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Motor for a sander

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Forum topic by BrianA posted 1599 days ago 2330 views 0 times favorited 6 replies Add to Favorites Watch
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BrianA

67 posts in 1660 days


1599 days ago

I am making a V drum sander and I need an RPM of 1725. I salvaged a treadmill for free on Craigs list (Heavy to move out of the guys basement). The motor is 6750RPM . Is there a way to run it at 1725RPM. I know it has variable speed, but I do not think I can use the controls for the treadmill to control my sander.

Any ideas?

Thanks
Brian


6 replies so far

View sras's profile

sras

3815 posts in 1760 days


#1 posted 1599 days ago

A 2 inch pulley on the motor and a 8 inch pulley on the drum gives you 1688 rpm on the drum. I’m doing the math in my head but I think that’s right.

-- Steve - Impatience is Expensive

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Abbott

2570 posts in 1935 days


#2 posted 1599 days ago

Hi Brian,

I am converting an upright wood cutting bandsaw to a metal cutting saw. I realize you are after a different configuration for a belt sander then I am for building an upright metal cutting bandsaw but I hope some of the following information will be useful;

I need to slow the blade speed way down so I am using a variable speed 2.50 horse DC motor from a Craigslist treadmill. BE CAREFUL a DC 130 volt circuit can shock the hell out of a guy!

The control pad with it’s digital controls is a real PITA (pain in the ass) and I don’t want to use it. With it’s push and hold controls of Mode, Incline, Speed, On/Off plus large black plastic control panel it’s pretty much useless for anything but a treadmill.

The power board, control board and transformer all need to be retained to make this work. The power board and control board on the unit I’m using was one board with two sections between the heat sinks. You can tell the difference by following the power wires to the board and the control wires to the control pad. (The controls on the unit I’m using are digital, real old units still use analog circuits).

To get rid of the large useless treadmill control pad I opened up the wire harness between the control board and the black plastic control pad’s board. While they were on a work bench I then traced the wires down by cutting one and marking both ends with tape and a number and powering the unit back up. (Not much to worry about here, these are low voltage digital circuits coming off the control board). Caution needs to be maintained if the controls are using larger analog circuits/wires. A larger voltage rheostat (then the digital one below) will also be needed for analog circuits.

I observed what each wire controlled as I powered the unit up then shut it back down and continued the observation. After awhile I had the control wires down to three. Two power wires and a voltage control wire which is the variable speed control.

I went to Radio Shack and picked up a low voltage (milivolt) rheostat. The center pole is the voltage control. I then hooked up the two power wires and the variable speed wire and I can now toss the big bulky control pad in the trash. I am left with a On/Off button and a small twist variable speed control.

My bandsaw is still in the process of being converted from a single speed 110 volt 1/2 horse analog motor (which was stock) to a much more powerful 2.50 horse 110 volt (because of the transformer) DC motor with precise variable speed controls. Total cost so far has been the time and gasoline used to pick up the old throwaway Craigslist treadmill, a few hours of labor and a $4.00 Radio Shack rheostat.

I still need to convert the serpentine belt treadmill motor pulley to a V belt. I don’t own a metal lathe so I am either going to have the serpentine pulley machined to handle a V belt. Or I am going to purchase a new V belt pulley and drill it out to fit the DC motors 43/64s shaft.

If I replace the pulley with a V belt pulley then I will also have to add a cooling fan as the DC motors original pulley also has fan blades on the back of the pulley to cool motor and circuit board. I have a small $6.00 household 3” or 4” 110 volt fan from Walmart that I will just wire into the conversion if need be.

-- Ohh mann...pancakes and boobies...I'll bet that's what Heaven is like! ♣ ♣ ♣ ♣

View BrianA's profile

BrianA

67 posts in 1660 days


#3 posted 1599 days ago

Abbott,

Thank you for the response. I appreciate the effort you put in to help me. It certainly will help my project.

Is it the fly wheel that gives the motor the extra HP? Seems odd that a small motor like that will replace the
large one (size) on the band saw.

Thanks again
Brian

View Abbott's profile

Abbott

2570 posts in 1935 days


#4 posted 1599 days ago

I believe it is the efficiency of DC (direct current) voltage when compared to AC (alternating current) that produces the horsepower. However retaining that heavy fly wheel certainly would be preferable as it may effect the torque you will need for your heavy drum sander, I do not know. I know that the fins on the back of the motor/flywheel I am using are designed to move air through the motor.

For my bandsaw conversion using a 2 1/2 horse motor should let me cut 1/4” plate steel without any issues and if the V belt doesn’t slip I will be able to cut up to 3/8” plate steel.

If belt slippage may be a problem for your sander application I know of a guy who converted his bandsaw to use timing belt pulleys rather then V belt pulleys. All of these parts are readily available from McMaster-Carr. I would also consider keeping the serpentine belt pulley if that’s what your motor has and setting your machine up with a serpentine pulley at the drum while keeping in mind what length serpentine belts are available.

-- Ohh mann...pancakes and boobies...I'll bet that's what Heaven is like! ♣ ♣ ♣ ♣

View Abbott's profile

Abbott

2570 posts in 1935 days


#5 posted 1598 days ago

Here is that other photo Brian.

-- Ohh mann...pancakes and boobies...I'll bet that's what Heaven is like! ♣ ♣ ♣ ♣

View BrianA's profile

BrianA

67 posts in 1660 days


#6 posted 1597 days ago

I think I have it but…the rheostat gets hot pretty quickly and the motor spins much faster at the start than with the up and down speed buttons on the treadmill panel. Could the rheostat be too small?

I had the red and black coming to the outer spots and a blue running to the middle of the rheostat. Similar to yours?

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