Model Engineers’ Workshop – July 2019

12 http://www.model-engineer.co.uk Model Engineers’ Workshop

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A trial assembly Cut the brass plate roughly to size

Finish the brass plate to size

Brass disc inside the brake disc

knocked off in the band saw. For jobs like
this I use a scrap of wood and a good size
wood screw, photo 8. Mount the 6 mm steel
disc on a mandrel with an 8mm bolt and
a large thick washer and turn to size. Aim
to get a really good close fit in the disc,

photo 9. Countersink the central hole

until an M8 countersunk socket head cap

screw sits just below the surface, photo

10. The brake disc is 6 mm thick at the

hole, so I skimmed a few thou of the 6 mm

steel disc so that it sits just a gnat’s (gnat’s

is a well known engineering technical term

for a few thou) below the surface. That’s it

for this part.

The 10mm thick steel base plate is next.

Drill and tap 8mm in the centre. Machine

two slots, one each end for mounting to the

milling machine table, in my case I used a

1/2” cutter to cut the slots, photo 11.

Time for a trial assembly. Bolt the 6 mm

steel disc to the 10mm base plate with an

M8 countersunk socket head screw and drop

the brake disc on, photo 12. Bolt the base

plate to the milling machine table and apply

a liberal coating of oil. If all is well the disc

should turn freely.

There’s a bit of video here http://www.youtu.

be/zCeSvCy-9Pk of yours truly trying the

fi t.

To hold it all together I used a bit of 1/4”

brass plate which is firstly cut roughly to

shape on the band saw, photo 13. Then

finished to size by filing and on the disc

sander, photo 14. Aim to get a good fit

inside the brake disc, photo 15. I just

managed to get it in the lathe chuck to

centre drill it, photo 16.

zTo be continued

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Centre drilling the brass plate