Intheswamp
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Post by Intheswamp on Oct 14, 2015 16:47:07 GMT -5
If you use spreadsheet software send a private message to Drummond Island Rocks (Chuck), he has a great spreadsheet to calculate pulley sizes and rpm.
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petrifried
starting to spend too much on rocks
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Post by petrifried on Oct 14, 2015 22:31:08 GMT -5
Intheswamp, it sounds like you have a 9inch roller pulley as well? I think I'm going to copy you and order a 4 inch motor pulley as well. I don't have spreadsheet... Thanks for all your input everyone and Jamesp for bringing that motor to my attention!
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jamesp
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Post by jamesp on Oct 15, 2015 5:04:26 GMT -5
4/9 X .75/6 X 1725RPM = 96 barrel RPM for 4 inch pulley TOO fast 2/9 X .75/6 X 1725 RPM =48 barrel RPM for 2 inch pulley Close
Assuming 3/4 shaft 6 inch barrel.
At 1125 RPM:
1125/1725 X 96 = 63 RPM TOO fast 1125/1725 X 48 = 31 RPM PERFECT
I would go with a 2 inch motor pulley. 4 inch too big too fast.
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jamesp
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Post by jamesp on Oct 15, 2015 5:15:38 GMT -5
2 inch motor pulley 9 inch shaft pulley 1125 RPM 7.3 inch barrel 3/4 inch shaft
Above arrangement for 6 inch PVC barrel(true 7.3 inches) has 26 RPM speed. That is about perfect. switch to 1725 RPM and barrel speed is 40 RPM, perfect for coarse grind and OK for 220-500-1000-poilsh 4 inch motor pulley is too fast---
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Intheswamp
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Post by Intheswamp on Oct 15, 2015 5:58:07 GMT -5
If using as a switched 2-speed motor that what Jim states above is definitely the sweet spot for those specs. The 4" pulley would really only be used for hi-speed with a 1140rpm....around 52rpm barrel speed and for hard rock (from what I understand).
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jamesp
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Post by jamesp on Oct 15, 2015 8:48:41 GMT -5
RPM and barrel size important. For 7 inch barrel 25-35 RPM and 45-55 RPM, finish grits and coarse grit respectively For 12 inch barrel slower RPM For 4 inch barrel faster RPM is OK Intheswamp, all discussion about barrel RPM was done on 7.3 inch sch 40 PVC
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Intheswamp
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Post by Intheswamp on Oct 15, 2015 9:32:15 GMT -5
Thanks for confirming the barrel size, Jim. I've had 7.27" barrel diameter (HDepot spec) plugged into the spreadsheet trying to figure this out. When I get the shafts in and some free time I'll be ready to build.
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jamesp
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Post by jamesp on Oct 15, 2015 9:52:00 GMT -5
All calculations were based on 7.27 barrel-no problem. To do final calculations you have to base them on a fixed barrel size to start with. Because you can put a 10 inch barrel on same gearing. Because 10 inch barrel will spin 7.27/10=27% slower which is perfect slower speed for 10 inch barrel. Or 12 inch barrel 7,27/12=39.5 % slower w/same gearing, which is perfect. Or a 10 foot barrel which will spin 7.27/120 =94% slower that 7.27 barrel. Perfect please do not attempt 120 inch barrel. And yes, I did tumble w/this 'barrel'
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Intheswamp
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Post by Intheswamp on Oct 15, 2015 10:37:03 GMT -5
It all comes down to the surface speed of the "avalanche" doesn't it? Surface Feet Per Minute? In other words, the time it takes the rocks at the "top of the hill" to reach the "bottom" of it?
A rock in a 12" barrel travels twice as far as a rock in a 6" barrel in one revolution, thus the 12" barrel for the same SFPM revolves only half as many times as the 6" to achieve the same distance. Am I getting there?
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jamesp
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Post by jamesp on Oct 15, 2015 10:55:09 GMT -5
Exactly Exactly it is ALL about the surface speed. Once geared for one size barrel, other sizes do fine.
SFPM rules !!
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petrifried
starting to spend too much on rocks
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Post by petrifried on Oct 15, 2015 11:36:10 GMT -5
just measured my barrel and it has a 9.5 inch diameter. I'm trying to do the math... The shafts with the rubber on them measure 7/8.
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petrifried
starting to spend too much on rocks
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Post by petrifried on Oct 15, 2015 11:56:50 GMT -5
So is this correct? 2.25 inch pulley
2.25/9 x .875/9.5 x 1725 = 39 RPM 2.25/9 x .875/9.5 x 1140 = 26 RPM
The .875 is for my 7/8 diameter rubber coated shaft...
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jamesp
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Post by jamesp on Oct 15, 2015 12:04:02 GMT -5
2/9 X .875/9.5 X 1725 RPM = 35 RPM 2/9 X .875/9.5 X 1125 RPM = 23 RPM
Looks to be right on for ~10 inch barrel. Need that 2 inch motor pulley....
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jamesp
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Post by jamesp on Oct 15, 2015 12:05:28 GMT -5
Yes. 39 and 26 perfect/way close enough
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Intheswamp
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Post by Intheswamp on Oct 15, 2015 12:30:35 GMT -5
Jim, what do you think about a fast speed, around 50rpm, for coarse grind if you're grinding hard rocks?
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Post by oregon on Oct 15, 2015 12:40:40 GMT -5
Jim, what do you think about a fast speed, around 50rpm, for coarse grind if you're grinding hard rocks? I was also wondering. I thought I had also read that some folks liked the ~50 rpm for coarse grinding. So If I build something with two shelves (two barrels on top, two on bottom) and connect them with a reducing pulley set, with this motor I could have lots of options, the motor speed ratios are ~1.5, and if I did another pulley ratio of ~1.5 , I could conceivably have 23,35,52 rpm's all available without changing pulleys/belts? In another related question - Has anyone experimented with rough grinding w/o grit for an initial pass? Starting with rough, would you get much accomplished w/o grit in the first stage? The rivers seem to do a pretty good job around here!
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jamesp
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Post by jamesp on Oct 15, 2015 13:05:47 GMT -5
Mine is set at 55 RPM for coarse on very mixed Rio Grande/pet wood/coral/agate using 6 inch PVC. It's great. 30 RPM (6 inch) for 220/500/1000/polish. Rough grinding with out grit-oh yes. Only if rock has a soft coating. Not going to help if it is straight hard agate unless knocking off sharp edges. Coral tumbled for 3 days with out grit, slurry thick : Before and as found:
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petrifried
starting to spend too much on rocks
Member since August 2015
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Post by petrifried on Oct 15, 2015 13:19:21 GMT -5
So now that I figured out what size pulley I need, I am struggling to figure out where to buy one at. Any suggestions? I need a 2.25 inch pulley with a half inch bore that will fit on the motor shaft with the flat key. I just called the surplus center they said they don't have one that will work with that motor.
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jamesp
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Post by jamesp on Oct 15, 2015 13:56:45 GMT -5
1-BK26-A All 1/2 inch bore. Gotta fit that motor. Horse shoes and hand grenades. .1-.2 inches difference 1-BK27-A 1-BK28-A they got 2 set screws, one pinches the flat part of motor, the other anywhere I found a couple of these in a junkyard. adjustable from 2" to 3", sweet.
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petrifried
starting to spend too much on rocks
Member since August 2015
Posts: 100
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Post by petrifried on Oct 15, 2015 15:07:02 GMT -5
Thanks, I thought it seemed like those should work. I was rummaging around the shop and found a pulley on an old electric motor that has a 2.25 OD, perfect! I got the 1/18-1/6 HP 1140/1725 RPM motor ordered and hopefully I'll actually be tumbling soon!
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