Cutting Precise Tenons

[MRKeyser01]

My project is the Lutyens Garden Bench by Norm Abrams. It's joinery is entirely mortises and tenons, which is what intrigued me about the project.
I have about $600 in white oak, so it is a bit pricey. All of the components are cut to size, and I have all of the mortises properly cut. This is the relatively easy part, because the mortises are precisely sized by the mortising bits and chisels. All I needed to to is properly locate. Done.

Now the hard part: Since the material is so expensive, I'm frozen with fear of making a cutting mistake on the tenons. The bench requires a high level of tenon precision so that the joints fit "perfectly snugly" and function properly over time, especially being outdoors. Tenons that are too large are better than tenons that are too small. At least I can zero in on the tenon's proper size, but I don't want to do that. I want to get the cuts "exact" the first time. Of course, tenons that are too small produce loose and useless joints. I want accuracy to within say +0.000/-0.005" primarily on the thickness. The width and length are not so critical. I would prefer +0.000/-0.0025" on the thickness if I can get it. Do I have this right?

So here's my question: How do I get each tenon "perfectly" sized with the first cuts? I'm guessing I need a tenoning jig of some sort? Some of the pieces are roughly five feet long with tenons on the ends. I have the Shopsmith tenoning jig, but it seems too small to me for my particular project. Is the Shopsmith table saw the best tool or should I use my bandsaw or router? My bandsaw blade will wander, and the router will be tedious.

[chapmanruss]

MRKeyser01,

Welcome to the Shopsmith Forum.

A Router Table setup would be the most accurate. Under table routing as opposed to overhead routing. Any accidental lifting of the board would cut deeper on overhead routing. Since you have longer boards to cut the Tenons on, having the boards lay on a table surface would be the most accurate and safest. Absent a Router Table to allow you to basically cut rabbits from below the table a Table Saw would be a second option. Using the Bandsaw as you said can have the blade wander a bit and holding the longer boards adds an additional challenge. Set up your method of cutting them and use some scrap to test cut.

[JPG]

Regardless of how you decide to do this, be aware of the effect of original thickness of the workpiece/long board will directly affect the tenon thickness since you will likely be using the board faces as reference.Especially with the close tolerances you are seeking.

[BuckeyeDennis]

So here's my question: How do I get each tenon "perfectly" sized with the first cuts?

That's a very interesting question. Holding a couple thousandths tolerance on a Shopsmith is one heckuva challenge. I usually shoot for 0.005", and sometimes settle for 0.010", for which a lot of folks think that I'm nuts. Even those accuracies require very careful setup to mitigate the structural compliances inherent in such a lightweight machine.

But I gave it some thought anyway, and have an idea that might get you close. If the moisture content of the wood is stable, that is -- otherwise wood expansion/contraction alone could easily eat up your entire desired thickness tolerance.

But first:

• What are your tenon dimensions?

• What model of Shopsmith do you have?

[IdahoEd]

I want to get the cuts "exact" the first time.

Mr K;

I am going to assume you mean "the first time" on the final "good wood" workpiece. As has been advised already, you can't get there unless you make preliminary test cuts on scrap pieces first.

The way I would go about this is with the table saw and a stop collar, either the adjustable one or the plain one. If you use the plain one, you will also need a set of feeler gages.

Layout your tenon the end of the board, then set the table height high, so the cut is less than the full desired depth. With a dado blade, cut the two faces of the tenon; this will result in a tenon that is thicker than what you want. With calipers, measure the tenon thickness. Find the difference between the measured thickness and the desired thickness and then use the stop collar to drop the table HALF that measurement. Again cut the two faces and you should have a tenon of the desired thickness. Leave the table set at that height and cut your good wood.

You did not mention whether the tenon would have 2 shoulders or 4, so I am going to assume it has 2. If it has 4, then repeat the procedure on those sides also.

Idaho Ed

[algale]

I've never had an issue cutting tight tenons on my 520 Shopsmith. I generally shoot for cutting them the exact same thickness as the mortises and then just lightly sand by hand if too tight.

My technique is to use a digital caliper set to 1/2 the width of the mortise to incise all the marks for the tenon. After ensuring my table is aligned to the blade and at 90 degrees to the blade, I lay the piece getting the tenon flat on the table and I very carefully adjust table height until the highest tooth is just kissing or a little shy of the incised mark (check at the ends and along the edges of the tenon). I sometimes tie the main table to the legged extension table with tubes that come with the 520. This stabilizes the table very well. To get the cheeks all the same I use a stop block clamped to the fence as a standoff. Make the first cheek cut and then nibble back to the end of the tenon. Do one side, flip it over, do the other side. Take your measurements. If you need to go a little deeper make the adjustment and run it again. It helps If you have scrap from the milled wood you are using for the pieces with the tenons (or extra length on the piece getting the tenon), so you can sneak up on the first tenon. Then once you are satisfied with the fit, just run them all off.

Once the cheeks are all cut, a similar technique is used on the shoulders. If you drilled or routed the mortise, you can either square off the mortise or round over the tenon. I find it easier to round the tenon but have done both

Also, put your mind at ease. Even if you cut a tenon a bit too thin for the mortise, all is not lost. You can mix a little two-part epoxy and thicken it with some sanding dust from a little scrap from the same wood you are using and you won't ever notice the difference and the joint will be rock solid.

[RFGuy]

This is the step that I think the OP is most worried about, i.e. how to cut a precise tenon on a 5ft long board on a Mark V table top. See video below for the master, Norm, where he cuts this tenon effortlessly on his cabinet TS. It is at 17 minutes and 17 seconds into the video so skip to this part (time references in YT clips no long work on this forum SW).

[chapmanruss]

Thanks to RFGuy for the link to Norm Abrams' video. I agree with the OP, MRKeyser01 about using the Shopsmith Tenoning Jig as being too small to hold that long of stock to cut the Tenon after the first cut. Norm suggested you could "nibble" away the wood for the tenon on the Table Saw but since he has a larger Tenoning Jig, he did it with that.

MRKeyser01, let us know how it is going. I would be interested in what way you decided to use to make the tenons and see the finished project.

[RFGuy]

Russ,

Yeah, that is why I wanted to share and point out how Norm did it. He has a very nice tenon jig for the tablesaw plus he has a decent cabinet tablesaw. There are several ways to accomplish this task. I would vote for the router approach for something like this. IMHO, and especially for making a tenon on the end of long stock like this, I would highly recommend bringing the tool to the workpiece, not the other way around. One of the reasons why I love my Festool Domino so much, i.e. being able to bring the tool to the workpiece. Woodworkers who have really nice bandsaws cut tenons like this effortlessly with them. IF I had a bigger shop, this would be the power tool method of choice I would choose for this task. Nibbling on the tablesaw works too, as Norm and Alan point out. Nothing wrong with this approach either, but just be carefeul with the tablesaw. Of course, you could always go old school and use hand saw and chisels.