Rib #1
I started by lightly sanding each gusset to remove any free fibers at the sawn edge. I also made one pass on each face to break the glaze or remove oils. I also ran a bit of steel wool along the spruce strips to clean up the mill fuzz. This has the added benefit of very effectively uncovering any minute, unopened splits or grain runout. The wool catches in the split and opens it up enough to see. I've discarded several pieces from these splits. There was some mention of concern for the oils on the steel wool as a rust preventative. I am using a well worn piece of wool, and use very little pressure near the glued ends. There is no evidence of oil affecting the joints of any of the test pieces, and the epoxy wets out nicely. However, it is enough of a concern that I am going to get some of the oil-free wool the next time I am at the store.
After dressing up the gussets and sticks, I mixed up the T-88. I have two pet medicine styringes that I use to get a 1:1 volume ratio of the two parts. With this first rib, I discovered that it takes about 7 ml of epoxy for all the joints and the test piece. I prefer to mix only one batch for each rib. That way, the test piece will accurately reflect the epoxy used for that entire rib.
The epoxy was first applied in a thin layer to the inside face of half the gussets, and the gussets were placed glue side up in position in the jig. The entire face was covered with this thin epoxy layer to ensure that the gusset remained sealed from moisture, even in the nooks and crannys that will be hard to coat with varnish later.
Next, epoxy was applied to the mating faces and ends of the vertical and diagonal members before being slipped into the jig. Mating faces of the capstrips were then coated with epoxy and the capstrips were put in position in the jig.
Finally, the remaining gussets were coated with epoxy and placed glue side down into position in the jig. PVC clamps were then applied. I used one large clamp at each joint to hold the capstrips tight horizontally against the HDPE blocks, and two smaller clamps to hold the gussets down (I'll take a picture later). Some places required extra clamps. With the clamps in place, I then inspected each joint to make sure the gussets were in position and the joints were tight.
With the remaining epoxy and some gusset and stick scraps, I made a test joint. The joint was basically a "T" with (unsanded) gussets on both sides. I left an inch or more of the stick ends free to be later attached to the test apparatus. I plan to make one test joint for each rib and then break them before putting the ribs on the spars. The rib and test piece each have a number so they can be matched up later.
The epoxy application and assembly of the rib takes a little over a half hour. My work area is about 65 degrees, so the T-88 is just starting to show signs of setting when I am making the test piece. I figure that the test piece has the most factors working against it, and should therefore fail before my carefully constructed rib.
6 hr
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( 2.9 / 21 )I have decided to miter the sticks into each corner. I know it isn't necessary, takes time, will never be seen, and actually adds a very small amount of weight. However, a tightly mitered joint leaves one less place for moisture to hide and is easier to seal.
After some fooling around with some available wood, I decided to purchase my Sitka Spruce ribstock milled to 1/4"x1/4" from Wicks Aircraft. My tablesaw wasted too much wood, and was located out in the bitter cold. While my bandsaw doesn't waste as much wood and does make nice cuts, it is just too slow when ripping. It is also fairly loud in the house, which is irritating.
So I ordered 150 5' sticks, which should be more than enough. It came in three bundles of 50 sticks each. After grading two of the bundles, I had just enough nice long pieces for the top and bottom capstrips. I only used perfectly clear strips with at least one ring running the entire length of the strip and with at least 3 rings appearing in cross section. Those would be the stronger pieces. I also only used strips with end grain oriented perpendicular to the side face (nearly vertical grain). This would allow me to limit warping to the braced direction, for the most part. The remainder of the sticks were cut up for diagonal and vertical members. The few areas with knots or excessive grain runout were easily removed from the finished stock.
I've decided to form the leading curve on the top capstrip to make assembly go a little easier. I could have dispensed with this step, but it takes a fair amount of force to hold the top strip in place. I was concerned that excessive clamping force might dent or ding the capstrip. From a 2x4, I cut a shape a little more curved than the forward portion of the capstrip. There is a notch for the front end of the capstrips to fit into. The bending jig is just wide enough to fit 5 strips at a time. I slip the ends of dry capstrips into the notch, then apply a little pressure to form the sticks over the curve. I then hold the strips in a jet of steam from an old teapot. After a minute or two, you can feel the wood get soft and begin to deform easily over the curve. I clamp the strips down, and leave them to dry for a few hours before removing them. So far they've held their shpe for several weeks.
6 hr
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( 2.9 / 21 )OK, this picture is actually from 2005-01-19, but it shows me trimming a gusset on the band saw. This should be the last of the gussets for now.
2 hr
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( 3 / 15 )Yep, more gussets.
4 hr
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( 2.8 / 11 )
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