All threaded endmills to the Clarkson standard are 20tpi Whitworth irrespective of whether the diameter is imperial or metric. There used to be other sorts of threaded endmills but the Clarkson standard is by far and away the most common, athough industrially it is pretty much obsolete.

There are two types of Clarkson Autolock collets, the older C-type and the newer S-type. The C-type has two spigots on the end of the collet. The S-type has a parallel flange on the end of the collet. They are incompatible with each other so make sure the type of collet holder is known.

When a Clarkson Autolock chuck is closed properly there should be no gap between the holder and the collet closer.

Andrew

I don’t think anyone has mentioned it yet, but the Metric Autolock Collets are easily identified by the presence of a circumferential groove.

… at least I thought-so until I saw this:

https://www.ebay.co.uk/itm/362620208556

MichaelG.

Michael,

Sadly all my Autolock collets (Vertex) with the exception of the largest sizes (5/8 and 16) have a rather wide circumferential groove (see Peak 4’s illustration above) in both imperial and metric sets. So it seems that identification by groove is not universally applied, mine are etched with the size on the body. All are 20 tpi though as Andrew says.

Well if appears you were taught incorrectly, see original Clarkson instructions

https://www.denfordata.com/bb/viewtopic.php?t=1057

This is also worth a squint for those unfamiliar with the damping ring[ can’t remember where I found the photo

See Here for the patent for the later chuck
https://worldwide.espacenet.com/patent/search/family/010277453/publication/GB915713A?q=GB915713A

and an earlier one
https://worldwide.espacenet.com/patent/search/family/035523252/publication/CA414067A?q=pn%3DCA414067A

Bill

Also think about what cutters are available, as Andrew says screwed shank are just about obsolete for commercial use so there will be less NOS to come buy and you will be limiting yourself to traditional cutters as the manufacturers simply don’t make screwed shank cutters now except for a few odd ones. If you want to use non ferrous specific cutters or maybe carbide then you are very unlikely to find them with screwed shank.

Also make sure anything you pick up second hand is sharp (unless you like sharpening) as most loose cutters on second hand stalls will have been used, bit safer if still boxed. Add to that the price you can buy half decent cutters for and the threaded option starts to have less appeal.

As Jason says threaded cutters are getting harder to find so committing yourself to a Clarkson as your forever system when starting out today isn’t a good idea. But if you have a Clarkson holder and collets then use what you have for now and figure out what will be best for you in future. As you only have imperial collets it may still be worth picking up the metric ones if the price is right.

Just accept that it’s temporary measure and that some time in the future you will change.

But nowt so permanent as a temporary measure.

I wonder how many milling cutters a Model Engineer / Home Workshop guy / gal gets through in a hobby lifetime. I took the opportunity to grab “lots” at low prices when I got serious about a milling machine maybe 30 + years ago. Most are still unused. Which is why I’ve never got my act together on cutter sharpening with the Clarkson. Back then retail prices for cutters were much higher in real terms than they are now so “grab anything that might be needed” when opportunity knocked was a good strategy. Today “buy when you need” is viable for hobbyists. I have a ton of stuff I shall probably never use but the economics still made sense. Back then!

I’d be unsurprised to discover that careful buying could net you a decade or twos worth of screwed shank cutters for less than the price of an ER collet and holder set. In that situation sorting out one of the simpler end sharpening jigs might be a sensible way of getting the best value out of your investment.

If I were starting out now and was sure I’d not be changing to a mill with different taper in the spindle I’d be tempted to copy the CNC folk by getting a bunch of side-lock “weldon” holders so I could leave a set of cutters permanently mounted and ready to go. Hobby time is precious and changing cutters in a collet gets old. I see no reason why the ends couldn’t be sharpened on one of the simple devices whilst still in a weldon holder.

I bought an ER 25 collet set early on only to find that I pretty much never use it. My Clarkson clone (posilock) native R8 collets and weldon holders do all I ever need. Nothing wrong with the ER system. It just doesn’t have a work niche for me.

Start slowly and don’t commit before you know what will work for you. The cutters and the Clarkson will still work just as well after should you switch systems so its not as if you are really loosing anything.

Clive

Though it’s nice to be getting some collet chucks with the machine you might find it useful to buy an ER collet chuck (ER25 or 32) with an appropriate shank as that will take all the threaded cutters as well as new non-threaded.  Or/and as Clive suggests if the shank is R8 some R8 collets.

On 18 May 2024 at 11:26 Andrew Johnston Said:

Annoyingly I can’t lay my hands on my Clarkson instruction card.

You left it here: https://www.model-engineer.co.uk/forums/topic/clarkson-autolock-help/#post-467791

Check the lost property department for the hammer you mention as it has been mislaid.

A little late but I photographed my chuck and instructions this afternoon so hope its helpful