Some interesting insights about how to get a Tyre-tumbler go

With permission from Alan Silverstein

From: Alan Silverstein
Date: 15 Sep 1999 12:16:28 -0600
Subject: Big Tumbler News :-)

Work continues on the Big Tumbler. Although so far it has produced no tumbled stones, it's been good for a lot of newsletters. :-)

Last night I tried to fire it up for the first time "for real". The paint was dry enough on the wood inserts (splash guards), and all other features were ready: Motor mount, pulley size adjustment, power switch on line cord, etc.

I added rocks and water "to capacity" and started it up.

First, the tire sagged enough to (1) contact the motor housing again. So I had to push down on the motor to let the tire clear it, and also to keep the belt from slipping on the motor pulley. (Lots of inertia with a fully-loaded tire!) It ran like this for a minute or two, but (2) water leaked out like crazy! Also, (3) the motor base apparently punched through to an old set of screw holes and ended up cockeyed on the base.

1+3. Solution: Switch to a bigger belt, and rebuild the motor base accordingly, to get the motor further out from the tire and also up at a higher angle for more gravity friction force. I'm using a 24" circumference belt and I have a 34" belt in hand. When I do the rebuild, I'll also make the motor base longer enough beyond the motor that I can add weight to it if necessary. (Sticking with gravity-tension rather than switching to an adjustable-tension flat motor base assembly.)

Perhaps using a longer belt will also result in proportionally longer belt life?

2. Probable causes: Motor to tire pulley ratios cause the tire to spin about twice as fast as I'd really like, meaning water flows closer to the edges of the tire than I'd like.

Workaround: Load the tire with less water, and maybe even less rock too. Instead of 5-6 times the capacity of the big Lortone 12 lb tumbler, run it at 3x?

Solution(?): Obtain a larger pulley (with 5/8" ID) and put it on the shaft, to slow down the tire drive shaft speed.

Now I doubt I'll have the monster ready to show off next Monday night at the monthly local rockhounds club meeting. Ah well.



From: Alan Silverstein
Date: 21 Oct 1999 18:31:15 -0600
Subject: Big Tumbler little news

For your amusement... Over the past week I finally found time to disassemble the base of the Big Tumbler and rebuild it longer in the long dimension, plus remount the motor better (?). This is to allow me to use a bigger pulley for slower tire speed, hence a bigger fan belt is required too. About 37 screws or bolts are involved. :-)

It's not quite back together yet, I still must build up and add the side bearings. It also needs a bit more tweaking, say to realign the drive shafts as parallel as possible, keep the pulley from rubbing on the wood, and wrap tape on the driven shaft to stick better to the tire. But soon(?) I'll really have it running! Just in time to let it sit all winter 'cause it's too cold in the garage overnight to operate!

Funny how people who describe building big tumblers make it sound so EASY... Email me for examples. I keep trying to purposely "overdesign and overbuild" this unit, but it's still tough to get it working right.



Date: Fri, 22 Oct 1999 12:05:40 -0600
From: Alan Silverstein
Subject: Big Tumbler -- it lives!

I stayed up too late again last night... And I got it working! After roughly 20 hours of work and $50 in parts (of which $40 for the pillow block bearings).

I let it run for several minutes. No immediate signs of big problems. Nothing got especially hot, the fan belt didn't shred, the tire didn't fall over, it wasn't even terribly loud. It works! It's a sight to behold! :-)

Imagine a 33" diameter, 12.5" wide (BIG) tire, standing up and rolling all by itself!

Something I learned experientially: You do not lift this tire except when it's empty, and even then that's asking for a hernia. When the tire is loaded, you ROLL it onto the tumbler base. And, you do not pull or lift it over the edge of the base and first drive shaft, you PUSH it up and over! :-)

The observed tire rotation speed of 8.2 RPM is within 0.5% of the calculated speed for the motor RPM, and pulley and shaft sizes. So driving a 6" pulley from a 1.5" pulley was a good move, though it slowed down the tire compared to using a 2" pulley; there's no slippage, even driving the 33" tire from a 5/8" steel shaft (wrapped with a little duct tape for friction). Thus the tire's edge speed ends up about 12% higher (!) than the 3 lb tumbler (which runs at 52 RPM), and 17% higher than the 12 lb barrel (at 28 RPM).

It sounds good when running; it should work pretty well. It produces great water from rocks with NO grit, in just a couple of minutes.

Two minor issues:

* I had to add a couple of bricks to the motor platform, which is mounted on a hinge to put pressure on the belt, to keep the belt from slipping. Probably OK, the force on the motor shaft isn't outrageous, and it holds down vibrations somewhat. I need to add one more block of wood to keep the bricks from vibrating off.

* It leaks. Not much, but enough to add up to a mess. Even with the splashguards in place and tightened down snug, a little fluid slowly works its way out over the tire's rim and drips around the base. Makes me wonder how anyone operates a tire tumbler at all. I let it run a while to see if it would stop, and then I'd know how full I could fill it. Well it didn't stop before I shut it off and went to bed.

The tire is only 2/3 full to the rim with rocks, and relative to a barrel tumbler, the water-to-rock ratio is already low. Maybe I just need to run it even drier, or maybe adding grit to form a slurry, it will be less likely to leak out. To be determined by experimenting...

I don't know why the tire tumbler pictured at doesn't leak. No splash guards, and it runs faster -- maybe more centrifugal force?



Date: Wed, 27 Oct 1999 09:55:39 -0600
From: Alan Silverstein
Subject: Big Tumbler News

Last night I added a brick holder to the Big Tumbler's motor platform. Then I let it run for over two hours -- the first time it's run for an extended period. It's functional! Again, nothing seemed to get hot, shredded, or otherwise done in by running.

It really is quite a sight to behold -- and with the splash guard off, quite a noise to hear too!

I started by scooping out all the rocks I had already dumped in the tire. I rinsed them and weighed them relatively dry before putting them back. The total was, coincidentally, right at 50 pounds. Possibly I could add 5-10 pounds more of small rocks. Even "just" 50 pounds is not bad, considering the nominal, expected ratio (by volume) with the 12 pound Lortone tumbler barrel is about 7. That would be 84 pounds, but you really can't fill the tire to the rim. So a ratio (by weight) of 4.2 is still great.

When I refilled the tire I added 1 gallon of water, but no grit (yet). Once again the tumbler made a weak slurry pretty quickly. And once again it leaked out slowly, all over the tire. I covered most of the base with plastic, put it up on 2x4s, and let the water collect on the garage floor. I'm going to try running with less water, plus weatherstripping the splashguards. If that doesn't work I might try Lennart's clever idea of sealing the center hole by inflating a small inner tube into it.



Date: Fri, 12 Nov 1999 11:22:12 -0700
From: Alan Silverstein
Subject: Big Tumbler News

For your further amusement...

* I've now figured out how to keep the big tumbler from leaking: Don't add very much water, not nearly the proportion you'd put in a barrel tumbler. Just an inch or two deep on the bottom of the tire suffices. It does make for a rather thick, sticky slurry in a hurry; but hardly any leakage.

* I've let the tumbler run overnight now twice, 12 hours each time. I'm gaining trust in it.

* This tumbler sure consumes grit in a hurry! Nominally at 4X the weight capacity of the 12 lb barrel tumbler, I should add 4 cups (4 pounds, about $7 worth) of grit. So far I've dumped in just one cup at a time, about three times. It's usually GONE in 3-6 hours of operation -- no palpable trace remains.

* The bottom line is, the tumbler works! And fast, too! This morning I did my first real "tumbler dump" on it, after about 30 total hours of operation. Funny how 50 pounds of rocks doesn't look like much in the tire, but it fills a five gallon bucket.

How do you empty a tire tumbler? Carefully! You hold a large wide-mouth cup, or a small bucket that fits, inside the tire, and flip on the power switch a moment until the cup is full! Then dump the cup out into a big bucket. Repeat until tire is pretty empty.

I need to find a sturdy plastic beer stein or equivalent with a 10" mouth. :-) Or maybe cut the bottom off a small vinegar bottle.

* Sorting the rocks into "more grind" and "ready to polish" buckets is remarkably time consuming... It's a lot of rock. :-) The operation is messy and requires more buckets and strainers than you'd think. You end up with about five gallons of grey water that needs to settle. Anyway, the rocks I sorted this morning were definitely getting ground, and about 1/5 of them were ready for polish!

* I'm looking forward to showng off the unit at Monday night's monthly local rockhounds club meeting.

* I'm writing up a comprehensive design document... :-)


  ..... to be continued

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