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Bandsaw and Gear Reducer?


JHCC

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I've been quite happy with my horizontal bandsaw for cutoff work, but I've been thinking that a vertical bandsaw would be convenient for lots of other tasks. One option that's occurred to me is to take a smallish bandsaw (like this 10" benchtop model from my local FB Marketplace: 
No photo description available.)
and using a gear reducer (like this one from my favorite industrial surplus place:
 20201020142021868_L.JPG&w=600&q=100)

to get the blade speed down to between 150 and 250 feet per minute. Any thoughts?

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Rigidity is the issue.  Most smaller bandsaws are not nearly rigid enough, even for wood cutting.  They can be a nightmare.  If you happen to find something old school and rigid, yes it can work for you to cut metal--but it is far better on sheet goods than thick stock.  Thick is quite slow and the high pressures you need to keep on the material make cutting it on a vertical a bit of a work-out.

I have a 14" vertical from Boeing surplus and it does work to profile some things but it's not a job I look forward to.  Sheet is not bad to work but 1/4" thick plate and a bit above is not fun.  Top quality sharp blades are a MUST.

My Delta 3-wheel 18" has a rigid cast iron frame. It came set up with 2 pulleys--one for wood and one for metal.  Same as the 14" above basically in function but the 3 wheel deltas with the cast frame are not a fan favorite so often are available for low pricing.   Costco sold them a couple of decades ago--after tweaking for belt tracking (that's why they weren't favorites--homeowners didn't know how to tweak), they are pretty good machines (Photo stolen from the internet).  These are pretty heavyweight.

2012-09-25_16-11-32_379-jpg.51665

 

I also have a disassembled (for restoration) Walker-Turner 2 wheel vertical from the 50's that is bench-top sized and has a full cast iron frame.  It was also a "universal" unit and spent a lot of time metal cutting.  Just pointing out that if you dig deep enough, there are some rigid units out there.  For ever good one there are about 100 terrible "homeowner woodworking" units without proper rigidity though so don't settle for those.  In a bandsaw, rigidity is EVERYTHING.

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Well, someone in my town has a 1950s-era Craftsman 12" band saw listed on CL. Judging from the photos and the manual (researched online), it looks like the entire back is a cast-iron web that should be pretty rigid. We shall see.

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I thought of this, but my horizontal bandsaw doesn't go vertical. I haven't measured it, but it only goes up about 30 degrees -- enough to get stock into the vise, but not enough to use it vertically.

Thanks for thinking of my back, though; it says Thank You.

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So, now we start looking at gearing down the speed. The motor is 1725 rpm with a 2" pulley, and there's a 5" pulley on the saw itself. If my math is correct, that means the saw itself is currently running at 690 rpm, which means a blade speed of about 2,165 fpm.

I gather (from the blade speed and feed speed chart at sawblade.com) that I need between 200 and 250 fpm, especially for the thinner stock that I plan to be using this for (mostly thin plate, but occasionally splitting a thicker square for a split cross).

I'm looking at the various bits of non-functioning machinery I have around the place, and I think I can cobble together a jackshaft from some of the parts. This includes a couple of pulleys that are also 2" and 5". That would presumably bring the rpm down to 276, which means a blade speed of about 865 fpm; that strikes me as still too fast.

I could get some 10" pulley wheels from Zoro for about $50, which would bring the rpm to about 70 and the blade speed to about 215 fpm. That looks okay to me.

I've given some more thought to using a gear reducer. While the cost is probably comparable, I'm thinking it would be a bit more of a stretch to get all the pieces working together and therefore probably not worth the effort.

Any thoughts?

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  Most (not all, mind you) of my homemade stuff is built by trial and error, Rube Goldberg style so I salute you for doing the math so to speak.  Looks like you are on the right track.   I can say small pillow block bearings are best for your shaft.  I used them on my hack saw.  Belt drive is best.

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There looks to be enough room for your gear reducer under there with the motor, John. 

If you're going to be cutting mostly thin stock you'll need a fine TPI, the rule of thumb is, "3 teeth on the cut face at all times." Variable pitch blades are getting pretty common and they work well. If you want to do intricate or tight turn cuts you'll need a narrow blade and they're very sensitive to feed pressure making cutting thick stock more difficult. Cuttings even starting to jam in the kerf or the slightest difference in sharpness on one side WILL cause curved cuts. If you're going to be cutting scrap be sure to brush any crud, rust, dirt even dust off first. Nothing dulls a saw blade like mineral grit in the kerf.

I have a Jet 7" x 13" horizontal vertical band saw and it's one of my favorite power tools. My worst complaint is the table is right where you need to stand using it vertically. I've thought about modifying the guide rollers so it'd cut in the same line the band takes off the drive and tensioner pullies but making it a quick change is problematic.

Frosty The Lucky.

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2 hours ago, Frosty said:

you'll need a fine TPI

TPI issues aside, what do you think about the blade speed question?

If I use a 15:1 gear reducer, that would bring the saw rpm to 115, which gives a blade speed of 360 sfm.  A 20:1 would give 85 and 270, 25:1 would give 70 and 215, 30 would give 60 and 180, and 40:1 would give 45 and 135. (All numbers rounded to the nearest 5.) That’s assuming I don’t do anything fancy with the pulleys. 

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(I was going through my collection of machine and motor bits this afternoon and found a nice 1/6 hp gear motor with a 30:1 reduction and 57 rpm output. Unfortunately, it’s 3-phase, so I can’t use it as it stands. Maybe I can take it apart and use the gearing....)

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By the way, here’s the ribbing on the inside of the back. Both front and back are made of cast aluminum. The front attaches to the back with four knobs, and I suspect that that adds some additional rigidity. Two are missing, so I’ll have to buy or make some replacements. 

12587DB0-6A13-4BCC-8302-B20F65645070.jpeg

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Sorry for the slow response John, I got involved around the house. I can't say off the top of my head, my saw has a 3 step pully and I adjust feed rate by sound. "SawBlade dot com has a good chart but it doesn't seem to think anybody is cutting less than 1" thickness. There are other charts though. 

It seems counter intuitive but a little too fast blade speed is better than a little too slow. You have to clear the cuttings faster than you make them or they ball up in the teeth and things go downhill rapidly from there.

Advancing the blade too slowly is better than too fast for the same reason. You can use a too coarse blade in too thin stock by advancing it slowly enough the teeth don't catch. A too fine "pitch" blade in too thick stock will have trouble clearing cuttings so you have to advance it more slowly. 

How slowly? You have to play it by ear and how well the cuttings are clearing the kerf.

The above chart lists SFPM for carbon steel @ 250sfpm for 1008- 1010 and 200sfpm for 1048-1095. The feed rate is listed in the next column. These speeds are for 1" thick stock though.

I don't have hard numbers I don't play it by the number but I've been doing it by hand, eye and ear my whole life.

The "ribbing" in your bandsaw does stiffen it up but it's going to be less than it should be for cutting metal. You'll need to feed the blade more slowly or the saw will move and you won't be able to cut a straight line. This won't be as much a factor on thin stock but any drift in the blade track increases the chance of snagging a tooth or wearing one side of the blade more quickly. The ribbing are structural shapes, triangles are GOOD unfortunately they're aluminum and open on one side. Mild steel wouldn't be as rigid as cast iron in this situation, that's why you see such heavy structural shapes used in home built saws. The successful ones that is.

Your saw'll work but I'd keep an eye open for something made of cast iron.

Frosty The Lucky.

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Thanks, Frosty; much appreciated. I see what you mean about too fast being better than too slow. You’ll be happy to know that I had already been thinking about chip clearance as it’s affected by feed speed. I guess I can be taught after all.

I see what you mean about rigidity, and I would be significantly concerned if I were anticipating using it for anything more than about 1/4” or so. I’m hoping that thinner stock wouldn’t present as much of an issue. 

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It's always my pleasure John. Presenting information and sources isn't really the same thing as teaching, especially when the "student" is actively teaching themselves and only need to be pointed in the right direction. 

Rigidity is always a concern with power saws and a source of flex is the natural vibration a saw causes as it cuts. Teeth of any kind, be it a saw or a wood chisel pulls itself into the stock it's cutting. Each tooth bites with a little tug as it first impacts the stock then as it progresses the pull stabilizes and no longer has as much effect. The initial impact tug is a shock that effects the entire machine and the sooner a tooth exits the kerf and releases the steady pull the greater the vibration through the machine.

It's not a serious factor but something to be aware of on a back burner level. It's usually dealt with by sound and feed speed adjustment. It is so minor a factor in a cast iron saw as to need sensitive instruments to detect but a thin wall structural aluminum casting is a different matter. When you get the chance to safely do so, touch the side cover over the top wheel and feel the vibration and how it reacts to changes in feed pressure. 

It's just something to bear in mind if your saw doesn't want to cut straight. If it pulls one direction it's probably the blade dulling on one side, our of alignment guide rolls are immediately apparent the blade won't track straight brand new. Guide rolls are usually the last thing to check. If the track seems to want to wander, first try using a guide for the stock, if that doesn't work try less feed pressure.

If I had another vertical band saw to experiment on I'd be sorely tempted to filling the "webbing" with concrete or similar but Bondo is too expensive and weight is a good thing on something like this.

Frosty The Lucky.

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I was actually thinking about something like that as an option. Hmmm....

 One other thing that I was wondering about: the linkage between the motor and the saw. Currently, the motor connects to the drive wheel by way of pulleys and a rubber V-belt, with the latter being tensioned by the weight of the motor, which is mounted on a hinged shelf. I’m wondering: does that act as a shock absorber, or does it add vibration from motor’s unsecured movement? If the latter, would the added weight of the gear reducer help reduce vibration by pulling the shelf down more? Would that effect be increased by adding a tensioning bolt between the shelf and the frame? Could I eliminate the problem altogether by using the gear reducer as a direct-drive between the motor and the saw? Or indeed am I overthinking this (again)?

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That's a good question John, I'd have to play it by ear, maybe even make a recording of how it sounds before I made the change to compare later. Do you have a fish type scale? One that you weight things by hanging them from it? If so I'd weigh  the motor on the hinge mount between the saw pully and motor pully. Then weight it with the gear reducer added, wire or duct tape would serve. 

I imagine it'll add a significant % of the weight of the gear reducer to the load on the saw's drive wheel's bearings and that might be a B A D thing. 

It's not too difficult in principle to adjust the weight hanging from the saw by moving the pivot of the hinge mount closer to the motor/reducer's  CM, (Center of Mass). The hinge mount is a lever and as it sits the saw is supporting close to 100% of the motor's weight. Moving the hinge pin closer to the CM causes the hinge pin to support a greater % and the saw lesser. Pass the CM and it'd be pushing the belt at the saw. Yes?

It'll be more work than it sounds but shouldn't be onerous and you'll be able to adjust it with micrometric precision. 

Frosty The Lucky.

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The reducers I’ve been looking at have been in the 25-30 lb range, so I see what you mean about potential problems with the additional load. I guess another option would be to make an adjustable support from threaded rod, with nuts both above and below the motor shelf. That would be fairly easy to tune up and down as needed, without having to shift the hinges.

 What do you think of the direct-drive option?

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Adding an adjustment screw should work well but I'd keep an ear on it till I was sure it worked well.

Direct to the saw? Too much weight on the saw shaft and there is no structural stiffening to the frame around the blade wheels. Also, it'd be hanging from the side of the blade wheel and torquing it not just pulling down from close to the bearing. That wins a loud NO from me. 

Frosty The Lucky.

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Would that be true even if the gear reducer and motor were mounted on something solid, so that the only force acting between them and the saw were the rotation of the motor transmitted through the reducer? Obviously, the motor and reducer can’t be supported by the drive shaft of the saw, because then they wouldn’t have anything to turn against.

This is kind of what I’m talking about (imagine the box of lights is the reducer and the red box is the motor, both mounted solidly to the shelf):

 

964F677C-DCF4-4E44-87DA-3406FDEF4FF2.jpeg

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ARGH! :wacko:

The image I had in mind is how the gear is connected to my bandsaw, not yours. That should be no problem John, work great in fact. 

If on the other hand, you use a hinge mount you could use a pair of step pullies and make it a 3 speed.

Frosty The Lucky.

 

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On 12/13/2020 at 1:19 PM, Frosty said:

If I had another vertical band saw to experiment on I'd be sorely tempted to filling the "webbing" with concrete or similar but Bondo is too expensive and weight is a good thing on something like this.

Would that be to add mass or to add rigidity -- or indeed both? I've got a whole bunch of little bits of steel and lead that I could easily glue inside with some Bondo, silicone, or something similarly sticky.

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