Shopsmith Forums

Recently, I re-discovered an old tip on how to make mortise/tennon joints fit tightly so there is absolutely no gap between rail and stile - Ever!. It's simple and only requires a sharp chisel. Just taper the inner faces of the mating surface around the tennon so that the faces are the first thing to contact the mating piece. Incidentally, this also makes a small reservoir to catch excess glue that might otherwise squeeze out to the face.
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Chuck,
Thanks for the tip. I think I've seen it before, but the reminder is appreciated.

Bruce

Chuck,

Thanks for the post on undercutting the shoulders. I've done this and it works great, but unfortunately and usually in too big a hurry.

I was wondering if anyone as tried tilting the blade slightly (table on the SS) when cutting the shoulders to create the same effect without needed to undercut with the chisel. Since I cut the shoulders first and use a tennon jig to cut the cheeks, it wouldn't be an extra step.

No, I haven't tried that. - Thinking this would cause another two problems. 1) You must get the shoulder placement exact the first (and maybe the only) time.
2) There would only be a very small area for contact with the stile (mating piece). This critical area would be very subject to damage (dents/chips) even while during assembly.

Chuck:

Thanks for the timely tip. Since the end stands for my doll cradles are mortise and tenon, I will try this on the current project.

John

Tonight, picked up my new "Fine Woodworking" Magazine. (Issue 193 - October 1007) They have a beautiful article on "The Secrets to Making Perfect Joints". They say the under cut on a tenon needs to be only 1/32" deep. They are probably right! Guess I've made mine a little deep. They also show undercutting wooden knobs and dovetails and more. It is a must for reading and learning. If you don't subscribe - I will recommend you pick up a copy at a bookstore, when they come available.

Under cuts are useful in many applications. I always use an undercut when fitting moulding. Just cut away the material from places no one will ever see and you end up with a knife like edge which is easily modified to make a absolutely tight joint.

In mortise and tendon joint where strength is important the under cut must be very small. Just enough to insure a perfect fit. Sometimes depending on how I cut the tendon (if I used a chisel) I will slightly bevel the edge of the mortise so that any roughness as the base of the tendon will have that extra room.

I watched an old world craftsman fit a piece of moulding around rough granite face. First he cut 45 under cut into the moulding that scribed (using needle compass) and later just eye and sand paper to fit the piece. When he was done you couldn't slip a piece of paper between the moulding the stone any where on the joint. The funny thing was he did it faster than it would have taken me to cut the moulding close, nail it up and then got the chaulking out to fix my gaps.

He was working at my neighbors house for about 2 weeks and I followed him around like a puppy, man was he good and he taught me many many tricks.

Oh by the way he was way less expensive than many of the commerical "finish or cabinet carpenters". He viewed himself as a old home handy man and priced his work accordingly.
Ed

If you've ever coped an inside corner molding, you know that undercutting gives you a tighter fitting joint.

charlese wrote:2) There would only be a very small area for contact with the stile (mating piece). This critical area would be very subject to damage (dents/chips) even while during assembly.

Very true...but, having said that, I will 'fess up to having done exactly this because it makes a knife edge on the shoulder of the joint which, when the tenon is clamped into the mortise, crushes slightly. After the glue has set, a moments work with a creased piece of sandpaper will remove the crushed fibers and leave an invisible joint. Note...this works only if the tenon is a nice snug fit, since the strength of the joint comes from a combination of the long grain glueing surfaces on the tenon face and the mechanical strength of the joinery itself.

Ed
Idaho Panhandle
MkV 500 morphed into a 505