# Ripping boards on Powermatic- pinching riving knife



## LlamaMama (May 27, 2020)

Hello my Friends - we are having a problem in my woodshop- when ripping a board it pinches the riving knife on the Powermatic table saw and gets stuck. I tried the low profile riving knife which didn't help much. We end up removing the riving knife to get our work done, other guards have to go too since they hang on the knife. Is it my wood? Is it the saw? Any help is appreciated.

Peace.

Llama Mama


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## controlfreak (Jun 29, 2019)

Are you using a thin kerf blade that is the same width as the knife width?


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## Loren (May 30, 2008)

Check your fence alignment. You can angle it away from the blade at the back a little, like 1/32" too. Another thing you can do is attach a short fence to your fence so it imitates European saws.

If you use a long fence with a riving knife if the wood has tension in it and wants to bend to the right, then it will push against the fence and thus against the side of the riving knife. If the wood tension bends to the left, it may pinch the knife but I usually just power through it and it's not a problem. I use a short fence though so I can always see which way the tension in the wood is going.

Riving knives come from Europe so it makes sense to use a short fence like they do there.


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## HokieKen (Apr 14, 2015)

Both good suggestions ^

I was going to suggest what Loren did. When I set up my fence, I have it so the back is .005-.010 inches further out than the front. That prevents pinching between the splitter and the fence.


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## tvrgeek (Nov 19, 2013)

Standard knives are for full 1/8 blades. You have to buy/make a thin kerf knife. Never seen a full guard for thin kerf, but I bet Shark has one. I started looking, but with my new 3 HP saw, went to all full width blades anyway. 
You could also make your own ZCI and use a micro-splitter or other thin splitter, but not quite as safe as a riving knife or full guard.

I won't use a saw on without one or the other in place. Been there, done that, got scared a couple of times. ( Dado's excepted, but that is another problem)


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## splintergroup (Jan 20, 2015)

If the wood is collapsing the saw kerf shut (and thus squeezing the riving knife), You can keep a shim handy such that as the cut clears the rear of the knife, drop the shim into the kerf to keep it from pinching closed.


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## Unknowncraftsman (Jun 23, 2013)

> If the wood is collapsing the saw kerf shut (and thus squeezing the riving knife), You can keep a shim handy such that as the cut clears the rear of the knife, drop the shim into the kerf to keep it from pinching closed.
> 
> - splintergroup


I've read about people this . How exactly does one add a shim to a board during a rip cut. Are you supposed reach to the back of the blade to insert the shim with the saw running. Or turn off the saw then add the shim turn I'm saw finish the cut. It seems unlikely anyone really doing this. ?
I rip on everything over size on my bandsaw first so I don't have a guard or splinter or riving knive on my saw.
I can spot unruly wood long time before it ever gets to my table saw.
Sure it's a few extra steps but we'll worth the time since I really don't want unruly boards in my builds.
Good Luck


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## MPython (Nov 30, 2018)

Does this problem happen with every rip cut? If so, then, as others have said, you have a misaligned fence or your riving knife is too thick for your blade. Sometimes, however, you run across a board that has internal stress that will cause the kerf to close behind the blade, pinching the riving knife and often the blade too. This is a dangerous situation. The saw is likely to throw the board back at you (kickback) or stall. Sometimes after a stall, the board has clamped so tight that it is very difficult to remove without damaging your blade or the riving knife or both. It almost always results in a badly burned cut. When you notice this happening, shut the saw off immediately, leaving the board in place. Insert a wedge in the end of the kerf and tap it in with a hammer far enough to force the kerf open. Then lift the board off the saw if you can, or complete the cut. If the latter and the board continues to bind, stop the saw again and tap the wedge in further. It's a delicate operation, so be careful. Don't try to force the board through the cut and don't stand directly behind the blade under any circumstances. Like AJ said, if the board has enough internal stress to cause this kind of problem, it's probably useless for your project. The object here is get the board off your saw without injuring yourself or damaging your saw.


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## SMP (Aug 29, 2018)

I do what Loren suggests. However, i have ripped 1×12 sugar pine where there was SO much tension in the boards they would lock up no matter what i did. So i ended up doing multiple passes to trim down before the final width. Like instead of ripping 6" just taking off 2-3" then going for my 6" piece


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## tvrgeek (Nov 19, 2013)

And it seems "unruly" wood can make a BS drift. Where a member used my saw for some 2 inch Poplar that was binding, it drifted. I went back and tested a bunch of wood I had. No drift at all.

Yes, if you know the wood will pinch, As it just passes the splitter ( guard in place) you can each over and put in a wedge. Even easier of you make a wedge in a "T" so it does not drop out. If you don't have a knife/splitter/guard, then shame on you to start with.

*But step one is to measure your knife width!* The knife needs to be a few thou thinner the the blade.

No reason for the fence to be out more than a thou or so. 10 thou I would consider totally unacceptable. 
I don't know the above reference to "short" fence. Is that length or height? "EU" style fences have a "lay flat" option that sits right on the top for thin stock. My "EU" style fence is as long as any, well past the back of the table. It has a tall and low option. Laguna does it with a flip-over section.


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## Loren (May 30, 2008)

See how it doesn't extend out very far and can even be pulled back. I pull back the fence on my felder all the time when ripping solid boards. On sheet goods the long fence is probably better but in any case, once the wood is at the riving knife the fence doesn't need to be there to guide it. I learned this trick and used it a lot when I had an INCA cabinet saw before the Felder. I also do that to have a cross cut stop on the right side of the blade.

More info on short fence usage here. Niki used to be on LJ but he passed away. Despite what he said, I have seen pictures of many European saws with a short fence only. Maybe they were missing a long extrusion that attaches to it.


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## tvrgeek (Nov 19, 2013)

I'll stick with my long fence and correct width knife, all aligned. Fence past the blade is still necessary to the end of a cut when there is not much left against the fence on the trailing side. The knife or splitter should not be the guide. It is there t prevent miss-alignment so bad as to allow a rear tooth to take a bite big enough to kick back. What excuse Makita has for that benchtop saw I don't know. I would not expect to rip a board strait on it! Maybe half-kiln dried framing lumber that comes out in a bent corkscrew.

I know. MJ splitters are made to provide bias toward the fence. I found they could actually cause slight fence deflection, so I used mine centered in the kerf and used proper feather boards and push blocks to maintain fence contact. I may eventually even pay the price for JessEm guides.


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## Loren (May 30, 2008)

I don't argue with people. I find your response arrogant and ungracious.


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## MrUnix (May 18, 2012)

Regarding the 'short' fence, here is a good article from Popular Woodworking:

Table Saws: Why the British Think We're Crazy

Note: The "This style of fence was once available on this side of the Atlantic from Delta" mentioned in the article is a reference to the now discontinued but well loved Unifence, which was ahead of its time IMO. Much safer design and much more versatile.

Cheers,
Brad


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## Tony_S (Dec 16, 2009)

Short fences aren't uncommon on European table saws and most have fences that can be adapted to be 'short'.
Ripping with a short fence is perfectly safe provided the saw has a riving knife. 
As usual, some people know not of what they speak, yet they choose to speak anyhow.


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## Jim2020 (Jun 26, 2020)

Looks like the Makita has a sliding table (doesn't look too good though). Sliding table saws change how you use the saw. I built a slider, and really don't have much use for splitters or riving knives. The sliding table and short fence solve kickback, so there's one less thing to go wrong. Jim


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## HokieKen (Apr 14, 2015)

As long as the fence goes to around the center of the blade, it will do the job. At that point, the cut is done and there is nothing to push the board against the back of the fence. I don't have a short fence but I don't think I'd have any problems if I did.


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## Davevand (Feb 10, 2016)

Check the riving knife and be sure it is perfectly aligned with the blade. Mine drifts out of alignment over time and I have check both the horizontal and vertical alignment. Also check for dust and debris in the slot when the knife seats.


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## MPython (Nov 30, 2018)

The Unifence on my Unisaw was designed so it could be loosened from the clamping bracket, pulled back, and retightened, giving you a "short fence." I used to use this feature a lot when I had the Uni. I can't do that with the Biesemeyer type fence on my SawStop.


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