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SFPM dilema and some questions on homemade bandsaw

In the process of making my 3 wheel bandsaw. I am wanting to use a DC motor of 1 1/2 hp with a speed controller, but would like to add a jack shaft. as well, just to make sure I can keep up the torque on the saw at the necessary speeds needed for general metal cutting. The motor I have is 1 1/2hp Leeson Electric, (removed from a typical treadmill) and runs up to 5120 rpm and pulls 15 amps. The controller I have for it is made by Dart and is supposedly capable of handling up to a 2 HP motor. I understand this controller is supposed to be able to keep the motors torque up at low speeds, but I would not bet my life on it. Guess I am just paranoid, as I do not have to much dealings with DC motors and controllers.

So what ratios would I need to go with to get the saw down to useable speeds for metal cutting? (Looking for 65 to 550 SFPM from what I have found out in regards to speed), although it would be nice to jack it up in speed for wood cutting.

Would I be better off initially reducing the speed with a gear reducer that drives a jackshaft and then the saw or what? Or should I still be able to get by with just a 4:1 ration jackshaft and rely on the speed controller to do its job?

So far except for this problem, the project is going fine. I have one more wheel (drive wheel) yet to cast and machine, shuld have my tires next week, have the caster / camber tension assembly made, starting to work on the blade guides. This brings anopther question to light. Lots of saws today use simple ball bearing for guides. They seem to last ok on my H/V bandsaw, but have a habit of allowing lots of crub get by or get beat into the bearings or blade, so I was thinking on using some guides similar to what DoAll uses. Is there any materials out there that I can machine in a home shop thatw ould serve usefull in making these guides. They need to work with 3/8" at a minimum to no more than a 3/4" blade. Buying those Cool Cut guides is out of the question, so I need to come up with a home brew deal. I was also thinking of using a small engine valve tappet (like found in B & S engines) that runs in a bushing and is adjustable in and out with a setscrew. Any other ideas greatly appreciated.

Presently I have just the basic shape of the frame laid out and am concentrating on making all the actual working parts, so I can juggle things here and there, and the frame will be built around these last.

Looks like it will have a 17" + - 1" throat size, 8 1/2" to 9" cutting height, stand 71" tall, have a width of 29" and be 8 1/2" in depth, take a 107" blade is usiing the three wheels or a 86" blade if utilizing just two wheels. Table size 20 x 22.

The table is still one item that I need to dio a bit of thinking on. I wiuld like to be able to mill it out so I can use a push type rip fence so it looks like a piece of steel plate or perhaps 1/2" thickness is in order, so if anyone has any other suggestions on a table they would also be appreciated. I already have a mitre / rip gauge from a large Delta belt / disk sander that I would like to use. Visit my website:

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Reply to
Roy
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Wood speed is something like 2000 to 3000 fpm or 5 times what you need for metal. If you want to do wood, I'd suggest some sort of belt deal to switch back and forth. You would need to change blades also so why not just make a big deal out of it and do it right.

You want the 5120 to match up with 565 fpm. You didn't say what size wheels you plan but assuming 14" or so you will need about

150rpm on the shaft or a 34 to 1 reduction. Only thing that will do that in one step is a worm drive. I'd suggest a belt reduction of about 6 or 8 with a gear reduction of 4:1 or 5:1. You might be able to use the gear reduction bearings for the drive pulley mount.

For 1-1/2 hp, the smallest v-belt drive pulley you should use is

2", 2-1/2" is better. Go smaller and you will have slippage and excessive belt wear. Assuiming you can even get a 12" pulley, that means a maximum of 6:1 reduction in a single V-belt recuction. 2x on this would be 36 to 1, about where you want to be. You can source the large pulleys at a farm store, they have an array of hubs, plus an array of wheels, weld them up. Sounds awful, works fine, about $16 for a 12" pulley in your choice of hub sizes. If you still want to do wood, use 1 reduction for wood, 2 reductions and a jackshaft for metal.

You should be able to get the DC motor to run at 1/10th rated speed if you have good parts. Keep in mind that the TORQUE available is the same at all the various speeds. Since HP is speed x torque you have 1/10th the HP at the lowest speed. Exceeding this means overheating the motor.

Cheers.

Roy wrote:

Reply to
Roy J

Roy, I run a speed of 125 linear FPM on my saw at work and 200 LFPM fixed on my upright home saw. The work saw has a mechanical variable speed, which I seldom change except in using it to cut wood. My home saw uses a reduction gearbox off of a conveyor system with a chain drive to the lower wheel. In cutting metal, it works perfectly fine. My bandsaw for wood however, runs at

4,300 LFPM fixed. That thing cuts most any wood faster than you can feed it. Hopefully these figures will be of some sort of help in your planning.

RJ

Reply to
Backlash

I forgot, the wheels are 12 inches in diameter that I cast for this saw as I could not swing larger and machine them in my lathe.

Regards

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Reply to
Roy

Ok, so the blade will move 3.14 feet for every rotation of the drive wheel (pi * diameter). With a motor speed of 5120 RPM, that's a blade speed of 16,077 feet per minute. That's *way* too fast even for sawing wood.

Typically for wood you'd want a blade speed of about 2000 FPM, or roughly an 8:1 speed reduction. For cutting steel, you want a blade speed of about 150-200 FPM, so you need a speed reduction of about 100 to 1.

Suppose you use a jackshaft and two sets of pulleys, each a 6:1 ratio, which will give a total of 36:1 speed reduction. Then you can use the electronic speed control to give the remaining 3:1 reduction for a total of 108:1. That should be reasonable, and still lets you speed up about 3x for cutting non-ferrous metals.

For cutting wood, you could swap one of the '1' pulleys for a '6' pulley. That'd give a 6:6 or 1:1 ratio for that set, leaving you with just the basic 6:1 reduction provided by the other set. The electronic speed control could then drop the speed the remaining amount to hit 2,000 FPM for cutting wood.

Gary

Reply to
Gary Coffman

I've pondered making a couple of tables with guide slots, but haven't gotten around to making them yet.

I think the way I'll approach the fabrication is to use 2 thinner plates (maybe 1/8") on each side of a bar. If the slot wouldn't be deep enough, the bar could have a slot milled in it. The plates could be welded to the bar, or attached with flat head countersunk screws (which could be filled with epoxy to avoid collecting chips in them).

Some reinforcement ribs could be added where needed. I'll most likely frame the underside of the tables with bar stock.

WB .............

Reply to
Wild Bill

When I went to work on an old wood cutting bandsaw, I started by reading up on bandsaws. It seems that the bandsaw that cuts dead straight in the plane of the blade has yet to be invented so instead of a table with guide slots, I made a flat table and supplied myself with a piece of angle and two C clamps. A careful test cut allows me to draw a line on the table in the direction the saw cuts. This changes slowly with use on a given blade and also changes from blade to blade. The line is easily erased and re-drawn. My experience with my metal cutting bandsaw has been similar.

Ted

Reply to
Ted Edwards

Yep, I know whatcha mean. The test cut generally reveals which way, how much to adjust for each time. It's almost funny that blades wander so much. Cuts made with narrow blades (on sabre saws, for example) seem to be even less predictable.

My other applications are for slots in tables for grinding operations, where they'll provide a reference angle.

WB ....................

Reply to
Wild Bill

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