Model Engineers’ Workshop – August 2019

August 2019 21

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Cutter Grinder

Ø30

See text for length

Knurl

Bore to close fit

on front bar, assemble,

cut back front face to give

clamping pinch

Use M6 screws

Thread M6, tight thread

Scribe arc in machine to

determine position & angle

of M6 hole

Engrave 5 divisions

numbered counterclockwise

Use two ‘O’ rings for friction

to allow adjustment

M6

‘Penguin’ Setting Arm

Mat’l: Aluminium, steel dial

50

26

12

30

20

5

170

contact with the detent. Swing towards
you, index and do the next one until all
teeth are ground. Repeat with more cuts
until all teeth are sharp, it’s a very simple
and quick operation.

Sharpening the end of end
mills and slot drills.
Oft en, sharpening only the end tips will do
the trick of revitalising the cutter; in theory
should be an easy process but again we
need extra kit to enable this to be achieved.
The problem is the controlling of the radial
in-feed needed when swinging the whole
work head and tool across the face of the
grinding wheel on the front bar needs to
be very carefully controlled or when one is
grinding the fi rst edge the opposite side
is so easily caught ruining the cutter or
giving you a lot more work. The grinder as
supplied, does have an in feed control, but
its use is extremely crude and insensitive
and it is impossible to quantify movement. It
consists of a bar about 40mm long inside the
headstock of the machine fi xed to the main
feed, and is controlled by a loose fi tting M8
screw. It is impossible to accurately control
the feed and crossing over the central hole
of an end mill or central gash of a slot drill is,
to say the least, a bit hit and miss. I know this
aft er completely destroying some already
very sad practice cutters.
The solution is to make a sensitive feed
control and remove the above mentioned
screw completely. Photograph 1 showed
this in position. I call it a Penguin arm due
to its obvious shape, fi g. 5. Start with
a piece of 10mm aluminium plate 175 x
50mm. The end is fi nished true in the mill,
and a small piece is fi tted to the end with
M6 cap screws. It is then a simple faceplate
or mill job to bore the arm to a precision fi t
on the front bar. On completion, separate
the components and remove from the front
edge only 1mm from the abutment face
to provide a pinch for the clamping screw
action. The length of the arm and screw
position is set to bring it to the centre of
the work head spindle by mounting a scribe
in the collet with every scale set at zero.

Scribe an arc on the end of the Penguin arm

to give the length position at the top end.

Convert the arc to a straight line with a ruler

and set this line vertical in the drill vice so

that the arm can be drilled 5mm for tapping

M6. This thread has a pitch of 1mm so it is

easy to control the in-feed. Now the shape

of the rest of the arm can be produced. I

made a card template fi rst to see the result

and modifi ed this until satisfi ed and the

arm was cut and suitably fi nished with fi le

and abrasive.

The design point here is that the

adjustment point is on the same radius as

Fig.5

With digital callipers, measure the length of the long lip to the centre
of the gash and make a note of this. Zero the callipers. Gosh they
didn’t look that dirty!

Measure the other lip, and what you now have is the diff erence in

the lip lengths. Let’s say for ease that this is 4mm and 2mm (1.95 in

reality!)

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