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Harold Hall

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Cutter chucks

Whilst milling can be carried out with just a lathe as supplied, typically milling the flat in Photograph 1, some additional items are really essential for more advanced work. Absolutely essential is a milling cutter chuck, as using a drill chuck, or the three jaw chuck, is a very risky approach. The problem is that the helix angle of the cutter attempts to, and very frequently does, draw the cutter from chuck even with a very light cut.

 

My preference is to use the type of collet chuck where the threaded end of the cutter shank is screwed into a matching thread in the base of the collet. With this method the cutter remains in the same relative position to the workpiece even if the cutter rotates as the end of the cutter is in contact with the base of the collet housing. Because of this, it does not run the cutter into the chuck but pulls the collet forward tightening it further.

 

Collets having a very gradual taper, typically the ER series or those based on a Morse taper, are also used with plain shank cutters and are capable of a substantial grip. They do not though have the absolute certainty of holding the cutter's position in use.

 

Chucks with a Morse taper shank, or similar, must be secured with a draw bar through the machine's spindle. This, because the cutter's helix can draw the chuck from its mating taper with potentially disastrous consequences.

 

As an alternative, collets that have a Morse taper body, Photograph 2, and are drawn into the taper with a draw bar have the advantage of minimal overhang from the lathes mandrel, as a result, improving rigidity. Also, being more compact,Photograph 3, there is more room for the workpiece, etc. which may be of use occasionally on the smaller lathe. However, on the down side, the end of the drawbar will need a tap with a hammer to loosen the  cutter and some owners may not like to submit the lathe's bearings to this force.    

 

Cutters are made with a number of shank sizes and in the home workshop this will normally mean 6 mm, 10 mm and 12 mm. Sixteen millimetre may also find a use so it is worth acquiring a chuck that will cope with that size if funds will run to it. Twelve millimetre collets will take cutters up to 14 mm and 16 mm collets up to 20 mm. Imperial sizes are 1/4", 3/8", 1/2" and 5/8" with similarly oversize cutters.

Metalworking

Workshop Processes

Milling on the Lathe
Morse Taper Collets.
Milling on the Lathe
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 1

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 2

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 3

All pictures can be clicked on to provide a larger view