# M&T chisel size?



## sunnybob (1 Sep 2019)

On the eve of attempting my first M&T joint since 1962, I'm in a quandry.
The Bubinga wood is 45 mm across and as far as I am aware it is best practice to make the mortice 1/3rd the width. That would require a 15 mm chisel.
Guess what? uh huh, I dont have one. And being as how this could easily be my last ever M&T if it goes bad, I'm not about to go out and buy one.
Using my vernier gauge on the chisels I do have, I can use either a 13 mm, or an 18.5 mm.

Answers please?


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## lurker (1 Sep 2019)

I have been cutting M&it's for 50 years and was not aware there was a LAW that said the chisels had to be a third of the size nor that only one chisel was allowed.
Stop over thinking it and use both were appropriate yer daft lad ( or are you just being ironic ???).


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## Trevanion (1 Sep 2019)

Double 8mm mortice and tenons?  

Just use either chisel and you'll be fine, I think the "Good Practice" part of it is purely aesthetical rather than structural, Rule of Thirds and all that. I'd personally go for the 13mm as it will be *ALOT* less work to hammer through Bubinga! :lol:


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## deema (1 Sep 2019)

The 1/3 is a good guide, I’d use the smaller chisel as the joint will look better than if it’s larger than 1/3 the width. You could always widen to be 1/3 if you really feel the need.


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## sunnybob (1 Sep 2019)

Trevanion....
The "less work" part of your advice was todays winning quote. =D> 
If I had a prize I'd award it to you :roll: 8) 

To use an amercanism (which I try to avoid) "confidence is high".


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## dzj (1 Sep 2019)

Now that you guys are leaving the EU, you can use any chisel you like.


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## sunnybob (1 Sep 2019)

dzj":waurgpo3 said:


> Now that you guys are leaving the EU, you can use any chisel you like.



Ahemm.... Not all English live in England. :shock: 

Next question; I watched a paul sellars video on M&T, just to refresh my ancient memory, and at no stage did he put a chisel to the sides of the mortice.

i think he was using oak, but he just kept dibbing in from each end. I suspect my Bubinga will chip badly if I try that.
Advice please?

Cyprus Bob 8) 8) 8)


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## AndyT (1 Sep 2019)

The key requirement is not to have a weak skinny tenon or only a few mm of wood left on either side of the mortice.
In your case Bob, with 45mm of hardwood, you'll have plenty of thickness and strength either way.


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## Trevanion (1 Sep 2019)

I haven't done hand mortices since my college days (Long live the Hollow Chisel Morticer :roll. But I always marked out the mortice with gauge lines to break the surface, then mortice in triangles with the bevel up if that makes any sense. You let the chisel calibrate the size of the mortice, you shouldn't really need to pare anything.

This video by Peter Follansbee is pretty much spot on what I'm talking about:
[youtube]N1bo6NVYCc0[/youtube]


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## dzj (1 Sep 2019)

sunnybob":6t5alk8p said:


> Ahemm.... Not all English live in England. :shock:



Then you'll have to conform to the regulations and guidelines set out by undemocratically elected officials.


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## Woody2Shoes (1 Sep 2019)

dzj":37czanak said:


> ..... guidelines set out by undemocratically elected officials.



You mean like Dominic Cummings for example ? :roll:


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## lurker (1 Sep 2019)

Woody2Shoes":bapr2wqo said:


> dzj":bapr2wqo said:
> 
> 
> > ..... guidelines set out by undemocratically elected officials.
> ...



I think this third rate Malcolm Tucker will be gone within weeks.
Unlike the jobs for life boys over at Brussels/Strasburg


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## Benchwayze (1 Sep 2019)

sunnybob":o8vg4msl said:


> dzj":o8vg4msl said:
> 
> 
> > Now that you guys are leaving the EU, you can use any chisel you like.
> ...



And not all mortices are cut along the centre line of the stock! 8) 

John (hammer)


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## Sgian Dubh (1 Sep 2019)

lurker":1vus9o2a said:


> I have been cutting M&it's for 50 years and was not aware there was a LAW that said the chisels had to be a third of the size nor that only one chisel was allowed.


I certainly don't think there's a law stating that, but there are useful guidelines, which I strongly suspect you are aware of, but I'll try and briefly summarise them here for others, which I hope will give decent reasoning for the guidance.

So, where the members are the same thickness, as in a typical door, the thickness is divided into three equal parts, and the mortice chopped out with the nearest larger chisel. This retains a little under 2/3 of the original material thickness in the morticed part. For example in a 25 mm thick stile divided into 3 = 8.33 mm the mortise would usually be cut with a 10 mm chisel leaving 7.5mm for each cheek. This ensures that a little over 1/3 of the wood remains in the tenoned member, which is the weaker partner, but bulking up the tenon this way strengthens it somewhat, and brings the volume of timber removed from each part closer to half each.

In addition, a 10mm (3/8”) chisel (or router bit, hollow chisel mortiser, chain mortiser, drill bit) is best suited to cut a 10mm (3/8”) wide mortise. The matching tenon can readily be adjusted to any width. 

Of course, there are always exceptions where, for example, something like a 12 - 13 mm wide mortice and thick tenon would probably be selected in an architectural door to accommodate a matching panel thickness and its groove, along with whatever mouldings are applied to stile/rail/muntin, etc, edges. 

And in sunnybob's case, depending on a variety of factors such as skill level, kit available, the end use of the product, the hardness of the wood, etc, he could select anything from his 13 mm chisel for the mortice width, up to 18 mm wide, or he could almost get all fancy and execute a finely wrought twin or double M&T in that 45 mm thickness. I can't see the last option really being ideal or, based on his opening post and his remarks there, taken up by sunnybob, ha, ha. Slainte.


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## sunnybob (1 Sep 2019)

No skill, no tools, no plan, no idea. :roll: 

I've decided to chicken out with the chisels. I discovered The only hammer I have thats suitable for continued use is a claw hammer. Everything else is 2lb plus metal working hammers, up to a 3 kg club. :roll: :roll: 
I have a very good router table which I enjoy using and I'm going to take out 90% of the mortice on that. Then I just need a bit of squaring up with hand tools.

Likewise with the tenon. I'm going to surf for how to make the tenon rounded on the table and if I can do that it would save me even more work (more work equates to more opportunities to screw up).
8) 8) 8) 8)


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## Trevanion (1 Sep 2019)

Can't you just round the tenon or square the mortice with a chisel? Saves even more time than devising a jig!


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## AndyT (1 Sep 2019)

Trevanion":3rt5hrxx said:


> Can't you just round the tenon or square the mortice with a chisel? Saves even more time than devising a jig!



If I needed to round the edges of a tenon to match a routed mortice, I'd use a rasp or a coarse file. Failing that, P80 abrasive paper stuck on a stick. 

Especially if I wasn't too sure of my chiselling skills.


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## Eric The Viking (1 Sep 2019)

Did you watch the Peter Follansbee video Bob? 

It's really easy: 

Set the gauge to the width of the chisel you CHOOSE to use, mark out the sides of the mortice and the ends and KEEP the gauge setting. Chop it out as he shows you (sharp tools and careful clobbering). You _can_ use a claw hammer, just be gentle-ish. The chisel breaks the fibres along the sides of the mortice - no need to worry about squaring up the sides.

When it's done, use the mortice gauge you set to give you the width of the corresponding tenon.

No actual measuring needed, unless you want to be really picky for some reason.

If it's a through mortice, you probably need to start from both sides, to avoid spliintering, but TBH, if you start on the face that's visible any splintering should be hidden behind the shoulders of the tenon anyway.

If there's any trick to it, it's probably keeping the chisel really sharp.


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## sunnybob (1 Sep 2019)

I tried the marking gauge trick, but either the gauge points are blunt, or the bubinga is just too much wood for it.
The scratch lines look like a drunken ant went past. Nothing straight about any of them, and I have FOUR mortices to cut :shock: 
Thats what decided me on using the router table. With the legs pushed back to the fence the cut will will be nicely square. Its going to kill the bit, but its a donkeys years old 3/8" straight so I can just throw it away when its done its job.

I've marked them out as haunched tenons, so that will hide most of the imperfections, but the haunches are sloped, so that will be another episode..
I'm hoping to do the mortices tomorrow, then decide if I want to round the tenon or square the hole. (sounds very secret society, doesnt it?  8)


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## Phil Pascoe (1 Sep 2019)

If it's a through tenon it's easier to square the mortice accurately than to round the tenon accurately.


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## Benchwayze (2 Sep 2019)

Just stick a piece of broom handle in a chunk of 4 x 2? That'll get you by...

John (hammer)


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## sunnybob (2 Sep 2019)

I've made the 4 leg mortices, and am very happy with the result.
Just my table saw and router table, no chisels or hammers were harmed in the making (hammer) (hammer) (hammer) (hammer)







The tenons are going to be a bit harder to make :roll: 8)


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