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Jensen-style Z-Chair #5: Seat frame - strap recesses

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Blog entry by Ross Leidy posted 05-19-2019 03:47 PM 450 reads 0 times favorited 6 comments Add to Favorites Watch
« Part 4: Slats Part 5 of Jensen-style Z-Chair series Part 6: Seat frame - shaping and joinery »

Since I was already working with 3/4” material on the slats, I opted to start on the seat frame next. I estimated a width of 2-1/2” for the seat frame, which now I think was a little wider than the original. I’m guessing it was more like 2-1/8” to 2-1/4”. The images I found don’t seem to be entirely consistent, so the manufacturer may have used different widths. I’m not sweating it though since the width of the frame won’t be visible once a cushion is in place. And I’d rather over-build than under-build.

Having looked at hundreds of photos of this chair, I saw 3 different ways that elastic straps were attached to the seat frame:
  • A wide-ish slot for the strap to go through, and presumably be held with a dowel through a loop in the end of the strap on the underside of the frame.
  • A long recessed channel with a thin angled slot the length of the channel, and Fagas straps clip into the slot. (This seemed to be the most common.)
  • Three individual recesses on each side of the frame, each with a slot for a Fagas strap clip. Now I swear that I’ve seen this configuration somewhere, but when I went back to try to find an example online, I couldn’t. So, it’s either not very common or I’m sadly mistaken. Whatever the case, this is what I did for my chair.

Instead of the Fagas-style clips, I went for the readily-available upholstery webbing clips that friction-fit into a 1/8” wide slot in the frame. I got both the clips and a roll of elastic webbing on eBay.

This is a test for the recess and clip slot. I ended up reducing the size of the recess and the radius of the corners.

On the CNC, I hogged-out the 1/8” deep recesses with an end mill and then went back with a core box bit to cove the edges. The piece of scrap on top is to prevent tear-out.

Though the side pieces of the seat frame will be 5” shorter than the front and back, I cut all the recesses on full length pieces to make clamping and indexing them on the CNC easier. The side pieces will be cut to the proper length later.

In retrospect, I should have made a smaller step-over for the end mill when cutting the recess. Those ridges were a pain to sand out in that small area.

Though the strap clips should hold fine with a simple vertical slot, I wanted to angle the slots a little just to be safe. A 10 degree angle off perpendicular was about all I could manage given the bit length of the 1/8” end mill. Any steeper of an angle and the collet would begin contacting the wood on the upper edge.

Strap recesses complete. Except for the sanding – yuck!



6 comments so far

View mafe's profile

mafe

12066 posts in 3483 days


#1 posted 05-22-2019 09:08 AM

Hi,
Really interesting with the explanations on the CNC work, thank you.
Wonderful that you explain so carefully, this makes it possible to learn from.
I can easy see that these clips are easy, but I have a hard time picture them in Danish classic furniture making, the loops and rod was quite common though.
When this is said, if it’s a lot easier and it’s a not visual detail, I guess it will be fair.
Fine work.
Best thoughts,
Mads

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

View kaerlighedsbamsen's profile

kaerlighedsbamsen

1291 posts in 2107 days


#2 posted 05-22-2019 10:41 AM

Good and simple solution to use the cnc for the job.
I too have newer seen these clips on Danish furniture, it seems these chairs were made by several manufacturers, some in the US.

-- "Do or Do not. There is no try." - Yoda

View Ross Leidy's profile

Ross Leidy

59 posts in 2336 days


#3 posted 05-22-2019 01:15 PM

Yes, this particular clip style was a compromise, but they were inexpensive so I thought I’d give them a try. Also, my primary goal was to match the overall shape and proportions of the original as best I could, not necessarily to match all the construction techniques. If after it’s complete and someone lifts the cushion and declares, “this isn’t original”, I’ll take my lumps. :)

View mafe's profile

mafe

12066 posts in 3483 days


#4 posted 05-22-2019 01:56 PM

As I said, it’s YOUR chair, so it’s not meant as a negative thing, it was just meant for info, from a Dane.
Laugh, I would also be surprised, if some one liftet the cushion and declares, “this isn’t original”. I might even answer them: ‘ohhh shut up and get a life’. Ha ha.
I have never ssen those cips befor, so I have to say you openend my eyes for something new, thank you.
Laugh and a smile Mads

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

View TEK73's profile

TEK73

88 posts in 101 days


#5 posted 06-10-2019 07:54 AM

Really nice build and a informative blog (I have read all parts available).

I’m just curious about the seat frame and the mounts.
It seems like the cnc’ed holes is aligned with the wood grains, and I get a tiny bit worried that the frame may split up along the grain if high pressure is applied.

But, it may not be a actual problem – First – maybe I’m just overthinking.
Second, I assume the seat pillow will rest on the frame itself as well as the strops, so the actually pressure on the strops will not be very high – as the cushin will divide the forces over the frame itself and all the straps.

So your probably all good :-)

-- It’s good to have an end to journey toward; but it is the journey that matters, in the end. - Ursula K. LeGuin

View Ross Leidy's profile

Ross Leidy

59 posts in 2336 days


#6 posted 06-10-2019 02:01 PM



Really nice build and a informative blog (I have read all parts available).

I’m just curious about the seat frame and the mounts.
It seems like the cnc’ed holes is aligned with the wood grains, and I get a tiny bit worried that the frame may split up along the grain if high pressure is applied.

But, it may not be a actual problem – First – maybe I’m just overthinking.
Second, I assume the seat pillow will rest on the frame itself as well as the strops, so the actually pressure on the strops will not be very high – as the cushin will divide the forces over the frame itself and all the straps.

So your probably all good :-)

- TEK73

Thanks, I’m glad you’re enjoying the build. I think I should be okay with the slots for the webbing. An alternative way to attach the straps that appears to be common to Danish chairs of this era uses even wider slots in the frame and the webbing/strap passes through to underneath. If the wide slots don’t present a problem, then I’m confident that my narrow slots should be okay.

Here’s an example of what I’m talking about:

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