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[4]

Quick Belt Grinder Question

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PHPaul

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#1
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?
 

BaronJ

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#2
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.
 

PHPaul

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#3
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.
 

BaronJ

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#4
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.
 

Firstram

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#5
Unless your motor is designed to be reversable running full time in reverse will prematurely wear out the brushes.
 

BaronJ

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#6
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.
 

PHPaul

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#7
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.
 

Firstram

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#8
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.
 

BaronJ

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#9
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.
 

PHPaul

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#10
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.
 

BaronJ

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#11
Hi Firstram

That doesn't surprise me at all. The primary reason the brushes are angled like that is to adjust the armature magnetic field forward relative to the stator magnetic field increasing motor efficiency. The brush configuration is called "Reaction Brush Gear".

Edit: It also increases the amount of width of brush that can be presented to the commutator for a given brush size.
 
Last edited:

BaronJ

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#12
Paul, Just be a bit careful running those motors unloaded, they can easily hit 20 K rpm and that could destroy the commutator.

I would check those belt speeds with manufactures data, 3 to 4 K linear feet per minute sounds wrong.
 

Firstram

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#13
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 Firstram

That doesn't surprise me at all. The primary reason the brushes are angled like that is to adjust the armature magnetic field forward relative to the stator magnetic field increasing motor efficiency. The brush configuration is called "Reaction Brush Gear".

????
 

PHPaul

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#15
Paul, Just be a bit careful running those motors unloaded, they can easily hit 20 K rpm and that could destroy the commutator.

I would check those belt speeds with manufactures data, 3 to 4 K linear feet per minute sounds wrong.
Those are the numbers I'm seeing on multiple sites. Some guys with ceramic belts are even advocating up to 7000SFPM

Unless I'm misunderstanding Surface Feet Per Minute?
 

BaronJ

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#16
Paul, I'm going to bed now, it is nearly midnight here. However I will check those belt speeds tomorrow.
 

BobSchu

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#17
I'm in the process of building my first belt grinder and I've been doing a ton of research. A good site for information is on Facebook called "Home Built Belt Grinders". A lot of knowledgeable people on the site and tons of helpful information. Also, some helpful fellows in finding the best deals on parts like contact wheels, idler and tracking wheels, drive wheels, etc....

They can also help you source a control unit for your DC motor if you need.

Yes, you do need around 2000-3000 sfpm minimum for most grinding belts and chores, slower speeds for detail work so your DC motor should work fine. The recommended speeds for Ceramic belts is around 5000-6000 sfpm as they won't work well unless they are being worked hard enough to break the abrasive and expose new cutting edges, which takes quite a bit of speed from my understanding. Best to check with the belt manufacturer, but my research shows these to be realistic numbers.

My motor is a 2 hp 3 phase motor at 1740 rpm, so with the speed requirements I needed to buy/install an 8" drive wheel. I'll only be at around 3600 sfpm, but that is about as big as I want to go on the drive wheel given my hp.

Post pics when you're done...

Bob
 

PHPaul

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#18
Bob, I don't do facebook, so that won't work for me.

Just picked up the treadmill (free!) at a yard sale today and stripped all the goodies out of it. Controller works perfectly.

The flywheel on the motor is 6.5" in diameter so IF I can use that to drive the belt directly, 2100 RPM would give me 3500 SFPM. Just need to check the available speed of the motor.

When I start the build, I'll document it on my website and link to it here.
 

BaronJ

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#19
Hi Guys,

I checked with Norton and 3M about belt SFPM speeds and it seems that I'm about a factor of 50 too slow !

I'll attribute it to slowing down as I get older :eek 2::wink::wink::wink:
 
Last edited:

PHPaul

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#20
Worked with the treadmill parts this morning, reducing things to the minimum needed to operate the motor. After wiring around the various interlocks and such, it's down to the sliding potentiometer, the motor controller board and the motor. Good stuff! Checked the motor with my tach and the no-load speed at about half-throttle is over 4000 RPM so that should be plenty even allowing for slower speeds under load.

As a bonus, it had "power incline" which is a reversible 120vac gear-motor with a rack and pinion setup. Not needed for the belt grinder, but went on my "stuff" shelf for later reference. Also simplified it to the associated wiring and a pair of micro-switches for forward/reverse. Didn't know there WAS such a thing as a single phase AC motor that was reversible. Plenty of experience with it in 3 phase.
 

BaronJ

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#21
Hi Paul,

It would be nice to get a hold of a circuit diagram for your treadmill. It would help to identify the various components. The power incline sounds interesting. All the ones that I have seen are a 24 volt DC motor. A similar layout I would think using micro switches at each end to limit the travel.

Did you salvage any of the steel tube ? Some could come in useful.
 

PHPaul

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#22
I do have the schematic for it, it was taped to the inside of the plastic housing over the motor.

I have plenty of heavier steel, the framework of the treadmill is VERY light stuff and oddly shaped.
 

BaronJ

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#23
Paul, that is great ! Getting that information is often quite difficult. Non of the treadmills I've stripped have that. I'd love to have a copy for reference if you would be so kind. I assume that this web site has a private mail system.

I kept some of the heavy stuff and a piece of the flat sheet off the bottom. The running boards are now part of a garden shed floor with the belt sliced and tacked to it. I've also used a belt as shingle on the roof. :)
 

PHPaul

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#24
I'll scan it and post it here as a .pdf (or .jpg if you prefer)

I've found the belting also makes excellent drawer liners for your tool box.
 

BaronJ

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#25
Hi Paul,

Thank you, much appreciated. Use any format that is convenient to you. The reason I mentioned PM was just in case there were any possible copyright issue.

Yes I agree about the belting. Almost a shame to cut it up, it is tough stuff.
 

PHPaul

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#26
tms1.jpg
tms2.jpg

Had to use the .jpg format, thought I had a PDF creator but it's a reader only.
 

BaronJ

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#27
Smashing ! Thank you very much. It gives me some useful info. Pity they don't include a circuit for the speed controller.
The speed controllers that I salvaged work, however where yours uses a potentiometer to control speed, mine require a pulse. Each pulse steps up the speed a little, then you either have to provide another pulse on another pin or disconnect the power momentarily to stop the motor.

A 555 timer IC works OK to make 5 volt pulses and gives the motor a slow ramp up, but it takes several seconds to get a few K rpm.

The lift motor you have looks to be a split wound one. Does it use brushes or does it have a capacitor on it ? Either way it could come in useful.
 

BaronJ

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#29
Thank You for the pictures.
Just as I suspected ! The motor has two windings with the capacitor connected across the ends. The other ends of the windings are connected together and would be the neutral supply. Live is just switched to one end or the other of the capacitor. Many induction motors are wired like that.

I use one from an old tumble dryer on a dedicated four facet drill sharpener I built. Being able to throw a switch to reverse the motor direction allows quick removal of the fine harrage on the new cutting edge.

I'm looking forward to seeing more your belt grinder as you work on it.
 

GoceKU

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#30
I've been reading this thread all day and i'm surprised that 2-3hp motor is needed to run a belt grinder.
 
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