Imagine a yacht's coachroof with a shallow curved companionway hatch cover forward of the sprayhood. If I wanted to shape a piece of wood to sit snugly over and across that curve, is there a technique for transferring the curve's shape onto a block of wood prior to cutting and shaping?
Technique for transferring a curve.
- Thread starter jonjo
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sarabande
Well-Known Member
sailorman
Well-Known Member
a pencil springs to mind 
make a template from card or hardboard
make a template from card or hardboard
prv
Well-Known Member
Tick-sticks as described above are good for some things, but for this purpose you may be better off with an offset-block.
Lay your piece of wood in position. It needs to be in the right place athwartships and fore-and-aft; obviously without the curve cut into the bottom it will sit higher than the final position.
Now take a block of wood whose thickness is about the same as the gap at either end of the wood. Lay the block on the deck with one side against the wood. Lay a pencil on top of the block, with its tip touching the wood. Now hold pencil and block tightly together, and slide them up and over the deck, drawing a line on the wood as they go. This line will exactly mirror the curve of the deck.
Pete
Lay your piece of wood in position. It needs to be in the right place athwartships and fore-and-aft; obviously without the curve cut into the bottom it will sit higher than the final position.
Now take a block of wood whose thickness is about the same as the gap at either end of the wood. Lay the block on the deck with one side against the wood. Lay a pencil on top of the block, with its tip touching the wood. Now hold pencil and block tightly together, and slide them up and over the deck, drawing a line on the wood as they go. This line will exactly mirror the curve of the deck.
Pete
sarabande
Well-Known Member
like that, simpler than sticks.
knuterikt
Well-Known Member
The same technique can be used with cardboard or any other material suited for a template.
Cap'n Creosote
Well-Known Member
I'm afraid it won't. It will describe a curve of a greater radius, by the width of the block.
Imagine you were using this method to mark out the curve including an upstand like a hatch. The width of the hatch cut out would be far too wide, by double the offset.
The correct way of doing this, is to mark the lines as you have described onto a different board, cardboard or ply. Take the cardboard or ply to the job, and transfer the lines back using the same offset. This will give you the correct shape.
Hmm yes I see your general point but the section of deck in question has a shallow curve perhaps a drop of 2" each side over a 30" length. As I pictured prv's suggestion I visualized the pen and marker block being kept vertical. I will use some plastic cardboard to transfer the shape before committing to cutting the real solid bit. An error of 2mm will be ok because a beadline of a hard silicone will seal the joint between the object on top and the deck antislip pattern.
prv
Well-Known Member
Woodlouse
Well-Known Member
Instead of a pencil and a block I find it easier to use a pair of compasses, taking care to keep them vertical when scribing.
fisherman
Well-Known Member
if you scribe with the pencil vertically above the point of contact it will be correct, best use something pointed rather than a block. Thin batten with a point cut and hole for the pencil is good. (All right, 'vertical' poor choice, but at 90 deg to the chord joining the ends of the arc.)
nigelmercier
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My method of doing this seems to work:
Measure the gap at either end. Mark a hole for the pencil at a little more than this distance from the end of a piece of wood, about 30cm long. Round the pencil end so it is the same radius to the centre of the pencil, drill the pencil hole and insert. Scribe the line keeping the wood vertical.
lw395
Well-Known Member
Spile the template as others have posted, onto a sheet of hardboard.
Lay roll of 40 grit paper across deck, rub template on paper for final fit.
Lay roll of 40 grit paper across deck, rub template on paper for final fit.
NealB
Well-Known Member
Get a bit of scrap wood, at least as wide as the shape you want to reproduce, and temporarily fix it in place across the deck.
Now cut a few other bits of scrap wood into V shaped pointers, long enough to reach from the fixed piece to the deck.
Position the pointers so they touch the deck, and use a glue gun to stick the pointers to the fixed bit.
Remove the fixed bit, with attached pointers.
You can now transfer the shape.
Easy....even I've done this successfully!
Now cut a few other bits of scrap wood into V shaped pointers, long enough to reach from the fixed piece to the deck.
Position the pointers so they touch the deck, and use a glue gun to stick the pointers to the fixed bit.
Remove the fixed bit, with attached pointers.
You can now transfer the shape.
Easy....even I've done this successfully!
