HF bandsaw/linkbelt conversion

[eddy merckx]

Hi everybody

There has been some discussion about converting a HF 4 speed bandsaw to one speed and installing a link belt. You reverse the stepped pulley on the motor and use the smallest pulley size. I did this conversion on mine and I must say that it really runs smoothly. The only problem is that it bogs down easily.

I did Loring's blade speed calculation, which shows that the pulley on the motor should be about 25% as large as the pulley which drives the bandsaw wheel, assuming that a 3500 rpm motor is used. This will yield about a 3000 fpm blade speed.

My saw seemed slower and less efficient though. I then looked at the motor and found that it is a 1720 rpm motor, not a 3500 motor. This yields closer to 1500 fpm blade speed. In order to get the desired 3000 fpm speed with a 1720 rpm motor, you will need a motor pulley which is 50% smaller than the wheel pulley.

The way I see it, since the wheel pulley is 6", you will need a 3" pulley on the motor. The 2nd smallest pulley on the stock stepped pulley is 2.5", which will get you in the ball park.

Am I completely off base here? Somebody please set me straight if I'm making an error.

Thanks, Eddy

[LCHIEN]

Hi everybody

There has been some discussion about converting a HF 4 speed bandsaw to one speed and installing a link belt. You reverse the stepped pulley on the motor and use the smallest pulley size. I did this conversion on mine and I must say that it really runs smoothly. The only problem is that it bogs down easily.

I did Loring's blade speed calculation, which shows that the pulley on the motor should be about 25% as large as the pulley which drives the bandsaw wheel, assuming that a 3500 rpm motor is used. This will yield about a 3000 fpm blade speed.

My saw seemed slower and less efficient though. I then looked at the motor and found that it is a 1720 rpm motor, not a 3500 motor. This yields closer to 1500 fpm blade speed. In order to get the desired 3000 fpm speed with a 1720 rpm motor, you will need a motor pulley which is 50% smaller than the wheel pulley.

The way I see it, since the wheel pulley is 6", you will need a 3" pulley on the motor. The 2nd smallest pulley on the stock stepped pulley is 2.5", which will get you in the ball park.

Am I completely off base here? Somebody please set me straight if I'm making an error.

Thanks, Eddy

Yeah that's right. Someone said the motor was 3500 RPM so that's what I used in my that example where i said 1:4 reduction was needed. I also gave the equation. and a illustration and related universal calculations for one- and two-belt bandsaws in a recent post.
http://www.bt3central.com/showthread...=speed+bandsaw

I don't have that bandsw but I understand the mechanics. Someone just has to give me the right numbers...

I have a partially complete Excel spreadsheet that works... for inches. Just put the numbers in. I was putting in options for metric but haven't finished that yet.

PM me for the spreadsheet.

The number will never be truly exact... The motor speed is a function of the load, the numbers 3400/3450/3500 and
1700/1725/1750 are all an estimation of the mostly unloaded speed which is theoretically 3600 or 1800 with truly ZERO LOAD.
And the pulley ratios are all close but not exact because they assume the belt is flat with zero thickness and rides on the outside of the pulley whereas the effective diameter is really about half a belt thickness below the belt surface which also varies in relation to the pulley and how tightly its tensioned and drawn into the "V".

About 10% or maybe 15% accuracy is about all you'll get... don't go shaving hairs, is what I'm trying to say. Somewhere in a range 2700-3300 FPM (+/-10%) is probably more than good enough.

[Popeye]

I worked this out with the Suffolk boys on the phone. Don't remember the numbers but Suffolk did the math and it has worked great.
Take out the middle pulley. Set the motor pulley so the largest step is next to the motor (this pretty closely lines up the pulley's coplaner. Put the belt on the next to the largest step on the motor and the drive pulley on the saw.
I've resawn 6" stuff for BS boxes with a 3/16" blade with this set up. Not very quickly of course but it didn't bog down. Pat

[eddy merckx]

Thanks Loring--I understand that your formula was a template that we could insert our numbers into. I didn't even think of the motor speed being different until Cabinetman mentioned that all his bandsaws had 1750 rpm motors. I really do appreciate your posting the charts and formulas. Very handy. It's a lot of fun tinkering with these machines.

Popeye, if your gearing is the same as mine, you should still be running quite a bit faster than 3000 fpm. Maybe you have different size pulleys though. I guess the main thing is that the saw runs smoothly and cuts well.

Thanks again guys.

Eddy