This is a topic that came up recently with some other woodworkers so I thought I'd shoot a short video to see just how much my blade wobbles at startup.  Turns out it's fairly slight and is over in about one second.  The video is less than two minutes if you're interested in watching.

 

doesn't seem like a problem that would affect anything.

 

my blade on my circular saw wobbles after it's been running a bit.  i think it gets warm and deforms.  not good when trying to cut a long, straight line.

Yes sir, it's not affecting anything at all.  It was a topic on another forum and I found it interesting so I made the video and shared it here.

to me it sounds like harmonics and vibration from the motor torque. once it's "at speed" the blade runs true.

 

9 hours ago, John Hechel said:

to me it sounds like harmonics and vibration from the motor torque. once it's "at speed" the blade runs true.

 

I agree, John.

Interesting David. Thanks for taking the time to record the video especially as various speeds. I assume the blade is a "thin" kerf blade? I wonder if the same results would occur with a wider kerf blade? Likewise if there would be any difference with other manufacturers or perhaps even a new blade from the same manufacturer? Just curious, if you've checked TIR of your current set-up? Regardless, I concur with your finally assessment. Thanks again.

Thanks, Dave!  Yes, it's a thin kerf blade that is just flexing at startup and I probably should have called it flexing rather than wobble.  I don't have a thicker blade or I would have done a comparison.  The current setup looks great with a dial indicator, fwiw.

MAYBE this flex is somewhat like helicopter blades. They flex down when motionless and under torque flatten out. So maybe it is the speed that makes the difference.

Could be, Gerald, could be.  I know that it only takes about one second to reach full speed and the flex/wobble is gone at that point.  Now, if my tablesaw begins hovering... 

15 minutes ago, difalkner said:

 Now, if my tablesaw begins hovering... 

Prolly make it easier to move.

23 minutes ago, Gene Howe said:

Prolly make it easier to move.

That it would, Gene, that it would! 

When I purchased my Jet tablesaw many years ago, I noticed a bit of vibration in the saw. I replaced the pulleys with precision pulleys and replaced the manufacturers belt with a link belt Probably not the same issue but the change really smoothed how the saw ran. Never really noticed if there was any wobble on start up.

1 hour ago, Al B said:

When I purchased my Jet tablesaw many years ago, I noticed a bit of vibration in the saw. I replaced the pulleys with precision pulleys and replaced the manufacturers belt with a link belt Probably not the same issue but the change really smoothed how the saw ran. Never really noticed if there was any wobble on start up.

This is a PM66 that I bought new in 1990 and fully restored a few years ago (made the mistake of loaning it to a 'friend' who left it in a building where rainwater poured on it for over a year - well rusted!).  The arbor, bearings, matched set of three belts, etc. were all replaced.  It is a very smooth saw with no noticeable vibration.

Wow!! Can't believe the misinformation here. At no time is that blade running "true". Probably caused by loose or worn bearings as the blade not only moves to left it also comes back right. Just because it is at full rpm with no load doesn't mean it is tracking true under load. Notice the slot in the crosscut sled is double the width of the blade. That isn't "true". Watch it at slower speed and you'll see the blade "wander". Prove me wrong.

51 minutes ago, DRAGON1 said:

Probably caused by loose or worn bearings...  Notice the slot in the crosscut sled is double the width of the blade.

I replaced the bearings not too long ago along with most of the components associated with that part of the saw, including a matched set of three belts. As for the slot width I cut it that way when I made the sled and I was playing with getting the guide runners locked down.  It's not wider because the blade is wobbling because it doesn't wobble or flex at speed.  Nice try, though. 

 

I think what you're seeing may be a function of the phone camera and the room lighting.  In either case, nothing is wrong with the saw or the blade or the arbor or the bearings; the saw with this blade cuts just fine and is very precise.  I've heard from more than a dozen people that their saws do the same thing with a thin kerf blade because it's just flexing under the startup load.  I just thought it was interesting enough to video and share here.

I think you will find that the kerf on a cross cut sled will always widen over time due to chips of wood knawing on it during use. 
Paul

On 1/3/2023 at 10:33 PM, difalkner said:

I replaced the bearings not too long ago along with most of the components associated with that part of the saw, including a matched set of three belts. As for the slot width I cut it that way when I made the sled and I was playing with getting the guide runners locked down.  It's not wider because the blade is wobbling because it doesn't wobble or flex at speed.  Nice try, though. 

 

I think what you're seeing may be a function of the phone camera and the room lighting.  In either case, nothing is wrong with the saw or the blade or the arbor or the bearings; the saw with this blade cuts just fine and is very precise.  I've heard from more than a dozen people that their saws do the same thing with a thin kerf blade because it's just flexing under the startup load.  I just thought it was interesting enough to video and share here.

I've never been a fan of thin kerf blades for that very reason. What are you actually saving? 1/32 of an inch? Get a good blade and cut a thinner slot in the sled. That way you can actually use the slot in the sled for an accurate cut instead of trying to use the blade.