What spectrum would you see if you have a warped saw blade? Would you see one or two times blade speed? What if it is flexing back and forth as it runs? I have a large saw blade 30" which is over hung that is strobed at 299 rpm but has a high spike only at 600rpm. I haven't been able to strobe the belts. You can visually see the wouble in the blade as it runs. Seems simple but when you think about it it is different from a bent shaft.

Thanks for your replies.

Isolate the wobble; is it the blade or is the wobble coming from the shaft (bent or bow) or excessive cleanances. And what are the characteristics under load? Is the blade 'as new'?

What spectrum: or, spectra from multiple plots especially axial. Present more info and data, please. Thank you.

Liver,

Yes, you could expect 1xSS and 2xSS, but also higher harmonics. I would expect higher levels or higher increase in axial direction. Blade vibration modes (natural frequencies) may also be excited and produce audible sound. The extent and shape of the warping and feed rate during sawing would affect the vibration spectrum frequencies and amplitudes.

Walt

Back in my paper days, the saws on our slasher deck (6') would work loose at the fit on the arbor and we'd see multiples of running speed. Can't remember too many blades being warped. With eight or so belts, we always had belt problems. Some phase data might help isolate loose fit vs. bent shaft.

Hi Liver
I believe the vibration would behave very much like angular missalignment (the face is not running true). In this case one would expect to see mainly 2X running speed and possibly higher in the axial direction.

Here are the readings from the high resolution reading taken on the inboard of the motor and the horizontal, vertical and axial of the inboard bearing of the saw. Blade is old and has been resharpend several times. A new blade has been ordered and will take readings when installed.

Readings_on_Saw.doc (86 Kb, 20 downloads)

Liver,

Can you check runout with a dial indicator when not running and safely tagged out? You could check runout on the shaft (radial) to rule out bent shaft, and you could figure out if the runout on the blade is due to mounting on the shaft or is a warping of the blade surface. Then it is important to figure out what caused the "wobble", so that it doesn't happen to the new blade. High temperatures could be responsible either during cutting, or during resharpening. Depending on the material of the blade, cryogenic treatment can improve thermal growth behavior from making the material more uniform, and extend the wear life as well. You should also consider how the blade gets loaded while in operation to ensure there isn't preferential heating on one side, or mechanical loading or blade pinching. When the blade does get resharpened, be sure there are strict controls on that process on the new blade so runout isn't introduced.

Good luck.

Rich Wurzbach
Maintenance Reliability Group, LLC
717-843-8884
rwurzbach@mrgcorp.com

I'd start by marking the axial runout of the blade and phase of the high spot to the shaft.
Out near the teeth, and also adjacent to the arbor hub. Then I'd check the arbor flange axially. I'd kind of expect to find a problem with Axial runout on the arbor that mounts the saw blade. If there was some runout in the arbor and some in the blade I'd probably try indexing the blade a few times to see how low I could get the runout.