Right tool for curved cupboard back?

[Bruce Collins]

I am building a corner cupboard with solid wood vertical strips about 3" wide for the back. The back is curved with a radius of about 16" and needs to fit flush to the rear of the curved display shelves. Thus the boards need to have a uniform concave profile over there 4' length. What is the best way to do this? The obvious way would be a molding machine (too expensive) or making a cove on the table saw but the radius would be too small. Is a round spokeshave the way to go? The only problem I see with this is it may be hard to keep it uniform (at least for a power tool kind of guy).

Any thoughts?

Thanks
Bruce

[Bob McGovern]

A scraper ground to the right curvature could do it. Lots of elbow work, tho. Could rough it with an angle grinder or dado stack, finish up with scraper or spokeshave or stepped grits (60-150) on a formed sanding block.

For power tools, you could mount a router on a base with two 16"r rockers, somewhat like a rocking horse turned perpendicular to your slats. Insert a cove bit (shallowest cove you can find < 16"r) and run the router down a couple parallel rails with the stock clamped between them. Rock the router, run it back. Repeat a number of passes, then clean up any ridges with sandpaper. Should be repeatable and fairly quick, once you knock together the sled & track.

Course, if your time is worth more than mine, your local millwork shop could probably custom grind & mount knives for about $150. I finally stopped making my ogee crown by hand tools (phew!) and had my lumber supplier grind knives off a sample. Paid for itself in one job.

[Ben Grunow]

Sounds like a job for the belt sander and some finer grit paper so you dont get into too much trouble too fast. Keep it moving.

Otherwise I think I remember someone using a hand plane with the iron ground back on the corners to make a slightly concave cut. Probably less chance to ruin the glue up but, of course, more work.

The plane post was not too old but I cant remember.

Ben

[Andrew Williams]

If I were doing this I would try to cooper the 3" wide pieces first, then use an inshave on the inside, plane on the outside. You could also have a curved-sole plane made.

[Jamie Buxton]

The Neanderthal way is to make a plane with a round bottom. Ron Hock sells blades for round-bottom Krenov-style planes.

The power-tool way is to use sanding discs on a 4" right-angle grinder. If you hold the sanding disc flat to a surface, it makes a cut with a very large radius. If you hold it at 90 degrees to the surface, it cuts a 2" radius. If you hold it in between, it cuts a radius somewhere between 2" and "very large". It turns out that it isn't very difficult to control just with a good eyeball. I've done the concave faces of coopered doors this way, and it works pretty well.

[Mark Singer]

Here are some of my techniques

http://www.sawmillcreek.org/showthread.php?t=14202&highlight=coopered

http://www.sawmillcreek.org/showthread.php?t=14547&highlight=coopered

[Bruce Collins]

Lots of good ideas here. Most involve buying a new tool (oh darn!) except for the router sled. I was not familiar with the Hock plane / blades so I went to his web site -they have some great online video infomercials. I think I will try roughing it out with a dado blade which will give me the proper depth at a couple of places and then grind the rest down.

Thanks for the suggestions! :)

[Quinn McCarthy]

I wonder if you could grind the knives for a power plane radiused? Once you had a coopered black you could finish it off with the power plane.

Just a thought.

Quinn