First time posters (been reading for 3 months).
I need some expert advice before I take the next steps of my saw project. I have a 14” woodworking bandsaw and I was thinking of modifying it to cut metal. I know you have to get the rpm’s down in order to cut metal and I was thinking of using a gearmotor instead of going the multi-pulley route. I happen to have a 1/3 hp 27 rpm gearmotor that has a rated torque of 700 inch/lbs. Does the motor have enough torque to cut metal (I did search the forum, but little info on torque) If it has the torque, I need to know what pulley combination would I need to get around 90-110 sfm (I will be cutting steel & aluminum ). The gearmotor ratio is 63.5 to 1. I have a 6” pulley attached to the lower 14” bandsaw wheel.
Any help would be greatly appreciated (kind-of new to all this).
Larry, I did a down and dirty in my head and i think a 6'' pully on the motor will give you about 100 fpm not taking in acount for motor load.
As you probably know, horsepower is proportional to torque times rpm. That said, if you are running at a recommended rpm (really feet per minute at the blade), then you really don't need to know torque, you can easily get by with horsepower. So if you get the blade moving at the right speed, then your ability to cut will depend on horsepower. I think 1/3 hp is a little light for a metal cutting bandsaw myself, but it would certainly work. I have three metal cutting saws, 3/4 hp, 1.5 hp and 2 hp. You just have to cut slower with less hp.
For the aluminum, just use the saw in "wood" setup. It works just fine, and I confirmed that the blades are suitable with my saw blade supplier. 1/3 hp will work fine, just slower. I have a power hacksaw with an ordinary hand hacksaw blade that uses a 1/6 hp gearmotor and it will cut a 3" bar of 12L14 in about 20 minutes.
I modified a woodcutting bandsaw to run at metal cutting speeds (80 fpm for steel and 200 fpm for alum). I used a 1/3hp motor and a two pulley system on a gearbox (30:1).
I cannot stall the motor before the belt slips. I think that the large diameter pulley that you have used will help in this regard as there is more surface area for grip.
To get 100 FPM blade speed, your 14" pulley must turn 27.3 RPM. If you have a 6" pulley on your bandsaw, and the gearmotor has an output of 27 RPM, then you need a 1:1 drive ratio, which means you need a 6" diameter pulley on the output shaft of your gearmotor. With a 1/3 HP motor driving thru a 63.5 ratio gear train, the torque at your gearmotor output shaft will be increase by a factor of 63.5 times greater than the torque of the motor itself, because as with all gear trains, RPM and torque are inversely proportional.
If your gearmotor has the right output speed for you drive wheel, a direct connection is by far the best. Most metal cutting bandsaws use a final stage of worm drive to avoid the belt slippage problem. You should also if you can.
So it looks doable.
Based on Brian's assumption (the 63.6 times torque), sounds like I have enough torque. I’m also thinking of mounting the motor directly to the 14" lower bandsaw wheel (Bruce's idea) to avoid slippage (and it’s a 1 to 1 ratio away).
Thanks again for some great feedback.
Delta 20" wood saw is rated for "non-ferrous" (not steel ) metal at about 2000sfpm . I think that's a little high...I would like to cut Aluminum at about 1000sfpm without flood coolant. I've done what you are thinking with a Rockwell 14" wood saw. Worked fine for home shop. I used a 1/2 hp motor, but I suspect the 1/3 will be fine ( unless you are trying to cut thru 6" steel plate ).
Actually, I had two motors on the saw ...one set up for wood and one for metal. Had to change the belt between motors to move between the two materials.
Last edited by Fred White; 05-20-2008 at 04:19 PM.
Brian's calculations seem to be right on.
As for torque, I would imagine the torque or HP will just determine how fast you can cut, not if you can or can't. I assume you will be cutting in a vertical configuration as wood saws do not often tilt. You should find out very fast if the cut is too agressive as the blade will slow down or stall. If it does, just feed slower. In this respect, a belt drive can be an advantage as breakage is less likely.
Sharp blade, proper feed rate and you should be able to cut aluminum and soft steel. A good cutting fluid will also help but it does not need to be flood. It can be brushed or sprayed on the blade. This is a bit more difficult to do in the vertical configuration but it can work.
Make it fit.