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
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.
On Wed, 25 Jan 2006 19:02:11 -0800, gizmodyne wrote:
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
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!
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.
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 Gorman, West Yorkshire, UK
email : Username is amgron
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.
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.
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.
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.
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.
On Fri, 27 Jan 2006 20:06:17 -0800, hylourgos wrote:
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.
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