Model Engineers’ Workshop – July 2019

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angle, mine was nonstandard. Machine the
bar to be parallel and of the correct width
for your machine. Set up an angle vice and
end mill one of the angles, or angle the mill
head, photo 2. Ensure you leave a short
witness of uncut material about 1mm
wide on the pointed edge of the dovetail;
we will need this as a machining reference
later. Invert and rough out the other
side. Take it out of the vice, but under no
circumstances should the vertical feed
of the mill be changed. Use two bars of
silver steel and measure the width of one
of the original work heads and repeat this
for the bar while clamped to something
flat, which will tell you exactly how much
to remove to get a fit. Be careful to
remove the material from the non witness
second side. Screw to the top plate with
countersunk cap screws in the bar, check
it fits in the machine and modify as
required.
Now we finish the multi plate parallel
with the dovetail bar. Set the dovetail bar
flat on a parallel in the mill vice and mill
round the edges of the top plate. Prepare
and fit the edge fence with three small

countersunk cap screws. The pillar at the

front is for mounting the slitting saw

detent assembly, but I tend to leave it on

as it makes a good handle. Fix the end

stop on the back edge, the gap is there to

enable screwdrivers or even chisels to be

clamped in place for grinding.

Four facet drill grinding.

I won’t go into the benefits of using four

facet drills, this has been covered many

times before, but I can honestly say their

functionality is quite amazing.

The task is easily achieved with the

use of ER20 collets in a dedicated holder.

The collets will enable the holding of

drills from about 3mm up to 13. Anything

bigger has pilot holes and for me, a

four facet point is not really needed.

For smaller drills I use Derek Brown’s

diamond sharpening system. Any four

facet grinding can only be achieved when

one can constantly check the state of

the grinding, so it will need to be easily

removed, inspected and replaced back in

exactly the same position.

Start with the collet chuck itself, fig. 2.

Use a piece of bar 85mm long of diameter

to finish at 25mm. Mount in the four-

jaw, face and centre the end for tailstock

support and turn the diameter to ¾” with

a fine finish. I did mine to 20mm, but the

imperial size will be more useful as it can

be held in the standard R8 collet and will

be useful in the mill so aim for 0.749” for

running clearance. Reverse in the four-jaw

chuck with shim protection and push it in

as far as it will go and set it very true with

the DTI (mine was ok in the ER 32 chuck).

Drill the clearance hole to about 14mm,

then skim the outside and turn boss to

25mm diameter. Make this too long for

now to give plenty of space for juggling

the angle when boring for the collet.

Set the top slide over to 8 degrees

and bore a socket just deep enough to

enter the socket about 10mm. This will

allow you to test the angle and adjust as

required. A simple wiggle test will soon

let you know if the angle is too steep or

shallow, this sort of angle setting can

be frustrating! Final testing is done by

putting micrometer blue in the socket,

then pushing the collet in and giving

The setup for fi xing the indexing plate, drill both pieces tapping size
then open up clearance, 4mm deep to the drill lip without unclamping.

Components for drill and slitting saws.

4 5

6 7

Screw cutting diameter 25 X 1.5mm Boring the mounting block to 0.75”