Petra Desk

[Jamie Baalmann]

First off I hope it is OK to post this.
I found the ad for this in a magazine, and I have been meaning to build it for a long time. My hand me down breakfast table/desk isn't working for me anymore. I can't figure out what kind of rod is going through the corners.... The website says "The innovative corner joinery incorporates cross-cut and flat-grain hardwood, concealing a steel tension rod, which results in the highest degree of strength and stability." I was also wondering if anyone had any bright ideas on how to cut these as well. I was planning on doing a typical 45 degree angle, assembling, and then making a jig to rough cut w/ router then clean up with chisel. Oh and one more thing what type of wood is this and what type would you use... I might try some Zebrawood for the first time:D most likely 8/4.

[Jamie Buxton]

I dunno what the steel tension rod might be. The desk sure looks like it is made the way you've outlined: miter the big planes of wood together, then cut lots of slots for loose quasi-tenons, and fill 'em up. With all the glue surface provided by those quasi-tenons, it will be a strong joint without any steel thingamajig.

I can't tell what the wood in the pic is. Use what you like, and don't try to slavishly imitate what you see. Heck, if you want exactly what you see, buy it instead of building your own.

[Jamie Baalmann]

THX for the response... I kind of thought the same thing about the joint... I just want it to be as strong as possible... I kind of overdo everything might make it hard to make money when I want to sell furniture but this is for me and I want it bulletproof... and I'm going to change it a little.... BUY IT HA.. I'm poor I only spend money on tools and lumber.

[John Schreiber]

The joinery they show is called a finger joint or a box joint. The addition of a steel rod through it is probably just for show. There is plenty of glue surface in a box joint to make a connection which will be at least as strong as the wood.

Google "box joint" and you will see a bunch of ways to make them with a table saw or with a router.

I don't know what 8/4 zebra wood will cost you, but it's not cheap. I would also think that with dramatic joinery like you are thinking of, a less dramatic wood might be preferred.

Good luck.

[Jamie Baalmann]

It isn't a simple box joint. They do not travel through... But I also thought about doing a greene style box joint and adding ebony or brass or something to each one. Yeh Zebrawood might not be the most suitable

[Jimmy Newman]

Looks to me like that's got the big pieces mitered together then cut for lots of splines to make it look pretty and be stronger. Lots of ways to do that.

The steel tension rod thing sounds to me like some pure grade A marketing BS ;). Steel tension rods are great if you're trying to make a structural member out of something that's a lot stronger in compression than in tension (like cement - which is how they make a lot of bridges). Parallel to the grain, tension rods actually would make the wood weaker. Across the grain, they could make it a little stronger if you got the tension right - but the tension would have to be HIGH, and there's already that big right angle joint there to add plenty of strength.

I sure think it's a good looking desk, though! I'd go ahead and build it and just not worry about the tension rods.

[John Schreiber]

It isn't a simple box joint.
It sure looked like one, but you are right. I Googled around and found the site (http://www.zelecompany.com/furniture/petracabinet.html#). The pictures below are from the same ones you posted, but I played with the contrast so I could see how the joints worked better.


66930 66931


I think you could tell from there that there are indeed pieces added in. The buttons look to be decorative only.

[John Schreiber]

Of course, then I started thinking about how to do it far too much.



66932 I'd start with a standard splined miter joint.

66933 Which would look like this when completed.

66934 Then turn it upside down at an angle in some kind of massive jig on a table saw and use a very good dado blade to cut out the spaces. Could also probably be done with a backsaw and chisels.

66935 Glue in the triangle shaped pieces leaving them a little proud.

66936 Plane them down and finish. That was fun.

[Jamie Buxton]

..... Then turn it upside down at an angle in some kind of massive jig on a table saw and use a very good dado blade to cut out the spaces. .....



If that is a full-size desk, it would need to be a truly massive jig. A better solution would be to move the tool, not the workpiece. The tool would be a router. The jig would be smaller, because it only needs to hold the router, not the whole desk. It would also have the advantage of giving you a flat-bottomed slot with no chip-out.

[Art Mulder]

Let me step back from the discussion of the corner joinery...

Personally, I would not make a desk like this without adding in a stretcher across the back. Otherwise, I would expect the top to develop some serious bow over time. Or worse.

In fact I'm very VERY puzzled that this is actually a commercial product, without such cross-support. Am I missing something in the photo? It looks like the top is no thicker than one inch, and there is no visible cross support at all under the top of the desk. It must be at least 4' wide, and maybe more like 5'. How can they expect it not to sag? And just wait until someone sits on it!

[Russ Filtz]

Maybe the small buttons actually hide the tension rods mentioned. I think tension rod would be a misnomer as they are really no more than pins holding the loose tenons in. Again, with so much glue, it's a belts & suspenders approach.

[Cliff Rohrabacher]

The corner joints are done using Keys inserted on the 45 so as to maximize surface area and glue area. I am guessing that the Rod runs front to back inside the corner joint.

I built a butcher block living room set some many years ago and the coffee table (1& 1/2" thick) was made from three pieces of butcher block using plain old fashioned end grain to long grain but joints with 3/8" furniture lags hidden under plugs on the table top. That was the entire joint. 4 lags on each end and an end grain joint. over the years I wondered If I should have made it a finger joint or what but when I built it that was the then vogue and I wanted that look. The table is still serving nicely. and Indeed I can still leap onto it landing on my feet from the floor.

So I'm guessing that they hid the steel rod that I am guessing runs front to back inside those keys with a carefully hidden plug.

In the alternative:
It is also possible that there are two long rods instead running the length of the table just i underneath the top maybe an inch low and inside enough so you can't see is without crawling under.

Making them work would require that they not exert either pull or push but, are in a dead rock solid fixed position embedded into the wood of the sides and not letting the sides move in or out.

[Jamie Baalmann]

I appreciate all the help so far....I might go with Teak or Ironwood... I don't know for sure on that part yet but as far as construction i am going to do typical 45's then built a jig that sits at a 45degree on the corner for a router with a straight bit, clean up cuts then install the triangles possibly of another type of wood maybe end grain like the one pictured then flip over the table and rout a pocket the full length to put some flat metal strips as to strengthen it lengthwise... Also thinking of doing the reverse of the woods on the file cabinet... so many ideas and so many unfinished projects.. :rolleyes: