Chuck Cunningham floats part 2

I used Titebond for the spines because I couldn’t find my Gorilla Glue, but I have some now because I went to the hardware store to get it.  Gorilla Glue is a superior adhesive for bonding things to foam because it expands to fill cracks.

First I checked the fit of the part.  I had to remember which end was the front.  Remember the dowels of different lengths?  I don’t want to attach the side wall backwards because that would leave me with dowels hanging down too far on the aft end of the float.

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Next, using an expired debit card, I spread Gorilla Glue in a very thin layer on the correct side of the sidewall.  Don’t spread it on the wrong side.  That would be silly.

Then the side was placed on the foam core.  With Titebond or epoxy the parts can float around when you don’t want them to, because the glue is too slippery.  A thin layer of Gorilla Glue is pretty tacky, so you don’t have to worry so much about the parts slipping out of place.  The core can be flipped over, and the other side can be attached.  After that, a long ruler is placed on top and the whole thing is weighted.  This stuff is supposed to set up in about 2 hours, and full cure is attained in 24 hours.  That’s a sand bag in the middle.  It holds the widest part of the sidewall down, where the ruler wasn’t wide enough to cover it.

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It’s tempting to jump right into cutting the bottom shape of the float now that the sides are stuck on, but it’s far more convenient to finish the top first, because it’s easy to place the floats on a flat surface and stack weights on top.  If I had cut the bottom first, the foam block would no longer be square.

The next part to be attached is the balsa top sheeting.  First I split a couple of 1/16 x 3 x 36 sheets in half.

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These strips are to be placed on either side of the plywood spine, as shown in the next photo.

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Once again, Gorilla Glue is spread very thin on one side, and the sheets are put into place beside the spine.  The surface of the 1/16 balsa sheeting is flush with the surface of the plywood spine, so the two floats can be stacked while curing.  First the bottom float is covered with a piece of Monokote backing plastic, then the second float is placed on top.  Two long rulers are placed side by side on top of the float to distribute the weight evenly, and then weights are placed on top.

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Now that the tops are all put together, it’s time to cut the hull with a hot wire.  The float sides are used as a cutting template.

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It looks a little bit rough, but it will work.  The main problem I had was the softness of the balsa sides.  The wire dug into the balsa a couple of times.  Fortunately these are floats and not wings.  If the shape gets a little bit messed up, it’s no big deal.

I was going to skin the hull with 1/16 ply, but I found a nice piece of very firm 3/32 x 4 x 36 balsa that didn’t look very good for cutting ribs for customers, so I figured I would use it for the main hull just in front of the step.  Medium balsa was used in the curved front of the hull, as well as the segment aft of the step.

I added balsa skin to the aft section before the front half.  Because the surface is a little bit lumpy I used a trick that I’ve used on foam floats before.  I applied Gorilla Glue to the foam, leaving about a quarter inch perimeter with no glue.  Then I put the skin in place  and glued it to the side wall with thin CA, holding the joint together firmly to assure a bond with no gaps.  CA glue dissolves foam, so you have to apply it sparingly to prevent it soaking through to the inside.

After the skin is glued around the edges the small vertical piece is added at the step to keep the Gorilla Glue from making the balsa bulge out.  The floats are left overnight with a sandbag on the tail and weights in the main section.  This looks just like every other time I used jars to weigh everything down, so let’s skip to the more interesting front half.

The long section is to be sheeted with hard balsa with the grain running lengthwise, and the curved segment is to be sheeted with medium balsa with the grain running crosswise to allow it to conform to the curve.  First I made a little piece of balsa for the curve.

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As you can see, the length of dowel #2 was miscalculated.  It was a bit too long and needed to be trimmed.  I did this with a big pair of wire cutters so I wouldn’t tear up the float in an attempt to sand the dowel or cut it off with a utility knife.  Next, the glue is applied to the foam. Notice the mark I made with a Sharpie to remind me of where the straight line turns into a curve.

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Next, the glue is spread out with an expired debit card.

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Never mind that yellow glue on the left.  That’s Titebond that seeped through the pores from the top of the float, and it’s been dry for days, so it can be ignored.  Now the skin is placed on the curve and the edges are glued with thin CA.

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The same process is repeated for the straight section.

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The flat balsa sheet is put into place and glued around the edges, including the butt joint between it and the curved skin.

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This could be considered finished, and it could just be left sitting until dry.  But Gorilla Glue expands as it cures, so you’d better weigh it down.  First the floats are placed side by side, and a sandbag is used to press the curved skin.

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Then the flat segment is given the usual treatment with jars of pickles.

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About the only thing left to add is a hard stern plate for mounting a water rudder.  I’m going to use 3 ply 1/8″ birch plywood.  Anything softer than that would probably not be able to hold screws if the rudder hits a floating obstacle.  The stern plate will be added the same way the rest of the wood was added.  I’m going to put a dab of Gorilla Glue on the foam, spread it thin, and secure the perimeter to the float skin with CA glue.

That about wraps it up.  All that’s left now is covering.