Tear/chip-out even with a backer board?

[Monte Milanuk]

Hello,

Working on a couple projects, and I've been getting some tear out on one edge of my dadoes even with a backer board, etc. A little bit on maple, noticeably more on some african orococo (sp?). Dado set is a Freud SD206 set (six inch stacked dado).

Any suggestions?

Thanks,

Monte

[Dick Rowe]

When that happens to me I have had success by making the dado in several smaller passes rather than 'hogging' it out all in one pass.

The first pass is usually no more than 1/16" deep to basically score the wood.

You might want to give that a try and see how it works for you.

[keith ouellette]

I just found what Dick said to be true about all my cutting. Take the extra step to allow for smaller cuts. I had a freud stacked dado (don't remember the model number and have since switched to the dial a dado and find the cuts a little better on the dial a dado than my old stacked dado.

[Monte Milanuk]

Hmm... thought I was safe on this one as I was having to take it in at least 3-4 passes (probably more like 6-8) due to the width - two main passes for the bulk of the width, and then however many small passes to fine-tune the exact width.

FWIW, if you were standing at the saw pushing the miter gauge forward, I'm not getting the tear out on the top of the cut, but on the left side - where I'm doing the fine passes. All along the left side... but really bad along the upper left corner.

So now I have to take this cut in multiple passes in width *and* height?

Thanks,

Monte

[John Thompson]

In addition to what has been suggested already... I would reverse the main cutter you now have on the right to the left and put the left main on the right. Then... the results would indicate if the problem is with that individual main. If that turns out to be the case, you could simply mark with a magic marker on the good cutter and use the better of the two to the side that will show.

If both sides will show... you will have to do some more digging.

Sarge..

[Steven Wilson]

A couple of other things you can try are; make a ZCI for your dato, score the edges of your dato with a knife prior to making the dato.

[Monte Milanuk]

Unfortunately, both sides will show in this instance. One much less so than the other so I could get away w/ a little fudging, but I'd rather not.

Not sure how a ZCI would help when the chipping/tearing is a good half inch off the table on the edge against the backer board?

I'll try the scoring; that should help. Since I'm kind of doing the 'creep up on it' approach to getting the cuts to fit (basically a 1.5" x 5" x 23" maple candle base w/ 1.5" x 1.5" x 3.5" orococo 'feet' / legs that have 1.5" x 0.5" dadoes that fit in corresponding 1.5" x 0.5" dadoes in the base) the *exact* location of the final whisper cut is kind of subject to fit.

Thanks,

Monte

[Jim Becker]

I though I posted in this thread earlier...I must have clicked to something else before completing it.

Anyway, the grind of the outside blades will affect it's ability to cut cleanly in species that tend to chip out. The dado sets that typically place "high" in the tests generally have a somewhat aggressive ATB grind with a high shear angle that is designed to slice across the grain like a knife blade. So I suspect the grind of your particular set is the culprit in those instances where the wood is particular. A good sharpener may be able to make an adjustment for you.

You can also try scoring the cut lines of the groove, rabbit or dado with a sharp knife before ploughing with the dado setup and/or using blue painter's tape to help keep things down.

[Lee Schierer]

I'm not sure why you are using a backer board. With that said, check your saw alignment. Dado blades (and all others as well) will tear out more if misaligned.

If the wood tears out easily use a zero clearance insert. Yes you can make them for a dado blade and they work exceptionally well. You just need a new one for each width of cut you make.

You can also apply regular masking tape (blue or purple painters tape doesn't work as well) along both sides of the cut line. The tape will help prevent tear out. Just be sure to remove the tape by peeling it toward the cut, not away from the cut. Tape thickness doesn't really affect the depth of cut enough in most cases to be a problem.

[Monte Milanuk]

Lee,

I have a ZCI throat plate for my dado set (well, as long as I use the full 3/4" stack :D ). I am not getting tearout along the edge facing down towards the table. That part is working. Never said it wasn't.

I have a backer board on the miter gage... in an attempt to keep the material from blowing out the *back* side (towards me) as the dado stack exits the material (which is *not* working).

I'm working on another project right now (blanket chest) so I haven't had a chance to try the scoring and/or tape ideas. Should be on it in the next day or two.

Monte

[glenn bradley]

Hmm... thought I was safe on this one as I was having to take it in at least 3-4 passes (probably more like 6-8) due to the width - two main passes for the bulk of the width, and then however many small passes to fine-tune the exact width.

FWIW, if you were standing at the saw pushing the miter gauge forward, I'm not getting the tear out on the top of the cut, but on the left side - where I'm doing the fine passes. All along the left side... but really bad along the upper left corner.

So now I have to take this cut in multiple passes in width *and* height?

Thanks,

Monte

Ah, we're talking about the exit point, not along the length . . . I have better luck with backer boards when they are clamped to the board to make as tight a 'joint' as possible. On smaller pieces if I am using a moter gauge I clamp the material to the miter gauge trapping the backer board between. If this is possible on your cut I would try it. Another thing I do is make the piece a little oversize and then trim the tearout edge off.

[Doug Shepard]

Probably too late for this project but I gave up trying to fight dado blade tearout. Anymore, I just make the pieces about 1/2" wider, put the dados in, then rip the excess 1/2" off.

[Lee Schierer]

I have a backer board on the miter gage... in an attempt to keep the material from blowing out the *back* side (towards me) as the dado stack exits the material (which is *not* working).

Okay. Now we are on the same page. Make your backer board a zero clearance set up as well. The wood will support the last fibers being cut and there should be little if any tear out. My box joint jig has a relplaceable hardbpoard insert so I can replace it for each width and height finger I need to cut. If the cleance hole in teh backer board fits the size of the cut being made

[Monte Milanuk]

Okay. Now we are on the same page. Make your backer board a zero clearance set up as well. The wood will support the last fibers being cut and there should be little if any tear out.

Lee,

I did, and it didn't work. Hence the point of the whole thread. ;)

Good to see we're finally working off the same page here though.

Thanks for all the help, folks. I'm stuck out of town for the next day or two; I'll try one or more of the tips/tricks when I get back sometime Thursday or Friday.

Thanks,

Monte

[Charlie Plesums]

Before I got a scoring blade on my table saw, I would sometimes make a very shallow CLIMB cut prior to the main cut... with either a regular or dado blade.

The one (perhaps only) virtue of a Radial Arm Saw is that the blade entered the face of the wood. with (theoretically) a zero clearance table on the exit side. However, since it was a climb cut, the RAS would tend to climb forward - even jump at the operator ... exciting.

To do a climb cut on a table saw, you go backwards over the blade on the table saw, a shallow cut with the blade entering the face and leaving in the kerf. Since it enters the face, no chip out. The blade will tend to pull the work forward (into the blade) and will tend to lift the work (how do you spell missle if you allow it to rise), so you have to be extremely careful, and make a very shallow and gradual cut. It is the same cut as the scoring blade makes on a two-blade saw - the scoring blade rotates in the direction opposite to the main blade, and is, in fact, a climb cut.

[Charles McCracken]

The dado sets that typically place "high" in the tests generally have a somewhat aggressive ATB grind with a high shear angle that is designed to slice across the grain like a knife blade.

All,

Jim is correct in this. The SD206 that Monte is using has the exact same grind angles as the SD500 series. The difference between them is that the SD500 has twice as many tips and an extra chipper.



Monte,

Since all of the blowout seems to be on one side I suggest you start by checking that outside saw for damage and also rechecking the saw alignment, particularly the blade parallelism to the miter slot.

[Lee Schierer]

Lee,

I did, and it didn't work. Hence the point of the whole thread. ;)


If the ZCI didn't work, then either the work isn't being held tightly against it or the blade is dull. If you clamp three pieces of wood togeher and then crosscut a dado through all three of them the first two peices should have zero tear out. The third will have tear out unless a ZCI of exactly the same size as the cut being made is held tightly behind it. Even a gap as small as 1/32 will give pretty significant tearout.

What kind of wood are you cutting and what is the backer made of?

[Monte Milanuk]

The wood with the worst tear out so far is an African hardwood... I didn't catch the exact spelling from the guy at the hardwood dealer... I'd wanted cocobolo per the plans I have, which he didn't have any of. I only need a few small pieces, and some digging through the 'miscellaneous' bin yielded some nice looking wood... dark, strong dark grain, looked like it would contrast the soft maple base nicely. I thought he said 'orococo' or something like that, but I'm not coming up w/ anything on the 'Net when I search for that. Might be off on the spelling, or just heard 'im wrong.

Second wood (base) is soft maple, and the backer was a scrap piece of 3/4" sugar pine w/ PSA 220gr paper on the face of it to keep things put.