Pulley size for motor

[jrokusek]

Still building my bandmill.  Quick question.  For the pulley size on the motor - I probably wouldn't want to go smaller than 4" would I?  I'm betting that smaller ones may slip more.  Here's what I'm working with:

13 HP horizontal shaft engine, 3600 RPM at full throttle
20.5" bandsaw tires (trailer tires)

Driven pulley?  15" or so?
Jim

[EZ]

My driven pulley is 24 inch (dia) and the motor pulley is 5 3/8, if this helps you got. I run a 16 hp and it saws good for me threw 35 inchers.
EZ

[D._Frederick]

J.,

What do you want your blade speed to be? This will determine what your pulley sizes should be.

[jrokusek]

I checked out www.ebandsawblades.com as someone suggested in another post.  Their site recommends 5300 sfpm.  It wasn't real clear, but I think that is the ideal speed based on the blade width.  Could be reading it wrong though.  I was shooting for the 5300 sfpm number.

BTW, the Cottonwood/Poplar thread that's running is real timely.  I have a feeling that'll be the first tree that I turn into lumber.  We don't even use it for firewood around here so if I screw it up no one will care.

Jim

[pigman]

Jim,
According to my $3.00 calculator the motor pulley needs to be about 4.5in to give the blade speed you wanted. That is assuming the motor does not slow down under load. 
Bob

[Fla._Deadheader]

  Here ya go. 

  Motor RPM X Motor Pulley dia. Divided by Driven Pulley Dia. X Band Wheel Dia. X 3.1416 Divided by 12 = SFPM

  Caint find that there Divided by little symbol thingy
 
 

[jrokusek]

I took that formula and put in an Excel spreadsheet a while ago.  It's a lot easier to play with combinations and get an instant answer. 

Being the cheap type of person that I am I was thinking of trying to use the smallest pulley's possible to save some money.  Then I got to thinking that small pulleys may slip more since less of the pulley is in contact with the belt.   I think I'll just go with 4" or larger so I don't have to worry if there is any slippage or not.

BTW, I was able to pick up some steel yesterday for a really good price.  I got 8' sections of 3"x3"x1/4" angle for $10 each.  I should have bought the whole lot of it.  I should have enough to make the track and crossmembers.

Jim