A study of joinery

A Japanese technique for joinery and a software tool for it, and a paper:

http://ma-la.com/Tsugite_UIST20.pdf

were recently mentioned at:

The specific joints of interest are Figures 28, 29, and 30:

(if folks want, we can move all the relevant posts here).

This will be an examination to see what is involved in cutting these joints using Carbide Create.

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The first consideration is how the stock will be secured — the upper limit is the extent of the overhang of the cutting area — a stock mount with HDZ will probably have the furthest reach (or one can fabricate a baseplate with hole and integrated workholding). A quick check of my machines seems to indicate ~80mm as the upper limit, and ~60mm as a lower. This should allow up to a 2" x 2" board to be used, so we will start with that dimension.

We will start with a 2" x 6" working area with the origin at the upper left (registered against the front plate of the machine):

The assumption is there will be two boards and a 2" spacer (an offcut from them):

You will need an endmill which can make a 2" cut w/o rubbing — sourcing that is left as an exercise for the reader — note that the material will need to mounted so that it projects at least 2" above the endplate.

Divide by thirds:

(Usually I would do this sort of thing in an application which supports PostScript Points and Picas so that rounding such as is seen above would not occur)

and center:

Then offset the square which defines the stock to cut by the endmill diameter plus 10% (we’ll assume an 0.25" endmill):

Draw in squares which are larger than the corners and go past the outer geometry:

Round them off to be a bit more than the endmill radius:

Boolean subtract each from the endmill radius plus offset geometry:

Duplicate the geometry:

and drag it into alignment:

Draw in a square which goes from corner-to-corner and is twice as large as needed:

and scale it down 0.5 to the size needed and drag it into alignment:

Boolean subtract the geometry which defines the area to be removed from the square:

Duplicate it three times and rotate and drag each duplicate into alignment:

Then set up the toolpaths:

(and change the stock depth to deep enough for the preview and add in some geometry and a toolpath for a better preview):

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Figure 29 is similar, just some more rounding — draw in geometry which defines where the endmill can ideally reach:

A circle of the appropriate radius:

a square to use to position:

and drag into position:

Add geometry which is as wide as necessary and drag into position:

Boolean union it

Position a circle for the outer radius:

Node edit the geometry so that it overlaps the two circles as necessary — it will be necessary to add one node:

Then Boolean Union:

and Boolean Subtract:

Select the geometry and one of the aligning squares and duplicate:

and draw in additional aligning geometry:

and then position:

Duplicate, mirror horizontally and repeat:

Select the added geometry and the previous geometry and Boolean Union:

This type of joinery would be great to make an overhang knee to machine these awesome joints.

Ref:

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Yeah, I put up a simpler design on Cutrocket:

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Increase the stock size to 8" wide, flip and re-arrange things a bit to better match the image and preview:

Draw in geometry to trim off the cut geometry on the left:

Since the other geometry is already the correct size/orientation, duplicate it and drag the duplicate into alignment:

and then align with the other geometry:

Select each pair and Boolean Intersect:

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Going into the Toolpath pane and adjusting the selections we get:

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Nice,

For people interested in the history of how and why the Japanese got so good at woodwork I can recommend the art of japanese joinery.

It’s not just their culture of respect for the world and natural things. Apparently Japan also did not have the natural materials easily available to build very much in stone and so the effort that Europeans put into masonry (see the Greeks and Romans) the Japanese put into perfecting joinery.

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Figure 29b requires 3 pieces, so extend the stock area, duplicate things as necessary, and draw in a square the size of the central piece:

and align it with the original:

and set the size appropriately:

Duplicate it and set the size to be wide enough to cut and drag the duplicate into alignment:

and then duplicate the rounding geometry, rotate and drag it into alignment:

then Boolean Subtract it:

Duplicate, horizontal mirror:

and drag into alignment:

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Another consideration is the frequency of earthquakes — wooden structures would tend to give and be safer during them.

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Draw in a square and set its width so that it will cut across the central section (at a different depth than the other cuts — merging a copy of this in with a replica of the other geometry is left as an exercise for the reader):

Adjust the size and eliminate unnecessary duplicates and rotate so as to get a good preview:

(note that the part on the right will need to be cut twice)

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The final joint requires 3 parts, so extend things again and make suitable rectangles:

Dupe the central square, set its height to a suitably large value, set the corner radius and drag into alignment:

Select the square which defines the end of the stock and offset by endmill radius

Boolean subtract the two aligned rectangles:

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Wow! That is a serious amount of work you did there Will. I am very much obliged to you. It looks like I am going to have a huge amount of time on my hands as the whole country is being locked down. I have been working with the SO3 today making a few simple jigs. The proof of the pudding is always in the eating and my circles are actually circular so it means that my adjustments a little while back were good. I have great confidence in the hardware now and I will start on the jointing exercise very soon. Thank you once again for showing the way with that superhuman effort.

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Great book recommendation Liam. I must see if I can persuade mty lady to buy it for me for Christmas.

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Perform a similar set of placements and cuts for the other end cut:

For the center part there will be two layers. For the first, drag in radiused rectangles and position them appropriately:

Then Boolean subtract from the square:

Placed radiused rectangles to finish the cuts:

and then set up suitable toolpaths.

Note that it will be necessary to set the central part cut up in layers, so the first is 2/3rds the way through:

The first preview shows the end pieces well:

Here is one with adjusted stock thickness to show the central piece:

In case anyone wants the files:

Tsugite_Figure28.c2d (119.7 KB) Tsugite_Figure29a.c2d (197.0 KB) Tsugite_Figure29b.c2d (296.5 KB)

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I found it a really interesting read, there was lots I didn’t know about Japanese history and their development of carpentry skills in there. Be careful though, you may end up buying Japaense planes and chisels and calling them dogu it could become an expensive habit :wink:

There’s not much about how the joints are actually made, for that I’d watch somebody like Dorian Bracht

He does introduce the major joint types and explain where they are used.

The other book, the genius of japanese carpentry, goes into a lot more detail about how a few specific buildings were built with photographs of the key construction joints as they’re being made.

Enjoy your reading.

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That is extraordinarily generous Will. Thank you very much. What a great Christmas present. In the American idiom, is it “Thanks a bunch”? :grin:

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Superb! thank you Liam, I can make good use of my tier 4 readjustment!
I was in Tier 3 this morning and had changed to Tier 4 by lunchtime. i was going to see my grandchildren, whom I have not seen since March but now that has been shelved.

The heck with it…books ordered from Amazon. :wink:

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My hat off to you @WillAdams, very good.

Funny this comes as I’m starting to read up on vertical work holding and CNC joinery.

Jay Bates has a great video on YouTube around templates for these jobs, the focus is more on mortise and tenon, and dovetailing but very applicable to Japanese joints