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I need ideas for a new spar lathe. My previous one held up pretty well, but the motor has cooked and the V belt gear reduction is worn out. I could just replace the motor and make a couple of new plywood pulleys, but I was never very satisfied with the gear reduction, the noise and space it ate up at the end of the bench.

With the 1,150 RPM motor I was using, I needed a 23:1 gear reduction to get it down to 50 RPM. I used a 3" pulley on the motor, V belted to a 24" plywood pulley I made, which gave me 8:1 and about 145 RPM. The 24" pulley had a 6" pulley (more plywood) screwed to it's center and V belted to the 18" disk, I used for the drive plate, on which the spar was clamped. This gave me about 50:1 and about 50 RPM, which is a good speed. All the belts and pulleys made a bit of racket and often some smoke, as the second belt rubbed against the 24" wheel.

I'm thinking maybe a gear motor. I have a windshield wiper motor (12 VDC) with a gear reduction built in and it's about 20 RPM. I can bump this up with a single belt to 50 RPM, which will increase the torque of this little motor. I also like the idea that I can use a step pulley so I can change ratios quickly with a tensioned or the motor mounted on a swinging arm. I figured I use a computer power supply for this motor, which is a 300 watt unit and should be able to handle the wiper motor. Maybe I'll throw a pancake fan on it (120 VAC), to keep it from cooking.

You need a fair bit of torque to spin a big mast. My next one is for a 3 5/8" thick 16' stick, so not very long, but pretty big in diameter. Knocking the corners off is easiest with a gouge on a tool rest. This makes it 16 sided (birdsmouth or any octagonal stock) really quickly. To finish it off I use a belt sander with an extra long belt (3"x18" sander with a 24" belt) wrapped around a rolling pin sort of thing I made. This can sand about 90 degrees around the mast as it rotates on the lathe. Progressing through 40, 60 and 80 grits, I move to using a loose piece of 100 grit paper, on a couple of wooden blocks to hold it. After turning it at 100, I hand sand with the grain to smooth it up.

Back to the lathe. I'm not sure this Mercedes wiper motor has enough nuts to spin a big stick, even geared up 2.5:1. I've seen some geared motors as low as single digit RPM's but these are usually pretty small, drawing less than an amp. The wiper motor is in the 8 to 10 amp range, judging by it's case and wire size. I could redesign the 120 VAC motor and belt setup to remove some of the friction and noise, but this is more work, making new pulleys and mounts. I have a need to spin a 24' mast coming after this one, so I'll need a beefy setup.

Any thoughts?

Have you thought about a treadle?  You could get plenty of torque and control the speed yourself, and it would be easy to make with stuff laying around.  I can't imagine how you could move along the stick with a foot powered lathe, but I bet there is a way to do it.

Al

Dancing on a treadle while working a compound belt sander just doesn't seem very appealing, maybe it's just me. I use to have a treadle grinding stone, but it too got a motor attached to save my legs.

So, you're just slowly spinning the spar while holding a belt sander over it as it turns?  I thought you were using a gouge to shave off the high points like turning a table leg.  Maybe you could make up a brace system that would allow the spar to turn with some resistance and let the sander turn it by lightly holding it to the spar. 

Am I getting too far out?

Al

The gouge removes the corners of the raw spar stock, basically the bulk is whacked off, then on to the belt sander. The belt sander works bets if it's rotation opposes the spar. I also have an attachment on the belt sander which holds a loose belt, so it can wrap around the spar as it sands. In fact, I've used this tool to round spars not on the lathe, but the counter rotating lathe makes things quicker. The process is fairly well fixed for predictable results, now it's just the spar spinning thing to address.

I have not a work experience on lathes, but instead of using a car wipe motor why don't you use a hand drill? I am sure you have more than one, you can easily build a drum to reach the right ratio and torque will be more than enough.
Gianluigi

If the biggest problem is gearing down to a reasonable speed, maybe you could cobble together a reduction gear setup out of an old junk 10 speed bike drive train.  If you put the pedal gear on the work piece and the wheel gears on the motor, you can get incredible torque and a pretty good reduction.  If you can't get enough reduction you can double the set up and gear down to almost nothing.  A human can't put out more than a fraction of a horse power, so that electric hand drill idea may work pretty well.

Al

Gearing down isn't an issue, I've done this before, but you have to look at the gear ratios and sit down and figure out how you'll accomplish this. Then balance this against a gear motor that does most of it for you, heat and noise issues should be addressed too.

I could use a 3,500 RPM fan motor, but that's a 70:1 reduction to get it to 50 RPM. I could use a drill motor, but again it's a huge reduction, for little gain. If I'm going to have a reduction, I'd like to take advantage of torque multiplication, so I can use a small motor, which means less noise and less draw. The wiper motor is very close with it's gear set, so stepping 2.5:1 makes a bit more torque and lowers amp draw, but it might be a bit too small to work well on a big stick.

Simply put I'm looking for alternatives to a low torque wiper motor that someone might just happen to think of. The original setup was an old fan motor that fell and broken the plastic fan, which was just pressed onto the shaft. The motor hadn't enough power (maybe 1/5th HP) to spin a mast by itself, plus spun way too fast, so a reduction increased torque and brought the RPM down to a manageable level. I still had to give the home made gear set a spin by hand to start the previous assembly up and spinning, but once at speed it was good enough for all but the biggest masts (the biggest I spun was ~32').

I'd like the new setup to be variable (one reason I'm looking at the DC motor) and reversible (another reason to look at DC motors), plus have the torque and speed to crank up by itself and not cook to death in a long sanding or grinding session. In other words, I'm sure I can come up with something, but I was thinking a bunch of new heads looking at it, might have an idea I haven't thought of yet. I even thought of a linear actuator working a treadle mechanism of sorts, but I figured this wouldn't be as smooth a rotation as a motor, maybe a bit jerky as the ram punches in and out, plus the "null" spot at the top and bottom of each stroke, having little torque value. Hell, if I really wanted to go crazy, I have a few gas engines I could gear up through a garden tractor transmission and could turn down masts for the USS Constitution, but this is a little over the top, noisy and smoky too.

Come on guys, I need a simply, possibly magical device to spin long, heavy sticks at slow speed, with enough torque to permit wholesale stock removal, without bogging down. Maybe a water wheel, now all I need a spring or river on my property, preferably next to the shop. Maybe an ox on a big crank, turning an overhead shaft that runs all the tools in the shop, but then I got to feed it and my other half will want to name it and put a bell around it's neck, so more issues. Save me from getting a ox called Betty . . .

Use a steam engine. High torque, no gear reduction required. When you're tired of it, put it in a nice little launch. You can get an engine from a company called "Tiny Power" or use EBay to find old U.S. Navy launch engines for around a thousand bucks, and make your own water-tube boiler. No problem for a guy like you. It would turn your lathe as slow as you would want, and you could fire it with shop scraps.

Edit. I just read your requirements again. Look for a "popcorn engine". They used them to power sewing machines, popcorn machines, washing machines, all kinds of stuff in the old days. That'd work.

There is a plenty of electric motors all around you: kitchen mixer, roaster, car starters, car windows lifters, car mirror trimmer... you just have to see what you have available and if it can run for the necessary time without overheating or turn you deaf.
As alternative you can take from an old tool an air pressure motor or an oil motor. Another very alternity way is trying to use a water pump (those with a shaft for the drill head) as a motor, if water is cheap and available in your city.

Gianluigi