Smoothing a curve

[Mark Engel]

I have a question about smoothing a curve.

A piece I am working on has a long inside curve. I cut the piece close to size on the bandsaw and then got it just about there with my Rigid oscillating sander. The sanding operation left a slightly undulating surface.

I have tried scraping it and sanding it, but I am not able to even out these high spots left by the sanding operation.

Does anyone have a tip that can help me to even out this surface.

I'm not sure I explained this very well, so ask any questions that may help me to clarilfy.

[Thomas Bennett]

Try a compass plane. I have an antique Stanley that I use with great results. Maybe you can borrow one if you don't want to buy one. Good luck!

[Mark Engel]

I don't have a compass plane or know anyone that may have one. As a matter of fact, I don't even know what it is. :mad:

Is that plane designed for this type of application?

[Jim Becker]

Mark, a compass plane is a hand plane that is specifically for working curves. The sole is a thin flexible metal that can be adjusted concave to convex to match the curve.

[David DeCristoforo]

"I don't have a compass plane or know anyone that may have one..."

Make a block with a curve that matches a small section of the curve you need to smooth. Glue on some sandpaper.

If the curve is radial, you will only need one. If the curve is "random", you may need a couple with different profiles.

YM

[Calvin Hobbs]

A compass plane works great, however I have had good success using a cabinetmaker's rasp, using the rounded side, and use your eye/hand to get out the high spots and then scrape smooth. Cal

[Cody Colston]

You could always go the David Marks route. Cut out a pattern from MDF and fair it with a flexible sanding strip...MDF sands and shapes very easily. When done, double-stick tape it to the piece and use a pattern making router bit to copy the pattern arc.

[Brian Kent]

Rosewood contour planes:

http://www.leevalley.com/wood/page.aspx?c=2&p=46321&cat=1,41182,46334

They cost $25 for two sizes and work better than any of my other spoke shaves.

[Mark Engel]

Well it certainly sounds like the compass plane is the right tool for this job. I will be adding that to my 'tools to buy list'.

I think I will try to get it smooth with a rasp/file as Calvin suggested and then finish it off with a curved block with attached sandpaper as suggested by Yoshikuni. I have the cutoffs from the curved section which should make a fairly well matched sanding block.

Thanks for all the tips. I will keep everyone informed of the results.

Hopefully I don't exacerbate the situation. :D
I kid, Jim, I kid! :D

[Steve Campbell]

Mark I find when I use my spindle sander on a curve that I have the best luck going slow until I am sanded up to my line. Then I make a few passes along the whole length real fast. If you go at a fast rate you kind of skip over the low spots and hit the high spots.
Hope that makes some sense..

Steve

[Mark Engel]

That makes a lot of sense, Steve, and I have tried that with success in the past. This time it just didn't seem to work out and I am now too close to finished size to be comfortable taking another pass on the sander.

[Mark Singer]

Using rasps or a finely tuned spokeshave is a great way to go. I have lots of sanders, but its the rasps that really make it happen

[Rich Schneider]

I agree with Mark on the use of a finely tuned spokeshave if your not having luck with a card scraper or don't have a compass plane. In the future when you sand out these curves on your OSS the key is to work the whole curve, or if it is long in halves. You need to really move the piece and only with light pressure...it can be a real workout. If you move to slow or get the piece hung up on the table you'll end up with the undulating surface. The other thing you could try at this point is touching up the high spots on the OSS by identifying their general location using chalk or pencil, very lightly work that high point for just a second on the OSS and start widening the area to feather into the surrounding. Use the largest practical spindle for the size of curve your working. It takes some practice but once you have the technique you can create incredibly smooth, non-undulating curves on the OSS.

[Bob Vallaster]

...to expand on what Cody suggested.
No need to make a new sanding block. The waste from cutting your curve is a mate to the curve---less the width of the kerf. Dress it smooth, line the edge with sandpaper (possibly doubled to made up for kerf loss)and use it to smooth its mate.

Bob V.

[Peter Quinn]

I often use the DJ Marks flexible sanding strip idea to fair the curve directly on the work piece if the inside curve is of sufficient radius to allow it. I typically resaw a strip thin enough to work on the given curve and start with a grit coarse enough to remove OSS marks quickly. Seems to work. Costs next to nothing.

[Mark Engel]

Thank you, all, for your helpful advice.

This morning I took another pass at it. I started with a card scraper and got most of the high spots down pretty close. I then used a section of the cutoff from the curve and carpet taped a piece of 80 grit sandpaper to it. The length of the sanding block allowed the sandpaper to hit the high spots without dipping into the valleys. It took about 30 minutes on each of the 2 pieces to get a nice smooth even curve.

Once again, thank you. :)

[Ben Grunow]

I have used the following method in the past for free formed curves.

Layout on sheet of plywood and nail a flexible strip (1/4 x 3/4) to the plywood/line with some blocks to back it up as often as you feel are necessary. Then place your peice over the plywood, align and route/trim using a flush cutting bit (piece should be rough cut as close as possible).

The real adavantage of bending a strip to a line and using the router is that the difficulty of fairing a curve is removed by the strip of wood as is makes gentle, even curves.