stone polisher 3

[stonekarver]

hi,i hope i'm in the right place.i'm building an automated stone polisher(fancy name for contraption to carry a 4 1/2" wet angle grinder back & forth 36").i want to use a 1800 rpm 1/2 hp cont.duty reversible motor to drive a 1" fine threaded rod(4:1 speed reduction via v-belt).firstly what kind of electrical equipment do i need & how do i wire them to allow for automatic reversal after hitting set limits?also will there be any detrimental effects on motor for continuously & instantaniously reversing rotation(every 30.sec to 1 min.)thanks in advance for any help that u might have to offer

 

[Skogsgurra]

It is not exactly the right forum. Electric motors and Motor controls would be more correct. But, since most people there also come here, the right people will see your question.

Your question: I think that your motor has a rather low inertia load. That makes stop and reversal every 30 seconds a reasonable proposition.

But, do not plug reverse. Switch motor off, wait until it has stopped - a second or so - then start in the other direction. It will reduce wear a lot.

I would use one of the little programmable relays for the control system. Cost is close to zero and they are very easy to use. For best result, I would use solid state relays for the power circuit. But, at that rate, a couple of simple contactors would also work.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Well that will be nasty to most motors.

A couple of possibilities.
Use a three phase motor with augmented cooling, and a VFD.

Use a servo motor and controller.

Use a stepper motor and controller.

You may be able to use a much smaller motor that runs at 10-20,000RPM and cog belt gear reduce to your threaded rod.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[OperaHouse]

I would consider using a three phase motor and a VFD. Most VFDs will reverse and they are available on ebay used for as low as $30. I've bought oddball ones for even less like .1KW Under light load 460 motors can be run on 230 and 3 phase input power can be used on single phase. The reversing and ramp up/down function of the controller would make this a slick operation. This is just all informational and would require a greater understanding of controls.

 

[boyceg]

Tell us more about the motor you are planning to use. Single phase? 3 phase?

 

[stonekarver]

Well i bit the bullet & bought a variable frequency drive & a 3 phase motor.I was under the assumption that to go with 3 phase i would need some type of phase converter.I don't understand the principles behind it but the vfd is the phase converter.I can't quite get my mind around it but i can input only 120v ac & it can run a 230/460v 3 phase motor with variable speed.Not to mention reversing the motor using simple limit switches.Its a very slick operation indeed.However, I ran into the limitations of using a 1"N.F. threaded rod to transfer linear motion very quickly.It took me all of an hour before i realized that galling occurs when using like materials for nut & rod.Also that n.f. thread(& n.c.) are designed strictly for fastener use & not to apply linear motion.I am patiently waiting for delivery of my 1" stainless acme thread rod & self lubing plastic acetal nut(no lubrication because any residual oil leakage would stain the stone)The reason i started with n.f. rod was to slow the linear motion further than just the drive/driven ratio of pulley sizes.The vfd takes care of that nicely.Anyway,I thank you for your input & maybe someday when i get up & running I can sell you a high end indoor fountain.Not meant as a solicitation.

 

[itsmoked]

Glad it's panning out.

A VFD takes power from the source and rectifies it to DC stored on a capacitor bank. This is called the "front end". The "back end" draws power from this capacitor bank and synthesises the complex waveforms allowing on-off power switching to simulate different frequency and voltage three phase power. Hence the use of single phase or three phase power as they can both be rectified into the same DC.

Do note that there are limitations to the single-phase to three phase trick. Typically since all the output power must be supplied thru fewer rectifiers in the single phase case the VFD may require you to use larger power versions than normally required. So you might need, say, a 5HP VFD to run a 3HP motor from single phase.

Sometimes you can run the output at twice the input voltage if the VFD allows voltage doubling on it's rectifier front end. I don't know of any that would allow a 120VAC single phase input and provide 460VAC output. Can't believe it.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com