Variable speed motor for a tumbler?

I'm sticking with AC motors and mechanical reduction.

Hmm. I'm trying to understand how that makes sense. Seems like slower speed should reduce torque which in turn should reduce current draw. Efficiency drops at lower speed, maybe it comes out a wash? You have tested the amp draw at different speeds? 

This is a great thread. Different speeds for coarse and finishing steps is all good. Certainly a forward move.

This is how I dealt with various speeds:

I have a slow running specialty tumbler set up for running SiC 500 for 10 days after the coarse grind.
It will run two 8 pound 6" made-to-vibe-size HDPE barrels at a slow 20 rpm, vibe has 8 pound capacity.
This is an intermediate step between coarse and the vibe.
The SiC 500 does a great job of removing the coarse scratches(instead of using SiC 220) and also preps for vibe abrasives.
This little tumbler does two 8 pound loads in 10 days and the vibe does one 8 pound load in 5 days.
So they are timed in harmony.

To feed this tumbler I load the big faster rolling coarse grind tumbler up with 6-7 barrels totaling 100+ pounds of rock.
I run it for 6 to 8 to 10 to 12 weeks until the rocks are well rounded and *shut it down for several months until the SiC 500 rotary and vibe has finished the 100+ pounds.
Some barrels have glass and are removed from the coarse grind early, the benefit of having multiple barrels instead of 1 or 2 large barrels.
This makes time to sort the coarse grind rocks, select good mixed size batches for SiC 500 tumbler, store rocks to avoid running big noisy tumbler outside in winter temps, and in general take a break from the labor of feeding the big tumbler coarse grit and constant clean outs.

Just saying, variable speed/different speeds can be organized in a way that the loads are reaching completion in harmony with your equipment.

The SiC 500 tumbler is barely loaded running two 8 pound barrels with this slow turning 1050 rpm AO Smith 1/8 hp air over motor.
It is near silent at 20 rpm barrel speed and works good in the home basement/carport.
Has a 1/2" shaft making it easy to use sheaves with long lasting automotive v-belts.
It will run a 10" diameter 40 pound barrel too. Even turning 40 pounds the air over motor is not loaded much at 12 rpm.
I get these small motors used at HVAC shops for cheap. The low rpm allows a smaller main sheave.

1/8, 1/10, 1/12 HP, 1050 RPM NEW CENTURY/AO SMITH ELECTRIC MOTOR.
A.O. Smith 98 1/8-1/10 -1/12 HP 115 Volt 1050 RPM Blower Motor
$95 on EBAY
Continuous Duty, Air Over
Shaded Pole
60 Hz
Auto Protector
40 Degrees C Ambient
OEM Replacement
1/2" Dia. Flatted Shaft
1/8~1/10 ~1/12 HP
1050 RPM
115 Volt
5.1-3.5-3.0 Amps
Sleeve Bearing
Rotation: CCWLE
3 Speed



This is the slow running intermediate tumbler and was built in a day on 2x10's.
3/4 inch shafts.
Sealmaster bearings with grease fittings.
Automotive v-belt.
11 inch/3/4 inch bore Taperlock Cast iron sheave.
1/8 hp with 1/2 inch bore pinion. Great motor for running 8 to 40 pound barrels at lower finishing speeds.
Runs tilted to keep barrel against single end roller.



Note slurry paint job on open cage motor. No ill effects so far but it will EAT bearings.
Had to post this for TheRock Bob in light of his totally awesome pristine shop.
Dammit Bob rock tumbling is just a nasty operation. I do keep the insides of those barrels well maintained. It's all about the rocks !
About 200 sq ft of the gravel floor is now concreted together with rock slurry. Man that slurry makes fine Portland.
The vibe is kept a distance away in much neater/cleaner conditions.



Note on HVAC grade 'air over' motor:

Roof top A/C units have seriously HOT air over them.
Not to mention driving a fan is brutal duty for a motor.
A well sized tumbler has much lighter duty demand.
1/8 hp is a good size for most tumblers running 12 to 24 pounds at most any speed.

wow....

That may be the least true thing I have ever seen posted on this forum in the 12 years that I have been here.

There are world class tumblers here that do all their finishing in a vibe.
I will happily go up against all of them using a rotary tumbler.
(no offense vibe guys!!!)

Is there a thread where you posted what you experienced and the steps you used in your failed attempt?

Following Thumler's beginner level instructions was probably the problem...

I would be happy to help ya come out with better results, as "world class" tumbles are quite possible using only a rotary tumbler.

caveat: I can't say (guarantee) that for 3 lb barrels as I have never used a barrel that small.
May be the same, but I wouldn't know.
Just sayin' that great tumbled rocks are just as possible using a rotary only as with using a rotary then finishing in a vibe.

Just takes time
time = patience

Rotary switching to vibe = same results, just faster.
I just don't care that much to worry about how long the rocks take.
Still being new to this, you may want to see the results sooner rather than later.
All good.

KISS

There was not any information on the power usage of that unit rockbiter. I did some searching, was curious.
The advertisement was a bit vague. Not sure if that is a DC or AC motor, just a servo motor.
Go for it ! Anxious to see your findings. If you bought that unit US made you'd probably pay triple.
Some of the oversea products are of very high quality. That unit looks well made.

Yep, those industrial junkyards were treasure troves and loaded with stuff to build tumblers.
Who builds a tumbler using 1.5 inch solid shafts ! They were cheap at 25 cents per pound. In 10 foot lengths.
At first I was going to leave those solid shafts 10 feet long and have only one set of shafts using 4 end bearings since shaft sag was no issue.
And use it only for coarse grind with like 8 barrels but changed plans and cut the shafts in half and do 2 sets of shafts with slow/fast.
The cost of coarse silicon carbide back then was over $2/pound and it would have cost a lot to run 8 barrels in coarse.
Then I found raw silicon carbide for 45 cents/pound and wish that I had made the 10 foot wide coarse grind tumbler.

The good old AC motor is going to be hard to beat since it is designed specifically to run directly off of pure 60 hertz AC.

With the salvage motors available so cheap I was able to try all kinds of expensive industrial AC motors from 1/12 to 1/2 hp.
Expensive motors like TEFC, 1.0 service factor, capacitor start, cooling fins, etc.

These ended up being the toughest most efficient motors sized well for tumblers:
1/12 and 1/8 hp air over fan motors could be found removed from A/C roof top units that apparently ran off the 110 VAC control voltage instead of 208/220.
Roof tops are big expensive units, last thing they want is a fan motor failure. Trane, Carrier, those guys have their own bad ass motors made specifically for their systems.
These 1/12 to 1/8 hp motors were big and heavy. Large in diameter, high in torque. Ran at lower rpm like 840 and 1140 rpm allowing smaller pulleys.
I used a current clamp on them and they used the least power per pound of rock.
Granted they were air over motors but designed for extra loads like hot air, dirty filters, leaf obstructions, bird's nests, etc. Had open cage for cooling. Fine for conservatively loaded tumbler.
If doing it all over again I would build several tumblers using these 1/8 hp motors and roll two 15 pound or three 12 pound barrels on each of them instead of the one big tumbler with 1/3-1/2 hp.
More diversity that way. Take a breather and run less barrels for a spell. Or go rock hunting and bring home a mother load and want to run 100+ pounds.

jamesp I'm sure you have said elsewhere, but where do you get your rough grit? I bought 10 lbs of 30 grit but that isn't going to last long if I actually ever get this tumbler completed.

Also, an old post talked about using 220 AO as the only step between rough grind and polish. Newer threads I don't see you recommending that. Does that work well? I bought some 220 AO from a sandblasting company.

WoW.... yeah I have to agree this is a good thread. James I may have a pristine shop but some days I'm feelin ole rusty and crusty like some of yer tumblers! Anyways I was off of here for a couple days and had some Catchin up to do on this Post. Well rockbiter in my 40+ years working on HVAC Equipment. I have to agree with what jamesp said the War of A/C and D/C was fought years ago between Edison & Tesla and Tesla won that battle. I will stick with my A/C Electric. As nik mentioned the theory of brushes and commutators burning up, and for that reason I have to back away. Something running 24/7 365 I am afraid it will fail, and you will be lucky not to burn a Com and if that happens you might as well pack it in and buy a new motor. At the beginning of this post I gave you my honest opinion on the way I would go and that would be a VFD.  At my last Job at Berrien County I wore two hats Mechanical Systems Manager, and Jail Maintenance Supervisor. And for that matter all of my staff maintained all the buildings in Berrien County. We had many VFD's on all our Big Air Handlers. The Largest probably being I think 30 HP 460V 3 Phase motor. They were all Belt Drive and Used a Set of 6 Matched Belts. Those Belts were LONG and when You replaced 1 you normally had to do them all, because they were a matched set. you would play hell just buying a couple that broke and getting them to be the same length because of wear Belts stretch with age and a set of belts like that cost over $300.00 for the set. A VFD starts the motor S L O W L Y which turns The Huge Squirrel Cage Fan 12' High anyway it starts slow as not to burn the belts. That was one benefit of using VFD's but the most benefit was the ability of having the choice of infinite speeds depending on the load or loss in HVAC.  In other words on a really cold day may require alot of generated heat and would require maybe a larger amount of CFM to push the heat. Anyway that's the biggest benefit of building a tumbler with a VFD system is the ability to having infinite speeds available with the turn of a dial and having the ability of being able to reverse the direction of the barrel and for the cost of less than $300.00 and with the ability for all that it can do, I pulled the trigger and got all the GROCERIES below. I Just recived  a Used Baldor 3PH 220V 1/2hp 1725 RPM Motor, A Automation Direct GS1 VFD and the Computer Interface Cable Package. I wont get to building this tumbler until spring or summer but getting some of the goodies never hurts.