Making Arcs

[jussi]

I'm thinking about making something similar to this martial art display for my nephew. How would you suggest making the top? I was thinking of making it in 3 pieces (3 arches). First by making templates out of mdf and then using a flush trim bit to follow the templates. But considering the thickest piece will be about 2", that doesn't sound feasible. I could just use the templates to draw a guide on the lumber and just cut it with the bs, but how can I make sure the radius of the arcs match up to one another. So that when I put them on top of each other there won't be a gap. This is probably something simple and I'm just not getting it.

[Uncle Cracker]

The top two layers seem to be of uniform thickness, so I think you could simply free-form the curve for the bottom piece first, and then bend and glue-up the top two pieces to conform to the bottom piece. Depending on the flex of the wood, you maybe will just need a glue-lam, or you might need to steam-bend it if it's more rigid.

[radhak]

How about cutting the top shape (3-rows) out of a single piece of wood and cutting bead-lines to simulate the look of 3 different pieces?

And/or you could use an appropriate sized spokeshave to get the right individual shapes and thickness.

[Norm in Fujino]

The overall design is that of a Japanese Shinto torii, and it looks like it was based on what's called ryobu Shinto, though it's not entirely accurate. If you just want some more ideas for torii designs, try using Google's image search function and looking for *torii*. You should keep in mind that not all torii have curved tops like that, and a straight-top is equally possible.

[jussi]

Thanks for all the suggestions. I'll probably be using Mahagony since that's what I have.

UC - I'll probably want the top 2 pieces to be around 5/8 which would be too thick to bend.

radhak - That would probably work if I had a spokeshave or know how to use one

Norm - Thanks for the architectural lesson. Making the pieces straight is something I hadn't thought of and I think would be much easier. I think I'm leaning in doing it that way.

[crokett]

I think the arched top looks much better than a straight top would. I also see in the pic that the bottom layer of the top is only curved on its top and the bottom is straight. I would make your MDF template, cut that piece first and use it as your form for the other two. I would also do this as a steam bend. I think it will look much better than a glue-lam and the radius is fairly gentle. If you can get the radius close with the steam bend, then glue+clamps or dare I say screws would pull it the rest of the way.

[Uncle Cracker]

UC - I'll probably want the top 2 pieces to be around 5/8 which would be too thick to bend.

Steam 'em...

[jussi]

Steam 'em...

I've never done that before. What's the process? Do you need a specific machine?

[LCHIEN]

I've never done that before. What's the process? Do you need a specific machine?

it's serious business
The ideal method is to make a heat insulated chamber long enough to hold your work piece. And pass steam through it which is of course 212F which will soften the wood and allow it to take a set at the new curve when cooled and dried. Not something you can go and buy at Rockler or woodcraft.

[Uncle Cracker]

It's easy... I use a piece of 4" heavy-wall PVC pipe, partially open on one end, tilted down to the open end to drain condensate, and my Shark Steamer hooked up to the closed end. No high pressure to deal with, no muss, no fuss, no worries. If you go to YouTube and search "steam bending wood", you will see how many others do it (such as alternate types of piping materials). Google that same phrase for even more information. It may be too elaborate a setup for you to do one small project, but it may open up possibilities for other stuff.

One caveat: It's a job that needs to be done on a patio or in a ventilated garage, so you are not trapping all that moisture inside an area where rust or mildew could become a problem...

[jussi]

Something like this? Anyone know what that black fitting is that he uses? I wonder why he didn't just His curve is much sharper than mine. I really like the jig he uses to make the form. Looks alot easier than trying to clamp everything.

http://www.youtube.com/watch?v=OOIJXDZXB3g

I probably won't have time to do this since I would need to order a steamer and build the little jig. Yes, I'm a severe procrastinator. But it would be nice for future projects. In doing this, do you do the glue up while the piece is still wet? Or do you just clamp it in place after steaming, let it dry to that shape, and then glue?

[JSUPreston]

Cut MDF templates on the BS, then use a router with a bearing bit. Seems to be the easiest to me.

[phrog]

Making arcs - I thought Noah wrote the book on that years ago. But, then, I never was a good speller.