Instrument case, continued
Aug. 14th, 2011 08:52 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
catsittingstillI'm making an instrument case for Pearl, since I can't find an octave mandolin case anywhere. It seems to me that if the wood strip method can make canoe hulls, it should be adaptable to other shapes.
So I glued up strips to make a flat top and bottom; that was relatively easy. Next I needed strips to make the sides. The curves involved are much too tight to bend strips around them, so I decided to run the strips the short way, and manage the bend by the way they fitted into each other. Like this:
Underneath, you can see the ends of the strips I glued up to make the flat bottom. A curved bottom would be stronger, but I couldn't figure out how to do one in the little space I had; strips on a canoe normally curve over seven feet or so, and the longest dimension on this instrument case is three. So flat it is.
You can also see there is a little gap; the distance around the form was not an integral multiple of the bead-to-cove distance on the strip. This is no particular surprise; there are something like a hundred strips going around the form so if I was off by even a thousanth of an inch in what I thought the bead-to-cove distance was, I'd be off by a tenth of an inch by the time I glued the strips all the way around. I handled this the way I would handle the whiskey plank on a canoe, except it was much easier because it was straight and only 5 inches long. I trimmed back the bead and cove on each side of the gap and jammed a piece of white pine in there with plenty of glue. The saw and the sander made everything smooth on the outside. The inside will require a little dookie schmutz but it will all be covered up by the padding anyway. I just need to get it smooth enough that I don't have too much trouble with bubbles.
To make the form I started with 1 x 6. I could have used plywood, but I anticipated doing a lot of the smoothing of the edge with hand tools, and plywood is not nice to work with and is hard on the tool edges. I went and got spruce 1 x 6 s and glued them together, edge to edge, to be wide enough for the wide part of the form. You can see the joins in this photo.
Basically once I had 1 x spruce that was wide enough, I traced out the pattern for the inside of the instrument case onto two separate pieces of it. I made the pattern in the first place by tracing around the instrument with a dollop added by eye to account for padding and then a fair amount of re-tracing, and flipping upside down to trace the right side from the left side, and so on to get it smooth looking. The bandsaw blade broke when I tried to saw it out--probably because the 1 x 6 plank was big enough to be unwieldy--so I sawed well away from the line with my rather unreliable jigsaw, and then used the Shopsmith disk sander to sand as close to the line as I dared. The inside curves I had to handle with the spokeshave (yay for the spokeshave--also a Christmas present!). I did try to check with the try square that I spokeshaved and planed the edges at a 90 degree angle, though I suppose if I had undercut a bit from the line that wouldn't have been a problem. I wasn't entirely successful there, but from the results I'm guessing I was close enough.
When I had both pieces cut out as nicely as I could, I cut three pieces of the leftover 1 x 1 1/2 inch true from the doors to be exactly 3 inches long, and as square as I could manage. I haggled out 3 little pieces of the 1 x 6 (in reality only 3/4 inch thick) to act as feet, then balanced the top shape on the pillars above the bottom shape. I used the try square and the combination square on each side of the "layer cake" to get the 2 layers exactly aligned vertically (or as exactly as I could manage.) Then I fastened the 1 x 1 1/2 inch "pillars" from each side with screws.
And now I have planked all the way around the form, using hot glue to hold the strips to the form while the carpenter's glue dries. Getting the form out of the strips will be a bit of a trick, but I have a clever plan (I think.)
I will flip the form over and lay it on the "bottom" flat side I have already made, draw around it, and rough cut the bottom side to that line. I will epoxy the strips, still hotglued to the form, to the bottom side, making an open box. I will fair and fiberglass the outside of the box. I can still get the form out by whacking it deeper into the box to break the hot glue.
However before I do that, I will tape around the top edge of the box, and screw the top flat side to the feet of the form, which are level with the top of the box. I will draw around the form-plus-strips, take the screws loose, and remove the top so I can rough cut to the line. I will screw the top back on, sand and spokeshave the edges of the top to match the side strips exactly, then make the lip by gluing 1 inch pieces of plank to each other and to the top, with the tape to make sure I don't permanently glue the lip to the side of the box. I will hotglue the 1 inch pieces to the taped part of the sides to hold them in place while the glue dries. Then I will remove the three screws holding the top to the feet of the form, drill out the screw holes and fill them with plugs, and fair and fiberglass the top, including the lip.
Now comes the tricky part. Hotglue's bond can be broken by whacking it sharply in line with the plane of the join. So I will whack the lid off as carefully as I can, by striking the lip upward (actually probably I will use a stick of 1 x 1 1/2 true, with a profile cut to match the lip as closely as possible, to discourage mushrooming.) Once I have the lid off, I will whack the form deeper into the box (that part should be fairly easy) then once it is loose in the box, grab it by its feet to pull it out. Hopefully the fiberglassed joints will be strong enough to take this whacking and booming; we will see. It worked with the canoes.
At this point I should have a fairly standard problem, removing the glue and hot glue from the insides, and fairing and fiberglassing the insides (it doesn't have to be pretty, just strong). Plus the usual headaches of latches, hinges (I wonder if a 1 inch lip, which will be 3/4 inch inside, will be too deep to let the hinges do their job) handle and feet.
I figure it will take a month at least, but I will be happy to have a case that doesn't chew on my fingers, and that will be uniquely mine.
So I glued up strips to make a flat top and bottom; that was relatively easy. Next I needed strips to make the sides. The curves involved are much too tight to bend strips around them, so I decided to run the strips the short way, and manage the bend by the way they fitted into each other. Like this:
Underneath, you can see the ends of the strips I glued up to make the flat bottom. A curved bottom would be stronger, but I couldn't figure out how to do one in the little space I had; strips on a canoe normally curve over seven feet or so, and the longest dimension on this instrument case is three. So flat it is.
You can also see there is a little gap; the distance around the form was not an integral multiple of the bead-to-cove distance on the strip. This is no particular surprise; there are something like a hundred strips going around the form so if I was off by even a thousanth of an inch in what I thought the bead-to-cove distance was, I'd be off by a tenth of an inch by the time I glued the strips all the way around. I handled this the way I would handle the whiskey plank on a canoe, except it was much easier because it was straight and only 5 inches long. I trimmed back the bead and cove on each side of the gap and jammed a piece of white pine in there with plenty of glue. The saw and the sander made everything smooth on the outside. The inside will require a little dookie schmutz but it will all be covered up by the padding anyway. I just need to get it smooth enough that I don't have too much trouble with bubbles.
To make the form I started with 1 x 6. I could have used plywood, but I anticipated doing a lot of the smoothing of the edge with hand tools, and plywood is not nice to work with and is hard on the tool edges. I went and got spruce 1 x 6 s and glued them together, edge to edge, to be wide enough for the wide part of the form. You can see the joins in this photo.
Basically once I had 1 x spruce that was wide enough, I traced out the pattern for the inside of the instrument case onto two separate pieces of it. I made the pattern in the first place by tracing around the instrument with a dollop added by eye to account for padding and then a fair amount of re-tracing, and flipping upside down to trace the right side from the left side, and so on to get it smooth looking. The bandsaw blade broke when I tried to saw it out--probably because the 1 x 6 plank was big enough to be unwieldy--so I sawed well away from the line with my rather unreliable jigsaw, and then used the Shopsmith disk sander to sand as close to the line as I dared. The inside curves I had to handle with the spokeshave (yay for the spokeshave--also a Christmas present!). I did try to check with the try square that I spokeshaved and planed the edges at a 90 degree angle, though I suppose if I had undercut a bit from the line that wouldn't have been a problem. I wasn't entirely successful there, but from the results I'm guessing I was close enough.
When I had both pieces cut out as nicely as I could, I cut three pieces of the leftover 1 x 1 1/2 inch true from the doors to be exactly 3 inches long, and as square as I could manage. I haggled out 3 little pieces of the 1 x 6 (in reality only 3/4 inch thick) to act as feet, then balanced the top shape on the pillars above the bottom shape. I used the try square and the combination square on each side of the "layer cake" to get the 2 layers exactly aligned vertically (or as exactly as I could manage.) Then I fastened the 1 x 1 1/2 inch "pillars" from each side with screws.
And now I have planked all the way around the form, using hot glue to hold the strips to the form while the carpenter's glue dries. Getting the form out of the strips will be a bit of a trick, but I have a clever plan (I think.)
I will flip the form over and lay it on the "bottom" flat side I have already made, draw around it, and rough cut the bottom side to that line. I will epoxy the strips, still hotglued to the form, to the bottom side, making an open box. I will fair and fiberglass the outside of the box. I can still get the form out by whacking it deeper into the box to break the hot glue.
However before I do that, I will tape around the top edge of the box, and screw the top flat side to the feet of the form, which are level with the top of the box. I will draw around the form-plus-strips, take the screws loose, and remove the top so I can rough cut to the line. I will screw the top back on, sand and spokeshave the edges of the top to match the side strips exactly, then make the lip by gluing 1 inch pieces of plank to each other and to the top, with the tape to make sure I don't permanently glue the lip to the side of the box. I will hotglue the 1 inch pieces to the taped part of the sides to hold them in place while the glue dries. Then I will remove the three screws holding the top to the feet of the form, drill out the screw holes and fill them with plugs, and fair and fiberglass the top, including the lip.
Now comes the tricky part. Hotglue's bond can be broken by whacking it sharply in line with the plane of the join. So I will whack the lid off as carefully as I can, by striking the lip upward (actually probably I will use a stick of 1 x 1 1/2 true, with a profile cut to match the lip as closely as possible, to discourage mushrooming.) Once I have the lid off, I will whack the form deeper into the box (that part should be fairly easy) then once it is loose in the box, grab it by its feet to pull it out. Hopefully the fiberglassed joints will be strong enough to take this whacking and booming; we will see. It worked with the canoes.
At this point I should have a fairly standard problem, removing the glue and hot glue from the insides, and fairing and fiberglassing the insides (it doesn't have to be pretty, just strong). Plus the usual headaches of latches, hinges (I wonder if a 1 inch lip, which will be 3/4 inch inside, will be too deep to let the hinges do their job) handle and feet.
I figure it will take a month at least, but I will be happy to have a case that doesn't chew on my fingers, and that will be uniquely mine.
