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Maybe a dumb beginner question - cut riving knife slot in zero clearance insert?

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Forum topic by Adam12Hicks posted 05-16-2015 01:44 PM 829 views 1 time favorited 8 replies Add to Favorites Watch
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Adam12Hicks

7 posts in 591 days


05-16-2015 01:44 PM

Well it’s certainly easy enough to make a zero clearance insert by clamping down the insert and running the blade through it, but are there any tricks for making additional clearance for the riving knife?

I am wanting to make a project with 3/4” oak plywood, and am hoping to avoid as much tearout as possible. I’ve seen using painters tape on the underside of the wood, and using a zero clearance insert will help. I do not want to rip down a large sheet of plywood without my riving knife.

Any tips are appreciated! Also, thinking out loud, but if I ran a thin sheet of MDF under the oak would that help with the tearout? Might be tough to rip them both together and might be unsafe thinking about it.

Anyways, thanks again!
Adam


8 replies so far

View Fred Hargis's profile

Fred Hargis

3945 posts in 1959 days


#1 posted 05-16-2015 03:06 PM

I can think of several ways to do it, but it may depend on what tools you have. Using a plunge router with a 1/4” bit would be one way. You could also cut it on a bandsaw, but this would mean making the slot all the way to thew rear of the insert (no big deal). Use a scrollsaw, drill an access hole and cut it out. You could also skip using the riving knife (let the safety police howl, I don’t care). It’s useful, no doubt, but serves a slightly less safety purpose with plywood…it’s probably not going to react the way hardwood does when cut

-- Our village hasn't lost it's idiot, he was elected to congress.

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firefighterontheside

13499 posts in 1322 days


#2 posted 05-16-2015 03:24 PM

What blade are you using? The most helpful thing I did to stop tear out on plywood was to buy a nice crosscut blade. I only use that blade for cross cutting plywood. The thing about zero clearance is it’s great for ripping, but you really don’t get any tear out when ripping. When crosscutting, the best thing IMO is to use a sled if the pieces are somewhat big. The sled can be made to be zero clearance with the blade, therefore providing tear out protection. For a while I wanted a zero clearance insert until I realized it leaves a lot more dust on top of the table.

-- Bill M. "People change, walnut doesn't" by Gene.

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OneAdamTwelve

14 posts in 574 days


#3 posted 05-16-2015 03:47 PM

Thanks guys. I have a Freud 80T ultimate cutoff blade and a 90T flawless finish blade. The problem I’ve had with the flawless finish blade is that it’s a thinner than standard kerf and hardwoods bind on my riving knife. I’ll use my router table (just built a Kreg table and cabinet. Good excuse to learn it!) for the riving knife slot.

I have an Incra miter gauge and sled but about 20” is all it’s good for before it gets wobbly. Looks like a need to build a full size crosscut sled as my next project!

Thanks,
Adam

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MrRon

3926 posts in 2709 days


#4 posted 05-16-2015 10:30 PM

If you can cut a slot in the zero insert the exact thickness of the riving knife, without permitting any side pressure on the knife, it should work. The insert would have to be a very tight fit in the saw’s top to prevent any side motion.

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MrRon

3926 posts in 2709 days


#5 posted 05-16-2015 10:31 PM

If you can cut a slot in the zero insert the exact thickness of the riving knife, without permitting any side pressure on the knife, it should work. The insert would have to be a very tight fit in the saw’s top to prevent any side motion.

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runswithscissors

2189 posts in 1490 days


#6 posted 05-17-2015 03:09 AM

This is so easy!! First saw your zero clearance slot as you described. Remove the insert. Put the regular insert back in. Turn the ZCI end for end. Move the fence over so the blade comes up through the slot you just cut. Raise the blade up high. Then, carefully feed the new insert into the blade until the slot is as long as you need it for the riving knife. Shut the saw down before trying to remove the newly cut ZCI.

I don’t agree that cutting plywood is safe without the RK. Watch some You Tube videos to see what happens when the plywood rotates into the blade. Ugly!

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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OneAdamTwelve

14 posts in 574 days


#7 posted 05-17-2015 04:02 AM

Hey that is easy! I’ll do it. Thank you!

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splatman

562 posts in 864 days


#8 posted 05-17-2015 05:04 AM

Semi-related: YouTube user Frank Howarth did something similar.

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