Model Engineers’ Workshop – July 2019

67

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Cutter Grinder

July 2019

Ø16

M6

Knurl

13

10

Fixture For 4 Faceting Drills

Lock Screw

25

Ø25 x 1.5

See text for details

of flats

Ø20Ø14

8°

21

15

80

Spindle

Ø4.5

(^320)
30
20
Index Plate
M6
45
13 24
M3 (typ.)
See etxt for details
Bore to close running
fit on spindle
35 10
72
Main Block
22
Check angle
See text
5°
25
70
Wedge
Mat’l: Steel
sliding portion for the cutter to move.
For a long time, this was not used, I
thought it was useless and the tool
rest was in completely the wrong
place, but now it’s great!
3) A holder for square lathe tools this
again was not used much as the tools
had to be removed and replaced at
times.
One frustration was the gib strip
always dropped out onto the floor when
changing the work heads, so a long
loose fitted retention pin was fitted. Drill
through the casting and the gib then
ream 1/8” or 3mm between the gib screws
and into one of the work heads. Ream the
hole, then remove the gib and glue a pin
at least 25mm long into it with Loctite or
similar retainer, then enlarge the hole in
the casting to provide ample clearance
on the pin. Anybody having a machine of
this type is no beginner, so I’m not giving
a blow by blow account of manufacture,
just the critical points.
For lathe tool grinding, I mainly use
8mm square tools. They are perfectly
adequate for reducing 25mm stock to
nothing in two cuts on my Myford and
are even used for all but very heavy
roughing on my Colchester Student. To
enable these to be ground, I have a ¾”
diameter holder with a square hole in the
centre. This was made from a piece of
25mm diameter stock about 160mm long
slotted 8.2mm wide (for tool bit clearance)
along its length in the mill to a depth of
16.5mm. Saw in half and braze together
ensuring correct alignment. Mount and
centre an 8mm square bar in the four-jaw,
centre the end for tailstock support. Tap
two M5 holes at right angles, true to the
central hole in the embryo holder which
is secured to the mandrel with the grub
at the headstock end along with a smear
of nut lock to stop rattling at the tailstock
end. Later, these holes will provide the
clamping for the tool bit while being
ground. Now it’s an easy matter to turn
the outside diameter to 0.748”, to fit the
R8 collet, skim the end, reverse and face
the other end. Smaller tool bits can be
used with two appropriately sized packings,
e.g. 1mm x 8mm for 6mm tool bits.
Multi use mounting plate
The centre of my system is a new plate to
hold the new components, fi g. 1. The plate
is cut from 6mm plate, initially oversized.
Start with the dovetail bar. We don’t need
tremendous accuracy of manufacture here,
there’s plenty of leeway with the gib, and
any slack will be taken up by the clamp
screw. We are not using the dovetail as a
slide; it is just for location and does not
move in use. Carefully measure the dovetail
Fig.2
2 3
Milling the fi rst side of the dovetail bar Checking the fi t of the ER 20 collet