Is my blade supposed to wobble?

[naubur]

I have the stock blade right now, and last night I noticed it wobble as it is slowing down - right before it stops. When running there is no discernable wobble, and the cuts are decent. Only when spinning relatively slowly is there an apparent wobble, and moving it by hand in my new ZCTP I can hear it rub a little.

I checked the nuts and spacers holding the blade and all is good. It doesn't seem to affect my cuts, so my question is - is it OK to wobble a little, or do I need a new blade? And if so, what causes a blade to wobble. I've only had it 2 months.


Jason

[RayintheUK]

You don't say whether the blade has been removed and put back on since you started using the saw, Jason. The reason I ask is that it's fairly easy to trap some sawdust in amongst the spacers when re-fitting, although this is not likely if you've not had the blade off since initial assembly.

Ideally, you should not have any run-out at all, yet you clearly do have because you can hear it on the ZCTP. The spinning speed of the blade is apparently helping to correct this centrifugally, so that you only notice it when the blade slows down enough for that effect to disappear.

What I would do is to take all the blade parts off the arbor and ensure that all parts are clean and that nothing is catching on the threads as it's being tightened - make sure everything is parallel as you tighten.

Don't heave on the wrench either, just a firm nip will suffice, in case you're putting any undue load on the plate and slightly deforming it (again, unlikely, but worth a check).

If none of the above sorts it out, then it will either be the blade, or the arbor. The blade is the most likely culprit and should be replaced, but if a new blade produces the same effect, then the arbor needs testing for run-out. HTH - let us know how you get on.

Ray.

[Russianwolf]

No, the blade shouldn't wobble.

How can it? If the blade is bent or warped it can wobble.

You mentioned having a zero clearance throught plate. Did you at any point try to tilt the blade for a bevel cut with the ZCTP in? even though it's plastic, it can bend your blade.

There has also been some quality concerns about the new blades that ryobi is packing with the BT's recently. It's a china blade as opposed to the Italian blade the older saws have and it's possible you just got a bad one.

The worse case scenario is that the arbor is bent. This will cause even a "true" blade to wobble.

take your blade off and lay it on a VERY flat surface and see if there is any noticable space between the teeth and surface (use feelers or pieces of paper). check from both sides. If you don't see anything there, get a new blade and test it on the saw. If it wobbles then it's likely the arbor.

[naubur]

I have had the blade off already. I will try reseating it, and cleaning it. I did test rip some long boards to practice on - could I have warped the blade by moving the board side to side during the cut? Not intentionally of course!

I haven't tried to tilt it with the ZCTP, good tip though!

When I get home I will put it on a flat surface to detect any warp and see what happens.

For the record it is a Taiwanese blade.


Jason

[Tom Miller]

An easy thing to check is the kerf width. It should be within a few mils of the blade (teeth) width. You can either make a partial through-cut into a board, or you can make a "pocket" cut, in which the blade is raised above the table less than the stock thickness. The latter requires removing the stock blade guard, though, unless you have a cut-down splitter (which is a good thing to have, BTW).

This will be the most direct measure of what really matters.

Another thing to check is blade runout, which usually requires a dial indicator, but you can get by without it.

Put a block between your (locked down) fence and blade until the block just touches. Now, rotate the blade by hand, and check to see if the blade moves away from the block. Measure how much it moves away with some type of feeler guage (a post-it is ~0.0035"). Adjust your fence as necessary to get a good measure. Keep in mind, though, that this runout is not necessarily how the blade acts at full revs.

Regards,
Tom

[naubur]

Last night I took off the blade and laid it on a smooth surface. I couldn't see any warp, even sliding a piece of paper under each tooth didn't provide any results.

So I remounted it after making sure all spacers were clean and installed correctly. Then I tightened the nut, and bearing the previous advice in mind I tried to do it not so tight. The blade still had some wobble, but less for sure. So I removed the blade and reseated it and then did up the nut with even less torque. Now it had even less wobble. So I then only undid the nut and tightened it even a little less. Now there was almost no wobble, so small that my manual run out test yielded the tiniest of variance, whereas the same test before (absolutely unscientific BTW) had about 3 - 4 times the variance in run out.

My next question would be, why is the blade so sensitive to torque on the nut? Or is it something else? And is just a little torque enough? My wrench is about 10" long and I gave it a moderate last 'push' to tighten. Maybe moving it 20 degrees.


Jason

[WayneJ]

This will sound wrong but it works well. Lossen the nut ,reseat the blade. Just barely tighten the nut, just a little more than finger tight. Turn on the saw and it will tighten it self. Thats as tight as the blade needs to be, it won't slip.

[Tundra_Man]

I've had the same situation going on for the last two years. Cleaned the arbor, spacers, etc and still the same problem. Blade lays flat on a plate of glass. Perhaps I've been over-torquing the arbor nut too.

I haven't noticed any change in the quality of cuts once it's running, so I've just been living with it.

I'll try loosening the nut and see if it helps.

[Tom Miller]

Maybe you guys (Jason, Terry) ought to try lapping your blade washers. Seems the only way you could get this kind of blade warping when you tighten is if the blade washers are not flat.

I'm sensing foggy memories of posts about this issue in the last year or so....

Regards,
Tom

[cgallery]

I had bad spacers. When I would loosen the nut so the blade could spin freely, there wouldn't be no discernable wobble. The tigher the nut, the more wobble I'd observe. I finally set each spacer on a reference flat, put a straight-edge on it, and observe just how unflat it was. Ryobi sent replacements and now my total blade runout is approx. .004" (measured at approx. 8" because I wanted to avoid the gullets). So .004"/8 gives me .0005" runout at the arbor. And that is assuming my Forrest WWII is perfectly flat.

BTW, I purchased several .5" arbor spacer at a local Ace Hardware and found that one was nearly dead-on, the other two weren't that much better than the stock Ryobi spacer.

Thanks,
Phil

[jabe]

Wayne is right! Most people tend to over tighten the arbor nut, just do as Wayne stated. The arbor is a reverse thread so it'll self tighten as you run the saw.

[cgallery]

Wayne is right! Most people tend to over tighten the arbor nut, just do as Wayne stated. The arbor is a reverse thread so it'll self tighten as you run the saw.

But isn't it possible for the blade to spin without causing the nut to tighten? I mean, I know it won't loosen, but is it guaranteed to tighten?

[LCHIEN]

Last night I took off the blade and laid it on a smooth surface. I couldn't see any warp, even sliding a piece of paper under each tooth didn't provide any results.

So I remounted it after making sure all spacers were clean and installed correctly. Then I tightened the nut, and bearing the previous advice in mind I tried to do it not so tight. The blade still had some wobble, but less for sure. So I removed the blade and reseated it and then did up the nut with even less torque. Now it had even less wobble. So I then only undid the nut and tightened it even a little less. Now there was almost no wobble, so small that my manual run out test yielded the tiniest of variance, whereas the same test before (absolutely unscientific BTW) had about 3 - 4 times the variance in run out.

My next question would be, why is the blade so sensitive to torque on the nut? Or is it something else? And is just a little torque enough? My wrench is about 10" long and I gave it a moderate last 'push' to tighten. Maybe moving it 20 degrees.


Jason

The advice here is always just tighten the nut snug and a hair more. No "death grip" as one guy used to put it.

I guess one reason is that it can distort the blade.

[jabe]

If you tighten the arbor nut finger tight plus a snug more it'll be OK. Like Wayne & LCHIEN suggest. I've never had a TS blade come loose while the saw is running. This also makes changing the blade easier, you don't have to bust your knuckles to loosen the arbor nut.

[leehljp]

Wobble during spin down not uncommon

I am surprised that Loring didn't mention something that happens often. Blades can be mounted with very little run out - say .001 to .004 or even 005. When cutting it will make glass smooth cuts, but during spin up or spin down, it is very common for it to flex.

Let me state that again: It is very common for a blade to flex when spinning up and especially when spinning down because the blade goes through some tremendous tension pressure change differences from the outer edger of the blade versus the inner part - as it goes through different speed ranges and harmonics during the slow down process.

This is taken into account by the engineers, designers and manufacturers of even high quality blades. It is generally more pronounced on thin kerf blades.

This could be a thing of the past in 2006 but it was not uncommon at the turn of this century.

ON THE OTHER hand, when turning it by hand - if you find and see run out, you probably do need to check it. One of the wonders of the built in tensioning is that at certain speeds it can and will occasionally smooth it self out even if it has minor but noticable runout when turned by hand.