How much torque necessary for metal cutting bandsaw?

I was wondering what the torque at the blade of a metal cutting bandsaw
would be for a lighter duty machine. Or how powerful a motor do these
machines run, and what type of gear reduction do they use.
Thanks.
Reply to
Terry G
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Dunno, but I built a 3 wheeled 20+ inch vertical bandsaw and utilized a gear box with a 10:1 reduction in it and a 1.5 hp motor (DC) and it has more guts than needed. I am sur I culd have gotten away with the 3/4 hp DC motor just as fine. It has yet to be pulled down and I have cut 4" thick alum as well as 1 1/4" steel plate already without a problem. Visit my website:
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Reply to
Roy
What RPM does your motor run at? With a 10:1 reduction I would guess around 1700rpm or so.
Reply to
Terry G
My DC motor is controlable, and max's out at 3900 rpm.........so I have a ful range of speeds from slow to fast for cutting various materials. A VFD would be a good suitable choice as well. Visit my website:
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Reply to
Roy
You have to look at the design of the saw. The blade needs to run at a certain speed. This is a product of the wheel diameter and it's speed. The speed of the wheel gives you your gear ratio. The torque requirements are determined by the width of the blade (kerf), the feed speed and the material being cut. Generally, saws should be designed around the blade. The blade supplier should be able to give you the minimum bend radius for the wheel as well as the power requirements in various common materials. If in doubt, oversize the motor and underspeed/underfeed the blade. The minimum wheel size can be exceeded for a larger throat. Generally, the larger the better for the saw wheels as the blade is flexed less.
John
Reply to
John Manders
You need about 3/4 HP minimum(more is better) for decent cutting speed. The blade speed should be between 100 and 150 ft/min for ferrous metals. These two numbers along with the wheel diameter and the motor speed determine your total reduction ratio and the torque required.
Belt drive is iffy for the final drive to the blade drive wheel because of slippage with reasonable size pulleys, say 6" or less. It can be done if you use a tight belt and keep it tight with an adjustable mount. Bicycle chain or cog belt drive is better. You need a constant hp drive( belts and pulleys or gears) which rules out a VFD if you are looking to get max. performance of the saw and motor at any speed.
Commercial saws such as the Delta or Wilton wood/metal use a combination of belt and gear drive to get about 8 different speeds. You can get by with 2500 ft/min for wood/plastic/brass/aluminum and 100 ft./min for ferrous metals.
Randy
Reply to
Randal O'Brian
Thanks for all the advice. I am pretty familiar with the ratios I need to achieve, and the blade speeds, but I was just looking for an average torque so I can determine the size motor to get.
I am going to be installing a second motor, along with my current 1720 RPM 1HP that I currently use for wood. I have a 10 to 1 reduction at the slowest speed using 3 pulleys and two belts. I will be installing an ac gearmotor that will run around 150 to 250 rpm, and use the existing 10 to 1 reduction I have. This will bring my spindle RPM down to around 20, which will make my blade speed around 80 FPM.
I am a little concerned about belt slippage, but I won't be doing to much heavy duty cutting, and I am usually not in any rush. I can tighten the belts up pretty well.
So my last bit of missing information is what power ac gearmotor do I buy. Since I am going through another 10 : 1 reduction I should be able to multiply the torque rating of the motor by 10 and get my final torque at the blade.
Almost all the ac gearmotors I have looked at have a torque rating. I am looking at a 1/3HP motor that turns 180 RPM with 100 in/lbs of torque. So after I go through my pulley reduction, I should have about 65 FPM blade speed with around 1000 in/lbs of torque. Does this sound like it would work? I am not sure what type of steel, or exactly how thick I will be cutting, therefore I am not sure what blade I will be buying. But I will be doing lighter duty stuff, probably no more than 1/2" steel, and very little of it.
I just want to make sure I buy a motor that will be sufficient enough since I really have no idea what type of motors, and gear reduction the average lower cost metal band saws use.
Thanks.
Reply to
Terry G
It sounds like you've got the basics there. Power = Torque x speed so you can calculate one from the other two. Your easiest option isn't to re-invent the wheel but to look at other bandsaws that use a similar blade and note their motor power. Exceeding this by one step is generally a good idea, especially if you're looking at real budget machines.
John
Reply to
John Manders
Buy the biggest gearmotor you can fit into your machine design. My 14" Delta has a 1HP motor and it is pretty slow cutting 1/2" mild steel with the 14 tpi blade running at 100 ft/min. In general, the required torque varies with the thickness of the workpiece, workpiece material, blade tpi, feed pressure, lube or not, wheel dia., etc. Hp determines the cutting speed once you get the blade fpm correct for the workpiece material and I recommend you go for at least 3/4 hp as an absolute minimum. 1 hp is about right for a hand fed saw .
Randy
Reply to
Randal O'Brian
Thanks for all the advice.
I haven't had much luck finding a 1 hp ac gearmotor. The biggest I found, and was considering getting was a 1/2 HP gearmotor that turned 151 rpm with 180 in/lbs of torque. With the proper gear reduction, I will be able to get my blade around 80 FPM. Since I am running a 10:1 pulley reduction at the output of the gearmotor, that would translate to 1800 in/lbs of torque at the blade.
I don't know if it makes a difference if I am using a gearmotor, or a standard motor. I do have a 1HP 1720rpm motor that runs the saw normally, but could I go down in horsepower since I am now running through a gear box, and a 10:1 pulley reduction?
What other sources besides ebay, and varies surplus stores would have something like this at a reasonable price? Maybe I am looking for the wrong thing?
Thanks
Reply to
Terry G
You can use the 1/2hp gearmotor, the only problem will be a slower cutting rate than if you used the 1hp motor with additional speed reduction to get the same blade fpm. It doesn't matter where the speed reduction is located, built into the motor as with a gearmotor, or added on externally.
You can buy a new 1hp gear motor at industrial drive supply houses or at a place like Grainger, but it will be expensive. Most hobbyists use the motor that came with their saw and add on the required speed reduction with belts and pulleys. It just takes about 3 stages to get 100 fpm at the blade instead of just one stage when you use a gear motor.
Belts or gears have a pretty high efficiency and you won't lose more than about 10% of your motor power using either one. It all boils down to what you can buy, scrounge or dig out of your scrap box. Just remember that the motor HP determines the cutting rate through your workpiece and the workpiece material determines the blade speed in fpm.
Randy
Reply to
Randal O'Brian
Thanks for the advice.
I ended up picking up a 1/2 HP 150rpm 180 in/lbs of torque motor for $45.00. The price was right, so I will give it a try. My plan is to install both motors (one for wood, one for metal) side by side in my saw. I will use the existing 4 position pulley on my motor and install it on another shaft which will sit between the two motors. Then I can connect one motor or the other by just switching the belt over. This will let me keep my adjustability of the wood cutting, and even give me a bit of flexibility with my metal cutting. We'll see if it works or not.
Terry
Reply to
Terry G

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