Model Engineers’ Workshop – July 2019

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

produced a shallow elliptical profile to the

form and left a flat, 19mm wide surface on

the periphery, which fitted comfortably in

my right hand, photo 6.

The original 50 mm diameter, was

further reduced down to 22 mm diameter

at the other end to that which had been

counter bored for the 8mm hexagon

socket headed machine screw, photo 7.

Using a piece of 20mm diameter brass

bar which had been drilled 8.2mm for its

entire 20mm length, I machined a bush

to dimensions for it to be a light force fit

into the 12mm central hole of the nylon

form of the handle. The clearance hole of

the bush enabled free concentric rotation

of the handle when fitted to the primary

wheel. The choice of brass in the making

of this component was simply from

convenience, as there had been a piece of

scrap lying in the tray beneath my lathe.

An “Oilite” bearing or a piece of phosphor

bronze would have sufficed had they been

close to hand. Whichever the choice, the

function is to allow free rotation without

consequent wear to the malleable nylon

form, photos 8, 9 and 10.

Probably the most critical fitting of the

entire assembly is the threaded length of

the 8mm socket headed machine screw.

Efficient function of the secondary

wheel is dependent on there being a very

small unthreaded space between the end

of the bush and the surface of the primary

Probably the most critical

fi tting of the entire

assembly is the threaded

length of the 8mm socket

headed machine screw.

10 11 12

13

Finished with bush and M8 screw. Unthreaded space on 8mm attachment screw. Secondary wheel in situ.

My hallway and machines.