I'm cobbling together a DIY band saw and I'm trying to size Pulleys.

Band wheels are 15 inch diameter.

I need around 75 fpm speed on the band (I'm guessing on this, waiting
on band specifications for real number)

I will have a double pulley directly connected to one of the band
wheels probably being 12 inch diameter

Motor will be 1800 rpm 10 hp gas No idea on the motor pulley size.

I could really use a formula that I could play with editing the sizes
of the wheels and pulleys.

Thanks folks.

P.S. on a different topic I going to try a few welding classes. It is
cheaper in the long run and in instruction.

Modat22 wrote:
I'm cobbling together a DIY band saw and I'm trying to size Pulleys.

Band wheels are 15 inch diameter.

I need around 75 fpm speed on the band (I'm guessing on this, waiting
on band specifications for real number)

I will have a double pulley directly connected to one of the band
wheels probably being 12 inch diameter

Motor will be 1800 rpm 10 hp gas No idea on the motor pulley size.

I could really use a formula that I could play with editing the sizes
of the wheels and pulleys.

Thanks folks.

P.S. on a different topic I going to try a few welding classes. It is
cheaper in the long run and in instruction.

75 feet/min = 900 inches/min

Pulley circumference = pi * 15 = 3.142 * 15 = 47 inches (approximately)

So each minute you need the pulleys to rotate 900/47 = 19 times

So pulley rotational speed = 19 rpm

To drive the pulleys from an engine running at 1800 rpm you're going to
need a reduction of around 100:1. This will probably require a three
stage belt drive with a reduction of somewhere between 4:1 and 5:1 per
stage. You might want to look at using an automobile gearbox to achieve
part of this reduction, or a worm and wheel gearbox if you can find a
suitable one. I recall seeing pictures of a saw driven by an automobile
engine and gearbox in a magazine once.

Hope this helps,

Chris

Modat22 wrote:
I'm cobbling together a DIY band saw and I'm trying to size Pulleys.

Band wheels are 15 inch diameter.

I need around 75 fpm speed on the band (I'm guessing on this, waiting
on band specifications for real number)

Hokay.
15" * 3.1415926538 = 48" (nearly)
Now, this is 4'.
The band and the triving pulley run at the same speed, so 75'/4' = 19RPM.

I will have a double pulley directly connected to one of the band
wheels probably being 12 inch diameter

Motor will be 1800 rpm 10 hp gas No idea on the motor pulley size.

Ok, so you need to go down a factor of a hundred in RPM terms.

I could really use a formula that I could play with editing the sizes
of the wheels and pulleys.

Belts are easy.

Unless you care about the last couple of percent accuracy, then you can
live with the approximation that all belts run at the same speed as the
driver/driven pulleys.
This means that the RPM of a pulley connected to a belt depends on its
diameter.
If one is twice as big as the other, then it turns half as fast as the
other.
If you're using a double pulley, the one on the motor needs to be 12"/100,
or .12".
So, you're going to need several.
Even with 2, you're looking at 10 speed reduction with each, which is a
bit much normally, unless you are willing to go for very large pulleys.
3 sounds likely.
3 stages of 4.5 reduction sounds in the ballpark, which would give you
(for example) the 12" pulley on the driver wheel, then a 2.5" -12" double
pulley (which turns at about 90RPM), and another similar one, which turns
at 420RPM, then another 2.5" pulley on the motor, to the large side, which
turns at 1800RPM.
(figures done in my head, and are approx)

I have doubts that a single belt will give you enough torque on the
driver pulley.

The other posters had the math right at about 100:1 reduction. A few
comments:

V belt pulley systems do not like to transmit heavy power loads at much
over 5:1 per stage so you would need at least 3 stages. You can go
higher but the drive pulley gets so small that it cannot handle much
torque.

You mention a 10 hp gas motor at 1800 rpm. this would calc to about 28
ft pounds of torque. Do a 100:1 speed reduction and you have 2800 ft
pounds, enough to do an 18 wheeler justice.

Consider using a purchased gear reduction box. This one is 20:1, would
work well with a 5:1 V belt off the motor. Bearings are probably good
enough to use it for the band saw wheel.
http://www.surpluscenter.com/item.as...ame=powerTrans
Note that this is only rated to 1/2 hp, not the 10 you are talking about.

Modat22 wrote:
I'm cobbling together a DIY band saw and I'm trying to size Pulleys.

Band wheels are 15 inch diameter.

I need around 75 fpm speed on the band (I'm guessing on this, waiting
on band specifications for real number)

I will have a double pulley directly connected to one of the band
wheels probably being 12 inch diameter

Motor will be 1800 rpm 10 hp gas No idea on the motor pulley size.

I could really use a formula that I could play with editing the sizes
of the wheels and pulleys.

Thanks folks.

P.S. on a different topic I going to try a few welding classes. It is
cheaper in the long run and in instruction.

On Tue, 03 May 2005 14:25:40 GMT, RoyJ wrote:

The other posters had the math right at about 100:1 reduction. A few
comments:

V belt pulley systems do not like to transmit heavy power loads at much
over 5:1 per stage so you would need at least 3 stages. You can go
higher but the drive pulley gets so small that it cannot handle much
torque.

You mention a 10 hp gas motor at 1800 rpm. this would calc to about 28
ft pounds of torque. Do a 100:1 speed reduction and you have 2800 ft
pounds, enough to do an 18 wheeler justice.

Consider using a purchased gear reduction box. This one is 20:1, would
work well with a 5:1 V belt off the motor. Bearings are probably good
enough to use it for the band saw wheel.
http://www.surpluscenter.com/item.as...ame=powerTrans
Note that this is only rated to 1/2 hp, not the 10 you are talking about.


The talk about using gear boxes got me thinking a bit, I've got a
couple old locked up 750 honda motors in the junk yard. I might just
take the cylinders and pistons off attach a drive pulley where the
alternator was and use the chain sprocket to drive a pulley reduction.
I'm not sure what the gear ratios are for these motors.

The only reason I'm using a 10 hp gas motor for this is basically its
what I have laying around.

"Christopher Tidy" wrote in message
...
Modat22 wrote:
I'm cobbling together a DIY band saw and I'm trying to size Pulleys.

Band wheels are 15 inch diameter.

I need around 75 fpm speed on the band (I'm guessing on this, waiting
on band specifications for real number)
I will have a double pulley directly connected to one of the band
wheels probably being 12 inch diameter
Motor will be 1800 rpm 10 hp gas No idea on the motor pulley size.

I could really use a formula that I could play with editing the sizes
of the wheels and pulleys.

Thanks folks.

P.S. on a different topic I going to try a few welding classes. It is
cheaper in the long run and in instruction.

75 feet/min = 900 inches/min

Pulley circumference = pi * 15 = 3.142 * 15 = 47 inches (approximately)

So each minute you need the pulleys to rotate 900/47 = 19 times

So pulley rotational speed = 19 rpm

To drive the pulleys from an engine running at 1800 rpm you're going to
need a reduction of around 100:1. This will probably require a three stage
belt drive with a reduction of somewhere between 4:1 and 5:1 per stage.
You might want to look at using an automobile gearbox to achieve part of
this reduction, or a worm and wheel gearbox if you can find a suitable
one. I recall seeing pictures of a saw driven by an automobile engine and
gearbox in a magazine once.

Hope this helps,



Was just thinking that the worm gear on a Roto Tiller would be the right
kind of gear reduction.


Doug

Was just thinking that the worm gear on a Roto Tiller would be the right
kind of gear reduction.


Doug


Ack!. I never thought of that. I just hauled a load of junk off to
salvage and had two old tillers in the mess with blown engines.
Figures that the moment I toss it I need it. Pfft!

Modat22 wrote:

I'm cobbling together a DIY band saw and I'm trying to size Pulleys.

Band wheels are 15 inch diameter.

I need around 75 fpm speed on the band (I'm guessing on this, waiting
on band specifications for real number)

I will have a double pulley directly connected to one of the band
wheels probably being 12 inch diameter

Motor will be 1800 rpm 10 hp gas No idea on the motor pulley size.

I could really use a formula that I could play with editing the sizes
of the wheels and pulleys.

Thanks folks.

P.S. on a different topic I going to try a few welding classes. It is
cheaper in the long run and in instruction.




If it's going to be a wood bandsaw, the speed is much higher than 75
fpm. More like 3000 fpm or more.
If so, a motor pulley about 5 inch diameter would do.

On Tue, 03 May 2005 18:55:40 GMT, Modat22 wrote:

Was just thinking that the worm gear on a Roto Tiller would be the right
kind of gear reduction.

Ack!. I never thought of that. I just hauled a load of junk off to
salvage and had two old tillers in the mess with blown engines.
Figures that the moment I toss it I need it. Pfft!

See, that's _exactly_ what I tell my wife would happen if I get rid of
the "crap you don't need in the garage".

Do yourself a big favor! Buy, borrow, beg..... a copy of Machinery's
Handbook.

I have the 25th edition, and on page 2282 is a section titled "Calculating
Diameters and Speeds of Pulleys".

Aside from the formula you want, it has diagrams showing the relationship of
the pulleys in the formula.
There is also extensive data on v-belt shapes, etc.

Good luck!
"Modat22" wrote in message
...
I'm cobbling together a DIY band saw and I'm trying to size Pulleys.

Band wheels are 15 inch diameter.

I need around 75 fpm speed on the band (I'm guessing on this, waiting
on band specifications for real number)

I will have a double pulley directly connected to one of the band
wheels probably being 12 inch diameter

Motor will be 1800 rpm 10 hp gas No idea on the motor pulley size.

I could really use a formula that I could play with editing the sizes
of the wheels and pulleys.

Thanks folks.

P.S. on a different topic I going to try a few welding classes. It is
cheaper in the long run and in instruction.

On Tue, 03 May 2005 14:47:23 GMT, Modat22 wrote:


The talk about using gear boxes got me thinking a bit, I've got a
couple old locked up 750 honda motors in the junk yard. I might just
take the cylinders and pistons off attach a drive pulley where the
alternator was and use the chain sprocket to drive a pulley reduction.
I'm not sure what the gear ratios are for these motors.

Not more than probably 15:1 in bottom gear.

I had a 750. IIRC I could do maybe 70KPH in first (???)
That's 44 mph, 3870 fpm.

Wheels were 2.3(?) ft diam = 7.2 feet circumference.
Therefore wheel RPM is 3870 / 7.2 = 540 RPm
8000 rpm / 540 rpm = 14.8


The only reason I'm using a 10 hp gas motor for this is basically its
what I have laying around.

It really is way overboard. Does it have to run at 1800 RPM? You could
probably go somewhere in between, use less gearing and still have
enough torque at the band. the motor would loaf along.

What are yuou cutting with this, BTW?

On Wed, 04 May 2005 13:35:31 +0800, Old Nick
nsnsafemail#iinet.net.au wrote:

On Tue, 03 May 2005 14:47:23 GMT, Modat22 wrote:


The talk about using gear boxes got me thinking a bit, I've got a
couple old locked up 750 honda motors in the junk yard. I might just
take the cylinders and pistons off attach a drive pulley where the
alternator was and use the chain sprocket to drive a pulley reduction.
I'm not sure what the gear ratios are for these motors.

Not more than probably 15:1 in bottom gear.

I had a 750. IIRC I could do maybe 70KPH in first (???)
That's 44 mph, 3870 fpm.

Wheels were 2.3(?) ft diam = 7.2 feet circumference.
Therefore wheel RPM is 3870 / 7.2 = 540 RPm
8000 rpm / 540 rpm = 14.8


The only reason I'm using a 10 hp gas motor for this is basically its
what I have laying around.

It really is way overboard. Does it have to run at 1800 RPM? You could
probably go somewhere in between, use less gearing and still have
enough torque at the band. the motor would loaf along.

What are yuou cutting with this, BTW?


I plan on cutting wood with this, Actually I'm waiting on the FPM
requirements from the saw blade manufacturer thats why I asked for the
formula to figure out my reductions. I'm still waiting on the FPM
specifications and got a little rapped up in all the idea
brainstorming going on. Someone said that I would be running my blade
at 3000 fpm for wood where as I was thinking it to be around 75 fpm
which is the speed my small metal cutting bandsaw.