Cutting/routing an irregular curve

Just trying to plan ahead (rather than behind as usual).

In the timber work of my house, there are two repeated motifs. One is three partly overlapping circles and the second is a shape a little like a comma (or a curved teardrop) on its side. The circles tend to go through the thickness of the wood but the commas are carved into the surface to a depth of about 1/4 inch. Since I shall have to replace some timbers with each motif in over the coming months (/ years!) it would be sensible to make up some jigs for the router so I can cut them reproducibly and regularly in the new wood.

The overlapping circles should be quite simple but the comma has me a little stumped: I seem to remember having a set of french curves when I were a lad about the same shape and it could easily be that the Victorian carpenters used something like that as a template. Naturally, according to Sod's law, none of the french curves I've found so far is the same, so I can't copy them. Since this motif never goes full depth (at least not in any place where I want to take it down) I can't really steal a bit from the building to make a jig.

I can't imagine ever getting a reasonable result either trying to draw the comma or, if I did, trying to cut a good template along a drawn line. I'm wondering if there's a way of using one of the originals in situ as a mould, then using the moulded piece as a template to make a jig. Has anyone ever com across/solved this one?

Reply to
GMM
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Could you use the same technique as brass rubbing to copy the shape?

Reply to
Mike Clarke

I had thought of that....and taking a photo....but even with the right

2-D shape I would have nothing to follow with a router so getting a template right would take a lot of trial and error, unless I can think of something that's flexible enough to bend and follow the curve, but rigid enough to run a guided cutter against....
Reply to
GMM

Stick a printed copy onto a board, and then cut out with a fretsaw/scroll saw to create a template?

Or, find a good clean example to copy, cover in a release agent and push modelling clay / plasticine into it and remove, giving you an "negative" model. Use that to make a fibreglass mould, and then cast new copies in either resin or plaster.

Reply to
John Rumm

What I would do is to take a photo, scale it to the right size then use image manipulation software to add a margin around it equal to the distance between the edge of the relevant cutter and the router guide bush. Then print it on paper, cut out the relevant part with a scalpel and use it and a fretsaw and rasps to make a template out of 6mm mdf.

I?m not sure I understand that. Isn?t it just a matter of pasting the paper picture to the template material and trimming it?

Reply to
Jon Fairbairn

I'm guessing your local sign maker could probably rout something out of plastic from a photo.

Reply to
stuart noble

How would you do that, using say gimp

Reply to
NT

Probably quite easy to put a border round whatever you've selected. Getting the selection accurate might take a while if the subject isn't clearly defined.

Reply to
stuart noble

Yes. Once you have got a path round the whatever, you can use the selection editor to paint along it with a given width in mm. You have to make sure that the resolution for the image is set correctly for this to make sense.

True. You can use various tricks both when taking the picture and after to get a good contrast between the figure and ground and then select by colour, but you?ll probably have to tweak it a bit to get it accurate.

Reply to
Jon Fairbairn

Select / Grow

or Select / Border

But when I had a woodworker in to carve some finials for me I showed him my Bosch PMF (Fein Multimaster) and asked him if it would help - He used it for most of the work (and saw, pencils, files)

[g]
Reply to
george [dicegeorge]

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That's sort of what I've been thinking of: Mould the shape then cut around it with a guided cutter, on the basis that the same size guided cutter could then be used against the template formed. Just a matter of making a sufficiently rigid impression I guess.

Reply to
GMM

I couldn't agree more. Unfortunately, by the time I serve a proper carpenter's apprenticeship to do a decent job of it, the house will have fallen down!

Reply to
GMM

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