Hf Bandsaw I need your help

[theminor]

Aha! Thanks to all! I went home at lunch and opened the door to look at my bandsaw and I figured out why removing the middle pulley will speed things up: the middle pulley always goes from a large diameter "gear" to a small one - I had been thinking that this pulley went from small to large before the second belt connected to the final gear, which would speed things up. But it actually slows things down. Strange design - I will definitely remove mine over the weekend. Maybe if I'm feeling up to it I'll attempt to measure the blade speed. I'm thinking I could attach some duct tape to the blade and count the number of times I see the tape pass by in a given amount of time. Then I'll calculate Feet per Minute with my known blade size. Hopefully it won't go by too fast to count...

[LCHIEN]

TB Roye and all who have removed the middle pulley,

I understand how this will help with vibration, but does it really increase the speed? It seems to me that removing one of the pulleys would slow down the speed, not speed it up. The pulleys are there to increase the motor speed by torquing up the belt speed as each belt attaches to a small diameter notch in the pulley and the next belt attaches at a large diameter, like gears on a bicycle. Can someone explain to me how the speed is actually increased by removing the middle pulley? Maybe I'm missing something here, but as of now, I don't quite understand! Has anyone actually measured the speed after making the change?

Thanks for any explanations - I'd love to make this modification if it does increase speed and reduce vibration!

I don't know what the configuration of the HF 4-spd bandsaw is other than two belts and some stepped pulleys somewhere.

But here is how pulleys work:

Shaft one is the motor. Shaft two is the center, Shaft 3 is the axle of the bandsaw wheel. RPM1= RPM of the shaft 1 RPM2=rpm of shaft 2 etc.
D1=dia of motor pulley
D2 = dia of driven pulley on shaft 2 (e.g the pulley attached to the belt to the motor)
D3=dia or driving pulley on shaft 2 (e.g. the pulley atta to the belt to the wheel)
D4 = dia of driven pulley on shaft 3
D5=dia of bandsaw wheel (e.g. 14")

The Motor turns at 3400 RPM
The shaft1 and pulley 1 turns at 3400 RPM
Shaft 2: RPM2= 3400 x D1/D2
Pulley 3 turns at RPM2 since its fixed to the shaft.
Pulley 4 and shaft 3 turn at RPM3 = RPM2 x D3/D4 = 3400 x D1 x D3 / (D2 x D4)

Band saw wheel turns at RPM3.
Linear velocity of the blade = RPM3 x 3.14 x D5/12" (in feet per minute. fpm)

= (3400 x D1 x D3/(D2 x D4)) x 3.14 x 14 / 12 feet per minute.
= 12,461 x D1 x D3 / (D2 x D4) fpm

If you eliminate the Shaft 2 an connect the motor pulley of D1 to the pulley on shaft 3 with D4 then the speed of the blade will be
= 12,461 x D1/D4 feet per minute


IIRC for a bandsaw cutting wood the desired speed is approx 3000 fpm.

so D1 should be about 1/4th the diameter of D4 in the one-belt system.

[TB Roye]

Loring

Wow! but that sounds about right. The machine is not screaming and the bottom pulley groove is about 1/4 the size of the pulley on the top wheel shaft. I just did not increase the speed that much in fact it might be the same as the single speed model. That is what great about this site sooner or later some one will come up with the explanation or answer.

Tom

[theminor]

Just an FYI for everyone - I finally got around to doing this mod on my HF bandsaw. I removed the middle pulley and attached my link belt between the motor and the pulley that drives the blade. Boy, it really makes a difference as far as vibration and noise are concerned! Very nice!

By pulling the motor pulley and drive pulley off, I was able to measure the diameters to calculate speed. The Smallest motor pulley is 1.75 inches and the pulley that drives the blade wheel is 6 inches in diameter. Following Loring's calculations, this yields a blade speed of 3634 fpm, a little faster than the recommended 3000 fpm. Putting the belt on the larger motor pulley sizes will only increase the blade speed, so if you want to get it to 3000 fpm, you'll need to go find a new pulley either for the drive shaft (a 7 inch diameter combined with your current stepped pulley currently on the motor will get you 3115 fpm) or for the motor pulley (a 1.5 inch diameter combined with your current 6 inch drive pulley will also get you 3115 fpm).

I can't decide if it is worth finding another pulley just get get the speed exactly to 3000. I'll try it at 3634 for a while and see how I like it, I suppose!

[John Williams]

HF bandsaw

I bought one for $219 and have never regreted it. I have had it for 3 years and think itis well worth the money. Throw the blade that comes with it away and forget the directions. I use this bandsaw at least 8 hrs. a week.

John

[eddy merckx]

If you are having cutting problems after doing the link belt/ stepped pulley removal conversion, take a look at this thread. It turns out that with the 6" pulley and 1.5" pulley combination actually yields around 1600 fpm instead of the desired 3000 fpm.
http://www.bt3central.com/showthread.php?t=30104



Best wishes, Eddy