tom
having dreams about rocks
Member since March 2009
Posts: 50
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Post by tom on Apr 14, 2009 21:04:53 GMT -5
Reading through some of the later post and replies, I cross paths with some saying to slow down on the speed when tumbling stones. Most store bought smaller tumblers spin their barrels at 60 rpm. Our 2 home made dual 3 lb barrels turn 72-78 rpm.
Is that bad or good through all stages of tumbling?
Most of our stones come out nice....just wondering if the rpm of the barrel really makes a difference. Unless I'm just a box of rocks. Can anyone help to explain the reason behind the slower speed reasoning?
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Post by LCARS on Apr 15, 2009 0:23:04 GMT -5
For the first stage it's "generally agreed" that a faster RPM is better to maximixe the tumbling action best for grinding and shaping rough stones... and to try and get most of that nasty chipping & splitting out of the way early. :cheesy: My 90's model Lortone 3A spins the 3lb barrel at a pretty steady 54-56RPM when it's running properly (which is most of the time).  After the fine grit stage it's also "generally agreed" that a slower RPM is better to reduce the chances of impacts causing the aforementioned chips and splits, shifting from a more agressive tumbling action to a more conservative sliding action that maximizes stone-grit-stone contact to smooth out all the scratches.  At this point (prepolish or polish stage) I usually switch to the 33B which has a slightly more powerful motor but it's geared lower for the extra strain of running two barrels.  The RPM I get with the 33B ranges from 38-46 depending on how well it's running (it's finnicky) and how much load is on it (1 or 2 barrels), but it is always consistently slower than the 3A on it's worst day.  This has turned out to be a good thing though because I find that I get a better polish with less stone damage when I finish off the tumble at the slower speed. Different barrel sizes and designs will behave differently though, especially when you start running mod'ed and/or home made rigs but experimentation is a constant part of this hobby, I still try things now and then myself.  |
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Brad
starting to spend too much on rocks
Member since July 2006
Posts: 161
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Post by Brad on Apr 15, 2009 13:18:35 GMT -5
I agree w/ LCARS. I've got my coarse & medium tumblers geared to go faster than my polish tumbler.
As far as different barrel sizes goes, I would expect the diameter to be a big factor. To use an extreme example, if a truck-tire tumbler and a Lortone 3A were going at the same RPMs, rocks next to the outer wall of the truck-tire tumbler would be moving much faster, creating harder impacts, than those in the 3A. (BTW, all of my barrels have the same diameter.)
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tom
having dreams about rocks
Member since March 2009
Posts: 50
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Post by tom on Apr 15, 2009 17:19:33 GMT -5
So, optimum speed on first and second stages would be between 60-78 rpm, 3rd and 4th stages between 35-50 rpm?
However, in general the same amount of run time, approximately 8 days for each stage?
I'll get a motor speed reducing switch and see if it helps on my next batch of stones. Just have to re-wire my tumbler to keep the 4" computer fan in high speed to cool the motor.
Thanks for your help.
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Post by Jack ( Yorkshire) on Apr 18, 2009 0:45:24 GMT -5
Hi Tom,
If you run at a slower speed you generaly need to run longer its all down to feet per minuite
(at 80 RPM the barrel goes X amount of feet at 40 RPM the barrel has only traveled 1/2 the amount of X feet)
A bigger size gives more "Load" to the grinding mass and is better
This is one point some people miss out on
Here is some Guide lines from the Victors Book "Gem Tumbling"
For a round barrel
6" 37 to 54 RPM Critical speed 108RPM
7" 35 to 50 RPM " " 100 RPM
8" 33 to 48 RPM " " 98 RPM
10" 30 to 42 RPM " " 84 RPM
12" 26 to 38 RPM " " 76 RPM
Round Barrels operating 35% to 50% of critical speed
Hexagonal Barrels operating speed 20% to 30% of critical speed
Hope this is of help
I run my 10" at 42 (a home built machine using a small CH furnace fuel pump /fan motor)
Jack
Yorkshire UK
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Post by MyNewHobby on Apr 21, 2009 19:46:28 GMT -5
Okay ... for those of us that do not want to electrocute ourselves dismantling our toys ... what brands/tumblers sell tumblers with speed selections.
As always!
Julie
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Brad
starting to spend too much on rocks
Member since July 2006
Posts: 161
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Post by Brad on Apr 21, 2009 20:17:02 GMT -5
I change speeds by changing the diameters of the pulleys, not by changing anything electrical.
Larger pulley connected to the motor and/or smaller pulley driving the barrels -> faster tumbling (or vice versa).
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tom
having dreams about rocks
Member since March 2009
Posts: 50
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Post by tom on Apr 27, 2009 18:22:49 GMT -5
Guess I got off the track. Thinking a faster rpm to would tumble the stones sooner. Everyone made your point clearer to me, thank you so very much.
I get it now. The crashing inside is the deal and a faster spin on earlier stages, helps. Later stages I need to slow down. Got mine geared up and ready, for our next stages.
Thanks Guys.
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