Bandsaw slowing down, under minor load

[dirk martin]

Resawing some 4" wide cedar today, and my bandsaw is slowing down part way thru the cut.

Blade is new.
No binding....cutting clean.
Minimax MM24. 5hp motor.

Ideas?

Capacitor?

[Dennis Ford]

My first guess is a drive belt slipping. If the motor has a run capacitor, it might be part of the problem. Most 1 phase motors only have a start capacitor, they are switched out of the circuit once motor is up to speed.

[Jeff Raefield]

Worked fine and NOW this started happening? Or it's a new saw and this is the first time you are using it?

Assuming it has worked fine and just started doing this, it might be the centrifugal switch (you said capacitor, so I assume it's single phase). If the Start cap is NOT switched out of the circuit by the centrifugal switch, the motor doesn't have it's full torque capacity. the start cap is at the same time at risk of over heating and popping, so DON'T USE IT!

The centrifugal switches get gummed up with sawdust and oil or moisture. Open up the non-drive end and blow it out. See if the switch is free to move.

[dirk martin]

My first guess is a drive belt slipping. If the motor has a run capacitor, it might be part of the problem. Most 1 phase motors only have a start capacitor, they are switched out of the circuit once motor is up to speed.

It's got dual drive belts.
Both are pretty tight, so I don't think that's the issue.

[dirk martin]

Worked fine and NOW this started happening? Or it's a new saw and this is the first time you are using it?

Assuming it has worked fine and just started doing this, it might be the centrifugal switch (you said capacitor, so I assume it's single phase). If the Start cap is NOT switched out of the circuit by the centrifugal switch, the motor doesn't have it's full torque capacity. the start cap is at the same time at risk of over heating and popping, so DON'T USE IT!

The centrifugal switches get gummed up with sawdust and oil or moisture. Open up the non-drive end and blow it out. See if the switch is free to move.

It's been in use for about 12 years.
Single phase.
If I open up the non-drive end of the motor, are you saying I'll see the centrifugal switch in there? Is it an obvious switch, with contacts? Just blow and clean it all out with my air compressor, and see if it's better?

[Allan Speers]

Are you by any chance cutting green wood?

[John Gustafson]

The switch is pretty obvious. Its mounted on the end of the shaft. It's got a little counterweight on it that opens the switch as the speed ramps up cutting out the capacitor. That weight should move freely and you should here a click as the switch opens up

[Bruce Wrenn]

Blade is new, but it doesn't mean it has enough set on the teeth. Also, tension in the wood could cause binding. After you have cut about 1/4 of the length, stop and drive a screw driver into saw kerf at end of piece of wood.

[Allan Speers]

Blade is new, but it doesn't mean it has enough set on the teeth. Also, tension in the wood could cause binding. After you have cut about 1/4 of the length, stop and drive a screw driver into saw kerf at end of piece of wood.

That's why I asked about green wood.

[Lee Schierer]

Get a helper to watch the motor while you make a cut to see if the motor slows down when the saw bogs down. This will tell you if the belts are slipping or not. 12 year old belts could be worn so they are not providing full power.

If your saw starts and gets up to speed, you can eliminate the centrifugal switch and capacitor as a problem.

How many TPI does the blade you are using have?

[Erik Loza]

....Assuming it has worked fine and just started doing this, it might be the centrifugal switch (you said capacitor, so I assume it's single phase). If the Start cap is NOT switched out of the circuit by the centrifugal switch, the motor doesn't have it's full torque capacity. the start cap is at the same time at risk of over heating and popping, so DON'T USE IT! The centrifugal switches get gummed up with sawdust and oil or moisture. Open up the non-drive end and blow it out. See if the switch is free to move.

+1 ^^^^

Erik

[dirk martin]

It does start fine, and gets up to full speed.
Is it true that that eliminates the cent. switch?

[Lee Schierer]

The purpose of the capacitor and centrifugal switch are to create a phase shift in the start windings to get the motor started so it can then run. Once the armature reaches a certain rpm, the switch opens and the capacitor is no longer part of the circuit. If your saw starts on its own and comes up to speed when the switch is thrown, then those two items are working just fine. If your saw were to just sit there and humm when you throw the switch, then either one or both could be the problem.

[Dave Cullen]

A 5 hp motor is a big mutha. I can't envision the motor slowing down with light load unless something is way wrong. Can one of the pulleys be slipping?

[Rod Sheridan]

Resawing some 4" wide cedar today, and my bandsaw is slowing down part way thru the cut.

Blade is new.
No binding....cutting clean.
Minimax MM24. 5hp motor.

Ideas?

Capacitor?

Blade on upside down?

Belts or pulleys slipping or loose?

Regards, Rod.

[Steve Kinnaird]

Have you ever replaced the belts?
Are the belts glazed over?
This could cause the belts to slip.

[Ken Harris]

Check the amp draw under load and no load,there should not be a significant difference,as listed on motor plate.If amp draw is high,possibly motor is laboring due to unusually high belt tension or bad bearings on the wheels or within the motor.Make sure your supply power is good under load, that will also cause high amp draw.Make sure to check voltage at the bandsaw.It is also possible though not probable the motor windings are defective,find out what resistance should be for the run and start windings,and check those.Do not continue to use your saw or you will surely burn up a very expensive motor.