I do find though that they need a substantial tightening torque, especially if the
collet has to be closed towards its smallest size, with the effect being particularly
apparent with the smaller size collets. This is so much so that it borders on being
impossible to carry out any substantial machining if closing to ones minimum diameter
in this range. For this reason, I would not be happy using them for milling cutters,
especially if say holding a 1/4” (6.35mm) cutter in a 7 to 6mm collet.
Whilst the ER system was first envisaged as just having metrically sized collets,
imperial sized collets are becoming available at the smaller sizes, obviously to
overcome the situation. Even then, there is no absolute certainty that the cutter
will not be withdrawn from its collet. For this reason, I would recommend using a
chuck designed for use with threaded shank cutters.
For more details on ER collets and making a chuck for these for use on the lathe,
see my pages elsewhere on the site
With either of my two cutter chucks, when closing, I frequently just hand tightened
them without any major problem. However, I did find that if only taking a very light
cut there was insufficient load on the cutter to cause it to rotate in the collet
and tighten it fully. This resulted in the finish achieved suffering a little. I
do now just very lightly tighten them using a C spanner and it works perfectly, not
worrying that the cutter may be pulled from the collet or the need to use a substantial
torque to fully secure it.
Photograph 2 does show that I have made non slotted adaptors for holding the smaller
throw away cutters which do not have threaded shanks. However, as I have larger non
threaded shank cutters I made adaptors for these also. These are also designed in
a way to eliminate the possibility of the cutter being withdrawn when in use, see
Sk. 2. They work well as can be seen in Photograph 3 where a substantial cut, 8mm
deep x 5mm wide, is being taken without any problem and it was only lightly tightened
using a C spanner.
Whilst economy milling cutter chucks can now be had, one that covers up to 5/8"/16mm
and with collets for both metric and imperial sizes in the range 6mm to 16mm shanks
would still be expensive compared to the cost of the milling machine. I therefore
think that making ones own would still be worth considering financially, with an
interesting project as a bonus, for some also a useful introduction to some aspects
of using a centre lathe.
Details for making this cutter chuck with collets can be found in my book, “Lathework,
a complete course” number 34 in the workshop practice series.