Sawing and Drying

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Got and 7.5 hp electric motor for my LT15

2/19/15       
Keith Newton

A good friend who had a machine shop just gave me a new 3540 rpm, 7.5 hp 3 ph, cast iron motor, in exchange for storing his goose neck trailer for a while.

I have 600 amps of 3ph service less than 50' from where I plan to build a shed for it. The biggest problem I'm concerned about, is that this motor which he already had, weighs 310 #. I think my kohler gas engine weighs less than 100#, so I was astounded by the weight when he brought it over.

I was expecting a TEFC, until he got here with it on the trailer. Will I be able to use a motor of this weight, on my totally manual mill?

If any of you own or know of others with electric motors, how much do they weigh?

2/19/15       #2: Got and 7.5 hp electric motor for m ...
Per-Olov Member

We have a 7,5 kW (10 hp) cast iron motor. I can't say its weight but it can be something like yours. We push our saw by hand, no power feed. The mass is not a problem it is an advantage in my opinion. The feed will be more even. The saw frame has to have a design with wheels and rails as can take the load. I would go for a motor with more power, 10-12 hp with 4 pol=1675rpm.

2/20/15       #3: Got and 7.5 hp electric motor for m ...
Keith Newton

Thanks Per-Olov, I'm not too concerned about the travel, but not sure about changing the elevation of the saw between cuts.

I think my saw takes 4 revs to move 1", and this will be triple the weight. I'm not sure what I can do to make that easier other than alter the crank handle, making it longer for better leverage.

If I'd been buying a new motor, I think now it would be a good idea to choose one with an aluminum frame.

Also, when I looked at some of the other threads, it seems the electric motor start-up is hard on the belt. Not having a starter yet, I was wondering about using a VFD for a softer start, but after doing some reading last night, it looks like there is some power lost, unless the rpms are set higher than the motor name-plate.

I think I have the right rpm speed for the size drive pulley that I can manage to get inside the housing, relative to what the gas motor had.

2/20/15       #4: Got and 7.5 hp electric motor for m ...
bob hardin Member

That must be a very old motor, it is more than double the weight of a typical modern motor. Bob

http://hardinsindustries.com

2/20/15       #5: Got and 7.5 hp electric motor for m ...
Keith Newton

It is a brand-new motor still in the crate. However, my friend that gave it to me had a motor re-wind business, which morphed into a machine shop, which he sold by auction about 5 years ago, so I guess this could be something he had for a long time, and didn't sell.

I would sure like to loose half this weight.

2/20/15       #6: Got and 7.5 hp electric motor for m ...
Per-Olov Member

If it is acceptable with the weight horizontaly you can reduce the work to crank the saw vertikaly with a counter weight. Connect a weight, 75 % of the saw weight, by a cable (rope) over a pulley. The lift- (connecting-) point would be located close to the center of gravity for the saw.
An other way could be to install a gas spring unit. (I don't know the correct name for it in English). It is the type of spring you can see for trunk doors on cars. It can be ordered for the force you need. It will not add so much weight to your saw.
A VFD would give you the best start and stop performance. To get the most sawing life out from the blades, it is good to keep the idle time down. That means a lot of start and stop.


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