variable speed grinder

[hunterjntx]

I have something for everybody to think about. Does anybody think it would be possible to use step down pulleys on a grinder to make it variable speed without having to shell out alot of money for a DC motor. Just thought I would get a little more insight.


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Jason:cool:

[Jamey Saunders]

Jason,

That's the cheapest way to get it done. It works pretty well. I have a wood lathe that uses that system. Works great.

One other option that has been mentioned on these boards is to get an inverter and a three-phase motor to use for variable speeds. I plan to look into this option when I go about putting together my next variable speed machine. I have read here that the inverter and three-phase motor is cheaper than a DC. It will be more expensive than a regular AC motor and pulleys, but will give true infinately variable speed.

I'm sure that step pulleys will work just fine.

[hunterjntx]

Thanks for the reply. What did you use as a belt tensioner or did you not use one. My only problem with the 3phase is my shop isn't wired for it.


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Jason

[Jamey Saunders]

I have a Wilton Square Wheel grinder, and a DC motor to drive it.

The great thing about the inverter is that it takes single phase power in and puts three phase out. You don't need to be wired for three phase. When you have three phase, the motor can easily be varied.

[hunterjntx]

Thanks for the info. I guess in the coal mine to long, don't know much about electronics!


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Jason

[Mike Hull]

That is not really variable speed. It is sort of adjustable speed. Its like your car being run at either 1800, or 3600 RPM with no way to change the RPM, you can shift, to get higher or lower speeds, but you are limited by the number of speeds in the tranny.
Now if you add a gas pedal, you have infinite speeds. This would be the difference between pulleys, and a true variable speed motor. All you do is turn the dial.

[hunterjntx]

That's true, not really variable speed motor but variable speed grinder. Kinda like a drill press still getting full HP from the motor but stuck a certain speed until you turn the machine off and change. Just a poor mans way.

_________________

Jason

[Bob Sigmon]

Jason,

Earlier Coop747 had a thread explaining how he set up his new grinder (with step pulleys). I'm pretty sure that it was in the Tool Time Forum.

Also Osprey Guy had had some threads on his new machine. He used step pulleys and a link belt with the motor mounted behind the grinder (due to space limitations)

Scroll through the old threads (you can also use the search function at the top of the page) most any topic has been covered at one time or another.

There is always more than one way to skin a cat.

Good Luck,

Bob Sigmon

[Osprey Guy]

Actually, the motor mounted behind the grinder had just as much to do with efficiency as space. I consulted with Rob Frink, the designer of the KMG1 (my terrific, new grinder), he prefers a short pulley belt, and as long as my motor was fully enclosed (it is) there was absolutely no reason why not to put it just behind the grinder, allowing me to set my link belt at only 21" total.

Like Coop, I used the "Maska" 2",3",4" step-down pulleys-cast iron, machined, and balanced, they come from Canada. I don't have so much as a whimper of a vibration. My grinder couldn't possibly run any more smooth, and I have 3 speeds from the 1725 RPM, 1 HP, AC Leeson...3500...1700...800 FPM.

Got the whole thing aligned, bolted down, and up and running in less than an hour. Couldn't be happier

Dennis

Yeah Baby!

[Vince]

Alright Den, Enough!
As we sit in anticipation.

We want Pics!

We want Pics!

Vince

[Geno]

Dennis, would you share with us where exactly you got the balanced pulleys, and how much they cost?

[Osprey Guy]

Thanks to some detective work on the part of Coop, I bought them from Piela Electric out of Connecticut. Not having the size I wanted in stock they arranged to have them shipped directly from the Canadian manufacturer for a nominal surcharge.

Piela's # 860-889-8476

Two-2", 3", 4" step-down Pulleys- one @5/8" (for motor) and one @1/2"(for KMG1)

They were $26.21 apiece, $10 special handling, $7 shipping for a total of $69.42

As far as I can tell (no vibrations), well worth the price.

Dennis

Yeah Baby!

PS. I'll try and get 1 or 2 pics posted by this evening.

[hunterjntx]

I did some research for another place to get step down pulleys.msc direct.com has a little bit of everthing. Also I asked this earlier but did you use anything to tension the belt. Oh one more thing for the unknowing how did you figure the belt speed with the different size pulleys.

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Thanks
Jason:cool:

[Jamey Saunders]

Jason,

On my wood lathe, the belt is somewhat slack, but just enough to allow me to push it to the side, rotate the pulley, and "walk" the belt out of the groove into a smaller one. This works very well in that application. I'm not sure about a grinder. Doing it that way may cause the grinder to bog down.

Some people (COOP) have mounted the motor on a hinged board so the weight of the motor will tension the belt. I have a jointer that uses this method, but the motor tends to bounce unless you have a very good belt.

[EDIT] To figure the belt speed, you have to know the speed of the drive wheel in RPM. You also have to know the circumference of the drive wheel in feet. Multiply the circumference by the speed of the drive wheel and you have the speed of the belt in feet per minute.

[Rob Frink]

Here is a pic of the recommended pulleys:



They are expensive...but clearly the best that I've found. They are cast iron, then machined, then balanced. They are Canadian made by Maska.

Jason, MSC has all sorts of pulleys..but, I've used them and tossed them due to poor quality. Their step pulleys are die cast and do not run very true. I've remachined them everytime I got them. They are about 1/2 the price of these cast iron pulleys.

Dennis, let me correct a typo in your last post. The pulley for the KMG1 needs to have a 3/4" bore rather than the 1/2" that you listed.

Jason with the 2",3",4" pulleys ...one on the motor and one on the grinder, you have 3 speed ratios 2:1, 1:1, and 1:2. If you use a 1725 rpm motor, then the drive shaft speeds will be 3450, 1725, and 860 rpm. The KMG1 has a 4" diameter drive roller for the abrasive belt...which is approx 1 foot in circumference. So the belt speed is approx equal to the rpm of the drive roller.

Which is about 3500, 1700, and 800 ft/min as Dennis stated above.


The best part of all of this is that if you use the 2,3,4" step pulleys on both the grinder and the motor...then you do not need to readjust the drive belt tension everytime you change speeds. This is because the center distance of the drive shaft and motor shaft are about the same for each belt postion. In fact, you can simply roll the belt out of one groove into the next smallet groove while rotation the shaft by hand...like changing speeds on a 10 spd bicycle. It makes for very quick speed changes without the cost of DC variable Speed motors and controllers.

I'll be at the New England Custom Knifemakers Assoc's Hammer-in this weekend (George Rebello's New Bedford, MA) with these machines set-up for demo's. I'll have one setup as described with the single speed motor and step pulleys...and next to it, I'll have a machine setup with a DC varaiable speed motor and controller. This way you can demo each machine side by side.



Sincerely,
Rob