Tapered mortice

[W Canaday]

Just took my first crack at making a mortice & tenon joint. I chose the 'through' style because I didn't want to fuss with getting the depth right on this practice piece. (My drill press leaves a great deal to be desired in that department.)

My question for the group is this: how can I insure that the sides of the mortice (hand cut) run straght through the wood? I ended up with a convex wall this time and want to know if there is anything I can do to reduce or eliminate the possibility of this happening again.

The top of the mortise was just about perfect. But the length of it flared out and the width of it bowed in. It was more of an 'exit wound' than a deliberate hole ... although it was prime for a wedged tenon. :-)

Also, what sort of a chisel should I be using and what feature of it makes the difference?

Bill

[gizmodyne]

how can I insure that the sides of the

Carefully mark your mortise on both sides of the stock. Drill out the middle, staying away from the edges of your mortise( try a forstener bit). You can use a block to guide your chisel straight, but should be cutting in from both sides. Chop out half way and then flip so you don't tear out. If you slightly undercut the mortise keep it tight where it is visible and deeper into the stock inside (concave) it's ok, but be more careful on the face grain (parallel to long side of mortise) where the glue joint is more critical. If you use just a bench chisel just take it easy near the corners so you don't cut in too deeply. Go slow to start.

Good luck,

J. Andrews

[Guess who]

Buy a better drill press.

A sharp one, and let the tool do the work. You might be bearing down too hard to compensate for a blunt tool. That causes drift. A mortising chisel set might help.

[W Canaday]

Thank you, Brer Andrews. Your answer was both thoughtful and useful. I hadn't considered the use of a guide block so I'll count that as a tip learned. Bravo.

I did mark both sides of the mortise and actually ended up with a serviceable (but not furniture grade) joint. I was just looking for improved technique since this particular mortise was a real splinter job.

I plan to buy the Delta mortising machine in the next month or so, but I want to be able to cut good ones by hand, too. Thanks for the tip!

Bill

[Leuf]

If you drill the mortice out with a forstner of the same size as the width of the mortice then all you are doing with the chisel is paring down the sides to remove the material left between your overlapping holes. The hole is your guide to how straight you are cutting, you can easily see if you are off and the closer you get to the end the more dramatically it shows you. It also helps to stand such that you can sight down the chisel when chopping, but I find it hard to do it when paring. I'm told you don't need to do this once you get the feel for it, but I haven't gotten there yet.

What's important about the chisel is that it be sharp, and the back be flat. If the back tapers as it reaches the point, either from not being flattened properly or when it was polished at the factory then it won't cut when held at 90 degrees, you'll have to tilt it a bit to get it to do anything and then you're in trouble.

I find a combination square is great for testing the mortise. Set it to the depth and then slide it around. If it doesn't hit at the top you know you need to remove more at the bottom. It's harder to tell if you've removed too much, but I always have the opposite problem so I just keep working at it till it hits at the top.

-Leuf

[Jeff Gorman]

"W Canaday" wrote

Whatever some writers may tell us, drilling is probably best kept for large mortises that require wide chisels that are difficult to use.

A basic non-drill method is illustrated on my web site - Mortising & Tenoning - A Familiar Basic Method ................. .

Jeff G

[hylourgos]

Take gizmodyne's advice on going halfway from both direction, aiming at concave angles as you slowly approach a tight fit. Using a board as a chisel guide works well too.

However, note that your reason for doing through mortises instead of blind makes your job harder, not easier. The depth of the mortise is not, within reason, important to the tightness of the joint, and glue on the endgrain of the tenon holds nothing.

H.

[kkfitzge]

I agree with hylourgos. There are many reasons to use through-mortises, but this isn't one of them. Blind mortises are more cosmetically forgiving, and the depth doesn't need to be precise. As other have said, if you're going to do a through mortise, work from both sides in.

[Chris Friesen]

From a purely mechanical point of view, doesn't a through mortise give you more glue area as well as additional leverage to resist racking?

It seems like many joints designed for strength (workbenches, for instance) use wedged through mortises.

Chris

[hylourgos]

Now that is true. Still, not doing a stopped mortise because of an inaccurate bottom doesn't make good sense, since the bottom doesn't have to be perfect: a perfect one adds no strength to the joint.

H

[Max Mahanke]

The tenon should not sit firmly in the bottom of the motise as the motise is usually cross grain and will expand and contract slightly. If the end of the tenon has no place to go the stress will weaken the glue joint over time - Frank Klaus is fond of pointing this out. Hmmm, I wonder, in our lifetime with today's modern glues? Don't know, havn't lived that long.

[W Canaday]

I'm the OP. My objection to doing a stopped mortise in this case (1st attempt / practice on scrap wood scrounged from the company dumpster) was to avoid having to make another trip to the drill press. Not so much that I am lazy but that I am often pressed for actual shop time.

On further reflection, I realize that even that objection wasn't valid. If the mortise was too shallow (within reason) all I had to do was lop the end of the tenon off. The real practice objective, after all, was simply to make a chiseled hole closely mate with a piece of wood without splitting. By making it a through mortise I could be certain it was deep enough on the first try.

I should get a chance to try again this afternoon. I have also built a jig that will let me clamp a board to my table saw vertically to give dovetail joints a try. The glue is dry; now I'll add some screws for added strength and give it a workout.

Bill