# Veriac or other alternatvie?



## Uglydog (Feb 15, 2015)

I made a bid on a barn find. 
As is, where is.
1930ish woodworking tools. Likely not used since 1970.
Dewalt 12" radial arm saw
8"x36" Wallace Jointer
Unlabeled floor drill press
16" Wallace Bandsaw

Scrap iron pricing: $66 for the lot.
I believe that after a little oil, some adjustments and new line cords that all except for the DP will be plug & play.
Everything is vintage heavy castings with actual bearings (no babbit).

Here's my question: no it's not- what should I do with my existing 1970ish woodworking equipment. 
I'm hoping to occasionally use the Wallace 16inch bandsaw to cut metal. 

I'm not yet sure the gearing, but unless the motor is trashed I'm likely to want to keep her original, if not I'll rig a jack shaft and step pulley system.

Would a Veriac be an appropriate application? I've never used one. Can they be shop built and remain safe? Will I lose much/any power? She's only a 1/2hp, 220v, 1ph. 3150feet per minute. Shes got a gear box. Some of the models offered alternative gearing options, but I'm not counting on it. Regardless, I'm also considering the real possibility of cutting a different making gears that would change the speeds.   

Suggestions?

When I attempt to upload pics or a pdf of the bandsaw, I'm getting a message that the file is to large. 
Thank you!
Daryl
MN


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## David S (Feb 15, 2015)

Hi Daryl,

You mentioned a bunch of equipment there.  I am not sure what type of motors they have.  
Some may be so called universal motors and some could be a/c induction motors.

Universal motors can be used with Variacs, however when you drop the voltage down to lower the speed you also reduce the fan cooling.  Also at half voltage you get 1/4 power so it will only be good for light loads.

As I read more of your post, if it for teh bandsaw then I think it will be an induction motor and a variac won't cut it.

David


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## Uglydog (Feb 15, 2015)

Sorry.
Yep it the band saw.
I was concerned there might be a drop in power.
Guess my best option is a gear change out.

Would you be able to expound on the feature/benefits of a/c and universal.
What is the difference between the two?
Why would a manufacture choose on vs the other?
How could I tell the difference?
Perhaps all the motor nameplates identify the detail. But, I've never noticed.

Daryl
MN


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## David S (Feb 15, 2015)

Sure Daryl.

Most a/c induction motor are large and run at about 1800 or 3600 rpm.. Actually a tad less but close and are used on lots of equipment.

Universal motors are those that are in most a/c hand drills, routers, etc.  They are a lot smaller and run at 18,000 rpm + and have brushes.  The reason for "universal" is that they can be run on a/c or d/c.  These can be run on variacs or other pwm motor controllers to lower the speed.  However the same caution applies regarding trying to load universal motors too much at low speeds due to the reduced fan cooling.
David


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## Uglydog (Feb 15, 2015)

It's my vague understanding that Hz (hertz?) has something to do with cycles.
Does this have influence on rpm? 
Is this the amount of times that the electricity moves through the sine wave? 
Please correct my terms and/or understanding if I'm in error.
If this is accurate, then isn't an electric motor subject to the input power?

Daryl
MN


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## Hawkeye (Feb 15, 2015)

Frequency (Hz) is the main factor that effects motor speed. Slowing the motor by reducing voltage (i.e. variac) has a major drawback. A motor is also a generator. Voltage generated is largely governed by RPM. As you slow down the motor, the generated voltage is reduced.

The reason that this is important is that this generated voltage is opposite to the applied voltage that got the motor moving in the first place. When the applied voltage and the generated voltage (counter-EMF, CEMF) match, they balance each other and the motor speed stops increasing and the current (amps) stops rising. When the motor is slowed down (usually due to increased load), the CEMF drops and current increases, giving the motor the ability to speed back up until balance is restored.

When the motor is slowed down by reducing the voltage, the current rises, but the motor doesn't have the rated voltage to allow it to speed up again to balance the voltages. It ends up drawing way too much current, heating up the motor until it eventually cooks. I have two variacs, one 5 amp and the other 8 amp. I wouldn't use either one to run a motor.

This is why the best industrial motor speed control is a VFD. The RPM is adjusted by varying the frequency.

When converting a wood-cutting saw to cut metal, the first step should be to reduce the speed through a countershaft or gearbox. After that, speeds can easily be changed with the usual step pulleys.


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## DMS (Feb 16, 2015)

I would not go with the variac for this. I would either get a 3 phase induction motor and VFD, or build a small reducer and use the existing motor. 

As others have said, a variac will not work for an AC induction motor (the most common type for equipment like this). Induction motors run at more or less a fixed frequency that is related to the line frequency they are connected to. 60 hz is the line frequency in the us (or 60 cycles per second). This happens to be 3600 cycles per minute. This is why lots of induction motors are either 3600 rpm or 1800RPM (1/2 of 3600). The nameplate rpm rating will actually be less than this by a tiny bit.

Universal motors are usually used on small, high speed devices, like routers, or rotary tools, and they are capable of much higher speeds.

Out of curiosity, how much reduction are you going for?


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## Uglydog (Feb 16, 2015)

DMS said:


> Out of curiosity, how much reduction are you going for?



Wow, this is really helpful for me! It all makes much more sense.

My thoughts on turning this into a metal saw are theoretical at this point. 
If the existing motor works, then I'm not going to mess with it, something about keeping it OEM.
Plus the tires seem pretty good, at least the top one.
Metal shavings supposedly break down tires pretty quick.
As far as speed goes, likely 100fpm, as that is most appropriate for steel. 
I'm trying to stay away from wanting a plasma cutter....

My eldest daughter and her fiance are talking, thinking, wishing, maybe about purchasing a home. 
They've hinted at cleaning out all my woodworking tools.
They're both into vintage. So this set up is nicely compatible with the 10 oak workbench, WT lathe, myriad of hand planes, chisels, and etc.

If I end up changing out the motor (only if the original is bad), then I'd likely go 3phase for me, but 1phase for them. Hmmm, hopefully she works and I don't have to make a decision.

Regardless, the electrical explanations are very helpful in helping me to understand.
Thank you!!

Daryl
MN


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