'Super Tumbler' was the first piece of kit I made (I know, it
shows) but it has worked almost continuously for the last 8 years.
The basic requirement for any tumbler is to rotate the barrels ( I use Lortone rubber
barrels) at the correct speed which I gathered from various texts was between 35 and 55
rpm.
There must be all sorts of formulae for working out rotational speed but the ratio of the
diameters of pulleys etc is nice and easy :- shaft diameter = 0.5 inch, barrel diameter =
4.5 inch so shafts need to run at 9 times the requied barrel speed - between 315 and 495
r.p.m. In the UK A.C. motors run at 1420 r.p.m. unless geared so a reduction of 3 to 1
between motor and shaft would give me a shaft speed of 466 - towards the upper end of the
range. A 4 inch motor pulley and 12 inch shaft pulley means no tight curves for the belt
at the expense of a larger machine.
I assembled the whole thing on a 3ft x 2ft sheet of ply using heavy timber to raise the
plumber's block bearings (self aligning if possible) off the deck and 2, 3ft long half
inch diameter mild
steel shafts set 4 inches apart.
The motor is a very old half horsepower unit, probably from a washing machine, which is
mounted on Dexion brackets as the slots allow belt tension adjustment.
So off we go - nope, with just one shaft driven the barrels just skidded about without
turning and sooner or later fell off!
A pair of 3 inch pulleys and an emergency fan belt (the plastic sort that you cut to size)
on the other end of the shafts made everything work. The plastic belt only lasts about 6
months but you do get 4 out of each one!
The next acquistion was some larger 6.5 inch diameter barrels which were turning too
slowly at 36 r.p.m. on the half inch shafts so a length of garden hose was pushed over a
length of both shafts to take the diameter up to 3/4 inch and the barrel speed to 54
r.p.m.
This combination of barrel sizes and shaft diameters gives a choice of combinations from
very aggresive to gentle grinds which I have found most useful - mostly by accident.
My tumbler runs behind a door under a bench - if you build one that is more easily
accesible then a belt guard would be a very good idea.