Belt & Pulley Sizing Resource! (for 20" bandsaw project)

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Forum topic by Rodango posted 03-20-2021 03:58 PM 409 views 0 times favorited 1 reply Add to Favorites Watch
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36 posts in 477 days

03-20-2021 03:58 PM

Topic tags/keywords: bandsaw monarch amt pullies calculator belt length blade length design engineering recommendations

Hi all,

I’m restoring a 20” AMT Monarch bandsaw. I may have to replace the motor. The original likely dates to the 1960’s or earlier, and it was likely a replacement to begin with. It’s a giant 5hp 3-phase industrial motor, and unsure if it works, though I plan to test it – it was working before the saw was torn down, but they were bolted separately to a floor and I plan to make a rolling carriage that holds both.

The original motor was 1725 RPM, but replacements are half the price for 3450 RPM at the power level in either 1 or 3 phase, and much more common. Any advice on motors gladly accepted – I’m considering a VFD and 3-phase replacement. I do plan to do some resawing of hardwoods, but also plan to use the saw for general tasks, ripping and crosscutting.

I’m giving consideration to the belt length, sizes of drive & driven pulleys with relation to motor speed and finally to the blade’s SFPM, or feet per minute of travel past a given point (surface feet per minute.) I’ve seen recommendations for resawing at ~3900 to 4100 SFPM. Also similar +/- speeds recommended for general bandsaw use cutting wood. Will gladly listen to any advice on blade speed.

Found a great resource that does the simple math for setting up the saw given the required inputs of wheel size & axle spacing, motor RPM and pulley sizes & spacing. The calculator modifies a diagram (animated!) with the inputs & outputs clearly laid out, and creates a pdf with the output, on demand. This is really useful for designing how to set up this saw. For instance, I can use a 2 5/8” drive pulley on a 3450RPM motor to drive a 12” pulley on the lower wheel shaft to get 3950SFPM. With 20” wheels 37”OC, it calculates a blade length of 136 13/6”. With (probably cast-iron & possibly double belt) pulley centers 17” apart, it shows a 58 1/4” drive belt, awesome!

This resource helps to simplify the design work and puts all the info in one place and one document.

-- I won't even try to tell other people how to live their lives: they're not listening and I'm probly wrong.

1 reply so far

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2292 posts in 2898 days

#1 posted 03-20-2021 04:22 PM

Several brain droppings:

  • Modern multi-rib belts run smoother if you can get the sheaves in the right size.
  • If old V belts, then I suggest Gates AX series.
  • Do pay attention to the smaller pulley size and their specs. It is all too common for woodworking machines to have a slammer pulley below the belt spec.
  • A VFD wil reduce your power. I might be inclined for just a good 3 or 4 HP single phase motor of the correct RPM and not have to re-design everything. You were looking at motor costs, but hang on to your britches when you look at quality ( as in actually round) machined iron pulleys.
    Gates and Continental have very good technical data.

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