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Clarkson, Osborn and ER

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john halfpenny12/02/2021 13:43:32
189 forum posts
27 photos

I couldn't find a clear direction from searching previous threads, so here goes. I have imperial Clarkson/MT3 and Osborn/R8 for my machines, which suit my collection of threaded cutters. I now expect to buy new cutters which will probably be plain shank metric. I am inclined to change to good quality ER metric, probably from ARC, with two new milling chucks, or perhaps just an MT3 with an R8 adapter for the mill. This will give me a wider range of gripping diameters, and I'll also add a couple of ER collets to suit my existing imperial cutters. I think ER will also give more versatility and allow me to use fixture blocks and the like.

Is there any good reason not to change, and to partially fund by selling the Clarkson and Osborn?

John Baron12/02/2021 14:02:24
488 forum posts
189 photos

Milling cutters tend to be standard sizes whether screwed or plain shank ! So I don't see any need to change to ER collets just to use them, particularly if you have the full set of collets for the Clarkson.

Clive Foster12/02/2021 14:13:07
2837 forum posts
103 photos


Seriously consider going for sidelock (weldon) holders. Decent quality cutters with suitable flats are readily available at negligible price premium over straight shank. Similar pull out resistance to threaded cutters and no need for the very high tightening torques demanded by ER systems.

Like you I mostly use threaded shank cutters. Although I bought an ER set early on it pretty much never gets used. My, relatively few, straight shank cutters almost invariably go in native spindle fit collets.

I'm slowly transitioning to sidelock having bought a set of holders. Any new cutters I buy have flats. Huge stash of threaded ones to use up.)

Sidelock holders always seem expensive in comparison to ER collet sets tho'.

One nice advantage is that you can have more than one cutter size mounted and ready to go. A great help when a job needs more than one cutter size. Especially if you have several of one part to do. Cutter projection remains the same when changing over which makes life easier when being creative with the zero position memories on a DRO set.

Arguably its worth having enough sidelock holders the one cutter of each size you use is set-up and ready to go.


Nigel Bennett12/02/2021 14:15:29
415 forum posts
11 photos

Carbide cutters - a very good reason to use ER collets. More expensive, perhaps, but you can remove a couple of sets of vice jaws (and a vice) before they need resharpening. (And yes, I did pinch that gag from Michael Oxley, who wrote in ME back in the 1950s)

Every time you use an additional interface between the cutter shank and the machine spindle you will introduce more eccentricity or runout. Hence I would go for a bespoke MT3 plus a bespoke R8 collet holder if funds permit.

You shouldn't need much in the way of "Imperial" ER collets because the metric ones will do admirably. There was a chap complaining on here a while back that he'd bought a set of "Imperial ER collets" to find that most of them were simply the nearest metric equivalent, some being +0,5mm on integer millimetre sizes - 6,5mm for 1/4", for example.

Dave Halford12/02/2021 14:19:33
1746 forum posts
19 photos

Only that the ER system requires a lot more force to tighten, you cant just nip them up like the osborne / clarkson chucks.

Thor 🇳🇴12/02/2021 14:41:24
1413 forum posts
41 photos

Hi John,

If your new cutters will be HSS, Tracy Tools still have threaded shank cutters (both imperial and metric) that should fit your present Collet Chucks. If you want tungsten carbide cutters they will probably be weldon shank. Where I live threaded shank cutters are very hard to find so I use ER collets to hold my milling cutters (and round stock in my lathe) and I have never had any problems.


john halfpenny12/02/2021 15:10:35
189 forum posts
27 photos

I don't have any metric collets, and the cost of getting them for one chuck would seem to get a full set of ER. I also like the idea of holding round stock in the lathe, which has an MT3 spindle bore.

Nigel McBurney 112/02/2021 15:26:34
923 forum posts
3 photos

I was trained on Clarkson,at that time they were the preferred cutter holder,they just did not slip or pull out, Much later on I had 2 large mills at home On the universal mill I always used Clarkson holders and arbours. on the turret mill I had Clarkson and Bristol Erickson collet holders, the latter were quicker to change.I downsized in recent years to a single Omnimill so went from 30 int to 3 MT and a small Clarkson came with the mill,I tried some ER collets and found that they had a wide gripping range and a much better grip, I have retained my Clarkson holders and use them on jobs where if a cutter did pull out and wreck the job it would be a disaster.I still take on vintage work for customers so cannot take the risk of a cutter slip. The ER collets also grip plain shank carbide cutters and any drill size within the range of the collet.

Neil Wyatt12/02/2021 16:09:05
18777 forum posts
733 photos
80 articles

I bought my Osborn about 10 years ago.

Others commented that I would hardly use it as I had an ER25 chuck.

I've used it... two or three times. Its main disadvantage is that it is huge compared to an ER25 chuck.

Don't expect to get a lot of money for one, I only paid about £30 even then.


old mart12/02/2021 16:42:43
3347 forum posts
208 photos

The er chuck will be able to hold most threaded shank cutters you have. There are a lot of Clarkson and some Osborn holders on ebay at the moment, many overpriced. It would be worth checking out the prices and aim to pitch a bit lower for easy selling. I have two R8 osborn Titanic II holders in new condition for up to 5/8" and 16mm shank as well as a lot of cutters, and they come in handy from time to time. I also have er25 R8 which hold up to 16mm shank, mostly solid carbide which gets used most often. If you also have a lathe,it might be better to get er32 and then you could buy an er32 holder to mount on a backplate and share the er system between two machines.

Hollowpoint12/02/2021 17:37:42
442 forum posts
56 photos
Posted by Dave Halford on 12/02/2021 14:19:33:

Only that the ER system requires a lot more force to tighten, you cant just nip them up like the osborne / clarkson chucks.

Yes, a ball bearing type collet nut helps with that.

john halfpenny12/02/2021 20:33:00
189 forum posts
27 photos

Thank you for your comments. I have a few things to think about.

Nicholas Wheeler 112/02/2021 23:29:44
740 forum posts
51 photos

I bought a Clarkson clone when I first got the mill. But it didn't come with a full set of imperial collets let alone metric ones, which was limiting. And you need threaded cutters. So I bought an ER32 chuck and set of collets for about what I would have spent on the rest of the collets.

I soon gave the original chuck away as it wasn't just limited in size, but is more of a pain to use.

other things to consider:

the ball-bearing nuts make tightening much easier

square and hex collet blocks make lots of small workholding easier, and their indexing capability is equally handy

ER collets are cheap enough that it's worth having some extras to match your commonly used cutters

colin hawes13/02/2021 12:56:18
543 forum posts
18 photos

I favour the ER collets for a light machine they can hold any tool with a parallel shank. Colin

Brian H13/02/2021 13:06:47
2230 forum posts
113 photos

I have a set of metric and a set of Imperial ER32 collets mainly for use on the vertical mill as I can hold metric cutters in the spindle and Imperial material in chucks on the mill.


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