old mart on 24/10/2019 21:22:33

Nigel Graham 224/10/2019 21:25:26
581 forum posts

That looks a fine machine!

To answer the question... I advise continue using the Clarkson. As I believe someone noted on another thread recently, it gives a strong grip and positive end-location for the cutter. (A back-stop, yet!) Milling-cutters and FC3 cutter-holders have that tail-end thread for a very good reason.

A through-collet has some risk, albeit fairly low, of the cutter slipping back. That would not help machining accuracy though at least the resulting depth error is usually on the safe side so can be corrected. Worse though, slipping cutter shanks and the likely resulting hefty re-tightening are not good for the health of precision-ground collets and collet-chucks.

A cutter held by friction alone in a spring-collet can in certain circumstances, slip by winding itself down into the work... and perhaps even through the packing and into the machine table until the changing swarf suggests summat up. (Ummm, yes..., on my previous, Warco mill-drill; despite using the Autolock; but because I had unwittingly failed to engage the cutter thread.)

I have had cutters slip in R8 collets on my Myford VMC, luckily upwards, so now normally use those collets only for very small cutters, alignment tools and centre-drills.

Trying to maintain accessory interchangeability between machine-tools is an entirely laudable aim, but needs considerable discretion. Tool- and work- holders are designed the way they are for a reason. Whilst I accept they are used as cutter-holders and no doubt by far better craftsmen than me, I regard the ER collet and similar (e.g. the Myford spindle-collets) as a work-holder for small-diameter turning and dividing.

thaiguzzi25/10/2019 16:20:10
688 forum posts
131 photos

To the OP;

that is one very attractive milling machine. Congrats.

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