1 st post newbie regarding drive pulley size and relay pullies?

[ray299]

Hi all, forgive me if this has been posted but I don't know the name of the "thingy" to search for. I'm building a band saw based off multiple different designs I found on the web as well as my own materials available. I'm working on the drive system for the wheels now. I did see in another post there was an online formula to calculate pulley size. I have a 10 hp motor (hoping to upgrade at some point to a 20ish hp some day). I have a 4" pulley for the motor size and based off the online calculator ( https://forestryforum.com/members/donp/bandspeedcalc.htm ) I ordered a 13.75" pulley for the drive wheel.
SO here is my question- in some designs I've seen a belt go from the motor straight to the drive wheel and other designs, the belt goes from the motor to the "thingy" (intermediate pulley system?) which has different size pulleys and then another belt travels from the thingy to the drive wheel...  can anyone tell me about what this does and how to figure out if I want to incorporate this in my rig? When I build I like to get things done so I'm not one to let this sit for a year or more but I do want to make sure I build it the way I need it built.
What am I cutting? Mostly planks, 4x4 fence posts and building materials (I think that about sums up everything lol). The wood type is mostly hard woods- ash, locust, oak but I do want to do pine too.
So... why is the "thingy" there on some designs and not on others but in their videos they both seem to work fine?
I'm a youtubeaholic when it comes to building things I've never done before.

[Ox]

The thingy you're referring to is called a jackshaft.  It's a way to "change gears" using belts and different sized pulleys.  It's also a way to transfer power across things (think of moving the drive belt away from the engine, sideways, a few inches or a few feet).  It's a way to get power around obstacles.  It's not needed if you build your mill with everything you need the first time.  Sometimes people have gotten in too far with a salvage build and don't want to spend money and they need a jackshaft to slow down or speed up the blade speed.  If you just do your 2 pulleys straight inline you'll be fine.  I used a centrifugal clutch from Surplus Center.  With a lower power engine, I would recommend going down a size on the drive pulley, not up.  It's like a lower gear for smaller engines.  I went with a 3.7" pulley, wish I had gone to the 3.2" or whatever it was.  Plans called for a 3.5" but I didn't want to buy from a retailer.  Surplus Center is our friend!

[ray299]

The thingy you're referring to is called a jackshaft.  It's a way to "change gears" using belts and different sized pulleys.  It's also a way to transfer power across things (think of moving the drive belt away from the engine, sideways, a few inches or a few feet).  It's a way to get power around obstacles.  It's not needed if you build your mill with everything you need the first time.  Sometimes people have gotten in too far with a salvage build and don't want to spend money and they need a jackshaft to slow down or speed up the blade speed.  If you just do your 2 pulleys straight inline you'll be fine.  I used a centrifugal clutch from Surplus Center.  With a lower power engine, I would recommend going down a size on the drive pulley, not up.  It's like a lower gear for smaller engines.  I went with a 3.7" pulley, wish I had gone to the 3.2" or whatever it was.  Plans called for a 3.5" but I didn't want to buy from a retailer.  Surplus Center is our friend!

Oh that makes it easier. Thank you for that explanation. I got the 4 inch pulley free but I'll have to try fabricating something smaller to swap out if I need. That should be a fairly easy adjustment once cutting starts. Thank you!

[Muddsaw]

I'm building a chainsaw mill out of a rideing mower I got for $100 has pullys an engine and various other things that I can use. Just something to consider when building and fabricateing is ( what I can use that will make the most out of what I'm spending. ) I build and fabricate all manner of stuff, and what I build out of something else might shock you. U are only limited to what u can come up with, what tools I have and materials. Plan and blueprint too seeing things spark ideas. That's why jacklegs like me need Jack thingys, cause they don't think of something they need till there done with a build. Planning is critical so take the time to do it right the first time. I promise it will be better, and you will enjoy building it more. You will have a better whatever it is ur building.
Mudd Saw.