Quick Belt Grinder Question

PHPaul

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Finally came across a suitable motor as the basis of a belt grinder (2.25 horse treadmill motor) and have spend a fair bit of time reading related threads here. Stol...uh, I mean... picked up a lot of good ideas, thanks!

I notice several references to needing a motor that turns CCW. Looking at how they are mounted (motor to left, drive pulley on right) and applying a little common sense, I'm guessing the object is to have the belt moving down in relation to the tool rest. IE, from top roller to bottom roller on a vertical setup.

So, if I mount my CW motor facing the other way (motor on right, drive pulley on left) I'll still have that top-down rotation on the belt and all will be well, right?
 
Hi Paul,

Unless I am mistaken, the treadmill motor is a DC motor, which means that if you reverse the supply polarity it will run in the opposite direction.
You can test this quite easily by connecting it to a car battery. It will run quite slowly, but will show you which way round to connect it.

Whilst you are correct that the belt should run towards the grinding rest, ie downwards, because the motor is reversible it won't matter which side it is mounted on.
 
Thought so. Thanks!

I'm left-handed. All of my "imaginary" designs have had the motor on the left side anyway, but as you say, I can always swap the polarity if needed.
 
Hi Paul,

Actually I tend to put the drive on the left hand side as well. But I'm not a leftie, but do tend to use which ever hand is most convenient. You should see the look on peoples face when you pick up a hammer and use it with your left hand after using it in your right. Its like you have just grown a second head.

Good luck with your designs.
 
Unless your motor is designed to be reversable running full time in reverse will prematurely wear out the brushes.
 
Hi Guys,

I haven't yet seen a treadmill motor with offset brush gear ! However virtually all the domestic appliance brush motors I've seen do have offset brush gear, but it doesn't seem to cause them any problem running them in reverse, although much slower.
 
Hi Paul,

Actually I tend to put the drive on the left hand side as well. But I'm not a leftie, but do tend to use which ever hand is most convenient. You should see the look on peoples face when you pick up a hammer and use it with your left hand after using it in your right. Its like you have just grown a second head.

Good luck with your designs.

Thank you. Main sticking point right now is the rollers. I'm both cheap and (at the moment) out of toy money so I don't see myself paying $100+ for a set of machined rollers.

I think the first pass at this will be based on a set of 5x2 phenolic caster wheels from Surplus Center . I can true them up a bit on my lathe and crown one as a tracking adjuster. Big question mark on them is whether or not the roller bearing is up to the load and speeds involved. Cheap enough to find out, I guess.
 
Hi Guys,

I haven't yet seen a treadmill motor with offset brush gear ! However virtually all the domestic appliance brush motors I've seen do have offset brush gear, but it doesn't seem to cause them any problem running them in reverse, although much slower.

The motor i ended up with for my 7x10, the brushes are angled toward the the direction of rotation. I do run it in reverse but it doesn't run as well when its pushing against the brushes.
 
Hi Paul,

Depending upon the diameter of the driving pulley, Pi X D and the motor speed in revolutions per minute will give you the linear belt speed. I would guess you want to aim for about 100 feet per minute. Remembering that the motor speed can be varied by altering the voltage across it, you can get an idea of how fast a pulley is going to run.

So a five inch diameter pulley, Pi = 22/7 = 3.1428 X 5" = 15.7" therefore 1200" inches / 15.7 = 76.04 rpm.
So not very fast at all. The load will be what ever the belt tension is plus the amount of pressure you use to push the work against the belt.

HTH.
 
Most of my reading puts desired belt speed in the 3000-4000 FPM area, depending on the composition of the belt and the material being ground.

Still easily obtainable with the proper drive pulley diameter. Next time I'm puttering in the shop I'll check the max motor speed with my tach.
 
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