Dado blades - was I expecting too much?

[Brian Henderson]

You have to remember that with each individual pass, the blades are in a slightly different place, the chippers are not solid blades like a normal saw blade is. One thing you can do at the end is carefully run the wood across the dado set perpendicular to the normal direction of cut and that will clean up all of those ridges and make it smooth.

[George Bokros]

You have to remember that with each individual pass, the blades are in a slightly different place, the chippers are not solid blades like a normal saw blade is. One thing you can do at the end is carefully run the wood across the dado set perpendicular to the normal direction of cut and that will clean up all of those ridges and make it smooth.

This pretty much what I said in my previous post.

[Art Mann]

You have to remember that with each individual pass, the blades are in a slightly different place, the chippers are not solid blades like a normal saw blade is. One thing you can do at the end is carefully run the wood across the dado set perpendicular to the normal direction of cut and that will clean up all of those ridges and make it smooth.

I am not sure what you mean by the chippers being in a different place. The chippers aren't creating those small grooves in the original poster's photo. It is the outside blades that do that. The chippers will leave a flat surface in the bottom of a dado. More passes in any direction will create more grooves in the cut surface. Dado blades are not designed to cut perfectly flat half lap joints. Fortunately, It doesn't seem to make any difference after the joint is glued up, at least in my observation.

[Ryan Mooney]

Another option if you really need a flat bottomed cut and don't want to do post cut cleanup is to buy a box joint or finger joint blade that has flat topped teeth. The downside is that its more likely to have some blow out on the sides/back so a backer board is more necessary.

[Ray Newman]

If you desire smooth/clean tenon cheeks, and as others posted, a tenoning jig makes shortwork of it. A shop-fabricated slip on over the fence jig for the table saw is easily fabricated. Such a jig can be simple or complex. An example of an easily constructed one -- www.highlandwoodworking.com/tablesawtenonjig.aspx

If you have arouter table, you could cut them on it and have clean/smooth cheeks. A bit more time consuming, but if a smooth/clean cut is desired, that is another way to cut tenons. Or to save some time, quickly rough cut the tenons on the band saw and finish them on the router table.

[Len Rosenberg]

Forrest will custom make any of their blades with flat teeth if you want that. I ordered a blade with flat teeth to use with a table saw tenon jig and it worked beautifully.

[Rick Moyer]

Just curious, what saw? I had better results from my Grizzly 3 HP cabinet saw than I did with my Craftsman, supposedly 3HP but really 1HP, contractor saw with the same dado set. I don't know why, but the better saw made much better dadoes.

[Jebediah Eckert]

Thanks for the responses. That makes sense about the grind for a cleaner cut causing the "bat wings." I guess I just didn't realize that's how it worked. The results are fine I guess, I just wanted to make sure there wasn't anything wrong.

The cuts were made on a 3hp cabinet saw using a miter gauge. I'm sure it's not the saw, but I did make several passes, apparently making it worse (now that I understand how it works). Live in learn, now I know.

If I used a wider stack and didn't overlap I'm sure now it would be cleaner. At the end of the day I'm sure it will be plenty strong I'm just not sure how the joint line will look. I will glue up one Off the saw and one cleaned up with a plane and see if it's worth the extra work.

Thanks again.

[Jim Dwight]

The right answer was already stated but not seconded, I will do that. When I cut tenons with a dado set, I cut them a little oversize and trim with a shoulder plane. I tried for years to cut tenons including with a good tenon jig and was never satisfied. Minor thickness variation would make some tenons tight and some loose. But by cutting slightly oversize and trimming with a shoulder plane, I can get consistently good fitting joints. Hand tools have their place.

[scott spencer]

Thanks for the responses. That makes sense about the grind for a cleaner cut causing the "bat wings." I guess I just didn't realize that's how it worked. The results are fine I guess, I just wanted to make sure there wasn't anything wrong.

The cuts were made on a 3hp cabinet saw using a miter gauge. I'm sure it's not the saw, but I did make several passes, apparently making it worse (now that I understand how it works). Live in learn, now I know.

If I used a wider stack and didn't overlap I'm sure now it would be cleaner. At the end of the day I'm sure it will be plenty strong I'm just not sure how the joint line will look. I will glue up one Off the saw and one cleaned up with a plane and see if it's worth the extra work.

Thanks again.

As a double check that the dado set is performing as it should, make a cut with close to a full stack....the only highly visible grooves should be at the outer edges. If you get significant grooves between the outside cutters, then there's a deviation in a chipper that really shouldn't be there.

A typical single pass from a decent set should like similar to this:

[Jebediah Eckert]

Thanks Scott, all is well. I checked an old test cut I made for a dado, just like that. I guess I never noticed the outside grooves until they were exaggerated on the lap joint.

[scott spencer]

Thanks Scott, all is well. I checked an old test cut I made for a dado, just like that. I guess I never noticed the outside grooves until they were exaggerated on the lap joint.

I suspect that's why people think their dado is creating a "perfectly flat bottom".....it is flat between those two grooves!

[Leo Graywacz]

The tenons are fine. Your glue joint will be stronger then the wood if the fit is snug. The scores in the tenon will form teeth that the glue will harden into and make it tougher to pull out.

If you want smooth tenons then use a tenon jig or push the wood through the blade vertically. I've done both. On small jobs I opt with just the fence, on large jobs I use the jig.

[Art Mann]

If it is any help to you, one of the first serious furniture building projects I ever did was a credenza for my mother-in-law. That was about 35 years ago. It had frames and panel doors made from red oak. All the joints were lap joints just like in your picture. The cut faces had the same little grooves and somewhat rough finish as what is in your picture. I used Elmer's wood glue if I remember correctly. I was at her home a couple of weeks ago and the credenza looks just like it did 36 years ago except the finish has darkened. The glue joints show no sign of separating.

[Dennis Aspö]

My saw can't take a dado stack and I am seeing less and less a need for one, I could cut tenons like that quite well on my bandsaw instead. A table saw sled with a flat topped blade and multiple cuts is also a method I've used as it requires little setup (90% of the time I have a flat topped rip blade in my saw, even for cross cutting I tend to use it).