Thursday, January 31, 2013

Stacking the odds

In true Nakashima style, I wanted the live edge top for my hall table to dictate the size and shape of the carcass that supports is. Since the front of the table top follows a gentle curved shape, I want to match the same curve to the front apron of the table.

In my curved front writing desk project from a few years back, I used a bent lamination technique to create the curved drawer fronts. The technique works great if you don't need to cut any big joinery into the components. But to created the crescent front for this hall table, I need to build an apron that can be tenoned into the legs. Unfortunately, the big weakness of bent lamination is that if you shape or cut the piece and sever too many glue joints, you can weaken the bond.

So for this project, I decided to use a stacked lamination technique where I built up the apron structure out of four pieces of stacked maple which I will ultimately veneer with cherry to match the rest of the carcass. I originally thought I was using soft maple, but it turns out I was working with rock maple, so there was a little more elbow grease involved than I had expected. But I'm sure going to have one strong front apron!




Right click to download the HD version of this video

7 comments:

Anonymous said...

Hey Rob can you elaborate more on your reasoning for not using bent lamination. I'm looking to incorporate a curved front into a project and was planning to use bent lamination for the apron that will have tenons cut into the ends along with bridal joints in the middle. Similar to this project:
http://www.youtube.com/watch?v=xfxgouMvAgo&list=UUjatELwdjLj3_03Q80iTc_g&index=13
I've never done this before, but I would think that if the laminated glue bond is compromised by cutting joinery into the lamination that it would regain its strength once the joint comes together. I know I'm missing something here, so any light you can shed would be greatly appreciated.

Rob Bois said...

Unlike a stacked lamination or steam bending, a bent laminated curve remains in tension indefinitely. It is only those glue lines that are holding the laminates from slipping and unbending. So as a general rule, I don't like cutting much joinery into a bent lamination. Every time you cut through a glue line, there is the opportunity for the piece to "unbend" slightly. Now at the ends for something like a tenon you should still be fine since the only part that could come out of bend is the tenon itself (not a problem). But in my case I am doing fairly long floating tenons, so I would be removing quite a bit of "glue line" surface inside the apron. So I don't think you run any real risk cutting tenons on the end, but those bridal joints really make me nervous. They are cut right in the middle of the bend severing probably two or three glue lines across the entire span. I think the piece in the video shows some "spokes" inside the table that probably help keep the bend after assembly. But the mating leg in the bridal joint won't do anything to shore up those severed glue lines even after they are glued up. Consider an extreme example where there are only three laminates in that bent piece and the bridal joint cuts completely through the outer two. The bend would spring back completely straight at the bridal joints. Obviously those bridal joints don't cut that deep but they must sever at least one or two glue lines on each side.

Adam Heckman said...

Rob:

I just found your blog thru a re-tweet from MWA. Thanks for putting this out there. Your videos are well done with good lighting, audio and editing. Your hosting style is relaxed as well. I'll definitely be diving into the back videos.

BTW, I also live in the Commonwealth, nice to see a local guy!

Rob Bois said...

Thanks Adam, I appreciate the kind words. Just as a word of caution, if you dive too deep in the archives, you may find the lighting, audio, and editing a bit more challenged ;)

Also, since you're in the Bay State, if you get a chance you should drop by the Furniture Project during the New England Home Show. I'll be exhibiting this very piece at the show. Details are here: http://designbuildshow.com/

Adam Heckman said...

Rob:

I will be at the Furniture Project probably Friday afternoon. I can sneak over after work. I work in the Design Center Building so I could walk there if I wanted. I went last year and it was great.

Thanks again for all the videos. I'll be downloading a few to the tablet to watch if the power goes out during this big snow we got coming.

Jim A said...

Rob,

I've laid awake for three nights trying to figure out how you are going to get slip tenons into that double compound angle on a curved piece. This morning in the shower it finally hit me.

Give up. Use that beautiful piece of walnut for a jewelry box. That's what I would do.

Yes, I am the guy who begged you to use the walnut for a sideboard, but I didn't think you'd actually try it. Man, you either have some serious skills or a serious pair (or both). Seriously, great work, guy.

Jim

Rob Bois said...

Sorry Jim, but I think it's going to be another 2 episodes before I reveal the secret to the joinery. Oh, and because this wasn't enough of a challenge, I decided to add some hidden drawers as well. What was I thinking?