speed reducer for band saw

[yankeeone]

Hi, I am going to use a speed reducer to make it posable to cut thin steel with what is currently a wood bandsaw, the motor is 1hp and 1750 rpm. I am looking at 30/1 ratio, I see some that look like they will do the job but they give max output torque at 300 or so inch pounds. What kind of values should I be looking for ?
Thanks

 

[metlmunchr]

torque in foot lbs = (5252 x 1 hp)/1725 rpm, or about 3 ft-lbs or 36 in lb for a 1 hp motor. Assuming 100% efficiency for the gearbox for worst case, the output would be 30 x 36 or 1080 in-lb.

It doesn't take much power to saw thin steel in a vertical, but the problem comes when the blade snags, and it will. At that point, the motor's full output is going to be fed into the gearbox and it likely won't survive.

A 1/3 hp motor should work, and used fractional hp motors are always around for dirt cheap prices. Would be a bunch cheaper than a speed reducer that'll handle a 1 hp motor.

Just curious.... what sort of blade speed in fpm would the 30 to 1 give you?

 

[p00p]

might be able to swap out the pulley to meet the drive speed needed.

 

[matt_i]

With a diameter measurement of the saw wheels it could be easily calculated.

I have always had it tucked back that a 30:1 was a good starting point if converting for metal sawing.

As the Metlmunchr is alluding, you want 3 teeth engaged in the thickness you are trying to saw or else the blade is rapidly trashed. For example, 16ga steel is a nightmare on most every bandsaw. Its also indirectly why shears exist.

 

[seber]

I did that some years ago with a jackshaft. I moved the motor down below and added the jackshaft where the motor had been. Giving a double reduction. The pulleys slip if the teeth catch on thin material. I believe I had to reverse the motor rotation, but it's been a long time and my memory is faded.

 

[yankeeone]

Thanks, I am basing the thirty to one on an chapter from how to book published in the mid fifty's ,The popular Mechanics do it yourself encyclopedia. I have had them since I was a kid and probably gone thru them a dozen times. I will check out what the blade speed should be with just the reducer, there are also some pully ratios added.
I agree about the 1 hp being a bit much, and I will look for a 1/3 hp

 

[yankeeone]

here are the photos from the book, there is also the lathe option

 

[Lucid Moments]

might be able to swap out the pulley to meet the drive speed needed.

Unlikely. I did some similar looking a while back. I did end up swapping out the drive pulley and that brought the blade speed down to about 60% of what it had been. There just isn't enough room to go much bigger on the driven pulley. Or at least not on the saw I have, and all their designs seem pretty similar to me.

 

[macgee]

Unlikely. I did some similar looking a while back. I did end up swapping out the drive pulley and that brought the blade speed down to about 60% of what it had been. There just isn't enough room to go much bigger on the driven pulley. Or at least not on the saw I have, and all their designs seem pretty similar to me.

Agree, and this has been discussed previously many times. Just changing out the pulley's will not give you remotely what you need. You literally have to slow down the bandsaw's FPM speed by 90%. That will require a jack shaft (additional pulleys) or:

You could try changing out the two pulley's and then getting a DC brushless servo motor with variable speed. Changing out the pulleys to help slow down the saw some and then let the variable speed motor do the rest. DC brushless servo motors are very good at delivering high toque at slow speeds. With this set up, you can then speed it up to cut aluminum and wood if you chose the right pulley combo to work for both scenario's. Three phase VFD is another option but the new inexpensive DC brushless servo motor setups in sewing are getting a lot of praise when using them for machines in shops.

As discussed, there is no cheap or low labor solution for this.

 

[MJD1]

I'm assuming a 14" saw when you say 30-1 reduction, should get you around 200 sfpm. I would use a right angle speed reducer. They come in left or right hand orientation. if using original motor, a shaft type would work, either with pulleys or a coupling. You could also use step pulleys on the reducer to give you a faster speed for soft metals. I would stay away from the vfd on a 3 phase or DC motor, since you would really be limiting the torque due to low motor speeds. Another issue is overheating due to slow fan speeds.

 

[macgee]

MJDI,

I agree about heat and torque with a VFD but you should look into the new brushless DC servo motor now being used in the sewing industry, it been a game changer for them for using super slow speeds with good torque compared to the previous DC bushed motors. Bandsaws and sewing machines have similar characteristics and issues.

Also, if you add a much larger pulley like a 8” dia. on BS side and a 1.25” pulley on motor side on a 14" BS, then you're already @ 987 SFPM (790 sfpm with 1.0" pulley & AX belt) when at full speed; this would really help the motor keep some of the rpm’s up that will help with heat and torque. Without changing the pulleys, then for sure you’re definitely asking for all kinds of real problems like the ones you brought up.

@30% (38%) motor speed giving you 290sfm which is fine for most carbon steel cuts, there should still be enough fan spin to help keep it cool and torque available and most motors are fine working at that speed, but it's not the same torque as 100%. All of this includes some labor and money but should be cheaper and much better (torque) than a treadmill motor scenario after its all said and done.

 

[seber]

If I were going to do this today, I'd look for a powered treadmill. Around here they sell for $50 pretty frequently. That gives you a variable speed DC motor and control.