Dado blades - was I expecting too much?

[Jebediah Eckert]

I bought my first dado blade a few months ago. I thought it had good reviews and it wasn't cheap. I have used it for some plywood dados and it has worked well and easy to dial in. I had a bunch of lap joints to make and broke it out. The results were..........horrible. As you can see from the pictures it is far from flat. I know how to clean it up but I guess I was expecting better. I ran them over a second time figuring maybe I missed something and it made it worse. I think it would have been quicker to just make a bunch of cuts with the WWII combo blade I usually use and clean it up with a plane.

1- were my expectations unrealistic ?

2- aside from the grooves is there enough flat service to go ahead and glue up, aside from the cosmetics of the joint?

3- is there something wrong with technique or setup maybe?

I read a bunch of the past threads on dado stacks and plenty of people boast of dead flat bottoms using their particular dado stack? Mostly it seemed the people who went cheap had the problems.

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[Ronald Blue]

That's very much like the results I get with my CMT set. Remember this is a slip fit on the arbor so precision isn't likely to happen. I don't know if it's typical as this is the only set I have ever used. The pro's can chime in here. I would like to know as well. I think that it will glue up just fine.

[Chris Merriam]

My tenons look like that too with my Freud. Never had another dado set so no other experience.

[glenn bradley]

I would prefer to do that cut with a tenoning jig. That being said, I think material control is part of your problem. If you cut from the shoulder out toward the tip there will be adequate material acting as a "bridge" so that the stock can be controlled with pressure from above (except for the last cut). If you start at the tip and work toward the shoulder the material becomes less and less controllable and you get the result you show.

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[John TenEyck]

Those score lines look like the ones the outer blades make when I use mine. The chippers on mine don't do that. How many chippers did you have installed? In any case, I don't think those scores lines weaken the resultant joint by a substantial amount. You've got huge surface area there between the two faces. A half lap joint typically is stronger than a M&T, so you have lots of safety margin. If they really bother you then either use a router to cut them or turn the parts up vertically to cut the cheeks on your TS with a regular blade. Personally, the only thing that bothers me about those score lines is they will show on the edge of the glued up joint. For that reason, I don't use my dado set to cut half laps for anything where appearance is important.

John

[Jebediah Eckert]

I did start at the shoulder and work my way out. That was just out of luck going in that direction but in the future I will make sure I keep with that, makes sense.

I had one chipper on at the time, so I guess it is the outer blades making the grooves.

In in an old thread some people said you can have you sharpener grind all the teeth flat so that doesn't happen. Why isn't it that way to begin with, isn't that the point of a dado? Is there any good reason for the outside blade cutting those grooves?

[Mike Henderson]

This isn't a solution to your problem, but cut your tenon a bit fat and then smooth it down with a plane.

Mike

[Martin Wasner]

Why isn't it that way to begin with, isn't that the point of a dado? Is there any good reason for the outside blade cutting those grooves?


Because it gives a cleaner cut at the edge. I don't care what the bottom of a dado looks like 99% of the time. I would think that is a common attitude towards it if most are using a dado head for milling sheet stock, which is what I mainly use one for. I've got two Forrest dado heads, two FS Tool, and a Freeborn. They all leave that same cut that you're showing

[Bruce Page]

It looks similar to the results I get with my Jesada set. Given the tolerances of the arbor diameter, hole diameter, and blade diameter it would be difficult to have everything spinning in perfect harmony.

[Mike Schuch]

Those tenons look great to me! You could use a tenon jig on a table saw and get a smoother cut but I doubt if the joint would hold better. The score marks on your joints give the glue plenty of surface area to grab onto and will make a very strong joint. If the tenons were glass smooth on the sides the joint would probably not be quite as strong.

On my table saw my dado set slips on the arbor easier/faster than my radial arm saw. I suspect the arbor on my table saw is just a few hundred thousands smaller than the arbor on my radial arm saw. My radial arm saw gives a bit smoother cut with the dado set than my table saw. I suspect this is just due to the tighter arbor to hole tolerance between radial arm saw and the dado set.

[Peter Quinn]

Here's the skinny. Dado sets are designed primarily to make dados and rabbits across the grain in plywood and solid panels, such as for carcass assembly of plywood cabinets. Look at the outer blades.....they have very high ATB teeth whose diameter is just a bit greater than the rest of the set. This arrangement works wonderfully to score delicate plywood veneers on those cross grain dados with minimal to no chipping. This is what all the manufacturers tout as their standard. But....the little "bats wings" they leave on tenons are part of the bargain. Unavoidable. And generally not even vaguely a problem for blind joinery. The "flat bottom" means the general plane is flat, and it is, perfectly strong glue surface. This flatness is versus the old "wobble dados" which as the name suggests would wobble through a cut so the bottom of the dado had a radius to it from the pendulum type movement of the cutter. Scary. Your cuts look exactly like every dado I've ever used, and I've used quite a few including Forrest, freud, fs tool, amana, and cmt.

For tenons your cuts are fine, use the widest stack you can, keep the overlap to a minimum and that will minimize the bats wings, once it's glued up only a furniture anthropologist will ever know the lines were there. For open joints like half laps or bridles.....either clean up with shoulder planes or use another method.....or get some wood filler. A box joint set might give you flat bottoms with no lines but a lot more passes would be required. And there is another method where you cut in the same orientation as with a dado, with a fence for a stop and a miter guage or sled as the pusher. But you run a single straight blade and advance the stock sideways into the blade, moving the sled or guage forward very incrementally with each pass. It's pretty quick, leaves a very smooth surface with no score lines, can feel a bit odd the first time you try it but it works great. There was a controversy over at the FWW forum maybe a year or two ago, one of their authors has a video highlighting this method, some say it's a revelation, others want criminal prosecution. I use it all the time. I forget the author but a search at FWW should produce a good video detailing the basics of that method.

[glenn bradley]

Those tenons look great to me! You could use a tenon jig on a table saw and get a smoother cut but I doubt if the joint would hold better.

Depending on the glue; tests show that PVA is strongest on two smooth surfaces. Any gaps weaken the joint. For gap filling there are other glues however. Not being argumentative, just providing info.

[scott spencer]

Here are some pics that help illustrate the issue. Since you're making multiple passes, you get multiple ridges from the "bat ear" effect of the outside cutters that's common to just about all decent stacked dado sets. A single pass should look cleaner, but not perfectly flat. Those who claim perfectly flat bottoms from a stacked dado set are generally mistaken. So to answer you're question....yes. The good news is that the tenon will be buried.

http://i6.photobucket.com/albums/y203/hewood/Saw%20Blades/outblades.gif

http://i6.photobucket.com/albums/y203/hewood/Saw%20Blades/Dado_channels_zpskpbcsc0p.jpghttp://i6.photobucket.com/albums/y203/hewood/Saw%20Blades/oshlundadocut.jpg

[Frederick Skelly]

Well, I had a long reply all typed up when I realized others had covered almost all of my points! :) The only thing I have to add that might help you is to find/make a hold down for your miter gauge that keeps the workpiece flat(ter) on the table. Some up/down vibration is inevitable, but that should help a little.My old delta miter gauge had such an add-on, it reminds me of the hold downs that come with miter saws. But truly Jebediah, I think that joint is about what I'd expect in a wide joint like that. As Mike mentioned, a hand plane will help some. But I think it will be just fine.

Take care,
Fred

[George Bokros]

Use a sacrificial fence attached to your rip fence. Use the rip fence to control the width of the cut and start from the shoulder and cut outward using your miter gauge. Once you have made all the required passes then move your miter gauge up to across from from the blade and slide your stock across the spinning blade with it against the miter gauge until it touches the rip fence and the entire width of your lap will have been in contact with the outer blades of the dado stack and your lap joint should be much smoother. I have done this many times and have never had any kick back or other issues.

[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 (http://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:
http://i6.photobucket.com/albums/y203/hewood/Saw%20Blades/FSDado.jpg

[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).