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I have made a curved top for a letterbox by mitering and gluing the edges of narrow pieces. I've then used my spokeshave and sandpaper to get a smooth outside surface. I intended to smooth the inside using my round card scraper but have realized it's not really practical to take that amount of material off with a scraper.

Curved Surface

There is a similar question here. My question differs in two ways. Firstly, I'm not asking specifically about 'old school' techniques. If someone has a way of doing it with a router then I'm all ears. Secondly, the suggestion of using a compass plane in the accepted answer wouldn't work for me as the curve is too tight and I would be planing against the grain. A scorp would probably be perfect for this but unfortunately I don't have one and would prefer not to get one for a single project.

Any other ideas for how to get it smooth?

sprinter
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  • I guess that depends on how curved/accessible the surface is, a picture of the piece would help to get better answers. – Stoppal Aug 02 '16 at 06:35
  • Possible duplicate of What is the old-school way of smoothing a curved surface? – Graphus Aug 02 '16 at 07:29
  • @Stoppal I've added a photo. – sprinter Aug 02 '16 at 11:17
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    You have this tagged hand-planing. This dupe would work well with that. This question would not be a dupe so long as you specifically look for power tool answers. Feel free to remove my edits if you would like. – Matt Aug 02 '16 at 12:06
  • are you really adamantly opposed to doing it by hand? I had a king sized bed headboard with a cupped back surface that I planed by hand... really not that hard once you have the right tool....which you pretty much have to make by hand. I made a convex scrub/molding plane to accomplish this: http://lumberjocks.com/projects/240626. I say you have to make it by hand because it really does have to be about as long as a jack plane in order to create a flat, level surface. You can then customize the radius of curvature to perfectly suit your work. – aaron Aug 02 '16 at 12:52
  • @aaron No not at all opposed to doing it by hand - the 'with power tools' in the title was added by someone else in an edit when I added a point that I'm not insisting on using hand tools. I've not made a plane before but something I would like to try. One complexity is that the curvature changes across the width of the piece. – sprinter Aug 02 '16 at 21:53
  • @sprinter planes like the one i made are super easy to make - google "krenov plane" and examples abound. The variable radius makes it a little interesting, but it just means that your sole/blade radius needs to be smaller than the minimum of the workpiece... no biggie! – aaron Aug 03 '16 at 13:37
  • Holy late edit Batman! – Graphus May 09 '21 at 22:17
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    @Graphus yep :-) I noticed this old question and the addition by someone else of the powertools tag and addition to the title annoyed me as it was misleading. So just a peace-of-mind edit! – sprinter May 09 '21 at 22:58
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    So, five years on (yikes, where does the time go?!) do you recall how you got this done? – Graphus May 10 '21 at 09:06
  • @Graphus yes I ended up using a gouge to get it close then a curved scraper set for an aggressive cut. It was actually faster than I thought it would be - maybe 2-3h to get it to a nice smooth surface. Unfortunately as a letterbox it only last about 3 years in the sun and rain before the glue started failing :-( Which taught me something about glue to use for its replacement! – sprinter May 10 '21 at 20:06
  • Good learning experience all round then! Shame about the glue failure in a relatively short time though, was it a PVA? – Graphus May 11 '21 at 00:04
  • Yes it was PVA. But cheap stuff not really meant for outdoor use. I used Titebond III on the next one and seems to be standing up better. – sprinter May 11 '21 at 00:08

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This may or may not be a duplicate. I think the best solutions were already covered in the "possible duplicate candidate". I'd go for a thick scraper.

The only other things i can think of from the top of my head that use power tools are:

Flap Sanders

Image from Instructables

There is an Instructable (picture is taken from there) and John Heisz has a pretty good video about it. That may be worth your while as it's not only usable with this particular project.

Handheld Spindle Sander

Izzy Swan has a video about making those yourself for a couple of bucks and I think those could work for you as well. Start with a pretty rough one(~ 60 grit) and progress to however fine you want it.

A Round Surform

I think surform is a term created by Stanley and I myself only own a plain old plane one (there might be a pun in there somewhere). They are available in round and half-round as well and this might be an option to pursue as they are not too expensive and are quite versatile. (Basically those surforms are bigger, fancier, lightweight files that pack quite a bite)

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Stoppal
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    Handheld spindle sander is a great idea. Will definitely give that a go. Thanks. – sprinter Aug 02 '16 at 12:31
  • The flap sander reminded me of an angle grinder disc: https://www.amazon.com/Angle-Grinder-Flap-Discs-Flat/dp/B0089F2OJI (not a recommendation -- just the first one that jumped out in search...) If you don't already have an angle grinder, consider one. They're super-useful. (Although somewhat dangerous!) – Aloysius Defenestrate Aug 03 '16 at 02:02