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Your first question involved a Dado cut with a Dado blade set. Now we drift off to Router jigs...(?) Remember that unles you have clean sharp bits , you will get the same tearout. I do both types of Dados TS w/Dado blade set and Router with a jig. They both require that the bit fits the thickness of the materials (often today's wood thickness is as varied as the opinions on Global Warming) A limitation that the Router bit has a harder time correcting w/o a tracer collar and a lot of extra figuring (brain thinking often clouds my mind)
Dado sets with shims can address the different sizes with less confusion.

I would seak out the problems that cause the tearout. If it is a material defect then the same problems will errupt with the router.

IMHO FWIW

BTW... Good advise here and a good jig, but may not be the perfect solution, remember the limits of material and equipment.
 
Your first question involved a Dado cut with a Dado blade set. Now we drift off to Router jigs...(?) Remember that unles you have clean sharp bits , you will get the same tearout. I do both types of Dados TS w/Dado blade set and Router with a jig. They both require that the bit fits the thickness of the materials (often today's wood thickness is as varied as the opinions on Global Warming) A limitation that the Router bit has a harder time correcting w/o a tracer collar and a lot of extra figuring (brain thinking often clouds my mind)
Dado sets with shims can address the different sizes with less confusion.

Bill,I have to respectfully disagree with you about the router jig requiring more complex figuring than using a dado set.

I have made and used both types of the router jigs shown in the above posts, as well as many different dado sets over the years, and have two good dado sets now, but I must admit that I rarely use them any more. I do highly prefer the one that Glen showed, that uses the guide collar because ALL routers are not round, (and some even have one flat side) and that means you must keep the same router orientation all the time or the cuts will not be true, and also the router bases seemed to me to have more "Drag" on the sides of the jig than the collar does.

I like to make the jig to use a 1" guide collar and a 1/2" bit, (doesn't matter what kind, straight bit, pattern bit, spiral bit or other as long as it is a true 1/2" so it will match the jig).

To use the jig, you simply clamp the lower edge of the guide to the line on one side of the dado to be cut, then place a scrap of whatever wood you will be fitting into the dado, (making sure it goes most of the length of the dado, OR use a shorter piece at each END of the dado, then slide the other guide up against the scrap and fasten that side of the jig, (as in Glen's jig) or just clamp that side down, then remove the scrap and rout along one side of the jig and then back up against the jig's guide on the other side, and you have a dado perfectly sized to the thickness of the wood that you will be fitting into the dado. I don't know how it could be any simpler OR faster. (and ME,.... I Like Simple):D

One other thing about using the router jig is that if it is made from stiff, solid material, I think it helps keep down tearout when it is clamped snugly to the material being cut, kind of like a zero clearance insert.

The SECRET of these jigs that make them so simple to use, is that the bit is always a smaller diameter than the dado width to be cut, and you make a pass along each side of the dado jig. (If you were making a dado smaller than 1/2" wide, you would need to make a new jig to use a smaller bit, probably a 1/4" dia bit).
 
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Now, I don't have much experience at all with dado set ups and use, but no one has mentioned having a zero clearance insert on the ts for the dado set. Will this help eliminate or lessen the likelihood of tear out of the veneer? I'm more asking to help educate myself, not necessarily giving a solution.
 
I would imagine that the zero clearance plate would only work if you ran the plywood finish side down and I would figure you run the chance of scratching or marking the finish surface.

I use a jig similar to the one shown here. I run the router for a first pass at the minimalest depth and then increment depth as I need to get the depth desired.

I remember seeing that jig on NYW. Mine is far simpler but I use it only for max 12" shelving sides.

Also remember that router bits are designed for certain speeds. If you are using a slower speed than recommended might it not cause tear out?

And on the other side if your router is too fast could that result in a similar problem?

(I skipped over a couple of posts, sorry if I am repeating)
 
Hi Doug

As you know, Melamine covered chipboard....chips like hell...

If we had TS with scoring blade, the cut would be very smooth and clean...

But we don't have...so I made one...well not exactly but, I use the same idea.

A scoring blade is rotating in opposite direction to the main blade and is set very low...just to score...

I set my fence, set the blade height to around 1mm (1/32") and instead of feeding in the normal direction, I fed from the opposite direction or if you like, I started the cut (the scoring) from behind the blade, pulling the board toward me.

Then, I lift the blade and make full cut at the normal way.

Maybe you can try the same idea with your boards...just make a few test cuts with blade height at 1/32" and/or the thickness of the veneer.

If you decide to go with the router...as Julio suggested (Hi Julio, long time no see), first make a score and than continue

Regards
niki
 
I would imagine that the zero clearance plate would only work if you ran the plywood finish side down and I would figure you run the chance of scratching or marking the finish surface.

Not trying to be argumentitive here, just trying to learn.

If the finish side of the plywood is the face that the dado groove needs to be cut in and all you have is the dado blade and ts, what would you do?

I would think there's always the chance that one might scratch the finish surface when working with veneered plywood, but what's one to do :dunno: Fixing scratches isn't to hard with a little steam. Also most inside surfaces are hidden inside a cabinet so one could sand out most shallow scratches without anyone noticing.

So, if I can ask again, wouldn't a new zero clearance plate take care of eliminating tear out in the veneer when cutting the dado?

Thanks for helping me learn and understand :)
 
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