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.

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.

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.

Thor

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.

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.

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