3-way intersection joinery

[4DThinker]

While teaching I would make samples of joinery I thought up to be a reference set to show my students.  Many complex joint solutions never found a customer, although they were usually inspired by a challenging past project done by students. This is a tale of one sample and one student who appreciated seeing the sample.

 

Summer shop classes often requested my help for CNC work that was beyond the capability or the instructor. One such day I was in the shop to help one student when I was asked by another (Abby D.) if I could show her how make a form for S shaped laminations.  I asked to see her design drawings to get a better idea of what she needed.   Her intent was to stack three S-shaped laminated curved to make a 3-legged end table. As my personal design process strives for simplicity I could see how a sample joint I made could greatly simplify her project.  Simple curves rather than stacked S shapes joined in the center the formwork was simpler and the result almost identical to her design drawings.  A single bolt through the center holds all 6 curve sections together.  The cables at the top lock the geometry.  I cut the joint end by clamping each curve over the end of the CNC.  The sample I showed her and the final project:

Edited July 18, 2022 by 4DThinker

[Woodman]

That Is AMAZING. 

[4DThinker]

Thanks Woodman.  I do have to give credit to Professor Steve Davidson (now retired) who was her instructor for the final cable work and details though. 

4D

[Woodman]

What would you recommend for a serious beginner for a CNC wood shaping set-up?  Able to shape an 8x8x8 block of wood as well as 5x5x16? Is it Mac OS laptop-controlled?

[4DThinker]

The CNCs I have are either run with a PC running Linux and LinuxCNC as the control software (Probotix.com CNCs), or with a windows PC and proprietary control software (CNC Shark).  The software I use to draw up vectors and turn them into toolpaths is Aspire from Vectric.com and runs on Windows. 

The size of your wood blocks are the challenge. Z axis (vertical) cutting range and the length of router bits limit what you can do and what can fit under the gantry.  With my probotix CNC and its open frame design I have been able to clamp cedar 4x4s vertically to shape their ends, and clamp them to the frame to cut notches or mortises into their sides.   I suspect I could  do the same with either of your blocks but it would take some rejigging to hold them and cut depth would be limited to 2" max. I have my probotix CNC mounted on 4 legs joined with wide plywood stretchers but nothing under the CNC frame.  With some frame bridges I've been able to hang a finished cabinet inside the frame to cut mortise arrays for feet to join to. 

4D 

[Woodman]

I see a carved wall sconce in the shape of a large molar. For my dentist. 
 

And a box with lid which looks like a wedge of Swiss cheese lying on its side. 
 

[4DThinker]

You're half way there Woodman.  Knowing what you want to make is the first half.  The second half is often 90% of the work though if you don't yet have the capability of making it.   I had a small CNC with less potential and a low price to learn on before moving up to a larger one with more potential.  With the large one it still took some time to let it reveal its unexpected features. Those have let me cut the challenging and unusual and rare things most don't expect a CNC to be capable of using it.   

https://4dfurniture.blogspot.com/2016/04/advanced-compound-angle-cnc-clamping.html 

https://4dfurniture.blogspot.com/2021/05/cnc-frame-bridges-as-alternative-to-t.html

https://4dfurniture.blogspot.com/2016/05/simple-desk-design-tenon-array-joint.html

https://4dfurniture.blogspot.com/2016/04/supporting-assembled-projects-beneath.html.

 

Much is possible if you can literally think outside the default X/Y/Z limits box. 

4D

[Woodman]

Witch! Warlock! That's Black Magic! 

 

 

 

[4DThinker]

That is the desk I'm sitting at.   Besides cutting the tenon array on the bottom of 27"ish long 4x4s the 4x4 was also angle 2 degrees forward (or back) and 4 degrees left (or right) so the legs would flair out some when attached. A compound angle which is apparently impossible with a 3-axis CNC. 

4D

[4DThinker]

"Wood Weaving" is so far the best name to describe the value of using tenon arrays rather than a single large tenon in cases like the legs top joint shown above. With good cross sectional surface are between parts the small tenons can still be large enough to not snap off easily.  The tenons can spread out to the corners of the part.  Surface area for glue is increased greatly.  The mortise array side still has a web of wood between the mortises. 

With gravity holding my desktop to the legs I haven 't yet glued them in place. There is enough friction in the joint to keep them snug in place even of I flip the desk over. I can wiggle them loose though with a little back and forth action while I pull on them. 

4D