I just joined today after reading some of the forums. I plan on building a timber frame home and to get their I am building a band saw mill. I have never sawed a single piece of lumber, fell a lot of trees though. I was confused by some of the discussions I found on blade speed. In my mind FPM would be the amount of blade traveling through the wood. With this in mind, the diameter of the wheel would only be the start. To me the length of the blade would be the revalent factor and not the wheel diameter. The wheel diameter to the engine speed give you the amount of RPMs of the wheel only. In my case there will be a 4.68 ratio. Running my engine at a conservative 3200 RPMs with a 4.68 ratio engine pulley to wheel pulley gives me 683 RPMs at the wheels. Every revolution the blade is traveling one revolution or 15'. So my blade will be traveling 10256 FPM at 683 RPMs. Is this correct?
On another note, I have viewed a some of the log turners. Im am designing a set of trunions with bearings on mine. I have read that it is best when box hearting to try and keep the distance from the center as equal as possible. I plan on drilling 1 1/4" hole about 1 1/2 deep at the center of each side of the log. The trunions will be mounted in these hole and screwed to prevent shifting. The trunions will include index hole for 90 degree turns and custom angles if need be. I should be able to pull a pin to rotate my 90 degrees with dead accuracy because I plan on machining the pin locations. I also plan on having the trunions adjustable in height and location allong the bed. I will load the logs with my tractor forks so pinning them in place should be simple. This also eliminates the log taper issue. They will also be removable for cutting standard boards down on the bed. What do you folks think?
Thanks, dra7
Welcome to the forum. You have a great ambition ahead of you, and you will get a lot of encouragement here. :)
Speed of the blade has to do with the circumference of the wheel in feet times the RPM of the wheel, and that will give you feet per minute blade speed. I think. :)
Circumference of the wheel is pi times the diameter in feet.
Try a search for blade speed formula. It's been posted many times, here.
True that fpm is the amount that the blade is traveling in the wood . But the blade can only travel the amount that the wheel moves it, so therefore the fpm is the amount that the wheel travels in a minute. I beleive the formula is {Diameter x3.14(pi)=Circumference , C x wheel RPM divided by 12 =Sfpm} ???
Welcome to the forum dra7.
10256 feet per minute at 683 RPM would take a 4.782 foot diameter band mill wheel.
10256/683=15.016 feet per revolution. Divide this by pi (3.14)=4.782 feet.
The wheels on my mill are 1.5 feet x 3.14 x 683= 3216 fmp.
Joe
Welcome dra7
What you are considering to hold your log sounds like end-dogging to me. It is a method of dogging a log generally used in Scragg mills. While it gives you a method of centering and cutting multiple faces, it suffers from lenth-of-log allowances and structural stability.
Laying a log flat on a steel surface and raising one end is stable and quick. Logs are tough on equipment because they are so heavy. Any kind of dogging must withstand a lot of weight changes, log dropping, off-center turning, etc.
It may take a lot more money to create an end dogging machine, but could be worth it if you need to make varying surfaces.
If it were me and I were thinking of just making timbers and boards with 90 degree angles, I would stick with the flat bed options.
Dr7,
Welcome to the forum. I think where you are having the problem with blade speed, is thinking the blade makes 1 complete revolution for each revolution of the drive wheel. If your band is 15' long and your driving band wheel is 19" in diameter ( example size ) the circumference is about 5', so it will take about 3 turns of the drive wheel to complete one full revolution of the band blade. Blade length doesn't affect blade speed.
VA-Sawyer
There was a stonecutting shop I used to drive by sometimes. They had a wire for the blade. It was strung around large wheels on telephone poles about 50' from each end of the building. The wire came through the building and returned over it, slowly sawing through slabs of granite. I don't think you could switch from sawing wood to sawing stone without some serious patience adjustments :). Just an extreme example, the drivewheel speed and circumference determined the speed of the wire.
There's a calculator here for figuring some of it out;
https://forestryforum.com/members/donp/bandspeedcalc.htm