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View EarlS's profile

Riving Knife Issue

by EarlS
posted 11-04-2018 09:28 PM


14 replies so far

View pintodeluxe's profile

pintodeluxe

5998 posts in 3350 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 (online now)

HokieKen

11325 posts in 1675 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

lumbering_on

578 posts in 1027 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

EarlS

3172 posts in 2885 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

WoodenDreams

796 posts in 448 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 (online now)

HokieKen

11325 posts in 1675 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

Kazooman

1377 posts in 2489 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

jonah

2089 posts in 3835 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 (online now)

HokieKen

11325 posts in 1675 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

EarlS

3172 posts in 2885 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

Andybb

2150 posts in 1140 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


+1
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

fivecodys

1519 posts in 2173 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.

-- When you leave your shop for the night, make sure you can always count to 10.

View hairy's profile

hairy

2964 posts in 4069 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

OSU55

2439 posts in 2526 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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