Quick Belt Grinder Question

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.
 
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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.
 
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".


????
 
Sorry Firstram, I don't understand what you are asking.
 
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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?
 
Paul, I'm going to bed now, it is nearly midnight here. However I will check those belt speeds tomorrow.
 
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
 
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.
 
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:
 
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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.
 
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