Need advice on making a large radius concave surface

[Joseph Hadley]

Hello all,

I am making a headboard with a curved surface (profile shown in the attached JPG). I've already planed the convex surface, and have hogged out the concave part with a series of dado cuts, but need advice on getting the concave surface smooth and true.

The radius of the concave surface is about 32", and this will need to be cut the full length of the headboard, which is roughly 80". I've considered a scrub plane, but the radius of the blade is 3" and I'm not sure this is the best way to get it close enough for sanding and scraping. Plus, there is a lot of figure in the wood, and a scrub plane may tear out too much.

Any advice you may have is welcome.

Thanks in advance,

Joe

[Ken Garlock]

Hi Joseph.

In one program on David Marks "Wood Works," David did what you want to do only his was only a 12" diameter. Take a look at the program on DIYNetwork.com (http://www.diynetwork.com/diy/ww_tables/article/0,2049,DIY_14446_3877250,00.html).

[Joseph Hadley]

Hi Ken, thanks for the link. I've used that technique before and it is good, although that radius is too tight for what I'm doing. I did a search using "convex sole plane" on this site and came up with a good link
http://www.sawmillcreek.org/showthre...opered+cabinet (http://www.sawmillcreek.org/showthread.php?t=14045&highlight=coopered+cabinet),
(many thanks to Mark Singer) which shows how to modify a wooden smoothing plane to whatever radius you want. This is in concert with a reference I found to classic boat building where you have a need to shape a convex hull...so. I'm off to find a wooden smoothing plane!

best,

Joe

[David Keller NC]

If you're good with hand tools, what you're describing would be ideally worked with about a #20 or #22 round plane. Not sure if you want to go that far, but large radius hollows and rounds are extremely common at flea markets (the little ones are hard to find). These planes were made with a lot of different blade pitches - from 45 degrees up to 60 degrees, and while the higher pitches aren't nearly as common as the joiner's pitch (45), they're still not rare.

If you can't find one suitable, you could also work a wide rabbet plane into a round plane as well.

Otherwise, the way I would do it is with a wide, shallow sweep gouge and mallet. You'd be amazed at how much wood you can hog off in short order with a carving gouge, and as long as you were careful with layout lines and sinking guide holes, it's actually quite straightforward and accurate. Use a drill bit with a stop collar, and drill a series of stopped holes across the headboard at the depth you want, and carve down to those. If you've a friend that has a travisher that you can borrow, that tool is next, and will take off the heavy gouge marks, get you close to the final profile, and greatly reduce the amount of sanding that you have to do.

[Chris Padilla]

http://www.sawmillcreek.org/showthread.php?t=108065

Read this thread...it might help you.

[Jamie Buxton]

This is a scheme that sounds inelegant, but works quite well: use an angle grinder equipped with sanding discs. If you hold a grinder down flat to the workpiece, it is cutting a radius which is very large. As you tilt the disc up away from flat, the radius it cuts gets smaller, until it approaches the diameter of the disc itself. By holding the grinder at some intermediate angle, you can fit the radius you need. You can smooth concave surfaces pretty easily. I've carved tractor-style chair seats, and shaped the concave face of coopered doors. With your big radius, you could use a 9" grinder. However, a 4" grinder will work -- just a little slower.

[Chris Padilla]

I've sat in Jamie's tractor-style seats and although a bit unorthodox looking IMO, a very comfortable fit!! :D

[David Winer]

I once had the problem of carving out a concave surface in a couple of pieces of wood that were somewhat smaller than a headboard, but the technique should work at any reasonable size.

1. Lay out your arc on the end of the piece.
2. Set a circular saw to the various depths needed to reach the arc, spacing each cut about ¾ inch from it’s neighbor.
3. Use a shallow gouge and mallet to chip out the waste between saw cuts.
4. Work the surface with the gouge until fairly uniform.
5. Fashion a sanding block to match the arc and, starting with very coarse, use successively fine grits to get to the finish you desire. (If you have the tool, the sanding disk idea mentioned previously sounds better to me than hand-sanding with a contoured block .)

[Mark Singer]

This may help:rolleyes:

http://sawmillcreek.org/showthread.php?t=14202&highlight=bath+cabinet