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I am building a tumbler and I have a 1hp motor. I need to be able to slow it down until I get to 15rpm (so pretty slow). What is the easiest way or best controller to do this? Thanks for the help in advance guys!

Thought I would add this to the original post as well since folks are asking for more info below :)
I have not built this yet, but I plan to build a drum style tumbler that rotates somewhere between 15-25 RPM. I wont know how fast I need it for sure until it is built and I experiment with it. I have a 1hp motor that has a maximum RPM of 1800 RPM. I also have a 1/2hp motor that has the same rated maximum RPM. The barrel will be roughly the size of a 55 gallon drum (not a 55 gallon drum though, it will be a custom built octagon). Think of it rotating like a hog on a spit. I need the room below it so I can open the hatch and release the contents into a tub below the unit. the plan is to have a pulley on a shaft at the motor and also at the drum and I would like the motor hooked up with a dial of some sort so that I may "dial" in the speed as needed.

I am pretty good with wood but no real experience with mechanicals so any advice or help is appreciated.
 

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Is the motor and induction motor (like on a furnace blower or a large table saw) or is it a universal motor with brushes (like a router or hand held circular saw)? Determining that would be the first step to establish the best way to achieve what you're trying to do.
 

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Are you wanting the tumbler to rotate at 15 RPM?
Or, do you already have the tumbler drive designed and need the motor to spin at 15 RPM?

There is a huge difference depending on how the tumbler is driven.

Is this a horizontal drum type tumbler; sitting on two sets of rollers?

Any more info you could share would help.
 

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Discussion Starter · #5 ·
I have not built this yet, but I plan to build a drum style tumbler that rotates somewhere between 15-25 RPM. I wont know how fast I need it for sure until it is built and I experiment with it. I have a 1hp motor that has a maximum RPM of 1800 RPM. I also have a 1/2hp motor that has the same rated maximum RPM. The barrel will be roughly the size of a 55 gallon drum (not a 55 gallon drum though, it will be a custom built octagon). Think of it rotating like a hog on a spit. I need the room below it so I can open the hatch and release the contents into a tub below the unit. the plan is to have a pulley on a shaft at the motor and also at the drum and I would like the motor hooked up with a dial of some sort so that I may "dial" in the speed as needed.

I am pretty good with wood but no real experience with mechanicals so any advice or help is appreciated.
 

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Cutting the motor speed electrically will also reduce your horse power. Given the size of the drum you are turning, I would recommend doing the bulk of speed reduction mechanically. You could fine tune it electrically.
 

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I'd guess your motor is an induction motor and that speed control is for a universal motor which won't work. You'd have to get a vfd or gear it down. Not sure how a vfd would affect the torque at Rpms that low.
 

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I have a similar drum tumbler. The drum sits on a pair of rollers and pulley size determines the drum speed. Mine works just like Jerry described above.
 

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I would recommend performing the reduction mechanically as doing so electrically could prove very expensive very quickly depending on what level of control and torque you are requiring. Will the drum be driven directly or are will it be set on a pair of rollers that will spin in turn rotating the drum at your desired 15rpm? Will you be fine tuning the speed on every batch of whatever you're making or do you need to dial it in only once to get the performance you need? If you only need to do it once then it would be less expensive to come as close as you can mathematically and adjust the size of the least expensive component, in this case the motor drive pulley.
 

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Discussion Starter · #12 ·
I believe I will only need to set it once as most of my parts are made from the same woods and roughly the same sizes. I planned on having the drum driven directly, it does not set on a pair of rollers. I attached a picture of what I am thinking in my head. My drum will be made of wood and solid to hold sanding media in but you get the rough idea at least.
Tire Wheel Automotive tire Mesh Gas


I'm afraid I am not nearly knowledgeable enough in this department to do the math to set this up properly managing the speed mechanically. Buying a commercial tumbler the size I need is super expensive, like new car expensive so that is out too.
 

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I d guess your motor is an induction motor and that speed control is for a universal motor which won t work. You d have to get a vfd or gear it down. Not sure how a vfd would affect the torque at Rpms that low.

- TheFridge
Does your motor have brushes! This is of prime importance! If it does not it is an induction motor. A common speed controller will kill that motor if it worked at all.
 

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I'm trying to sell my old bandsaw right now that has a 3/4 horse DC motor and a speed controller. It sounds like that is the sort of thing you need. I'm not sure how slow you can make the motor go, but with pulley sizes you could probably get the rest of the way. I bought this saw like this and never used the speed control as I don't cut metal. I looked at these systems after I bought the saw and they are not cheap. I'm hoping someone comes along and says he wants to pay what I'm asking just so he can have the motor and controller. I don't think it's gonna be possible to use two pulleys and go from 1725rpm down to 15.
 

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In the 45 years I was an electrician specializing in motors and controls, I discovered variable speed in AC motors is also variable HP. AC motors at low speed have no torque, that is why DC motors are required for low speed high torque applications. Do not waste your money trying to use variable speed in an AC motor for such a drastic speed reduction.
 

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I'm afraid I am not nearly knowledgeable enough in this department to do the math to set this up properly managing the speed mechanically.

It's pretty simple math.. speed of motor divided by pulley ratio.. so a 3450 RPM motor with a 2" pulley and a 4" driven pulley (2-1 ratio or 50%) would get you half the motor speed. There is a nice online calculator that you can use over at the vintagemachinery site so you can play with motor speed and pulley diameters to see what kind of combinations would work: http://vintagemachinery.org/math/arborrpm.aspx

Cheers,
Brad

PS: Just noticed you are shooting for 15-20rpm.. to do it mechanically, you will either need a very large driven pulley and very small motor pulley, or you will need to have the motor drive an intermediate countershaft.. not too difficult, but a bit more compilcated than just running the barrel directly with the motor.
 

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So I have a dual drum sander by General and the conveyor belt motor (1/6hp) has complete speed control and it moves slowly, like exactly what I want as far as speed and control of speed. I posted a link to it below. Is that an AC motor?

http://www.general.ca/products/1_general/15_sander/15-250.html

As for the question about the 1/2hp motor I have currently. I'm sorry, I dont know if it is a brushless motor. Not the same brand but very similar to this one I found online at harbor freight

http://www.harborfreight.com/engines-generators/electric-motors/12-hp-general-purpose-electric-motor-67839.html

I can buy a different motor if need be but I don't know which to buy to make this easiest?
 

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I would look at a surplus store for a motor with a gear reducution mechanism.

You can do it with pullyes but that is a very large reduction.

You have to think about the start up torque of the loaded drum and contents. Then the running time hours vs days.

All your bearings etc will have to be able to take the forces, side to side and turning from one end.

I think you should forget about designing the tumbler around the motor, VS get the tumbler made then power it.

I used to tumble rocks as a kid and have made a small paddle wheel pontoon boat. Good chance that your first try will need some work.

Go to a good store and look at how a low $ concrete mixer is made and driven, then look at the High $ one. This should help you imagine how to tackle the task at hand
 

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So I have a dual drum sander by General and the conveyor belt motor (1/6hp) has complete speed control and it moves slowly, like exactly what I want as far as speed and control of speed. I posted a link to it below. Is that an AC motor?

http://www.general.ca/products/1_general/15_sander/15-250.html

- Jesse
On the sander you are cutting the speed by a ratio of 6 or 7 to 1. The stated ratio for the tumbler is between 72 : 1 up to 120 : 1. It is not practical. The best you could hope for is a stalled motor doing it electronically. I seriously doubt if you could even burn it up letting it set there with the power requirements to run at 15 to 25 rpm. A DC motor could do that very easily. It may be too expensive plus you would need a DC power source.

Using pulleys, you will need an 80 inch pulley on the drum with a 1 inch on the motor to get in the range. Some type of reduction gear in addition to pulley ratios is probably the only practical way to do it.
 
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