Rebating a Round or Curved Shape
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For my first major project I have an old wall clock that I am attempting to replace the cheap distressed and woodworm ridden case, with a hand built oak one. However, I will be using the original lead lined glass panel taken from the door and the concaved glass plate that covered the clock face; and here’s my problem.
Both the glass for the door and the face were set in recesses or rebates and whilst I have no trouble producing straight rebates I have no idea how to go about making them for round (the clock face glass) or arched door glass (think of the M in the McDonald’s logo) shapes.
I have attached a picture of the original piece of wood that shows the clock face glass rebate as an example of what I need to do.The originals were obviously done by machine and that is definitely the road I do not want to go down.
A possibility is making a curved rebate plane. The other possibility that I see is to carve it out with a chisel.
There are tools to do this: https://www.amazon.de/dp/B002CB5HH6/ref=asc_df_B002CB5HH641154923?smid=A3JWKAKR8XB7XF&tag=wbmchd_homeimprovement-21&linkCode=df0&creative=22494&creativeASIN=B002CB5HH6 But they are quite expensive, and for a clean cut, you need a perfectly round knife wall first… However, these tools can be used without a machine, so they are “legal” 😉
If you have a router plane, you could fix it to a board and screw that board to the center of the hole, sort of a compass router plane. Before starting, better make a similar device with a knife to create a knife wall.
Alternatively, you could boil strips of wood in water and fit them to the round. If one piece is too thick, try laminating thinner strips.
Apart from that, perhaps you can save the original board. A mix of saw dust and animal hide glue works wonders on worm-bitten surfaces.
Dieter
There are marking / cutting gauges on which the headstock is not flat, but is pointed so that the gauge can follow a contour. I wonder if you could cut the central opening and then use such a gauge to define the edge of the rebate. Use a gouge to deepen the knife wall from the marking gauge and remove the waste as for any rebate. Work your way down in this way. You may be able to make a variation on Paul’s poor man’s quirking tool to make your marking gauge or cobble up something just for this job. I’ll bet you can use a router plane to flatten the bottom. Deepening the knife wall with the gouge won’t give a perfect circle, i.e, it will look carved, but that won’t matter here, will it? And you may be able to get it to be quite good, really.
I think it will be really easy to make a single-use tool to serve as the marking gauge. You know, you may even be able to use a regular marking gauge….
Thanks for the suggestions guys. Having considered it some more, I think the circular one can be achieved relatively easily if not a bit fiddly.
A cutting gauge with the stem pinned so it can rotate in a circle will help with the initial cut and marking out, and I can then use Paul’s poor man’s marking gauge/beading tool once I cut the hole to run round the inside edge to mark the depth. Thankfully the rebate doesn’t have to be too deep so it shouldn’t take too long to remove the waste wood. I think if I’m very careful I can remove most with my hand router used at an angle with small blade and finish off the wall with a small chisel. The double arched one may be a bit more tricky though; especially as the two arches are quite tight.
Anyhow, I will not resort to using a power router. I’d rather change the design of the clock.
If you look on the inside of old clocks, the glass or clock face rebates are often polygons that don’t necessarily follow the curve. ( especially glass)
That might make your task easier.
I never thought of that Larry but now that you’ve mentioned it, that’s worth considering.
Thanks
Apologies if this is a duplicate post, I thought I already posted but I don’t see it..
Anyways, I think Hugo’s recommendation is probably the best, but in the interests of completeness I didn’t see this recommended:
https://www.woodcraft.com/products/circle-cutter-large?gclid=CKL2j56v89ICFYlrfgodT9oNDA
They can be used with braces, and at least two links I’ve found say they should only be used with braces, because of the acute need to keep the rpms so low; here’s one: https://www.toolexperts.com/gasket-and-circle-cutter-maker.html
There’s a long history of braces and circle cutters:
https://p1.liveauctioneers.com/301/53793/26013195_1_x.jpg?version=1397154459
Both the cutters you linked to Ed look like they could do the job and they’re not extortionately priced either. As for the last link, I just knew the guys from bygone days would have had something to do the job.
I’m not sure if this has been suggested, or relevant but…
If the piece doesn’t have to be made out of one piece of wood then you could easily make it with two.
The front/visible piece has the circle cut out of it. On the back of this piece, knife wall, chop out and hand router a square recess that is slightly larger than the main circle.
The second piece is a square piece that is the same size and will fit into the recess in the back of the first piece. Cut a smaller circle in this piece, glue them together and voila.
It may not look so good from the inside, but whether that is an insurmountable problem is up to you.if the execution is good it could even look better or you could make a feature out of it.
Just as a follow up… if you also need an arched rebate for the door, then the two piece approach would still be possible and quite easy – you just need a slightly smaller template with the same contours to cut out of the backing piece.
The outer template is the preexisting arch. The inner template for the backing piece you can be marked up using the outer piece and scribing around the inside with an appropriate offset.
It occurred to me that in my suggestion I may have got my rebate backwards – it’s not clear to me which is the front and back of the piece. In any case, it may still be possible to do a two sheet/piece construction technique.
Maybe if you did this in two pieces as mentioned, cut a hole of each size in each piece. That could be done very easily with a coping saw, then glue the two pieces together. This will have the added benefit of stabilizing the wood when you glue it up with the grain opposing. I have used the cutters shown at Woodcraft. They can be quite flimsy and if you are doing it by hand very hard to keep square. They scare me in a drill press! You also have a lot of force acting against you with the cutter arm sticking way out there acting as a lever.
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