Model Engineers’ Workshop – July 2019

(Chris Devlin) #1

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.

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