Mortice & tenon - mixed machines and GUARDED

[Steve Maskery]

After the Sawstop discussion, which turned into more of a discussion about pushsticks and guards, I thought I'd show how I use the tablesaw - safely, in conjunction with the bandsaw and hand tools, to cut M&Ts that fit Right First Time Every Time.

I have several ways of cutting the mortices, in this case I'm using my hollow-chisel mortiser. I like the traditional square ends and it can get deeper than I can get with a router or Domino.

I cut the main mortice first, then reset the depth stop to take out the haunch.

Then it's time to set up the Ultimate Tablesaw Tenon Jig (TM). I fitted a new sacrificial back stop, which supports the workpiece and prevents any spelching out the back.

Then fix a toggle clamp to that. It makes loading up the workpiece quick and easy.

I have a set of spacers which fit the mortices made by my various chisels. This one is 1/4".

I mark where the tenon needs to be and, with the jig in the closed position, I set the fence so that the outside cheek will be cut. I know that the fit will be Right First Time Every Time, but in this case I want more than that, I want all the faces to be bang on flush, too. So I get it as close as I can by eye, by using the slot in the ZCI as a guide, and make a short tenon test cut. I'm using a Flat Top Grind rip blade.

The jig has three guards. There is one at the far side, so that the blade is covered even when the jig is pulled right back for changing the workpiece, one on the nearside, protecting my hand when the jig is furthest forward, and my stand-alone magnetic guard which stops me reaching in from the left. I'd have to be very determined to get my hand inside that lot.

The first cut is made with the jig closed and the second with the spacer in place. The jig itself takes care of the kerf.

The shoulders are roughly cut on the bandsaw so that I can tell how close to perfect I am. Close but no cigar. We can do better.

 

[Steve Maskery]

There is a fine adjuster on the back (which I forgot to photograph) which works on a M6 lead screw, so 0.1mm is just 6 minutes of the clock. Now the two parts are flush and pass the feather test. I can push a feather over the joint in both directions without it catching.

Now I can do the real thing.

I can cut both cheeks on both ends of a workpiece in less than 40 seconds, and that included operating the stopwatch

Then it is time for the shoulders. I really should have switched back to my ATB blade, but I didn't. The shoulders are not quite as clean as I would have liked them, but this is only a garden planter, so I'm not too bothered. I have a cross-cut sled which has the fence at the front. Jacob was on about this setup recently.

It does have advantages, but one big disadvantage is that you can easily get spelching, especially if you are using a Flat-top Grind rip blade as I have been using here. So a sacrificial backer block is required.

With the guard in place it is time to cut off the waste.

The waste drops onto the table and gradually builds up. It becomes rather dangerous. Look at this:

See that smaller one at the front? That is what is left after a piece got caught by the blade and got flung into the air. The other half is somewhere on the other side of the workshop. It made one helluva bang as it hit the guard, but it meant that it didn't hit me.

 

[Steve Maskery]

The rest of the tenon is cut on the bandsaw and by hand.

The completed M&T

Because the shoulders are good for square, the frame squares itself up as it is clamped, but just to be on the safe side:

So there we are. Quick to set up, very quick to cut the cheeks. Perfect fit, perfect position, all guarded. In short...

Right First Time Every Time.

 

[custard]

That's a great summary. Not much to add, just two minor points,

-the best method for cutting M&T's in your workshop depends on what equipment you have and on the job itself. What's optimum in one situation might not be optimum in another. So I'd suggest anyone wrestling with the decision on how to go about a M&T keeps an open mind to alternatives. For example, on very large and unwieldy components I'd probably cut the tenon shoulders with a bandsaw, but if I happened to be using a bi-metallic bandsaw blade then I wouldn't even consider that route for smaller components as the cut would then be a bit too rough.

-checking for square makes sense, but on something like the frame for a cabinet door that by itself wouldn't be sufficient, I'd also want a dry glue up to check for any twist or wind.

 

[Steve Maskery]

Good points, custard.

Actually I have an equivalent jig for the BS, the imaginatively-titled Ultimate Bandsaw Tenon Jig (TM). It does rely on the BS being set up perfectly though, which mine isn't at the mo, after some abuse it's had recently with recycled wood, but it does mean that I can cut tenons longer than the depth of cut of my TS blade, just under 80mm.

And whilst I didn't mention it in the write-up, I did do a dry run for assembly. Good job, too, as the tenons were all a tad long and were bottoming out. Easy to fix, not so easy if the part is already covered in glue, eh?

My main thrust, though, was to show how operations that require the removal of the standard crown guard can be carried out without compromising safety, just by being a bit imaginative with home-grown guarding.

Horses for courses, and all that.

 

[Peter Sefton]

Hi Steve always good to see how others work, I might suggest you turn your mortice chisel round by 90 degrees . It's common practice to use the open window into the open mortice to help the chips clear.

It usually keeps the chisel lasting longer.

Cheers Peter

 

[doctor Bob]

Very good. I do similar for big mortice and tenons such as on a table (50-60mm). I prefer to cut a full shoulder first, makes no difference I suppose. Smaller ones are on the spindle moulders.

 

[Steve Maskery]

Hi Steve always good to see how others work, I might suggest you turn your mortice chisel round by 90 degrees . It's common practice to use the open window into the open mortice to help the chips clear.

I usually do, Peter, but I was experimenting with sucking off the chips as they come out. I think Mortisers and Drill Presses are the hardest thing to keep clean while you are working. If anyone has some good ideas I'm all ears.

In that photo you can see that I have clamped up the end of a vac hose, so the window needs to be front facing. It didn't do a perfect job, but certainly better than not having it at all. I don't think it would have worked if I had had it in the conventional orientation.

Ideally I would have the DX pointing longitudinally, with the chisel oriented as you describe, but I have to operate the plunge on the RH side and the travel with a lever on the LH side, so whichever side I put the DX it's going to be in the way. It can only go at the front.

BTW, that tenon saw is one of yours And very nice it is too.

 

[Jacob]

Window lights and similar I got into the habit early to mark up everything from a rod. Can take several day if you have a big batch of small paned windows - there may be 100s of components. But then you are on autopilot and nothing can go wrong! (touch wood).

draw up rods from design drawings
make up cutting list
rip and crosscut stock to rough size for the whole project (some hand sawing but mainly TS with crown guard and push sticks)
plane everything up square all round to finished size (PT two push sticks over the top)
Mark everything with face and edge marks. All gauges etc are set to either face or edge and all cuts are made with either face or edge against the fence. This is really important for reducing error.
then mark up the whole lot
cut all mortices and their haunches - mortice machine
cut out all tenon haunches - band saw
run mouldings and rebates - spindle (shaw guard and push sticks if no power feed available - even then push stick handy to poke the thing through if it needs a nudge)
tenon cheeks against bandsaw fence (easier as the haunch has already been removed)
tenon shoulders over the TS - working to marks, not to stops, using the sliding table and fence as below but without crown guard and riving knife, no jigs stops toggles guards just push stick. Fingers always well away from blades at every stage.

The tedious marking up process pays back at every stage as you can get through the work brain off, fast, with marks as checks on every joint and the marks themselves identify the component ( a bit like a bar code) and all the final hand finishing of mitres/scribes is marked up already.
The marks help with the dry run and the glue up - you can see how/where things are supposed to line up.
It more or less eliminates basic mistakes (mortice in wrong place etc) but you have to take care to avoid small inaccuracies. "Systematically" accurate but sometimes small random errors of precision. I do use stops and/or fence for some processes but thorough 100% marking and simple handling suits me for most things.
NB once you've done the rods there is no more measuring required - you could throw the tape measure away, though it's handy for rough measuring for selecting stock to match the cutting list.
I keep having to edit this post as I think of other details! Good job I'm just sitting here watching cr*p on the telly with one eye
Basic rule NEVER take measurements or marks from another component ALWAYS from the rod (with occasional exceptions, DTs being the most obvious)
Big tenons may need a bit of fettling - surform, paring chisel, sanding block. I set aside new blades for very big tenons (e.g. on 12" door rails) and take them off again afterwards. Big tenons cheeks very much easier if you have taken out the haunches first.
Working to stops and marks never works too well - they end up not coinciding and you have to work out which is wrong; the dead length of the piece, the mark or the stop adjustment.

So when it comes to one offs would I go through the same thorough procedure? Yes definitely - it makes life so much easier.

Guarding - at least one pushstick all the time at every stage, usually two.
The single most critical moment is at end of cut when workpiece leaves the blades exposed and you are reaching over - push stick essential here.