vugs
starting to spend too much on rocks
Rockbiter
Member since February 2014
Posts: 225
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Post by vugs on Mar 7, 2014 0:09:50 GMT -5
hi all, i am in the planning stages of a diy tumbler and i've been searching threads trying to find the proper rpm for rocks. seems there are different opinions floating around as i've seen anywhere from 20-50 rpms and even a few using higher. i am planning to go with 40-45 but wanted to get some second opinions.
thanks in advance.
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Steve
has rocks in the head
Member since June 2005
Posts: 506
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Post by Steve on Mar 7, 2014 0:56:40 GMT -5
Depends on the barrel diameter. The larger the barrel the slower the rams. Even then you'll get different answers. The 12 lb Lortone barrels do well anywhere between 30 and 40 rpm. The factory Lortone QT12 runs at about 30 rpm.
When it comes down to it the only right answer is what gives you the results you want.
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vugs
starting to spend too much on rocks
Rockbiter
Member since February 2014
Posts: 225
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Post by vugs on Mar 7, 2014 1:29:18 GMT -5
yes i forgot to include the drum diameter which will be 6". i collect alot of agates so that will make up alot of the material that i'll be doing.
i dont have any experience tumbling so im having trouble figuring out what rpm range would be good. i am just relying on what i've read and it seems 40-45 would be an ok range to minimize/avoid chipping?
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1nickthegreek
spending too much on rocks
Member since February 2014
Posts: 383
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Post by 1nickthegreek on Mar 7, 2014 4:32:38 GMT -5
According to John Sinkakas' Gemstone & Mineral Data Book, the proper way to determine the speed is by figuring the SFPM for the drum. RPM = 1,200 ------ C C= Circumference of drum = 3.14 x diameter in inches Hope this helps
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Post by pauls on Mar 12, 2014 2:23:25 GMT -5
Make the position of your motor adjustable with slotted holes for the bolts and if you decide you want to change the speed just get a larger or smaller drive pulley for your motor, that small size pulley will be fairly cheap so no big deal. It sounds like you are pretty well right with the speed you are aiming for though. Yes and Nickthegreek up above is right with surface feet per minute calculations, I have used John Sinkankas' speeds for most of my equipment and as far as I am concerned they are pretty right.
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Post by deb193redux on Mar 12, 2014 9:35:04 GMT -5
According to John Sinkakas' Gemstone & Mineral Data Book, the proper way to determine the speed is by figuring the SFPM for the drum. RPM = 1.200 ------ C C= Circumference of drum = 3.14 x diameter in inches Hope this helps well for 6" the C is 3.14*6 = 18.84. and 1.2/18.84 = 0.063694268 seems something is missing. this does not work as SFPM or RPM
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Post by Drummond Island Rocks on Mar 12, 2014 9:46:42 GMT -5
When I built mine I took the easy route and just asked folks here what RPM their stock units from lortone were running at and I set mine up to be the same. I figure lortone has already done the homework. I customized a little from there but it was a great starting point. My homemade is only used for roughing now so I sped it up a bit. If I polished with it I would want to slow it back down.
Chuck
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Post by deb193redux on Mar 12, 2014 11:01:48 GMT -5
OK, I pulled out Sinkankas 1972 book. IT is 1200 not 1.200. I do wonder what the 1st row of the table is if it is not round or hexagonal? It does seem that the oft heard 40-45 is based on 8" drums. I do agree that polish should be slower, and that other variables like fill, water, material hardness, grits size, and rock size ratios also help dictate the most efficient speed. However, in most cases a bit higher or lower just means that you have 98% or 92% efficiency instead of an elusive 100%. Unless it is a large commercial operation with tight time=dollars constraints, the home user should not get too anxious about what will finish the batch 1/2 day sooner. Going a little slower to avoid chipping seems a reasonable precaution. Building a DYI machine with some amount of adjustability seems like a great idea.
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1nickthegreek
spending too much on rocks
Member since February 2014
Posts: 383
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Post by 1nickthegreek on Mar 12, 2014 13:15:47 GMT -5
Whoops, guess a decimal was transposed when I was trying to post the formula properly, my bad!!!!
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Post by deb193redux on Mar 12, 2014 16:11:51 GMT -5
I think you read the 1,200 as 1.200
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Steve
has rocks in the head
Member since June 2005
Posts: 506
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Post by Steve on Mar 12, 2014 17:36:04 GMT -5
I just assumed that he was from the other side of the pond.
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1nickthegreek
spending too much on rocks
Member since February 2014
Posts: 383
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Post by 1nickthegreek on Mar 12, 2014 18:29:48 GMT -5
Fixed it for all of yas!!
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grayfingers
Cave Dweller
Member since November 2007
Posts: 4,575
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Post by grayfingers on Mar 12, 2014 18:52:18 GMT -5
Just an opinion, I built a home made for 12 Lb. Lortone barrels. I stepped it up to 35 rpm from the 30 that the factory machine was at. I guess the smaller barrels must be okay with those high speeds, but any faster than 35 rpm will shock fracture stones (in my experience). The 12 lb. barrels are about 7 1/2 " diameter.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,548
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Post by jamesp on Mar 12, 2014 18:55:50 GMT -5
I run 7 inch w/round cavity at 50-60 RPM for coarse grind. Then 25 RPM for 220, 500/600 and polish. I get a not so good polish at high speeds.
Sensitive material like glass, crystal quartz, glass etc are best run on the slow machine.
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Post by Rockoonz on Mar 12, 2014 23:18:04 GMT -5
I don't tumble but I keep the tumblers working for Wifey and drool on the results when she's done. I wonder how one would factor in the shape of the inside of the drum. My SFPM is based on 30RPM with the hexagonal, or is it octogonal metal ones with the rubber inserts sold as 15 pounders but more like 12 in reality. She doesn't like what she gets from the rubber Lortone 12lb (really 10?) on the base I built.
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vugs
starting to spend too much on rocks
Rockbiter
Member since February 2014
Posts: 225
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Post by vugs on Mar 12, 2014 23:34:17 GMT -5
thanks all for the good info. i was considering swapping pulleys in and out but i think a variable speed motor may be the way i'd like to go on this since polishing should be done at a much lower rpm (from what i have read) and i'd like the option to use 6" or 8" drums.
if i cant find a good deal on a variable speed motor then swapping pulleys would be plan b.
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jamesp
Cave Dweller
Member since October 2012
Posts: 36,548
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Post by jamesp on Mar 13, 2014 18:18:00 GMT -5
Most people run single speed vugs. The 2 speed idea works well for me. But it is not required. Factory tumblers are about all single speed. You may want to make your project simple and modify it later. My experience is faster for the longest process which is the coarse grind for most stones. It gets it done faster. But it can be a problem for sensitive stones. I polish agates for the most part. They all go in the fast speed for coarse grind. But rose quartz, obsidian, glass all goes in the slow speed tumbler for coarse grind. The most common symptom is frosting. It is like frosted glass. Tiny chips or surface fractures making the surface frosted. it can be difficult to tumble away in 220 grit stage. My tumbler has one motor. But 2 sets of shafts. The 2nd set is driven off one of the fast shafts at exactly a 50% speed reduction. Let me do a photo
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vugs
starting to spend too much on rocks
Rockbiter
Member since February 2014
Posts: 225
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Post by vugs on Mar 14, 2014 12:51:11 GMT -5
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Post by Drummond Island Rocks on Mar 14, 2014 13:42:06 GMT -5
That's a good looking frame and simple design. I would highly advise to make both shafts driven instead of having one free rolling. It don't add much cost add eliminates any worry of slippage. Mine is setup like James with two different sets of rollers at different speeds and all four shafts are driven. Chuck
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vugs
starting to spend too much on rocks
Rockbiter
Member since February 2014
Posts: 225
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Post by vugs on Mar 14, 2014 14:01:14 GMT -5
thanks chuck. that makes sense.
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