Arched top door questions?

[Esteban]

I've built side frames for my teardrop with one by (3/4") lumber that'll be skinned inside and outside with plywood. The doors will have arched tops. We cut the top arches with a jig saw and they need smoothing to a more precise curve. I'm pondering cutting a strip of plywood (as sort of a a swing arm) long enough to go from a pin near the center of the door bottom that'd, somehow, be attached to the router so I can finish shaping and smoothing the curve with a straight bit. The router base would rest on the flat wood surface above the arch. Could this work, or is there an easier way?


The door dimensions are to be 31" wide, 36" high on each side, and about 39" tall in the top middle o the arch.

[BrwBier]

You could use a belt sander and get something you are not completely happy with like mine. Or your way sounds like what I wish I had thought of. I'd say go for it, should work out good.
Brwbier

[tk]

Steve, a router compass works great. I usually make it out of 1/4 or 3/8 inch plywood. Cut a piece of appropriate length, drill a one inch diameter hole for the router bit, a smaller hole for a pivot pin, and countersink holes for the mounting screws. Remove the router base faceplate, attach the compass, insert a straight-cutting bit, pin the compass to the piece you wish to cut, and go like hell. (Actually, multiple passes at a slow and steady pace works better.) I have made them up to 84" long but there's really no limit other than what space you have available.

Best,
Tom

[madjack]

Steve, a router compass works great. I usually make it out of 1/4 or 3/8 inch plywood. Cut a piece of appropriate length, drill a one inch diameter hole for the router bit, a smaller hole for a pivot pin, and countersink holes for the mounting screws. Remove the router base faceplate, attach the compass, insert a straight-cutting bit, pin the compass to the piece you wish to cut, and go like hell. (Actually, multiple passes at a slow and steady pace works better.) I have made them up to 84" long but there's really no limit other than what space you have available.

Best,
Tom

...yep that is the way to doit...we have several different lengths made up in the shop...if you want an accurate and relatively easy way to swing an arc, that is the to doit(echoechoecho)............
madjack

[Esteban]

Steve, a router compass works great. I usually make it out of 1/4 or 3/8 inch plywood. Cut a piece of appropriate length, drill a one inch diameter hole for the router bit, a smaller hole for a pivot pin, and countersink holes for the mounting screws. Remove the router base faceplate, attach the compass, insert a straight-cutting bit, pin the compass to the piece you wish to cut, and go like hell. (Actually, multiple passes at a slow and steady pace works better.) I have made them up to 84" long but there's really no limit other than what space you have available.

Tom, thank you very much for fleshing out more detail for a router compass. MJ, thanks for your endorsement of the idea, too. I'm a newbie using a router. My "pondering" idea sensed that there must be a way to do it. I'll make a compass and practice on some scrap to get it done right. My side frames are nearly done. Getting a nice even curve to the frame above the door is the only part left I have some trepidation about. You've calmed it.


Googled router compass for examples. Found a few:

Big circles are tough to cut, especially when they need to be perfectly round. Make a compass arm for your router from 1/4-in. plywood or hardboard. Remove your router’s plastic base and drill corresponding holes in your compass arm. Attach the arm to your router and install a straight-cutting 1/2-in. carbide bit. Pin the compass arm to the plywood with a 6d nail. The top of your finished circle will face down. Start the cut with the bit depth set at 1/4 in. and increase the depth of cut about 5/16 in. for each pass. When you start, gently ease the router down into the workpiece and push counterclockwise. Reset the depth for each cut and be sure to support the cutout on each side with your sawhorses as you make the final “through” cut. A firm grip is necessary to keep the router steady on the last cut.

Links to make, or buy, a router compass (the first link shows how to make a adjustable marking compass):
instructions for a hand made compass Good for marking a pattern.
Homemade router compass jig Easy instructions to make a router compass for shaping a curved door top.
Lewin router compass A commercial source for a router compass.
Rockler router compass Another commercial source for a router compass.

[madjack]

Steve, we usually use masonite for the smaller compasses(upto a couple of feet or so)...by measuring, you can drill pin hole at several places as needed...luan makes a pretty good one as well...praticepracticepractice.......
madjack

[Esteban]

Thanks again MadJack. I have plenty of luan cut offs to make a router compass. We made a pencil compass to mark the door top curve we cut out. So the compass length is pretty much set. Will make one to fit the router tomorrow. Joy, joy, joy!

[Gene C]

Try these
I run a lumber yard and this could help

www.arch-it-co.com

[Esteban]

I will post pictures of the homemade router compass I made and used. It was easy to make from scrap 1/4" plywood and it worked very well. First we made a pencil compass with a long stick to mark the curve of the arch. The second step was to cut the arch out with a jig saw. The third step used the router compass and a straight bit to accurately cut and smooth the arch in the wall frame above the door opening.

If I were to do it over I'd cut and shape the piece of wood we made the arch from before gluing and installing it in the wall frame. Then we could have made it a little wide and cut it down to the correct width to install it in the wall frame. That would have avoided making the little dimples where the router bit cut a little bit too far into the straight sides of the door frame I'll need to fill with a mixture of epoxy and sawdust.