Jensen-style Z-Chair #2: Planning and Prototyping

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Blog entry by Ross Leidy posted 05-18-2019 02:41 AM 459 reads 0 times favorited 3 comments Add to Favorites Watch
« Part 1: Introduction Part 2 of Jensen-style Z-Chair series Part 3: A Jig Interlude »

My first thought was that I would try to find some plans for this chair on the internet. Nope. All I found were some plans for a really atrocious mockery of the design. Not even close to the proportions and style of the original. So, armed with some basic dimensions that I found here and there, a decent side-view photo that I could scale and trace to get the angles right (or close), and hours of google searches studying images of this chair for telling details, I set to work.

I have a CNC machine, and I’ll be using it to cut out many of the pieces. I loaded the chair side-view image into Vectric’s CAM program, scaled the image to make the height of the back 28”, and then started working on vectors to outline the side assembly. I was prepared to deviate from the original’s MT joinery by using puzzle-piece joints as shown below (I know, sacrilege). Primarily because I wanted to try it, but also because at the time I wasn’t setup to cut mortises for floating tenons. Ultimately, I abandoned this approach for aesthetic reasons and because I was concerned that the back-to-leg joint might be too weak. But, I used them for a plywood prototype that let me play around with proportions of the rails and seat before committing to real wood.

Plywood front leg and back stile:

Testing the fit of the joint with a scrap piece prior to cutting the long rear leg:

The long rear leg exceeds the bed size of the CNC, so here I’m “tiling” the cut, where as section of the leg is cut, then re-positioned to cut the next section. It takes 3 tiles to complete the leg.

This is the final tile. The dowels are used to index the piece as it’s re-positioned for each subsequent tile.

A good dry fit.

This was as far as I took the prototype. It helped me tweak the dimensions of some of the remaining pieces. I used dowels to attach the rails to the sides, which made me realize that I didn’t want use dowels. They were too fiddly for me with the drilling jig that I had. This is when I started seriously considering floating tenons and how I could make the mortises.

3 comments so far

View mafe's profile


12042 posts in 3477 days

#1 posted 05-18-2019 11:03 PM

Truly an inspiration.
Love the way you use the CNC.
Cobining the old and new.
Best thoughts,

-- MAD F, the fanatical rhykenologist and vintage architect. Democraticwoodworking.

View Ross Leidy's profile

Ross Leidy

51 posts in 2329 days

#2 posted 05-19-2019 01:07 AM

The CNC definitely exercises different skills – modeling, toolpath planning, creative hold-downs. I promise that all the slat sanding was done by hand, though. :)

View mafe's profile


12042 posts in 3477 days

#3 posted 05-19-2019 09:53 AM

Ha ha ha, I have never worked with a CNC, but would love to one fine day.
Woodworking don’t have rules, just ways, CNC is one of them.

-- MAD F, the fanatical rhykenologist and vintage architect. Democraticwoodworking.

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