Table saw : Curved cut when ripping

[transatlantic]

I've noticed that I'm not getting straight cuts when ripping pieces through my table saw. When I place a straight edge against the sawn edge, it touches on either end, but then has a shallow curved gap between the two ends, about 0.5mm at it's largest in the middle.

I'm guessing this is either to do with my fence, or more likely my technqiue, but I can't think of a case which would produce this kind of geometry?

I should point out that it has happened on mosts cut I make with varying material (pine, ply, mdf), so pretty sure it's not to do with the material.

 

[Sgian Dubh]

Fence toeing out significantly? It should be parallel to the blade, or with no more than just the tiniest hint of toe-out, certainly not toeing in. Slainte.

 

[transatlantic]

Fence toeing out significantly? It should be parallel to the blade, or with no more than just the tiniest hint of toe-out, certainly not toeing in. Slainte.

Pretty sure it's parallel to the blade. My technqiue being to put a steel ruler between the two to align them. I was wondering if perhaps the curve is being formed by the back end of the blade due to me not putting enough pressure against the fence?

 

[Peter Sefton]

My first thought is the same as Richards but if the fence toe-out is OK then my next thought would be, is the riving knife bent, out of line with the saw blade?

Cheers Peter

 

[doctor Bob]

Is the blade sharp?

 

[jnw010]

Is the blade sharper on one side? I've not seen it on a table saw, but I've had chainsaws and bandsaws pull to one direction or the other because one side was blunted and cutting slower.

 

[woodbrains]

Hello,

Fence flex would be my guess.

Start of cut, deliberate effort is made to register material against fence, high sideways pressure exerted, fence flexes slightly away from blade. During the majority of the cut, operator relaxes sideways pressure, concentrating on moving material forward, fence moves back towards blade. End of cut, operator concentrates on keeping the ever diminishing board against fence, sideways pressure is increase and fence flexes away from blade again. Half a millimeter flex will not even be felt during the cut.

Mike.

 

[MattRoberts]

Have you tried cutting with a feather board to eliminate the question of technique?

 

[transatlantic]

Thank you for the suggestions - I'll be out in my garage tonight trying to diagnose this.

 

[dkaardal]

Woodbrains beat me too it. I've seen strange rip cuts like what you're describing and the commonality has always been the fence. On hobby class machines, the fence isn't as robust as it is on the professional ones and deflection can occur if you put too much pressure against the fence when you're running your board through.

That being said, you don't need to push the wood against the fence with any real force. It's there as a guide more then anything else, so just use the fence to keep your board aligned when your running it through.

One thing you can try to test this is to use a featherboard. Set the featherboard so that it's just before the blade and let it apply the force to keep the board against your fence. The force will be consistent throughout the cut, so if you can get a nice straight rip using the featherboard then you'll have confirmation on where the problem is. Then you can start to work out ways to fix it.

 

[woodbrains]

Hello,

Alternatively, I would put a board on the outfeed table, butt it against the fence and clamp it. This will eliminate any fence deflection if there is any, then make your cut against the fence as usual. See if that eliminates the problem. If it does, you'll need some convenient method of preventing fence flex during normal use.

Mike.