Riving Knife Issue

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Forum topic by EarlS posted 11-04-2018 09:28 PM 785 views 0 times favorited 14 replies Add to Favorites Watch
View EarlS's profile


3411 posts in 2951 days

11-04-2018 09:28 PM

Topic tags/keywords: table saw riving knife sharkguard

Here’s my dilemma:

I was trying to rip some 7/8”x 5” width walnut to 3-3/8” width that I had just planed and the boards pulled towards the blade after going through the saw blade. I have a Sharkguard dust hood with an adjustable riving knife, a Delta 3 HP Unisaw, and an after-market 4’ extruded aluminum fence. I had the problem with both a 3/32 thin kerf rip blade and a 1/8” combination blade (both Freud, both sharp).

Using a TS-Aligner (miter slot dial indicator set up) I checked the blade to make sure it was parallel to the miter slot (within 0.003), checked to make sure the blade was perpendicular to the table (within 0.001), checked the blade to make sure it wasn’t cupped, warped, bent or something like that, (within 0.002). The fence was parallel to the miter slot as well (within 0.005 – mostly due to scratches in the UHMW HDPE). Then, for good measure I also pulled out the 3 ft extruded aluminum that I use as a straight edge and ran it between the fence and blade to visually verify that the fence and blade were parallel.

The riving knife is set up to be in-line with the inside edge of the blade (nearest the fence) and is 3/32” thick.

I took off the riving knife and Sharkguard and re-set the fence to 3-5/16” to clean things up. No pulling or burning when I ran the boards through.

I’ve never had this problem before and I’m at a loss for what to check next. Thoughts, ideas, suggestions?

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

14 replies so far

View pintodeluxe's profile


6032 posts in 3416 days

#1 posted 11-04-2018 09:50 PM

Could be a lumber issue, and not a saw issue.
Ripping boards often releases internal stress. I’ve seen this from time to time with Walnut and oak.

If so, rip them extra wide so you can re-joint them and establish final width in a second pass.

Cutting to rough length before ripping will also make life easier.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View HokieKen's profile


11984 posts in 1741 days

#2 posted 11-04-2018 10:04 PM

Are you saying the boards pulled off of the fence or tried to “close” up the kerf after passing the blade?

You said the riving knife was “set to be” aligned with the inside edge of blade. Did you verify that it was before you removed it?

To Willie’s point, if the issue persists, I would try at least 2 different tupes of wood just to rule out stress release issues.

-- Kenny, SW VA, Go Hokies!!!

View lumbering_on's profile


578 posts in 1093 days

#3 posted 11-04-2018 10:09 PM

I think the other posts here are quite good, but another question would be if you changed to a blade with a different kerf recently? Some riving knives are set to work with standard kerfs, so if you switched to a thinner kerf, that could cause issues.

View EarlS's profile


3411 posts in 2951 days

#4 posted 11-04-2018 11:35 PM

Pinto – I thought it might be a wood problem at first, but the walnut came from several different boards. They were rough cut to length prior to ripping them to width.

Kenny – The shorter (12-14”) boards made it thru, but you could see daylight between the edge of the board and the fence which was why, at first, I thought the fence was not parallel to the blade.

I ran the 50” piece thru after checking everything, thinking everything was OK. The edge of the 50” long board along the fence pulled 1/16” or more off the fence when the piece was about 1/2 thru the cut (about 12” past the riving knife) and the blade was nearly nearly bound up. I shut the saw off when it became difficult to push the piece. I tried a second board thinking it might have been warped or something but had the same thing happen.

I checked the riving knife before the initial cut. I had a 1/8” kerf blade with a 3/32” knife so there should have been some give in the far side of the riving knife. One piece did close up which is the reason for the riving knif in the first place.

I haven’t run a different species through the saw yet. I’ll give it a go tomorrow. I’m also going to see how it does without the riving knife. Worst case, maybe the knife is bent or twisted? If so, I’ll give Lee a shout and order a new one. I’ll also look at the instructions and make sure I didn’t miss something when I put it back on.

This is one of those odd things that doesn’t make sense to me. Hopefully I’m explaining it well enough.

Lumbering – thanks for your questions as well. The riving knife is for thin kerf blades and has worked perfectly in the past with both 3/32” and 1/8” blades.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View WoodenDreams's profile


882 posts in 514 days

#5 posted 11-05-2018 12:25 AM

This has happened a dozen times or so in the last couple years, but only with Aromatic Red Cedar. I cross cut the 8’ & 10’ boards to 4’ lengths. Then the ripping the 6” or 8” x 4’ Aromatic Red Cedar, in about 2’ or 3’ through the rip the boards would close and pinch the riving knife or while using feather board, the wood would pull away from the fence and into the riving knife after passing the blade. In my case, it’s been the wood. I have not had this issue with any other woods.

View HokieKen's profile


11984 posts in 1741 days

#6 posted 11-05-2018 01:19 AM

Sounds like you’ve covered the bases Earl. Only other check that comes to mind is to lay a straight edge along the side of the blade and be sure the riving knife is aligned along its full length and doesn’t skew back to the other side of the blade.

Trying it without the riving knife and trying different species would be my next steps as well.

-- Kenny, SW VA, Go Hokies!!!

View Kazooman's profile


1408 posts in 2555 days

#7 posted 11-05-2018 02:45 PM

If it is the wood and it is closing in on the riving knife then the “no riving knife” experiment is not a good idea.

View jonah's profile


2092 posts in 3901 days

#8 posted 11-05-2018 04:02 PM

I’ve had this happen twice. Once it was some case hardened wood that might have killed me if I hadn’t had the riving knife (and stopped immediately once I noticed it).

The other time it was a thin board on my previous saw and the throat plate was somehow catching on a bit of wood and funneling it back into the blade. I’m not exactly sure how it happened, but again, I stopped the cut immediately and just went about it a different way.

View HokieKen's profile


11984 posts in 1741 days

#9 posted 11-05-2018 04:33 PM

If it is the wood and it is closing in on the riving knife then the “no riving knife” experiment is not a good idea.

- Kazooman

Excellent point…

-- Kenny, SW VA, Go Hokies!!!

View EarlS's profile


3411 posts in 2951 days

#10 posted 11-05-2018 06:08 PM

I’ll do some more checking and try out some other types of wood the next time I’m in the shop. I’m wondering if something didn’t get installed exactly right when I put the Sharkguard back on the saw. At any rate, there will be plenty more checking, rechecking, and verifiying before I start pushing wood through the blade. I’m not interested in seeing really bad kickback first hand.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View Andybb's profile


2349 posts in 1206 days

#11 posted 11-05-2018 06:26 PM

If it is the wood and it is closing in on the riving knife then the “no riving knife” experiment is not a good idea.

- Kazooman

If I suspected that the wood was going to move (in any direction) the last thing I’d do would be to remove the knife. Since the only 2 times I’ve had kickback in 20 years is when I had removed the riving knife I am very leery about not having one.

-- Andy - Seattle USA

View fivecodys's profile


1559 posts in 2239 days

#12 posted 11-05-2018 10:13 PM

I have had this happen also. I’m leaning towards internal stress in the board as the cause.
I have not found a good way to predict it either.
(If one of you knows how to do this please share it.)
I kind of chalked it up to using an under-powered table saw at first but I have ripped 8/4 oak and my saw had no problem and then soon after had it pulls this crap ripping 1” mahogany.
I have got into the practice of ripping long stock on the band-saw then letting the wood rest. It’s a trip when you do this and then lay them side by side and they aren’t even close to parallel.

-- A bad day woodworking is still better than a good day working.

View hairy's profile


3004 posts in 4135 days

#13 posted 11-06-2018 12:58 PM

If possible, I always use a featherboard when ripping. If the back of the board moves sideways, the front will move the opposite way, or at least try to.

-- Genghis Khan and his brother Don, couldn't keep on keeping on...

View OSU55's profile


2498 posts in 2592 days

#14 posted 11-06-2018 02:52 PM

I’ve had this happen many times – its the wood. Use a lot of rough red oak with internal stresses, but its happened with different species. Cut wide then recut to width.

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