Multi Grinder, buffer, disc sander, belt grinder design questions

[andrsn]

I’m taking on a new project and I’m looking for some input. I've currently got a little 2 wheel 6” bench grinder and of course I want something bigger and more powerful. It’s got a tiny motor and I feel like I’m routinely changing wheels for different grinding applications. I’d also like to have a buffer, disc sander and belt grinder at my disposal. I don’t have room or $$$ for all those independent machines so I’d like to build some sort of mulit-purpose machine.

I scored a great condition baldor 3hp compressor motor for 50$ to power it. I’m going to either use a VFD or a pulley and v-belt system to control/adjust speeds for given applications.
Design wise, I plan to mount the motor near the floor, run a belt up to power a shaft that has opposing ER40 collet chucks on either end. I can then make various arbors and attachments to plug into the collet chucks to spin grinding wheels, buffing wheels, disc sander etc… I’ll have a way to easily mount guards and adjustable tables as well.

My biggest questions are:
What is the difference between a typical grinder/buffer motor and the compressor motor I have? If its just the enclosure its not a big deal because it won’t be exposed to grinding dust or anything like that the way I’m envisioning it. I've heard they have more torque? Can’t imagine why that would be a problem…. can’t find any definitive answers to this online.
Will the ER40 chucks be relatively safe spinning at high speeds while i apply normal grinding/buffing pressures on 10” wheels? I’m planning on ⅞” or 1” arbors and mounting the shaft bearings as close to the chuck as possible for support. I’m assuming it’ll be fine since they are designed to experience (presumably) much greater forces when spinning end mills through materials.

[Hotz]

Hello andrsn welcome



I have not met the engine you have, but if it is TRIPHASE to vary the rotation think if you use a frequency inverter.
Does not lose power but can vary the rotation perfectly, equipment used there in America should be inexpensive : Idea:

Hotz ..

[Toolmaker51]

Hi andrsn;
Hotz is correct about electrical phasing, and the best place to start. ER collets are dependable to RPM's effective for grinding, sanding, and polishing.
The concern will be attachments and SPM [surface feet per minute]. I'd pirate RPM info from commercial tools and reduce by a good percentage until proven safe. Some people get 12" disks to shear flange screws or fly apart at speeds a common motor will attain. Grinding wheels are sensitive to this, sanding less so, a buffing wheel can decorate your shop like a pillow fight.

[Imbeciliac]

Hi andrsn,
I have a question for you: is your motor single phase or three phase? If it's single phase, you'll need to make sure the VFD you choose (should you decide to use one) is compatible. They are available but most are intended to drive a 3-phase motor. Also, unless you have 3-phase power available you'll need to ensure the drive is capable of operating on single phase. Again, they're available but not as common.
If it's single phase I'm going to make some assumptions here: it's probably wired for 208/230VAC, will draw about 18 amps and run at 3450 RPM. If this is correct, you have an ideal motor for your intended application since most grinding wheels are made to run at between 3600-4200 max RPM. Compressor motors are very ruggedly built and well suited to your application provided you prevent particulate infiltration.
Good score, by the way, that motor is worth a lot more than $50.

[eddowens]

Imbeciliac is right the motor you have will be just fine as for the VFD all I have seen where 3 phas I do know they make them for single phase but remember these all are spendy , I have a good up to 5 hp 3phase rotor converter to give away to someone but is so heavy the cost of shipping is out of reach, I would figure out speeds and go with a pully system it would save you tons of cash

[Moby Duck]

Yes compressors need more torque to start up because the compressor itself may be locked up by residual air etc and may be very hard to turn once stopped. I can't see a high torque on start motor being a problem running what you are proposing. Very old workshops often had similar set ups with a motor driven overhead shaft driving grinding wheels, buffers, discs, drill presses etc at bench level via flat belt drives, but none of these were high speed. The flat belts were usually on stepped pulleys and could be mechanically clutched in or out. Often the whole shop was driven by one motor using this system. Might be an idea to check out some heritage blacksmith shops etc to see how they did it.