August 2019 29
Milling for Beginners
The items featured in this series are
available from Arc Euro Trade, http://www.
arceurotrade.co.uk, who also sell the X
series of mills.
See the accompanying thread on
Model Engineer Forum http://www.model-
engineer.co.uk/mfb for more
discussions about this series.
Video Link http://www.model-engineer.
co.uk/mfb 1Which allowing for the fact the dividing
will be exact and my calculator has rounded
things up very slightly will give an exactly
equal spacing.
Putting that into practice aft er removing
the hand wheel the correct plate with the
21 hole pattern is mounted onto the rotary
table and then the dividing handle fi tted
to the worm and the detent positioned
along the handle so that it lines up with the
correct ring of holes, in this case the second
ring from the middle.
Wind the table around to where you want
the fi rst hole or cut positioned and let the
pin of the detent drop into the nearest hole.
Loosen the two arms and bring one up to
touch the pin on the opposite side to the
way you want to rotate the handle. Then
move the other arm so that you have the
required number of holes between the two
arms, don’t make the mistake of counting
the hole with the pin in it as one of the six,
you actually need seven holes - one for the
pin and six empty holes, lock the two arms
together when you have then set correctly,
photo 156.
You can then make your fi rst cut. When
this is done pull the detent out of the hole
and turn the handle carefully counting ten full
turns from where it was and then put it back
in the hole adjacent to the second arm which
will be the additional six holes, photo 157.
Follow this by rotating the pair of arms in the
same direction that the handle was turned
until the fi rst arm touches the pin. You can
then make your second cut, photo 158. and
carry on like this. For your fi rst few attempts
it would be wise to put a fi ne pen or point in
the mill and use that to mark each position to
check you have things correct and return to
the same starting point as nobody wants half
a hole or gear tooth, photo 159.
I have done a short video which shows the
above procedure, there’s a link at end of this
article.Compound and Electronic
Dividing
Looking at the charts that come with
dividing heads and rotary tables you will
see that not all divisions are possible with
the supplied dividing plates, in these cases
it may be possible to work out the required
number of holes and make a custom plate
but another way around it if you have a
dividing head is to use what is known as
compound dividing. This involves using a
hole plate to drive the worm via a train of
gears instead of directly which increases the
possible combinations to give the number
of divisions wanted.
In more recent times the use of
electronics to send a signal to a stepper
motor that is used to drive the worm hasbecome more common and due to the small
increments that the motor can be rotated
gives a similar eff ect to compound dividing
but with the bonus of letting the controller
do all the maths and it does not over or
under wind the handle or loose count part
way through.
To fi nish off this part of the series I have
included a couple of photos of a typical
setup using a rotary table to cut gears.
When cutting small gears, the chuck can
get in the way of the cutter so the blank is
best mounted on an arbor so it can be held
where the gear cutter can pass right across
unimpeded. If just cut like this the work
would fl ex away from the cutter so it is
usual to use a tailstock that can be bought
as an accessory for most rotary tables to
support the far end of the arbor, photos
160 & 161. ■158 159
160 161
Arms moved ready to start the next sequence 7 holes drilled and ending up inline with the fi rst hole
Typical set-up for cutting small gears Close up showing cutter clear of work and chuck