Can you explain this table saw cut?

[Njl]

Hello,

I made this rip on an evolution rage 5s, with a feattherboard giving consistent pressure against the fence and me pushing the piece onto the blade. As far as I can tell fence and blade set up right. The piece between saw and fence came out ok. But the other piece came out with a kind of bow, and is thicker at each end and narrower in the middle. (You can see measurements in pencil on the photo). I cannot understand how this happened. It is an aftermarket wood blade, not the general purpose one that comes with the saw.

I am still learning on this so grateful for any explanations as to what went wrong and how I can fix it.

Thank you

 

[Wilson joinery]

Hi there, daft question but was the timber the same width along its length before the cut?

 

[Jacob]

I guess the cut released tension and the offcut piece bent.
If you didn't have a riving knife in place it might get get cut again as it went past the far edge of the blade.
Or with the knife in place it would just stay bent
Or something along those lines!

 

[Bingy man]

Hello,

I made this rip on an evolution rage 5s, with a feattherboard giving consistent pressure against the fence and me pushing the piece onto the blade. As far as I can tell fence and blade set up right. The piece between saw and fence came out ok. But the other piece came out with a kind of bow, and is thicker at each end and narrower in the middle. (You can see measurements in pencil on the photo). I cannot understand how this happened. It is an aftermarket wood blade, not the general purpose one that comes with the saw.

I am still learning on this so grateful for any explanations as to what went wrong and how I can fix it.

Thank you



View attachment 185658

Why is the riving knife off set from the blade not to mention the invisible guard? ? Has that timber been dropped onto the blade ??

 

[Wilson joinery]

Good spot bingy man but I’m hoping the riving knife offset is just a trick of the camera!!

 

[Bingy man]

Good spot bingy man but I’m hoping the riving knife offset is just a trick of the camera!!

I hope so , I had to look at the pic several times as it looks like the kerf stops an inch or so from either end .. so hopefully same applies to the riving knife..

 

[Doug71]

It's the stress being released in the wood as you cut it.

It looks like the board was trying to close up behind the blade so the back of the blade was probably also cutting the wood hence taking a bit more out of the middle. Thing is the back of the blade is cutting with an upwards action which can cause the board to be lifted and thrown back at you, using a crown guard helps avoid this.

 

[niall Y]

It looks to be mild, case hardening of the timber, most likely caused during kiln drying. Tension has been released resulting in the cut pieces bowing slightly , In really bad cases the cut pieces can try and bind on the saw blade even before the riving knife is engaged, or around the knife itself. One usually sticks a wedge in the cut just after it has passed the riving knife., to ease the problem. Worst case scenario, is that you can end up with two pieces of unusable timber.

 

[Njl]

The riving knife is in line, that is just the angle of the camera. Not sure I understand how releasing tension works, but something to investigate! thanks very much.

 

[Njl]

The riving knife is in line, that is the camera angle. I don’t understand how releasing tension works but will investigate. Thanks very much.

 

[AndyMc]

You mentioned you've changed the blade from the stock Evolution multi-material blade. Have you checked the dimensions of the new blade are appropriate for the kerf of the riving knife? Perhaps your new blade is thicker than the old blade, allowing more play around the workpiece as it moves across the riving knife, exacerbating the effects of the wood de-tensioning, as others have suggested. There are threads on this forum covering the sizing of riving knives, although not sure I've seen any alternatives to the stock Evolution knife.

The fence on the 5S also has quite a lot of slop, be very careful when aligning it to the blade so that you don't end up forcing the workpiece into a narrower channel at the rear of the blade compared to the front. You can get kickback in this situation, or perhaps additional vibration that will reduce your cut accuracy.

 

[Sgian Dubh]

I guess the cut released tension and the offcut piece bent.
If you didn't have a riving knife in place it might get get cut again as it went past the far edge of the blade.
Or with the knife in place it would just stay bent
Or something along those lines!

I'd say "something along those lines" is a pretty good description, but I'd eliminate specifying tension release as the cause of the very slight bend visible in the supplied image. I'd say, if was going to say anything at all about that tiny deviation of a bit of sawn wood, "stress was released" during sawing which covers a broad field including tension, compression, shear, torsional, etc, all stresses, each of which can be sub-divided into, for example, tension with the grain, tension across the grain, compression across the grain, compression parallel with the grain, and so on. Not only that, but any material may be experiencing more than one form of stress simultaneously, e.g. it's experiencing both compression forces and tension forces, and in multiple directions.

So, in answer to the OP, nothing really went wrong at all; just a tiny amount of inconsequential stress was released as you were ripping your bit of wood into two pieces, and one bit bowed slightly (the offcut bit by the look of it [I could be wrong]) and seems to have been sawn a bit more by the upcutting teeth at the outfeed end of the cut by saw blade.

Having just said that there's a slight possibility that your rip fence arrangement might benefit from a little bit of checking, but that's only a suggestion. Evidence of a fault is virtually non-existent. Slainte.

 

[Limey Lurker]

Are you using a full-length fence, or a rip fence?

 

[Stanleymonkey]

Can you cut something man made (and hopefully stable) like plywood or mdf? If the cut is true - that would point to it being tension.

 

[duke]

I guess the cut released tension and the offcut piece bent.
If you didn't have a riving knife in place it might get get cut again as it went past the far edge of the blade.
Or with the knife in place it would just stay bent
Or something along those lines!

And possibly the stresses in wood are bending the riving knife?

 

[imageel]

Hello,

I made this rip on an evolution rage 5s, with a feattherboard giving consistent pressure against the fence and me pushing the piece onto the blade. As far as I can tell fence and blade set up right. The piece between saw and fence came out ok. But the other piece came out with a kind of bow, and is thicker at each end and narrower in the middle. (You can see measurements in pencil on the photo). I cannot understand how this happened. It is an aftermarket wood blade, not the general purpose one that comes with the saw.

I am still learning on this so grateful for any explanations as to what went wrong and how I can fix it.

Thank you



View attachment 185658

Have you checked that the uncut edge nearest the blade in the photo is still dead straight?
As others suggest this has likely happened because of stresses building up in the timber when it was drying out and as you've cut it you have released those stresses and it has tried to close up such that the trailing part of the blade has shaved the timber on the up-cut.
Quite likely with such small sections the entire upper piece ( or both) may now be banana shaped

 

[johnnyb]

Very very common occurrence. Happens less on old wood. Often the thin offcut piece goes like a twiglet! They can open up from the fence pushing the wood into the blade. I do have a wedge near the outfeed but I need to stop the blade to put the wedge in. It baffles many when mdf/mfc springs on panel saws. It just takes a small amount of tension.

 

[johnnyb]

This is why a well set riving knife that tilts with the saw should be welded behind any saw blade. Never ever take it off.

 

[TRITON]

I'd say "something along those lines" is a pretty good description, but I'd eliminate specifying tension release as the cause of the very slight bend visible in the supplied image. I'd say, if was going to say anything at all about that tiny deviation of a bit of sawn wood, "stress was released" during sawing which covers a broad field including tension, compression, shear, torsional, etc, all stresses, each of which can be sub-divided into, for example, tension with the grain, tension across the grain, compression across the grain, compression parallel with the grain, and so on. Not only that, but any material may be experiencing more than one form of stress simultaneously, e.g. it's experiencing both compression forces and tension forces, and in multiple directions.

So, in answer to the OP, nothing really went wrong at all; just a tiny amount of inconsequential stress was released as you were ripping your bit of wood into two pieces, and one bit bowed slightly (the offcut bit by the look of it [I could be wrong]) and seems to have been sawn a bit more by the upcutting teeth at the outfeed end of the cut by saw blade.

Having just said that there's a slight possibility that your rip fence arrangement might benefit from a little bit of checking, but that's only a suggestion. Evidence of a fault is virtually non-existent. Slainte.

tension can be pretty mental cutting down boards. I've had big oak boards, 12'x200mm that started off straight and flat before it went through the saw and what comes out the other side is bent and twisted and pretty much useless as a long length.

A lot of times it cant be helped given how a tree lays down each layer of growth.Then in the saw mill as its cut green into boards, and kilned with the weight of the multiple boards pressing down it remains relatively straight and flat, til we buy it, where it goes all to hell

Unless of course you happen to own a surface planer

 

[Njl]

This is all much food for thought and experimentation. Am trying to avoid having to buy a planer. Thanks all (the fence is full length).