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designing and building with wood channels my creativity and challenges my mind.
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Wednesday, January 19, 2011

Band Saw Upgrade: From light-duty to medium duty

I haven't yet learned much about the band saw, which is considered by many furniture-makers to be "the most important saw in the shop".  Still, I do own a band saw: I was given one by a friend a few months ago.  It languished in storage until yesterday, when I bit the bullet and pulled it out in order to cut a curve in a thick lamination of Purple Heart and Maple.

My band saw, a Delta 14" from 1990, is low-powered by any standard of stationary (floor-standing) band saw.  Its motor was rated at only 1/2 HP.  By comparison, Delta's current 14" band saw has a 3/4 HP motor, which is still small, but appropriate for a 14" band saw, which is the smallest of the floor-standing saws.  Strangely, the previous owner of the saw had installed a riser block, which increases the vertical capacity of the saw by 5 inches.  I say this is strange because with a 1/2 HP motor no blade would be able to cut through stock as thick as the maximum capacity of a regular 14" band saw, let alone as thick as the riser block allows.    



I fired up my saw, which I hadn't cleaned or modified from its 1990 condition, and tried to make the cut.  There was a lot of smoke, a lot of pushing, and eventually, the blade snapped.


stock 1/2 HP motor
I knew my saw would need an upgrade if I planned to do much cutting of these 3"-thick blanks (and I do).

Luckily, I had a 1 HP motor sitting around the shop.  Using this motor would double the power of my saw and permit cutting of thicker stock.   The only wrinkle was that the new motor spun at 3450 RPM, while the stock motor spun at 1740 RPM.  I had to reduce the final blade speed by half when using the new motor, which would require changing the size(s) of the drive pulley on the motor and/or the driven pulley on the saw.
new 1 HP motor

Using a pulley drive ratio calculator at http://www.csgnetwork.com/pulleybeltcalc.html, I was able to calculate that I would need to cut the ratio in half in order to achieve an additional one-half step-down in motor speed. 

Pulling out my Grainger catalog, I looked up sheaves, and found a sheave with a 1.35" belt pitch (the diameter of the curve made by the belt as it turns around the pulley).  This compared favorably with the 2 1/2" pitch pulley from the original motor.  The new pulley meant I couldn't use the original belt, so I pulled a link belt from one of my belt sanders, removed a few links, and connected the two pulleys.
old pulley (L), new pulley (R)

According to the calculator, my new setup would give me a final RPM of 730, versus 640 for the original setup.  Since my link belt is wider than the original belt (L4 versus L3), the belt pitch at the driven pulley increased slightly from the stock setup.  This reduces the final RPM, but I don't know by exactly how much. 

After the new motor and pulley were set up, I replaced the stock guide blocks with ceramic blocks, and put on a new blade.

new ceramic blocks
I powered up the saw, and made the cut again.  This time, the blade sailed through the stock, and with much less wandering and difficulty in keeping the cut on my line.

SUCCESS!! :)

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