Through Mortises

[Stefan Antwarg]

Could you give me advice on making clean and straight through mortises? My plan says to rough it out with a drill bit and clean it up with a chisel, jigsaw, or scroll saw. I don't own a scroll saw and I am sure the other 2 methods will not make it perfectly straight and square. It needs to be neat so the tenon looks snug on the other side.

Thanks,
Stefan

[Mark Singer]

I usually put a sacrificial piece on the back and clamp tightly...use a router and in many passes rout through. An up cut spiral tends to chip a little at the top and a down cut on the bottom...the down cut is the better bit in this case with the backing behind. If you need square corners chisel them. A dedicated mortiser will do the same thing.

Or drill through a series of holes and clean up with a chisel

[Norman Hitt]

Stefan, I don't know how the "BEST" way to do it is, but what I do first is carefully mark Both entry and exit sides of the mortise, then drill the holes. After that is done, I take a short block of a 2 x 4, (that I have face jointed and then squared the edge to the face), and clamp it along the one of the lines outlining the mortise, and use it to keep the chisle square and clean up the mortise about half way through, then reclamp it to another line til all 4 sides on the exit side of the mortise are cleaned up about half way through the piece. Next, turn the piece over and repeat the steps to clean up the entry side of the mortise. The reason I like to do the exit side first is because that is the side that will be seen, and should there be ANY adjustment necessary to make a proper fit for the tenon, it should be done on the entry side as it will be hidden.

There may be better ways, but I seem to always need a "Little" help keeping the chisle flat/perpendicular to the workpiece face, , so this is my "Cheat Trick".

Oh, yes, I forgot to say to either drill half way through from each side, OR, clamp a bl;ock to the bottom side to prevent tearout. I prefer the first method to be sure that the holes don't drift out of the marked box of the mortise.

[Jamie Buxton]

I use a plunge router with a template guide, and square up the corners with chisel. The mostly-rectangular hole left by the router provides lots of guidance for the chisel.

I generally make the template on the tablesaw, holding the stock down on the table and cranking the blade up to plunge through the stock. This makes nice straight sides to the hole. You can run the saw cuts past the edge of the hole.

[Dale Rodabaugh]

I spoiled myself a few yrs.ago and bought a General dedicated Mortiser.Dont use it often,but when I do I am glad I bought it.A good item to put on your wish list.

[Ken Fitzgerald]

Ah......Stefan's looking for an argument to justify a new tool.. .......Well, I'd buy the scroll saw first. ...butcher the through mortises. .....Then purchase the dedicated mortiser!

[Mike Cutler]

Stefan. Imho, there is no 100% solution for all applications. Each project may require a slightly different technique. I like to start by marking the mortise on both sides and use an razor knife to break the surface of the wood. I then mortise from the exposed side, because the other side will have the shoulders to hide any slight imperfections. Just like Mark, I use a backer material of equal hardness.
I recently bought a benchtop mortiser which makes this a little easier, but time consuming. A router with spiral upcuts, and downcut bits, and some flush bottom cutting straight bits, along with a good set of mortise, not bench chisels, and a corner chisel is also effective, and fast.
You also could haunch the non exposed side of the M&T joint. This way any imperfections or "blowout" could be hidden by the haunch.
One more solution is to incorporate a foxtail, or wedge tenon into your design. This will "spread" the exposed part of the tenon, and hide any slight imperfections in the mortise.
If this still doesn't solve the problem. mortise from both sides and use a "Faux thru tenon". You should be able to cut it so close, that unless someone wants to use a vernier to measure it you'll never know it isn't one thru tenon.
I don't think I would want to use either a jig saw or a scroll saw, not that they won't work, but you would need a pretty good quality jigsaw or scrollsaw to be effective.
Sorry for the long post. I thought I'd offer some alternatives. Good luck

[Larry Copas]

Drill from both sides, chisel from both sides, and use a utility knife to cut a line on the pencil marks. The chisel fits in the knife cut leaving sharp edges. Sometimes I’ll just work from one side and let the shoulder of the tenon cover up my slop. If I’m careful I get a better mortise than what I can do on a mortise machine.

Router also works good...but takes time to make a jig, corners still need cleaned up with a chisel, and sometimes the mortise is to thick for a router bit to reach all the way through from one side.

[Jim Becker]

I will go so far to say that you will likely use multiple methods, even on the same project sometimes. No matter how you do it, you still need really, really sharp chisels to finish things off, especially if the mortise will be visible. Start sharpening now...

[Jay Fields]

Stefan -

Excellent question. Followed by many excellent answers.
It is threads like these that keep me lurking and learning here.
Thanks all.

JF

[Stefan Antwarg]

Thanks everyone. It sounds like chisels are the way to go. But, it wouldn't have occured to me to do the cutting from the exposed end. I do have a mortising attachment for my drill press.


I will not be buying a scroll saw (I can't even master the lathe yet.) But I think I need to get some accessories to make sure I do this right. A better table for my drill press, a sharpening guide for my chisels.

Stefan

[Roger Myers]

Stefan,
Many good suggestions...I'll add in my 2 cents on this as well...

To do by hand, I would do it all with chisels, or drill out the center and clean up with chisels. Either method will work - a mortise chisel will make fairly quick work of the mortise without the need for drilling - some people find that the drilling and clean up is more challenging, but both methods have their advocates. Invest in the mortise chisel as this is a case where the tool designed for the task really makes a difference.

The first time you do these, or if the mortise is near the end of a piece, or if the remaining side walls are thin, you may want to clamp some wood to the outside of the piece being mortised (or use a wooden hand screw clamp) to prevent blowing out the side of the mortise....

I agree that you want to work from both sides and treat the exposed side with care, but I'll add the following - the other tool you should be using is a mortise marking gauge (marking gauge with two cutters, set to the width of the tenon). All marking (inside and outside of mortise) is done with the gauge riding on the same reference surface (get in the habit of marking reference faces) - this insures that the mortise will line up - errors from laying out with a rule/square and pencil can add up quick. A mortise marking gauge is not that expensive, is a one time purchase, and it also scores the wood (as described by Larry using a utility knife) - chisel will set right into these refernce marks. You will still need to mark the cross grain parts of the mortise with a knife...

And finally, practice a few times...it really is not as difficult as people often make it out to be, and it is really very satisfying work. Unless you are making a large number, the use of routers or mortise machines is really not much of an advantage... I have both, and use both, but Can chop a few mortises by hand quicker than making the jigs and setting up the power tools... and I can hear the music in the background.
Roger

[Keith Christopher]

When I built the mission mirror I cut 1/4" thru mortises in 4.5" stock by drilling out most of the waste and then chiseling out the rest. Actually that is what made me buy my HC mortiser. :P Like Jim and others have said keep your chisels sharp and 90deg to the edges and you'll be fine. How thick are the pieces ?

[Kirk (KC) Constable]

I do it 'upside down'....I cut with the 'exit' hole on top, and with a sacrificial piece underneath. Even with the sacrificial piece, I get a bit of tearout, but since it's upside down, the tearout is on the 'enrty' side of the mortise, and most usually covered by a shoulder of the tenoned piece. Does this make sense?

I use a mortiser, but it seems like the same principle would apply to drill bits.

KC