Getting consistent parallel edges on curved piece

[Charles P. Wright]

I want to make a bed frame for my niece and my sister would like to have something other than just a rectangular headboard and foot board. I'm thinking something fairly simple, but with a curve on top of the headboard and footboard.

To make a curved piece like that at least for one of the dimensions; my initial thought would be to draw the curve on some plywood and make a template for the router. Then with the template, glue up some 5/4 stock with waste to match the rough curve, copy the curve onto the glued up 5/4 stock with a pencil, bring it to the bandsaw, and then finish up with the router.

But that would only do the outside, and I also need to do the inside. This is where I'm getting stuck on process. I can use the template and draw the line; but I'm worried about getting an edge that is parallel for final machining. Is there some "trick" to it, like making an inverse template (if so how), or should I just cut and sand carefully and it will probably work out

[Mel Fulks]

Since you don't need multiple pieces you could bandsaw carefully ,then use a piece of the removed scrap as a sanding block with coarse paper to fair and smooth the curve. To make more than one or two pieces I would use a plywood template on shaper with a bearing and cutter head.

[Peter Christensen]

If the curve is a section of a circle you can do the whole thing with a router and a trammel. Glue up the stock and then use a straight bit in the router to cut the inner/outer arc a little with each pass until through. You just adjust the trammel pivot distance to get the width of the piece you’re making. Don’t forget to allow for the bit diameter from inside to outside.

[Mike Cutler]

Charles

You can do all of the math and arrive at different radii values for each chord of those curve, or based on that example, make a disc with a radius of the thickness of that headboard, and footboard, outside radius and copy the line.
The center of the disc will have a hole for a pencil, or scribe and will transmit a new radius line for the inside. ( It would work either way actually.) That distance can never be anything other than the dimension you establish.It will also have no choice but establish a new line for the parts that you need to have parallel.

Edit
I do a fair amount of this type of work, oddly enough, and if it were me I would do the math and draw it out on MDF to make a full sized template. I would back up the template lines with the disc I referred to as a check.
A full sized template will take you some time, but once you're done you can now put the pieces through a router table, or shaper, and have as perfect a piece as possible. It's an extra step, time consuming also, but you will know before any real wood is ever cut that it will work.

[Mel Fulks]

And Mike's suggestion is especially good for making real ellipse pieces with consistant accurate widths.

[Doug Dawson]

I want to make a bed frame for my niece and my sister would like to have something other than just a rectangular headboard and foot board. I'm thinking something fairly simple, but with a curve on top of the headboard and footboard.

To make a curved piece like that at least for one of the dimensions; my initial thought would be to draw the curve on some plywood and make a template for the router. Then with the template, glue up some 5/4 stock with waste to match the rough curve, copy the curve onto the glued up 5/4 stock with a pencil, bring it to the bandsaw, and then finish up with the router.

But that would only do the outside, and I also need to do the inside. This is where I'm getting stuck on process. I can use the template and draw the line; but I'm worried about getting an edge that is parallel for final machining. Is there some "trick" to it, like making an inverse template (if so how), or should I just cut and sand carefully and it will probably work out

Cutting gauge. The TiteMark would work well for this. (The cheaper copies are just that.) Rough it on the bandsaw and then file/shave it to tune. Patterns should symmetrical, i.e. draw one and then mirror it to the other.

Doug

[John TenEyck]

I'd make 1/4" Masonite or MDF templates, rough the stock on the bandsaw, and then trim to final shape with a handheld router using those templates. Make the templates any way you like; if you hose up you can always make another.

John

[Brian Tymchak]

If the curve is a section of a circle you can do the whole thing with a router and a trammel. Glue up the stock and then use a straight bit in the router to cut the inner/outer arc a little with each pass until through. You just adjust the trammel pivot distance to get the width of the piece you’re making. Don’t forget to allow for the bit diameter from inside to outside.

+1. This is how I would do it. Takes a bit of workspace, but you have finished edges right off the router.

[Bruce Wrenn]

If the curve is a section of a circle you can do the whole thing with a router and a trammel. Glue up the stock and then use a straight bit in the router to cut the inner/outer arc a little with each pass until through. You just adjust the trammel pivot distance to get the width of the piece you’re making. Don’t forget to allow for the bit diameter from inside to outside.

DON'T change trammel pivot point. Instead change location of router in trammel. Simplest way to do this is to use a guide bushing in router, and drill the correctly spaced holes in trammel. Route one edge, and then move router to other hole and do second edge. The largest trammel I have ever used was over 50' to do curved front on a pulpit for local church. Used threaded rod and connector nuts for trammel.

[Peter Christensen]

Bruce I said change the distance, not the location of the pivot point. We are saying the same thing. It doesn’t mater how the radius is shortened, whether by a siries of holes to pivot on or a method of shortening the trammel, the result will be the same if the pivot point doesn’t change. Change the pivot location and the routed part won’t be parallel.

[Greg Hines, MD]

On the subject of trammel arms, when I make them, I do not mount the router to the trammel, but instead drill an oversized hole at the end of it, so that you can use a guide bushing to allow the router to pivot, and keep your registration to the arc consistent to give a more consistent cut.

Doc