Mortise and Tenon Advise Needed

[Raymond Fries]

This is my very first mortise and tenon project and I was hoping to get some advise from the M & T experts.

The project is a rocking chair with the sides made from 1 7/8” finished maple; four pieces make up the sides with a M & T joint at each location.

I made hardboard templates to make sure that all pieces fit together gap free. I was planning on rough cutting the parts and using my flush trim bit in my router to cut the parts to finished size. The problem is that I need to extend the length of four of the pieces to make a 2” tenon on the end of each one.

In the pictures you can see one of the joints I have to make where the back connects to the rocker.

The 2” wide block between the parts is added to show the tenon length needed on the back part.

I thought about using the flush trim bit against the template to cut the sides of the tenon and remove the edge material with a chisel but I am not sure if I want to do this. I prefer the accuracy of machinery but just not sure how to set this one up because of all of the curved parts.

Any suggestions on the best way to make accurate tenon cuts on the parts. I do have a tenon jig.

[Neal Clayton]

the tenon jig is how you do it on the faces, you just need a flat reference. looks like the bottom of the joint will be flat? in that case just make sure it's flat on the table when you clamp it in the jig.

for the edges on the tenon, if you wanted to make a template to do it with a flush trim bit that would be fine, but you could just as well do that with a hand saw. clamp a board on the top to use on the face of the hand saw as a guide if you think you need it to keep it straight.

short answer: there is no way, outside of using a router jig that cuts both mortise and tenon, to avoid 'some' hand tool work with mortises and tenons. 'some' is relative depending on the other things in proximity to the joint itself. hollow chisel mortiers don't leave flat bottomed holes, you have to clean those out by hand with a chisel anyway. if you have to have tenons fit in around other joints, within rail/stile joints for example, you have to cut those out either with a handsaw or a jigsaw, and a chisel, as well.

now, on the plus side, all is not lost if mistakes are made. after all, the size of the tenon is subjective. if you make a mistake on a tenon edge, just cut a little more and clean it up, and make the hole a little smaller. the faces need to be snug. the edges can have whatever leeway you need, within reason. if an edge winds up too lose simply wedge it, and convince yourself that you designed it that way (wedged tenons are like diamonds, forever ;)). so don't stress over it too much, just do what you can on the machines and hand tool the rest, it's not rocket science.

i can show you plenty of examples of what we would consider half-assed tenons cut pretty rough and quick-like with hand tools on-site that have lasted well over a century. not everyone was a master with a chisel and a handsaw back then, either. yet i'm still stressing alot of their joints around my 100 year old house on a daily basis and they're holding up fine.

[Matt Zettl]

As a general rule, it is easier to cut both mortises and tenons before any shaping of the piece is done. This allows you to work from flat, straight reference planes as opposed to compensating for and working around curved or angled surfaces. You can take your templates and layout the shapes on the prepared stock in a way that optimizes grain direction while keeping in mind the processes you will use for cutting the M&T's. This technique may not be applicable 100% of the time, but in my experience if you can cut the joints before shaping, the entire process is simplified, even if you are cutting all of the joints by hand.

Hope this helps.

Matt

[Scott Cardais]

Raymond:

Have you considered using floating tenons rather than conventional mortise and tenons? Using FT's would eliminate the need to add 2" to the sides of your pieces. Joint strength tests show that they are equally strong, too.

Just a thought.

Scott C.

[Raymond Fries]

I have not heard of floating tenons but I really like the idea. This technique would ensure that the faces of all four parts are mated perfectly since I already have the templates.

I might have to get creative if that 45" long back part does not have enough angle to get it in my bench top drill press. This technique will definately work with my equipment for the other three joints.

Thanks for the tip!

[Scott Cardais]

Raymond:

See this link to a commercial jig called Mortise Pal.

http://www.mortisepal.com/

There are several video reviews of this device including this one.

http://lumberjocks.com/Gord/blog/11891

I'm not suggesting you buy the jig (or not buy it), but I think it's a good introduction to floating tenons in general.

Hope this helps.

Scott C.

P.S. I did buy it and I like it. Search SMC for other comments on this jig though.

[Prashun Patel]

Since you are not married to M&T, you might even consider a doweled joint.

In fact, if you don't mind a plugged joint (the rocker I'm working on has many of them) then you might consider drilling through the bottom of the rocker and countersinking a screw or dowel into the leg stem.

[Raymond Fries]

Has anyone ever used a tenon jig for a table saw on their router table to hold parts and use the router to bore holes upward to form the mortise?

[Neal Clayton]

no reason why that wouldn't work, but i wouldn't use a straight bit for the mortise, use a spiral bit, need something to channel the shavings out.

also come from the opposite side with a light pass to start the tenons. a typical cut against the bit tends to tear, a climb cut will cut smoother on that first pass, and give you a clean shoulder.