72" belt sanding

bscofield · Post by **bscofield** » Mon May 08, 2006 12:21 pm

For those of you who have a 72" belt sander, I was wondering what you would think of a motor that will run (at it's slowest) at 1725 RPM's. Is this slow enough? The motor right now is a variable speed grinder. I was thinking of purchasing it and adapting it to be the motor for a large belt sander.

Thoughts or ideas?

JBW · Post by **JBW** » Mon May 08, 2006 8:46 pm

I would think the HP of the motor would have more effect on the performance than the RPM's. The ratio of the drive wheel diameter to the RPM's will determine the surface feet per minute of the belt. If the HP is lacking, you cannot maintain the torque needed to drive the belt under load.
Not sure if this answers your question or if it's just me rambling on again.

mahaffy · Post by **mahaffy** » Tue May 09, 2006 1:22 am

You can also use a (variable) speed reducer, but again the HP would determine how efficacious that would be. At least you're starting out at half speed, as it were, but I'd probably be most comfortable if I could change the speed to suit the task.

JHowell · Post by **JHowell** » Wed May 10, 2006 9:57 pm

I used a Variable Frequency Drive made by AC Tech with a 3-phase 1/3 hp motor. Works like a charm, is highly controllable and programmable, minimal loss of torque at low rpm. I rewired a cheap guitar volume pedal to serve as the speed control.

Nick · Post by **Nick** » Thu May 11, 2006 8:49 am

What a cool idea buddy, a foot pedal to conrol the speed! Neat work.

bscofield · Post by **bscofield** » Thu May 11, 2006 4:33 pm

JHowell wrote:I used a Variable Frequency Drive made by AC Tech with a 3-phase 1/3 hp motor. Works like a charm, is highly controllable and programmable, minimal loss of torque at low rpm. I rewired a cheap guitar volume pedal to serve as the speed control.

So you must have a brush face or universal motor? What kind is it?

JHowell · Post by **JHowell** » Sat May 13, 2006 1:34 am

No, it's a regular 3-phase industrial motor. Sorry, don't know the terminology, but it's not a noisy, whiny one. You can get variable frequency drives to run motors up to several hundred horsepower, but what I have is the smallest one AC Tech makes. The VFD is very different from a varistor or router speed control, it controls the frequency of the alternating current while maintaining amplitude, and the motor will pull pretty hard from just a few hertz and will go up to 240hz if I want (which I don't), or 4x the motor's faceplate RPM. I don't pretend to understand 3-phase power, I just have some incantations that allow me to use it. The VFD takes a 110v single phase input, puts out variable frequency 240v 3-phase AC. You can program just about any parameter you want, like minimum and maximum speeds, rate at which the motor ramps up and down, a bunch of stuff. I intended to set up my sander with a 3/4 hp DC motor I had lying around, but 0-90v power supplies are expensive, and I'm sold on VFDs now. My next project is to put one on a buffer. If you search for AC Tech, they'll give you the name of a local rep. The only downside is that it isn't a kit. There are some pretty specific requirements for shielding and wiring and if you don't hook it up just right it won't work. Total cost for the motor and drive was around $300, but it's real industrial stuff, not a makeshift rig. Well, except for the volume pedal, that's kind of makeshift. But it works great, lets me control the belt like a potter's wheel, turn it on and change speeds while using both my hands to control the belt and the pipe.

mahaffy · Post by **mahaffy** » Sat May 13, 2006 12:57 pm

Oh lordy, my wish-list keeps getting bigger and bigger. But great info to have handy in the clutter at the back of my mind. Thanks.