hi/lo speed gear box for bandsaw
I'd like to use a 2 speed gearbox on my band saw in conjuction with a variable speed motor...for a variable speed band saw.
I figure I need a gear box with 2 speeds, about 20:1 and about 1:1. I've done this in the past with pulleys and shafts...where I've unhooked one shaft and ran a belt to a different pulley set for a different speed. This time I need more convinience where I can just flip a lever for hi/low gear then use the invertor speed control to dial in for task at hand.
This saw will be used for wood and tool steel and I'de like to have speeds from about 2000ft/min to about 80ft/min.
Maybe I'm missing something here????
If you are planning on using a variable speed motor. Why do you need a 2 speed gearbox?
And besides that....unless I'm mistaken (which isn't unusual), without going to some kind of "transmission" (which has to be "real" expensive) how can you get more than 1 speed out of a gearbox. [I do seem to remember some special gearboxes that had some internal "cone-type" gears that could be manually adjusted to change the pitch diameter of the gear engagement, but if your looking for something like that, you would be better off buying a variable speed bandsaw outright. Those gearboxes would be just as expensive (or more) than a transmission.]
I don't see why not. Getting single stage 20:1 using belt might be difficult although as you noted if you want to run one side on a shaft that should be doable. This too is on my long list of to do.
Rpease, I want to cut a variety of materials with blade speeds of say 2000sfpm to 20sfpm. Hence the total reduction is about 100X. If I slow my motor down 100X then there is no HP left for sawing. My 1725 rpm motor would only run 17 rpm!
"Gearbox", "transmission", "cone thingy"....whatever we call it, I think it needs two speed ratios, 1:1 and 1:20. And a quick way to change speeds...like a lever, knob...or something. I don't want to use any tools or spend more than a few seconds changing speeds.
Rotate, yes...20:1 is tough to get with belts and pulleys. I did this on an older saw and it required 2 intermediate shafts to get the reduction. Other wise you need a monster-sized 40" pulley on the saw and a mini 2" pulley on the motor.
post your ideas!
Well, I'd say that a 20 tooth worm gear/worm setup should do the 20:1 real compact and shouldn't cost too much (depending on your definition of cost), plus there should be tons of low speed torque.
Making that 90deg turn jive with the 1:1 could be tricky tho. Check ebay for a reducer, I've seen them there cheap.
For 20:1 with gears I think you would have to compound them to keep the size down otherwise you'd need a 200:10 gear set. I figure that 200 could get big to have a decent tooth. But a 50:10 to 40:10 could be real sweet in size.
You could do that with belts too.
For shifting - I was just reading about a older gearbox method that used a "spring key" to engage a gear/pulley on a shaft. Picture a driven shaft with a keyway running the length. Your 2 pulleys free spin on it and are both belted to your bandsaw pulley shaft full-time. Instead of a fixed key locking the pulley to the drive shaft, they used a long key that was undercut and spring loaded (like a cantalever) that could slide in the key way on the shaft. The key's top surface was only long enough to engage one gear at a time.
I put an image here to illustrate it http://www.vers5d.com/metal/spring-key.gif
That's my 2 cents
several years ago, i did just that same thing, but i used the transmission out of a
lawn tractor, don't know what brand it was,
but it had 3 speeds and it was belt drive in
and belt drive out, had a gear shift, but
you had to stop the motor to change speeds,
i used a portable tach. to determine wheel
speeds, and did a little math! first gear
worked out perfect for mild steel and high
gear was great for wood! wish i still had it!
Many years ago I did just what you are looking for. I used a "transmission" from an early automatic washing machine. I think it was a "Westinghouse Laundramat". These havent been made many years, however if you can find one it works well. This thing has a planetary gear train built into it with co-axial input and output shafts. It is solonoid operated which means you can change gears while running with a toggle switch. It changes from a straight thru speed to a 10:1 reduction. Just right for a band saw. There are still places around that repair and/or trade in used washers. Check around, you just may find one.
good luck, Wayne
Rob it sounds to me like you have already spent a lot of thinking about sawing. Two speed motors are a little costy but cheaper than gear boxes. I have worked on many machines that used two speed motors to get the speed range they needed ..... go for it.
I see your point. I was thinking along a different line. Also, I missed one of the "0's" in your statement. Thought you said 200 ft/min.
I'll be quiet and listen now........
Brunneng, thanks for the post! I like that idea and I think the concept maybe a good solution. I've seen something similiar called a "rolling key". I'm thinking that it could be used to engage one gear while simultaneously disconnecting a different gear.
For me, this project is for the "journey" rather than the "destination".
I ordered a catalogue this morning...from there I'll start the design using off the shelf gears.
In the mean time, I've already installed the Invertor on the saw...and confirmed that the invertor will provide the speed range needed...but not the HP when things really get slowed down...hence I do need a reducer to get the motor speed back up in a useable range.