Christopher Tidy wrote:
Hi all,
When I was about 8 or 9 years old I really, really wanted a stone
polisher. I think they were rather expensive and also (probably
wisely) my parents thought that I would be bored having to wait months
for results, so I didn't get one for my birthday. Anyway, I woke up in
the night and it occurred to me that a stone polisher (or rock tumbler
as some people call them) would make a great home shop project.
I figure I can make a drum (probably cube-shaped) from welded 1/4"
plate. The drive is going to be more of a challenge (I don't have a
great deal of cash to spend on this). I reckon I probably need about a
30 rpm drum speed and 50 W of power for a small polisher. But the
drive needs to be sturdy and energy efficient if I'm going to leave it
running in the shed all year. A mulit-stage belt drive will be fiddly
and probably not very energy efficient. It seems to me that the best
solution would be an oil-filled worm and wheel gearbox, but I'm not
sure where to scrounge one from. Can anyone think of pieces of
industrial equipment which use a suitable gearbox, which I could look
out for in piles of junk etc? Has anyone built one of these before?
Any ideas would be welcome.
Best wishes,
Chris
Ok...from scratch and hopefully building on what other's have said:
1) round is better. The goal is a rolling motion with very little
actual sliding as the sliding causes flat spots. Rather than speed
itself being the most critical (other than running so fast that they
don't tumble), load is more important. For example, a drum 1/8 full may
not tumble at all (will slide) but the same speed and tub will tumble
perfectly when half full of rocks.
2) Start with the harbor freight cheepie..at 20 bucks for your first
try it's a cheap way to find out if you hate waiting it or not.
3) Part of tumbling is critically choosing the stones to charge the
machine with. You want a load that is all roughly the same hardness.
Also, youwant a mix of sizes from large to small rather than mostly
unifrom sizes. All large or all small will not polish well as surface
contact between the pieces is reduced.
4) Because you will be going through at least 4 grit sizes (5 for
some), clenliness is CRITICAL. If even one piece of coarse grit makes
it through to the finer stages you may have to start all over to get a
goood polish. The best solution is to have different drums for each
grit. Of course, you have to meticulously wash the stone load when
changing grits.
5) harbor freight does sell grit but you can probably get it cheaper in
greater bulk (5 pound containers) if you are really interested. When
you get to the polish stage, you'll also need plastic pellets to add to
the mix. These are readily available and really improve the polish time
and quality. Following the last polish, most rocks benefit from a run
of several days in a clean tumbler with a little borax added to the
water. Oh yea....in the coarser grits, gas can build up in the drum so
you either need to "burp" a closed drum or have provision for the gas to
come out by itself.
6) For the impatient, a vibratory tumbler is a LOT faster. If you are
actually going to invest more than a hundred bucks in the project, go
with a vibratory. One nice thing about vibratories is that you can
diamond saw shapes and the finished stones will maintain roughly the
same shape rather than having all the "points" rounded off as a rotary
tumbler does.
7) There's almost no money it...you have to do it all for the pleasure
of finding "treasures". The only money is in the really good stuff like
meteorites and hard rock digging that you need a saw to slab the good
stuff from. You can get lucky and find some worthwhile stuff here and
there but it usually takes more effort than just wandering arond picking
up rocks. Richardson Ranch in central Oregon is a wonderful (pay by
weight) place to go in an effort to find some "better" items. Free
camping, about a buck a pound, and to the best of my memory, 15000 acres
of ground with several locations of thunder eggs, agate, jasper, and
other goodies already located for you to do the digging yourself. The
prinevill. OR chamber of commerce also holds several mining claims for
agate beds in order to kep them open free to the public and encourage
tourism. Heck, basically anywhere you go there is something to be had.
Many books on "sites" are available (many sites are mostly played out
as it used to be a popular hobby.)
I hope this gets you started....it can be a real joy for the family to
go on treasure hunts for suitable rocks. Although kids tend to not
understand that granite, sandstone and some similar don't polish well
(you have to find a way to tell them it's pretty for them to keep but
not to polish), they still love the looking for pretties at the beach
and elsewhere. Almost anywhere you go you have something to keep busy
doing. Heck, I found some of the most beautiful jasper pieces as the
gravel topping of the truck parking by a hotel in Ontario, OR.
If you have more questions, let me know. I aint an expert but might be
able to help a bit.
Koz
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