tearout on plywood

[jeff oldham]

this might seem like a silly question,,,but I just bought some dado blades and was planning on dadoing some shelves across plywood,,and this is my first attempt at it and it splintered really bad,,,the blades I have are not cheap,,i bought them from amazon and they had a good rating,,and I paid 90.00 for them,,,but the crosscut across plwood was terrible,,so I tried using a palm router and the cut was better but it seemed like a lot of effort on the router,,,can anyone help me or tell me what I was dong wrong,,,thank you

[Thomas McCurnin]

The veneer is thin and unsupported. Do any or all of these:

Score the projected cut with a knife or razor blade.. Heck, make a knife wall if you want.

Tape over the area of the projected cut with masking tape.

[Steve Fish]

Make a zero clearance insert for your saw. I also like Tom’s advice using tape and or pre scoring with a razor.

[Lee Schierer]

If it is a nice piece of furniture I would opt for the painters tape and zero clearance insert method. Regular masking tape works better than painters tape, but it is rare these days. After making the cuts be sure to peel the tape off toward the cut edge so you don't lift any loose fibers.

[Jim Becker]

I'm with Lee...use multiple techniques to help mitigate risk of splintered veneer edges.

What you're experiencing is also related to why some dado sets are better for veneered goods than others. It has to do with how the outside blades' teeth are designed. The higher end setups have a very steep and sharp angle and also tend to project a hair more than the chippers. While that leaves a noticeable mark at the bottom of a groove, rabbit or dado, it's what cleanly slices the veneer before the rest of the tooth geometry comes crashing down.

[michael dilday]

Slow feed rate of the material is helpful. Make a very light pass taking off a minimum material then a final pass to full depth. All the other suggestions are good.

[Charles Lent]

I agree with everyone's suggestions, but would like to know more about your specific dado blade and the type/kind/thickness and number of layers of the plywood that you are cutting.

I make quite a few boxes with box jointed corners in Baltic Birch plywood and I don't have problems with splintered edges, but most of the time I'm using the Freud SBOX8 blade set and a zero clearance insert. I use a Freud Dial-A-Width dado blade for larger box joints and they aren't quite as smooth on the bottom of the cut, but the sides are just as clean.

Charley

[Michael Drew]

I've had a few different dado sets. They do not all work as advertised, despite their price point. I have been using an Infinity Dadonator the past few years, and there is no tear out whatsoever. Nice flat dados too. I make all kinds of shelving units, and I often use that cheap crap you find at the big box stores. There's little point in wasting a zero clearance insert, unless you plan to only cut dado's of one size.

[Mark Daily]

If you have a good sharpening service nearby it might help to have them sharpened, even if they are new.

I did that with mine and they came back much sharper than they were from the factory.

[Mark Daily]

I agree with everyone's suggestions, but would like to know more about your specific dado blade and the type/kind/thickness and number of layers of the plywood that you are cutting.

I make quite a few boxes with box jointed corners in Baltic Birch plywood and I don't have problems with splintered edges, but most of the time I'm using the Freud SBOX8 blade set and a zero clearance insert. I use a Freud Dial-A-Width dado blade for larger box joints and they aren't quite as smooth on the bottom of the cut, but the sides are just as clean.

Charley

Those are beautiful boxes Charley!

[Christopher Giles]

Jeff,
You may want to try taking an initial light cut, maybe a 1/16" deep or so. This should be far less likely to tear out, and then you can proceed to full depth. Keep track of the depth adjustments as you go through your parts by how many turns of the crank arrived at the proper depth.

regards,
Chris Giles

[Ray Newman]

Speaking from experience, tape, scoring, and a zero clearance insert (ZCI) will work. learned this one the hard way.

I made several dado ZCI inserts for my old Uni-saw from 1/2" plyw'd and labeled each one as to what chippers were utilized. As I now run a SawStop, ICS with a Colliflower replaceable insert, I still do the same. http://www.colliflower-zci.com/

Resharpening is a good idea. Just be sure to tell the sharpener to grind the blades and chippers to the same diameter for flat bottoms. Another lesson learned the hard way.

As always, the dado cut quality will depend upon the quality of the work material.

Cha's Lent: nice looking boxes.

[Rick Potter]

I wonder what plywood you are cutting? If it is from a big box store, the show layer is so thin that it shatters often on crosscutting.

How does it cut on Baltic birch, or solid hardwood, like oak?

[glenn bradley]

I wonder what plywood you are cutting? If it is from a big box store, the show layer is so thin that it shatters often on crosscutting.

How does it cut on Baltic birch, or solid hardwood, like oak?


Rick beat me to it. Before we blame the dado stack, let's look at what we are cutting. High quality, thickly veneered hardwood plywood and/or plywood with many thin layers will do better than soft lumber core plys with tissue thin veneer. I use a scoring line for veneers and even on some tearout prone hardwoods. I will also use a scoring cut with a marking knife or razor for a critical cut in any material. Tape can sometimes tear loose the fibers that it just saved from tearout so test some cuts on some scrap of the material you want to use. If the tape pulls up fibers, skip the tape and just slice a scoring line.

[Richard Coers]

A $90 dado set is a cheap set in my opinion.

[johnny means]

I'm in the scoring pass camp. I don't even do a 16th, just enough to shave off the veneer. The key is to plan for easy reliability between setups. I'll usually clock my handwheel so I can raise and lower to the same heights easily.

[Ray Gutnick]

I've had pretty good luck with painters tape, but the other suggestions are solid

[Warren Lake]

They make negative hook dadoes for plywood. The blade on the bottom is from one of my regular sets, the blade on top is from a plywood set. The outside chipper on the bottom blade leans well forward, on the top blade the teeth lean backwards. Your material needs to be decent quality. I havent bought dadoe sets for years but all of them were likely 225.00 - 250.00 Can a set and im going way back.



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[Bob Jones 5443]

Johnny Means sums it up for me. Set up the fence for the cut. Raise the blade just enough to kiss the sheet. Run it through, making the very slightest of scoring lines. You should then be able to raise the blade for the full dado depth and get no tearout.

[Curt Harms]

Johnny Means sums it up for me. Set up the fence for the cut. Raise the blade just enough to kiss the sheet. Run it through, making the very slightest of scoring lines. You should then be able to raise the blade for the full dado depth and get no tearout.

I do that when cutting melamine. I use a triple chip grind blade and make a very shallow pass first then cut off. My dado has the little 'bat ears' I think they're called. I think my next dados are going to be cut with a router. I made a jig that when used in conjunction with a top bearing 1/2" X 1/2" straight bit cuts very clean dados. The jig enables me to set the dado width to the plywood as long as the dado is at least 1/2". There's a jig that uses a bushing but works similarly. I haven't messed with that one yet.

[Gordon Stump]

https://www.amazon.com/Freud-Super-Dado-Sets-SD508/dp/B00004RK0P (https://www.amazon.com/Freud-Super-Dado-Sets-SD508/dp/B00004RK0P)

All of the suggestions are right on. But a dado set designed for veneered plywood is a good start. I found that expensive old stock birch plywood from my lumber yard had more chip out than cheaper poplar core plywood. The fir core or the gluing process seemed to chip out even with a dado blade designed for melamine or veneer plywood.

[Kevin Jenness]

For shelving, why use a dado anyway? Butt joints with biscuits , splines or dominos are sufficiently strong.

[Jim Becker]

For shelving, why use a dado anyway? Butt joints with biscuits , splines or dominos are sufficiently strong.

Dados likely are stronger and help to deal with racking, but even if that isn't the case (pardon the expression... :D ) there is the appearance factor. Some folks like the look of the exposed joinery; some do not. That's subjective.