Big thru mortise how

[Wongdai]

Hi all

I need to make 8 through mortises for the legs, base and top support for my bench. They will be through 4" thick karri. If I chisel it out it will take me a week for each one.

What is the best method for such large mortises through hard wood?

[Afro Boy]

Could you drill a series of holes through it first and then chisel away the waste to square it all up?

I don't know of a 4" router bit but you could get part way with that too.

[Marginata]

What Afro Boy said. Waste out the bulk of the material from the mortice area using a spade bit or auger bit. This is best done on a drill press unless you are using an auger bit with a hand brace. Have fund doing that today!:sweatdrop: If you don't have a drill press just be really carefull to drill sraight. Seeing as they are going to be through mortices drill half way through from one side and then drill the other half from the other side. This will ensure that you don't bust out the timber by drilling right through. Use a very sharp wide chisel to pare out and square up. Again do this half way through from each side.

[Ravi]

I'd make a jig to use with a router using a straight bit and a bush. You could make it with registration blocks so that you don't need to mark out.

[Wongdai]

Nice tips there.

Thanks

[GraemeCook]

A slight variation on the above as I do not like making router bits work that hard - too much heat build up.

My approach would be to:


pre-drill, preferably using a drill press,
clean mortise with 50mm strait router from one side,
ease router bit about 6-7mm out of chuck and clean deeper,
put roller bearing bit into router and clean mortise from other side,
Remember, reserve best work for "presentation side", invisible gap filling glue is stronger than the wood!
Either, leave mortise corners round and round off tenon corners, or, chisel out mortise corners.

Cheers

Graeme

[Rocker]

McJing sell a 3/8" solid carbide spiral upcut bit with a 2" cutter length. This will do a much better job than a straight router bit and will be much faster and less effort than using a drill-press and chisel, if you make a suitable jig.

Rocker

[powderpost]

Bore out the waste and trim with a chisel and mallet is the way to go.
Jim

[mic-d]

What Jim and others have said. Coincidentally I was doing a 2" square mortice for a planing stop today. It was 31ºC and 55% humidity in the workshop today, phew I;m glad there was only one.:screwy::stretcher:

Cheers
Michael

[weisyboy]

What Jim and others have said. Coincidentally I was doing a 2" square mortice for a planing stop today. It was 31ºC and 55% humidity in the workshop today, phew I;m glad there was only one.:screwy::stretcher:

Cheers
Michael

where were you today mate it got up to 35* and 75% humidity here. luckily we have a pool.

i am a big fan of drilling out then cleaning up with a router but i just do the trimming free hand:2tsup:

[GraemeCook]

McJing sell a 3/8" solid carbide spiral upcut bit with a 2" cutter length. This will do a much better job than a straight router bit and will be much faster and less effort than using a drill-press and chisel, if you make a suitable jig.

Rocker


This is probably better than my above suggestion, but I do not have spiral router bit - Santa, you forgot! so I just make do.

Happy New Year

Graeme

[simon d]

Wongdai. Though you have probably done the work already, I recommend also the drill right through method and then clean up with a good sharp chisel. However the method is important. This is what I do. If you clamp a piece of scrap to the bottom of the piece when you drill , either press or auger, you wont have to turn the piece over to avoid breaking out the other side. If using an auger, clamp the piece in your vice and go through sideways, not down. Using a self pulling bit, this will give you an accurate push. I use a long piece of scrap tack nailed square to the work piece to use as a travelling sight guide as your drilling through. If you've got a large mortice try an inch auger and drill only two or three holes down the centre. Don't try and go close to the edge of the intended sides of the mortice.
Once through, turn the work onto your bench and clamp it firmly with a bit of waste under it. Use a chisel two thirds the size of the shortest side and use the hinge cut away method to clear the mortice. This is a series of heavy cuts in a 5 to 7 mm stepped sequence from the short side to short side but well inside the mortise. Then get a wide chisel and working just inside your mark on the long sides, not on the mark but near to, give an angled whack from each side with your bevell out (as in facing the flat side into the mortise) and the chisel slightly angled into the mortice. This should have the guts of the job flying out of there in little pieces that are easy to clear. Basically you are using the bevell of the chisel to act as a lever wedge against the firm wood. As you cut the wedging effect forces the wood grain to shear off as well as cut, as you've already loosened it with your perpendicular hinge cuts you'll find it literally explodes out of the mortise, so wear eye protection.
As you get deeper you'll have to stand the chisel up more but then you turn the work over to come from the other side if you have to. After you've got most of it clear, turn your bevell into the mortise and from the inside of your marks start to cut straight down. I use a wide edged vernier depth guage to act like a set square to keep checking that my cuts are not straying from the vertical and of course you start this process from your presentation side and a fresly sharpened chisel.
If you use the flat of your chisel to guide you when you've got deeper you'll find that the chisel jumps out of the cut and your mortise starts to get narrower and ugly. It is much better to slightly angle the chisel into the wood to counteract and counter-balance this bouncing effect and keep using the vernier as a guide. After that's done then you use the flat of the chisel as a guide to thinly slice the mortise sides true to a dull polish.
Hope that's of assitance.
Regards Simon.

[Wongdai]

Thanks all, and especially Simon.

Even though I have three routers, I only have two router bits, so I will stick to the drill press method.

I haven't done the mortises yet, as I have only just finished the tenons. Not sure which you would normally do first but I chose tenons.

I'm wondering for such an industrial object like a bench, should I be using wedged tenons, or are today's glues so strong that it doesn't really matter?

[Afro Boy]

Even though I have three routers, I only have two router bits, so I will stick to the drill press method.
Make sure you post pictures of your progress!


I haven't done the mortises yet, as I have only just finished the tenons. Not sure which you would normally do first but I chose tenons.
Whilst I'm no expert at this, I would personally do the mortises first. Tenons might be easier to trim and shape to fit the mortises.

[simon d]

From my experience joins are easier if tenons are done first because if you mark out the mortises from your completed tenons then your marking out is more accurate. Mark both out first of course but because tenons are a lot easier to cut they are also a lot easier to make a mistake on. If you make a mistake and have to trim the tenon square again then it is a lot easier to make the correction in the cutting of the mortise. That way you shouldn't have loose joins.

Another good tip. use a 2H pencil to mark out with and keep it sharp always. The sharper your pencil the tighter your joins. Another good tool for the tightest joins is a set of little engineers squares. 25mm blade is the one I use the most, and calipers
I'd probably use glue and wedges and I'd use a contrasting color wood for them if you can. When you sand the join back you get a lovely detail to look at every day. Also this is where a set of calipers and verniers come in handy. (check out my pics of a hell tenon in pics) if you've got a through mortise they'll be easier than hell tenons as you can flare the end of the mortise easily. You carefully cut the tenon for about an inch at most for a 4 inch tenon, near the edge on the short side leaving a sliver at least as wide as the wedge used. You can do one at each end or just one on the low side of the final join. They won't work on the top side as that is the hinging point of a bench join. You then carefully cut your wedges using wood harder than or equal to the tenon wood. You must cut them a bit longer than the cut in the tenon. Cut them with a pitch that gives you a wedge at least twice as thick as the saw cut in the tenon but not more than three times as thick. Now mark the wedge where it will go deepest into the cut on the tenon, minus a mm. Now with your steel ruler add up the wood dimensions including the mark point on the wedge and the total tenon width, minus the thickness of your saw cuts and the width of your mortise. This will give you the exact dimension of wood you remove from the top of the mortise. Measure the depth of your wedge and mark the mortise depth you cut to. Just shave the mortise carefully and check it with your calipers as you go. (get an iny and and outy set. If you fall in love with joinery you'll use them a lot) The sliver will bend as the wedge is driven in and it will lay snugly in the mortice with an equal pressure along its width and length. This will ensure that it doesn't break off as its inserted or under pressure as a finished join. If it's not square or too bent from too wide a wedge or too loose or too crushed from innacuracy it'll eventually fail, even if glued. It has to be just right to work forever.
Enjoy

[Wongdai]

Oh wow. I guess that answered my next question. :D I'm going to bookmark that post for later consumption.

I probably won't go with the wedged tenon, for this particular joint, as the wedges will never be seen. However, for the rails (the bits that join the legs together at each end, I'm thinking the wedged tenons might be a good look, although I have no contrasting timber harder than Karri.

I will practice a couple first though. :p