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Stevenson's ER32 Collet Blocks

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Collet blocks are used to simplify the milling of square and hexagonal shapes on round bar. The block use standard ER collets and are available in ER25, 32 and 40 sizes.



If you are like me and don't have a collet chuck on the lathe you can mount the hex block in the 3 jaw lathe chuck or the square block in the 4 jaw chuck. The accuracy of the set up depends on the accuracy of the lathe chuck. Fortunately mine is pretty good. By using the collet chuck I can hold smaller diameter bar (down to .040") and of course I avoid the jaws damaging the bar.


I bought mine from www.arceurotrade.co.uk - they ship abroad.






Edited by KeithAug
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Levin, Hardinge and other manufacturers of watchmaking lathes have been selling such collet-blocks for a long time. They come together with a sort of V-block for simple grinding, sawing, or milling operations in the lathe:



Picture borrowed from http://www.geocities.ws/dushang2000/Horology/Lathe Tools/Lathe Tools.html, as I was to lazy to take a picture of my own set.


These blocks can be used with collets as well as the various types of chucks. I also use them, of course, in the vice on my milling machines. In the picture you see at the end a knurled wheel. This is not the draw-bar wheel, but sits on a fine thread at the back of the holder and thus forms a finely adjustable depth-stop.


Some time ago I got some hexagonal bar-stock and plan to fashion a hexagonal collet holder from it, when I have time ...


Incidentally, many year ago I also fashioned an upright collet holder that clamps to the table of the mill:





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Personally, I would not put a collet-block into a lathe-chuck. If you are looking for something to hold smaller diameter stuff and can't exchange the 3-jaw-chuck on the lathe with a collet-chuck, or if you lathe spindle doesn't have a taper to take in collets, I would use a round collet-holder like this one seen in a random ebay-offer:



There are literally dozens of offers. They are too long to be taken into a 3-jaw-chuck, but you can shorten them using an abrasive disk or even on the lathe itself with a carbide cut-off tool. They start from ER8 collets upwards and cost from 6€ upwards.

Another option would be to fashion the blocks oneself from square or hexgonal stock. The threaded clamping nut is a bit special inside and is best bought in.

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You need to think about getting something with a decent sized hole through it to take longer stock. Not all round collet holders have a decent bore. The ER collet blocks work fine in the lathe chuck if you are wanting to quickly mount something that isn't going to damage a finished surface of softer bar stock such as aluminium or brass (the 3 jaw chuck can damage these quite easily). If you don't want to go through the bother of dismounting and remounting the chuck then the collet blocks are a quick and easy solution and do have a decent bore. It isn't as accurate as a collet chuck but I checked my set up and can get concentricity of better than .002" which is good enough for most of what I do. I do have a collet chuck which I use for more accurate work. If you need smaller then you can get ER25 versions. 

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