Model Engineers’ Workshop – August 2019

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the work head, so that one turns of the
adjusting screw i.e. 1mm feed when clamped
to the main bar will thus move the work
head by almost exactly the same amount.
Now we have a controllable movement. The
knurled screw in fi g. 5 should be made with
a tight thread. The length of the thread will
need to be adjusted according to the fi nal
width of your penguin arm plus 2mm more
than the radius of the largest cutter you
intend to sharpen, plus the thickness of the
dial. Dome and polish the end.
The dial, which is tapped M6, has 5
graduations, so that each gives 0.2mm feed.
I did the division with the aid of a digital
angle gauge sat on the chuck jaw. Use a
sharp V-tool set vertically and incise it about
0.1mm deep. Set the angle gauge on the

chuck jaw and zero it exactly where it is.

Now it’s easy to rotate the chuck until the

gauge reads 72 degrees and the next line is

engraved. Stamp the numbers 0 to 5 going

anticlockwise then it’s back in the lathe to

part off ; I used a thin disc and soft jaws. Fit

the dial, with the end in contact with the

grinder and screw the adjuster in until you

just feel the arm move.

We need an aid to setting the cutter in

the correct position. With the setting pin

supplied with the machine is very diffi cult to

see what’s going on, but with the work-head

off the machine it still isn’t easy. Another

setting jig is required, it is very similar to the

one we have already made.

Using the setting block to set the cutting lip level. On some end mills
the cutting lips are not radial so then just get the gap between the
edge and block parallel. Lock the spindle, tighten the collet and fi nally
zero the degree scale on the work head for “indexing”.

Mount the work-head, the cutter facing the cup wheel, and add

the appropriate clearance, usually 6 degrees by rotating the head

downwards. With the machine switched off bring the cutter say 3mm

to the left of the face of the wheel and adjust it so that the long lip side

of the cutter just contacts the wheel and lock the front bar in position.

This time Fig. 3 and photo 8 show the

strips fi xed onto the base plate. These

are needed to clear the dovetail slides so

that the work head is mounted on the

operational part of the dovetail the notch in

the front bar is to clear the micro adjuster.

Now we need the setting block for the

cutter lip position, done in exactly the same

way as for the four-facet grinding jig. I drilled

a hole in the back a small clearance on a pin

fi tted into the plate so that it didn’t get lost.

Grinding the ends of

milling cutters.

I will cover slot drills here as they are the

most diffi cult due to one edge being longer

than the other. Photographs 16 to 23

show this better than text, it uses the

standard R8 work head.

When the long edge has been ground,

ground ensure the penguin screw is against

the machine frame, lock the front bar,

slacken its indexing screw then reposition

the penguin arm into contact with the

machine head and lock it. This maintains

the setting for the long edge. We will need

to limit the in-feed swing of the work-head

for the short lip by the diff erence between

the lip lengths i.e. 2mm. Unlock the front

bar; add two turns of the penguin screw

which will push the work head outwards.

The short edge can now be ground aft er

Slacken the penguin stop on the front bar
and swing it into contact with the machine
frame. Rotate the setting dial until it just
starts to move the arm. Add the required
4 turns plus 0.2mm to fully enter the gash
to match the 4mm long lip length. Lock the
penguin arm to the main bar which itself is
unlocked. Move the cutter to the right then
back off the penguin screw to zero rotating
the main bar, thus adding precisely the
required 4mm advancement of the cutter
onto the grinding wheel and the gash will be
centred on the very corner of the wheel and
the short lip is protected. (The fi nal stages
are in the text).

The crude inaccurate and redundant original

feed control, drill then split with a chisel.

Cutting the toggle switch hole in the front of

the machine. Much easier than expected.

The modifi ed motor connections take care

and ask if uncertain!

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