Tuesday, February 26, 2008

Bed progress

Legs joined to panel, sanded to 150, 2 coats black ink, second coat of Waterlox Original Sealer/Finish wet. The recessed panels are a different color because they had no finish applied when the pic was taken. The gloss is largely the finish being wet.

...an idea of color. Consider: this is with poor lighting, poor camera, and poor photographer. Add to that the color differences imparted by your monitor. It really looks black, grain is more obscured than I thought it would be.

End-grain cutting board

Walnut, cherry, and maple end-grain cutting board. Mineral oil and wax finish. This picture is after about a year of use.

Monday, February 11, 2008

Post tops




Left: the "finial version". Right: the "chamfered post" version.

Click image for larger picture.

Sunday, February 10, 2008

Torsion box

Core:
I = 1/12 x (W x T^3); W = rib width, T = rib height


Skin:
I = A x D^2; A = breadth x thickness of skin, D = centerline of skin to neutral axis of box.
Itotal = I top skin + I bottom skin + I each core element



Deflection:
Y = (.021 x W x L^3) / (MOE x I), where;
Y = deflection (inches)
W = Weight/ load (pounds)
L = span
MOE = modulus of elasticity (1.5 E6 is avg for wood)
I = Itotal from above.


Torsion box pictured: 61" span, 3" x 3/8" web, 3/8" skins. Deflection: .018" (~1/64") @ 1000lb.

video

Monday, February 4, 2008

Glue lam, forms, biscuits and top cap

Here's one set of forms used to make the "glue lam" panel top caps. A stack of thin strips is glued into a sandwich and clamped between these forms so they'll dry in the desired shape. In the upper left of the pic you can see the resulting glue-lam top cap laying on top of the panel.
These same forms have already been used to pattern-route the curved rails, and they'll be used again as a caul to attach the top caps to the panel frames. There's a separate set for the headboard because the radius of it's curvature is different than that of the footboard.

I just bought a biscuit jointer. Biscuits don't add strength to a long-grain glue-up like this, but it keeps things aligned while gluing and clamping. The only effort here is to get the slots centered in each of the pieces, since they're different widths.
The trial fit.




The glue-up. The biscuits automatically align the top cap, which makes the glue-up as stress-free as a glue-up can be. The form is used as a caul to distribute the clamping pressure evenly across the curved surface. Of little note: since the curves are true arcs (instead of parabolic arcs formed by bending something and tracing it), the position of the caul left-to-right doesn't matter much. There's a bit more hanging off the right side than the left, but I didn't even notice until uploading this pic. If this were a parabolic arc, that would mean that parts of the caul would be exerting no pressure.

The top cap for the headboard isn't a very good glue-up, but I'm going to try to salvage it with epoxy or cyanoacrylate. I don't know if I have enough stock left to make another, and it's not a fun process.

Sunday, February 3, 2008

Side rails

A router template is made to mortise the end-grain of the rails to accept the hardware. The mortise is not centered on the height of the rail, so it has to go on the "right way" - it's easy to screw this up and wind up with mortises at different locations on each end of the rail.
Since I didn't have a top-bearing pattern bit at the time, I made it to work with a bushing and a 1/2" bit: the window will guide the bushing, and has to be oversized the proper amount to end up with the right sized mortise (5" x 5/8" x 1/8"deep).



A brass bushing guide is installed in the router sub-base. The bushing will follow the template "window", which will limit it's travel. The bit depth is set, and ...
...the mortise is routed, then this bogus picture is posed hours later...


After squaring off the mortise corners by hand, the hardware is fit into the mortise.



This hardware has two little pieces of meat on the backside where the hooks are crimped. It won't sit flat in the mortise, so some shallow reliefs are drilled with a Forstner bit.



The screws which hold the hardware to the end of the rail are going into end grain, which is not very good at holding onto the threads. Some 3/4"d flat-bottomed holes are made with a Forstner bit behind the screw holes. Short pieces of dowel will be glued into these holes - when the screws are driven in from the end, they'll get a good "bite" into the side grain of the dowels. This is supposed to be a much stronger attachment, but I can't see how the rail hardware screws could back out once the whole thing's assembled.
Another easy thing to screw up: you don't want these holes to go all the way thru, and you want them all on the back side of the rail, so they face the inside of the bed frame.



Having no 3/4" dowels, I turned from some scrap, but it's so dark in the lathe corner I couldn't get a good pic of that.

Also not pictured: the rails had to be cut to length with a circular saw and jig, because they're too long to cut on my table saw. It was a simple jig to make, but yet another step.
One of the rails had an end check that wasn't entirely cut away when they were cut to length, so I glued it with poly glue (gap-filling).
I saved myself a bunch of sanding by planing all the edges of the rails, which led to a sharpening diversion.
I started trying out some finishing schedules on scrap. Right now undiluted black ink soaked into the raw wood seems to be the best coverage, but the top coat (shellac is the plan) will HAVE to be sprayed, since the ink is apparently soluble in alcohol (which is also the solvent for shellac). Maybe a water-based lacquer is in order.