[How do I?] Variable speed grinder

[DavidR8]

David, I've been looking at that one for $25, they are similar and most likely will perform the same but based on reviews I read a few years ago the one from Busy bee is more durable or reliable. of course this is just my opinion .

I’d go for the Busy Bee unit myself


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[matthewsx]

The good news for you @DavidR8 is you own a welder and machine tools. Get busy modifying that thing to use a 3 phase or treadmill motor

John

 

[silverchips]

I have a 2x42 belt grinder that I use for grinding HSS bits and general sharpening and shaping.
This is the unit I have.

https://www.grainger.com/product/DAYTON-Belt-Disc-Sander-6Y945

This is a common topic in knife making, variable speed in a belt grinder is very desirable for a number of reasons, all depends on which grit being used and material being grounded. This is a very common and well addressed topic among knife makers who use belt grinders for hours on end.
Unfortunately I don't think a cheap speed adjuster will work well or healthy for your Grainger motor and won't have the need torque at lower speeds.

The correct set-up for 2" x 72" belt grinders is a 2HP 1725rpm three phase motor with a VFD to control speeds and typically cranked up to 120 herz. Now thats a serious set up but what most knife makers use. Another option (cheaper) is to use a DC motor from a treadmill with a speed controller.

However, you don't have that option with a built in motor, you can try the inexpensive speed controller from Harbor Freight (use 20% coupon) and see if that works but be prepared if your motor overheats or lose needed torque. Later on, try looking for an old 1"x42" Dayton or Delta belt sander and easily convert it with a treadmill motor and speed controller at a fraction of the price of what knife makers are doing if your only grinding small items

 

[C-Bag]

The potential problem with a treadmill motor is it’s more or less open frame and will suck up all that grit. It being DC it loses torque when slowed down. 3ph & VFD is the way to go.

The Foredom is a cool rig because it hangs over the work. I find I don’t need to run it too slow so it has mucho power. I’ve never been able to stall mine unlike the Dremel.

 

[silverchips]

The potential problem with a treadmill motor is it’s more or less open frame and will suck up all that grit. It being DC it loses torque when slowed down. 3ph & VFD is the way to go.

The Foredom is a cool rig because it hangs over the work. I find I need to run it too slow so it has mucho power. I’ve never been able to stall mine unlike the Dremel.

While its very true grit can get in a treadmill motor and can be a problem but many have successfully have used them for years with a dust shield built protecting the motor while still being able to cool it. It can be a very cheap solution if you know how to cobble one together.

Please correct me if I'm wrong but a DC treadmill motor can deliver high torque at lower speed speeds with a PWM DC controller that has a constant torque operation feature on it giving it the rated torque at the rated armature current independent of speed allowing a constant torque capacity regardless of speed.
VFD are also excellent, especially since there prices have dropped so much recently and the availability of used & cheap 3 phase motors.

My apologies to the OP as we've digressed and gone off topic.

 

[DavidR8]

While its very true grit can get in a treadmill motor and can be a problem but many have successfully have used them for years with a dust shield built protecting the motor while still being able to cool it. It can be a very cheap solution if you know how to cobble one together.

Please correct me if I'm wrong but a DC treadmill motor can deliver high torque at lower speed speeds with a PWM DC controller that has a constant torque operation feature on it giving it the rated torque at the rated armature current independent of speed allowing a constant torque capacity regardless of speed.
VFD are also excellent, especially since there prices have dropped so much recently and the availability of used & cheap 3 phase motors.

My apologies to the OP as we've digressed and gone off topic.

No worries, I'm watching and learning!

 

[C-Bag]

While its very true grit can get in a treadmill motor and can be a problem but many have successfully have used them for years with a dust shield built protecting the motor while still being able to cool it. It can be a very cheap solution if you know how to cobble one together.

Please correct me if I'm wrong but a DC treadmill motor can deliver high torque at lower speed speeds with a PWM DC controller that has a constant torque operation feature on it giving it the rated torque at the rated armature current independent of speed allowing a constant torque capacity regardless of speed.
VFD are also excellent, especially since there prices have dropped so much recently and the availability of used & cheap 3 phase motors.

My apologies to the OP as we've digressed and gone off topic.

As I punched send I remembered about PWM controllers but the reviews I’ve read say even with the controller they still get pretty puny the slower you go. In my experience with treadmills they are more like speed controls more than powering something like a motor on a machine tool. They just have to get going then I‘m doing the work, not the motor. On the one we had I got the best workout by basically turning the motor off. I still am thinking about using my treadmill motor for my 9x20 lathe where the motor would be under and behind a chip shield with a computer fan on it to cool. I feel like a belt sander is a whole ‘nuther animal with flying grit. It’s why most good industrial motors are sealed with built in fans and big cooling fins. The unit I wish I would have known about before is industrial sewing machine motors. Sealed, lots of low end torque and built in speed control.