Making a convex template that matches a concave template

[JJ]

I want to build 3 doors for an audio/video equipment cabinet. The doors will have 5 vertical pieces of varying widths and will have a horizontal rail across the bottom and a curved rail across the top. The doors are about 18 inches wide, and the radius of the curve at the top is about 264 inches. I need to make the convex ends of the tops the vertical pieces match the concave curve of the lower side of the top rail. I would like to make templates to use to guide a router to make the final curves.

I have made many curved templates by laying out a pencil line for the arc, bandsawing close to the line, then sanding essentially "to the line". As long as the curve appears smooth, it doesn't matter if I deviate slightly from the line. However, now I need to make 2 templates that match exactly the same line, one from the convex side, and one from the concave side. I doubt I have the skill (or the patience) to sand exactly to the same line twice.

I'm sure this problem has been handled before, so I invite your suggestions.

[Frank Ketchum]

You could produce the curve once the way you suggest and then use it for a router guide to rout through an underlying piece. Then you would have a copy of the one you made and on the waste side, you would have the other one. They would not be identical, the radius would be off by the diameter of the router bit you used, but this might be close enough.

Frank

[Bernard Randall]

Unless you intend to somehow butt the panel to the rail and stiles, not practical if it is wood as opposed to ply due to shrinkage, you are talking a normal arched door in which case the panel fits in a rebate that is routed into frame. (Do a Google search on 'Raised Arch Panel Doors). Cheap doors just use flat plywood for the panel but better class work used a raised panel. In either case hairline accuracy in matching to the top curved stile is no that important.

Before I made my CNC machine I used to lay out the curve on a piece of ply so that both the stile and panel templates came off the one cut and then smoothed out as necessary.

Bernard R

[John Crea]

Draw curve on piece of MDF, cut out TO THE LINE on bandsaw, one piece will be concave, the other a convex exact match

Go slow, easy on the bandsaw with a good, sharp blade and the templates will need little sanding

John

[Routerman P. Warner]

Did a few pages on this topic in my "The Router Book", might be in your library. Essentially you make a master of the intended net design, lay that on some templet material and cut a + & - templet (the working templets)from the master on to the templet material. Discard the master and use the working templets on the work. Cutter diameters and bearings can be selected for an exact match.

(Routers)

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[Sir Edgar]

JJ wrote: Group: rec.woodworking Date: Fri, Mar 5, 2004, 11:33pm From: [e-mail] (JJ) I want to build 3 doors for an audio/video equipment cabinet. The doors will have 5 vertical pieces of varying widths and will have a horizontal rail across the bottom and a curved rail across the top. The doors are about 18 inches wide, and the radius of the curve at the top is about

264 inches. I need to make the convex ends of the tops the vertical pieces match the concave curve of the lower side of the top rail. I would like to make templates to use to guide a router to make the final curves.

****************************************************** My humble suggestion is to use the "pin and hole method" to make the arcs. Use a flush cutting straight router bit with a bearing. Rout first template. Move pin a distance of 1/2 the diameter of the bit. Rout second template.

Peace ~ Sir Edgar =F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8= =F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8=F8