Mortice & Tenon Calculator

[Windows]

Does anyone use a mortice & tenon calculator spreadsheet/website/app for working out sizing & placement of your m&t joints?

I’m likely to create my own specifically for wedged m&t in rebated material (because it helps me cement knowledge in my brain more than because it makes the calculations easier), but if there’s an existing one that you like or dislike I’d be interested to know about it.

One parameter I’m not sure about is minimal distance of the mortice from the end of the receiving piece. When you think about this, is it a fixed minimum for all wood types & mortice sizes? Do you use different minima depending on the wood species? Do you consider that it depends on the expected size of the mortice or of the material and if so is that about strength or aesthetics?

 

[Trevanion]

Trouble is that mortice placement is somewhat subjective to the work being undertaken. For example, on a sash or door the mortice placement in the width of the stile is generally dictated by the moulding.

Then it’s also dictated by the section sizes and the number of mortices/tenons. On a 45mm square section sash you might want a 20mm haunch/franking with a 25mm tenon, so your mortice placement will be 20mm inside the total length measurement, but on a door with a 95mm top rail with a single tenon and a 200mm bottom rail with a double tenon you may have 30mm on the top rail and 40mm on the bottom rail, if the sections are even larger you can obviously allow more.

 

[Windows]

Indeed. My calculator would be focused on single, wedged, through tenons on rebated material used at the corner of a frame, which could be written to handle material of any size, but it’d be nice to produce a warning when material dimensions suggest two tenons would be better for example.

For me, capturing the subjectivity is the point of writing the calculator: it makes the design criteria and decision points explicit; it defines the edges of applicability of a particular approach. Once I understand that, I often don’t need to actually use the calculator.

 

[Mike G]

Go for it. I wish you luck. However, I'm not sure it will be very enlightening, because of the limited wiggle room in the parameters. In designing a joint, you're essentially trading short grain at the end of the mortice for width in the tenon, (with a haunch to prevent twisting).

 

[slimshady]

I would prefer to have an example diagram / picture of several doors, windows, table frames, etc all in one place like a Zeus book.?
At the moment I photo copy several books and annotate the reverse with applicable dimensions.

Alex.

 

[Windows]

Well there was enough there to keep me occupied.

Here is a sketchy first version that only provides info for the mortice, but hopefully gives some idea of what I’m going for:

Single Wedged Through Mortice & Tenon in Rebated Material - Calculator

It’s got:
1. Picking mortice width based on chisel size
2. Aligning the edges of the mortice to the rebate when close
3. Using a different height based on whether the mortice overlaps the rebate or not
4. Ensuring that the mortice isn’t weak at the end
5. Providing the outer (large) and inner (small) dimensions and positions for both sides of the mortice

It’s not super complicated, but there’s a reasonable number of decision points. I’ll probably update with diagrams at some point.

 

[Windows]

I would prefer to have an example diagram / picture of several doors, windows, table frames, etc all in one place like a Zeus book.?
At the moment I photo copy several books and annotate the reverse with applicable dimensions.

Alex.

Interesting idea