Homemade Brass Tumbler Math Demystified.
The latest craze in how to clean your brass is with stainless steel media in a rock polisher instead of in a vibratory cleaner as was the norm for years. Living in Canada we of course get taken to the cleaners when it comes to cross border shipping and sometimes buying local can be just as hard on the wallet.
A trip to my local rock polishing store reveled that I can get a 12 lb. rock tumbler for only $330.00 and Cabelas Canada has the Thumler for $229.99 for there 12 lb capacity tumbler. Some of the bigger ones have a 15 lb capacity.
I thought that I should be able to make one cheaper and be able to hold more than 12-15 lbs total of water,pins and brass. Water itself weighs 8.3 lbs (US Gallon) and then they say you need 5 lbs of pins so that only leaves 1.7 lbs of brass (15lbs-8.3-5). Not sure exactly how much 1.7 lbs of brass is but the amount that I shoot when I get home from the range the bag is heavy and to clean all that brass would take about 4 trips in the tumbler.
So I cobbled together a very crude mock-up of what I wanted the tumbler to look like after watching lots of you tube videos. I did a rough layout on my bench with a piece of wood, some crude bearings, some redi rod, a couple of pulley’s and an old treadmill motor and controller. I put a roller on each end to prevent the drum from walking across the shafts. Threw it all together and tested it out and it worked great.
I then saw a you tube video of a design I liked and welded up a steel frame and used some of the posters idea’s on what to cover the shafts with and away I went. Had trouble with the bearings not turning correctly but after I ran them for a bit they loosened up and are now working great.
http://www.youtube.com/watch?v=TtVHvMNf6tM&feature=youtu.be
All I did was mount the treadmill motor and associated controller on the new frame. I left off the rollers on each end because with adjustable legs I could perfectly balance the base to keep the drum in the middle and not walk along the shaft.
Well I built 4 of them now for my friends over the weekend and every one of them asked me what parts are needed to make the drum spin at the correct amount if you only have a single speed motor like out of a furnace or washer/dryer.
To calculate the size of the pulleys needed with a certain speed of the motor we can use this simple formula.
Motor RPM x Motor Pulley Diameter = Driven Pulley Diameter x Driven RPM
After we are done figuring, this only gives us the speed of the driven shaft on the tumbler
Since we want the speed of the driven shaft on the tumbler we can re write the formula as:
Motor RPM x Motor Pulley Diameter
---------------------------------------------- = Driven Rpm (Speed of the driven shaft)
Driven Pulley Diameter
Then you use the speed of the driven shaft on the tumbler to figure out what the speed of your Tumbler’s Drum is going to be. I combined both formulas into one to make it easier to figure out the speed of the drum. I made up some letter designations to make it easier to follow the formula and here they are:
Motor Rpm= M
Motor Pulley Diameter= MP
Driven Pulley Diameter = DP
Diameter of Driven Shaft = DS
Diameter of Tumbler Drum = TD
Driven RPM of the Drum = DR
M x MP x DS
------------------- = DR or the speed of drum on the tumbler.
TD x DP
Lets try one .
You found a motor at the dump that has a sticker on it that says it turns at 1725 RPM.
You go to Princess Auto and find a pulley that fits the motor and it has a diameter of 2”.
You buy some bearings for the shaft to run on and they are ½ “ size for your ½” shafts.
You buy a 6” pulley for the driven shaft for the tumbler drum to run on.
You make a 6” tumbler drum out of a empty plastic jar.
How quick will your tumbler drum be turning at?
With our handy dandy formula we can plug in some numbers and find out.
1725rpm x 2” x ½”shaft
--------------------------- = 47.9 RPM or about 48 RPM the tumbler drum will be going.
6” drum x 6”pulley
The Thumlers regular speed is 30 rpm and the high speed is 40 rpm. We don’t want anything quicker than 60 rpm because the brass and contents will just stick to the outside wall due to centripetal force. So in this case we guessed correctly for the size of drum we want and the pulley needed to obtain that speed.
So let’s say we find some 5/8” bearings on sale and our drum size is 8” instead of the 6” we had before.
Using the same motor and pulley sizes what would be our drum speed?
1725 x 2” x 5/8”
------------------- = 44.9 RPM So 45 RPM is right in the ballpark .
8” x 6”
You can always buy an adjustable pulley for the motor that varies so you can fine tune the speed of the drum but figuring out what size of drum you want to make and the smallest size of the motor pulley, you can mix and match the size of the shaft and pulley on that shaft so you don’t have to spend extra money experimenting on what you want.
If you know the size of your Drum that you want to make and the size of the motor pulley then with algebra we can manipulate the formula to come up with the size of the pulley on the driven shaft.
M x MP x DS
---------------------= DP (The size of the pulley needed to put on the driven shaft)
DR x TD
Let’s try one out.
You have a 7” drum, a 1725 rpm motor with a 3” pulley on it and you have some 7/8” bearings and 7/8” shaft to use for your tumbler. What size of pulley do I need to put on the 7/8” shaft to give me 60 RPM for the Drum?
1725 RPM x 3” x 7/8”
-------------------- = 10.8” (You would need about a 11” pulley)
60 RPM x 7”
It would be hard to find an 11” pulley so your better bet would be to drop the 3” pulley on the motor to a 2” pulley which running it thru the formula again would give you about a 7” pulley which is more realistic.
You have the driven shaft pulley diameter of 7” on a 5/8” shaft and you want to know what size of pulley I need to buy to put on the motor to give me 55 rpm for my 8” drum.
Manipulate the formula to give you this.
DR x TD x DP
------------------ = MP (Size of the pulley needed on the motor shaft)
M x DS
Let’s try it.
55RPM x 8” x 7”
-------------------- = 2.85” ( You would buy a 3” pulley and that will get you close)
1725 RPM x 5/8”
With an adjustable DC motor like on a treadmill then just buy any two pulley's that you need and you can adjust the speed of the motor to get what you want.
How much to make the Tumbler?
3” pulley 6.00
4.5” pulley 9.00
½ “ shaft for 5 ‘ 9.00
½” Pillow Bearing 13.00 each (52.00 total)
½” heater hose 4.00
Base mounts 12.00 (rubber cups I put over adjustable screw in legs)
1 ½” Square tubing 30.00 for a 8 foot length and I had 4” left over
Motor found at scrap yard
Total $122.00
I could have skipped the welded square tubing and substituted wood which would have been cheaper but I wanted something to last. As far as the motor goes, look in kijiji or visit a furnace replacement company or find an old washer or dryer, there are lots of free motors out there.
One online store wants 799.99 US for a 40 lb tumbler. Mine was 122.00 and is just as good and will actually hold more weight.
Only thing left is the drum, I made one out of 8” PVC from plumber’s village with a neck down coupler and a cap on the end. Cost me about 18 bucks but I can fill the thing with the brass, pins and water and when I weigh it the scales tip at 55 lbs. A far cry from 15 lbs max in the store bought one and I have a 3/4hp motor driving it instead of 1/30th HP.
The latest craze in how to clean your brass is with stainless steel media in a rock polisher instead of in a vibratory cleaner as was the norm for years. Living in Canada we of course get taken to the cleaners when it comes to cross border shipping and sometimes buying local can be just as hard on the wallet.
A trip to my local rock polishing store reveled that I can get a 12 lb. rock tumbler for only $330.00 and Cabelas Canada has the Thumler for $229.99 for there 12 lb capacity tumbler. Some of the bigger ones have a 15 lb capacity.
I thought that I should be able to make one cheaper and be able to hold more than 12-15 lbs total of water,pins and brass. Water itself weighs 8.3 lbs (US Gallon) and then they say you need 5 lbs of pins so that only leaves 1.7 lbs of brass (15lbs-8.3-5). Not sure exactly how much 1.7 lbs of brass is but the amount that I shoot when I get home from the range the bag is heavy and to clean all that brass would take about 4 trips in the tumbler.
So I cobbled together a very crude mock-up of what I wanted the tumbler to look like after watching lots of you tube videos. I did a rough layout on my bench with a piece of wood, some crude bearings, some redi rod, a couple of pulley’s and an old treadmill motor and controller. I put a roller on each end to prevent the drum from walking across the shafts. Threw it all together and tested it out and it worked great.
I then saw a you tube video of a design I liked and welded up a steel frame and used some of the posters idea’s on what to cover the shafts with and away I went. Had trouble with the bearings not turning correctly but after I ran them for a bit they loosened up and are now working great.
http://www.youtube.com/watch?v=TtVHvMNf6tM&feature=youtu.be
All I did was mount the treadmill motor and associated controller on the new frame. I left off the rollers on each end because with adjustable legs I could perfectly balance the base to keep the drum in the middle and not walk along the shaft.
Well I built 4 of them now for my friends over the weekend and every one of them asked me what parts are needed to make the drum spin at the correct amount if you only have a single speed motor like out of a furnace or washer/dryer.
To calculate the size of the pulleys needed with a certain speed of the motor we can use this simple formula.
Motor RPM x Motor Pulley Diameter = Driven Pulley Diameter x Driven RPM
After we are done figuring, this only gives us the speed of the driven shaft on the tumbler
Since we want the speed of the driven shaft on the tumbler we can re write the formula as:
Motor RPM x Motor Pulley Diameter
---------------------------------------------- = Driven Rpm (Speed of the driven shaft)
Driven Pulley Diameter
Then you use the speed of the driven shaft on the tumbler to figure out what the speed of your Tumbler’s Drum is going to be. I combined both formulas into one to make it easier to figure out the speed of the drum. I made up some letter designations to make it easier to follow the formula and here they are:
Motor Rpm= M
Motor Pulley Diameter= MP
Driven Pulley Diameter = DP
Diameter of Driven Shaft = DS
Diameter of Tumbler Drum = TD
Driven RPM of the Drum = DR
M x MP x DS
------------------- = DR or the speed of drum on the tumbler.
TD x DP
Lets try one .
You found a motor at the dump that has a sticker on it that says it turns at 1725 RPM.
You go to Princess Auto and find a pulley that fits the motor and it has a diameter of 2”.
You buy some bearings for the shaft to run on and they are ½ “ size for your ½” shafts.
You buy a 6” pulley for the driven shaft for the tumbler drum to run on.
You make a 6” tumbler drum out of a empty plastic jar.
How quick will your tumbler drum be turning at?
With our handy dandy formula we can plug in some numbers and find out.
1725rpm x 2” x ½”shaft
--------------------------- = 47.9 RPM or about 48 RPM the tumbler drum will be going.
6” drum x 6”pulley
The Thumlers regular speed is 30 rpm and the high speed is 40 rpm. We don’t want anything quicker than 60 rpm because the brass and contents will just stick to the outside wall due to centripetal force. So in this case we guessed correctly for the size of drum we want and the pulley needed to obtain that speed.
So let’s say we find some 5/8” bearings on sale and our drum size is 8” instead of the 6” we had before.
Using the same motor and pulley sizes what would be our drum speed?
1725 x 2” x 5/8”
------------------- = 44.9 RPM So 45 RPM is right in the ballpark .
8” x 6”
You can always buy an adjustable pulley for the motor that varies so you can fine tune the speed of the drum but figuring out what size of drum you want to make and the smallest size of the motor pulley, you can mix and match the size of the shaft and pulley on that shaft so you don’t have to spend extra money experimenting on what you want.
If you know the size of your Drum that you want to make and the size of the motor pulley then with algebra we can manipulate the formula to come up with the size of the pulley on the driven shaft.
M x MP x DS
---------------------= DP (The size of the pulley needed to put on the driven shaft)
DR x TD
Let’s try one out.
You have a 7” drum, a 1725 rpm motor with a 3” pulley on it and you have some 7/8” bearings and 7/8” shaft to use for your tumbler. What size of pulley do I need to put on the 7/8” shaft to give me 60 RPM for the Drum?
1725 RPM x 3” x 7/8”
-------------------- = 10.8” (You would need about a 11” pulley)
60 RPM x 7”
It would be hard to find an 11” pulley so your better bet would be to drop the 3” pulley on the motor to a 2” pulley which running it thru the formula again would give you about a 7” pulley which is more realistic.
You have the driven shaft pulley diameter of 7” on a 5/8” shaft and you want to know what size of pulley I need to buy to put on the motor to give me 55 rpm for my 8” drum.
Manipulate the formula to give you this.
DR x TD x DP
------------------ = MP (Size of the pulley needed on the motor shaft)
M x DS
Let’s try it.
55RPM x 8” x 7”
-------------------- = 2.85” ( You would buy a 3” pulley and that will get you close)
1725 RPM x 5/8”
With an adjustable DC motor like on a treadmill then just buy any two pulley's that you need and you can adjust the speed of the motor to get what you want.
How much to make the Tumbler?
3” pulley 6.00
4.5” pulley 9.00
½ “ shaft for 5 ‘ 9.00
½” Pillow Bearing 13.00 each (52.00 total)
½” heater hose 4.00
Base mounts 12.00 (rubber cups I put over adjustable screw in legs)
1 ½” Square tubing 30.00 for a 8 foot length and I had 4” left over
Motor found at scrap yard
Total $122.00
I could have skipped the welded square tubing and substituted wood which would have been cheaper but I wanted something to last. As far as the motor goes, look in kijiji or visit a furnace replacement company or find an old washer or dryer, there are lots of free motors out there.
One online store wants 799.99 US for a 40 lb tumbler. Mine was 122.00 and is just as good and will actually hold more weight.
Only thing left is the drum, I made one out of 8” PVC from plumber’s village with a neck down coupler and a cap on the end. Cost me about 18 bucks but I can fill the thing with the brass, pins and water and when I weigh it the scales tip at 55 lbs. A far cry from 15 lbs max in the store bought one and I have a 3/4hp motor driving it instead of 1/30th HP.
....i love the way you made up a mock set up before you started to hack up some steel...
