Model Engineers’ Workshop – July 2019

July 2019 69

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Cutter Grinder

110

Fit with single csk. 12

screw from underneath

This edge must

be in line with

centre of hole

To fit saw

mounting pillar

Outside profile is

cosmetic & for

clearance of

wheel guard

Cut out for clearance,

extended length for

fixing ease

M.S. 10 x 12

27

25 x 25 x 12

20 x 25 x 12

16 x 3

4 x M5

csk. from

below

Aluminium plates

180 x 65 x 12

Setting Jig For 4 Facet Drill Grinding

Slitting Saw Setting Plate

Setting Jig For

End Mills

Setting Block With Loose Mounting Hole

See text

it a slight twist. Don’t let it rock. Any
adjustment in the contact will be obvious.
As an alternative, if you have an existing
ER chuck for the lathe, the top slide can
be pre-set at the angle using the dti in
existing socket before commencing work
on the screw thread. This is what I did, and
the result was right fi rst time, photo 3.
When the angle is correct, face the end
until the end is 25mm from the shoulder of
the ¾” shank then re-bore the socket and
so that the collet projects 11.5 - 12mm from
the face of the embryo holder. Doing it this
way gives you plenty of margin for error.
Screw cut the thread to 1.5mm pitch,
photo 4. If you have an imperial Myford
lathe, change the gear on the tumbler
reverse cluster to a 34 tooth, and set
the gearbox to cut 24 tpi. This will cut a
thread with pitch error of 1 micron. The
collet nut itself is not worth making, it’s
complicated machining and a relatively
low cost item, so buy one, then use it to
gauge the thread.
The indexing flats must be exactly
equidistant from the spindle axis. Set the
spindle in the dividing head chuck and
clock it very true. Form the two flats, but
the depth must not cut into the ¾” body
or the indexing won’t work.

Making the collet block
I used cast iron for this as I had it already a
block I ground true at College 45 years ago
just waiting for a use. Finish the front face
fl at by milling or fl y cutting then this face is
the datum against the fi xed jaw of the mill
vice to fi nish the bottom.
Mark the position of the bore on the
big end, mount on an angle plate on the
faceplate and set the punch mark running
true using a wobbler. This is not as easy as
it sounds, we need clearance for the boring
tool at the faceplate end and the block must
be perfectly square, so fi rstly lightly clamp it
to the angle plate off the machine checking
with a V block or 123 block to get this right.

Don’t rely on an engineer’s square here.

Now the centring positional adjustments

are made to the angle plate not to the

block. Face the end fl at then produce the

bore for a precision running fi t on the shaft

aim for a clearance of plus 0.001” relative

to the exact shaft diameter, photo 5. The

angled face can now be set approximately

horizontal clamped to an angle plate, the

bottom face being set to 15 degrees which

will give the diff erence between the angle

of the primary and secondary clearance

on the drill. Use a ¾” bar in the hole to aid

setting up. To fi nish, drill and tap the M6

clamp screw (not oft en used). Produce the

indexing plate, oversized at fi rst. This is

tightly clamped to the spindle for drilling

the fi xing screws. Photograph 6 clearly

shows the setup. Check when the plate is

fi xed that there is almost zero clearance on

either spindle fl at. If there is any problem,

it will need very careful adjustment with

Mount the drill in the collet and fi nger tighten the nut to just grip it,

then tuck the back of the block against the setting plate step and

angle the lot down pushing the drill just into contact with the length

block. Move it to the left and press the drill lip fi rmly down onto the

height setting block and tighten the collet nut. Very occasionally, the

drill will rotate during this process, so it is wise to check it aft erwards

Setting plates.

8 9

Fig.3