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Bandsaw - diy.

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NeoTech:
Im mainly looking to making a bandsaw to cut steel and aluminium and maybe plastics.. But its mainly for being able to countouring knife blanks before grinding and milling. =)

S. Heslop:
If he's using thin blades, the wheel diameter shouldn't be a problem. It's a quite vertically compact design.

One of the things i'm planning to build in the near future is a Matthias Wandel style bandsaw, but without easy access to a planer thicknesser i'm considering making the frame from welded box section, although that might become quite pricey so i'm still thinking about it.

S. Heslop:
How thick is the material you're going to be cutting? A thicker (and wider!) blade allows for more tension and beam strength to try prevent it from deflecting when cutting through very thick materials, 12 inch slabs of hardwood kind of thick, but if you're only planning to rough cut thin stock there's no reason why a thin wheel and blade would be a problem, but it'd give the saw less versatility.

NeoTech:
thickets blade stock i use is 6mm A1, and the more common is 4mm D2 and some O1  (AISI standards).. So its not that thick.. And then of course i could cut tubing, pipe and sheets on that thing.. I dont expect to cut 200mm thicj slabs of steel on it anyway.. =)

vtsteam:
I have 3 band saws, one of which I built. They are the usual 4x6 metal cutting Chinese mfg type, A 24" home built bandsaw mill for lumber making, and a 3 wheel Duplicarver 24" throat bandsaw that I have owned for 32 years. I once owned a 28" cast iron vertical bandsaw made by American Sawmill Machinery Company, which I used in my boatshop

Definitely blade life is reduced on multi wheel band saws used for cutting wood. Why is wood worse? Because the blade speed is higher by a big factor. Why are multi wheel saws worse -- two reasons. They have smaller wheels, AND they are seen as bigger saws. Bigger saws are used on heavier stock. Heavier stock implies thicker and wider blades. Thicker and wider blades fatigue faster. Metal fatigue is what kills the blades much more quickly than any other cause in a multi wheel band saw.

Would I trade my multi-wheel 24" saw for another two wheel band saw? No. Why? Because I can move it into a boat and do joinery there, rather than hopping into and out of a hull to make my cuts with a more massive two wheel wide throat saw. It is compact. That is its only advantage.

Shortly after I bought my saw, the manufacturer spent a lot of money to send out, at cost, a speed reducer for the saw, because the rate of blade breakage was so severe that customers were returning them left and right. I believe that Duplicarver may be out of business now -- possibly long since gone. Not sure.

Speed reduction helps, but it's not a particularly good way to solve the problem. Kind of a band-aidapproach.I also buy relatively thin and narrow (3/8") blades for it (actually, I have a roll of blade stock, and silver solder bands now.)

The wheels are 8-1/4" diameter. Ideally, for wood cutting, bandsaw wheels should be 12 for good blade life and a good range of blade widths. Six inches seems like a very small diameter, to me. I suppose a 4 wheel might be better than a 3 if the angle of the turn is less (90 deg vs 120 deg), but I don't know the answer to that. Radius and the number of flexes would seem to me the real determinant to metal fatigue. As soon as a crack starts, you're done.

A multi wheel saw shows its greatest advantage if it is portable, I think. So a 4 wheel, to me looks bulkier and heavier than a 3 wheel. Seems to me, different ready made wheels could have been chosen with a little more diameter, and a 3 wheeler produced. They don't have to be solid wheels, by the way. My big sawmill uses pneumatic trailer tires and wheels.

Anyway just my experience here, yours may and will vary -- and our purposes and usage are/were probably different. Hope it helps.

EDIT: just saw further down the thread where you say the main usage is cutting steel and aluminum and making knife blanks -- so wood cutting isn't much of a concern. I would say that wheel diameter is far less of a concern with a slow turning metal cutting blade compared to wood cutting. Although I do wonder why such a large saw was wanted then.  Maybe you also want to mill wood for handle blanks from timber?

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