Curved chair backs- compass plane?

[david blumberg]

Hi,

starting this as a new thread, originally was about finding a 3" pattern (flush trim) router bit...

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Thanks for all the comments...a 3" bit seemed like a scary idea to me, also...

I recently built 4 red oak hi-chairs for the kitchen island, and the hardest part was the curved chair backs. I cut them from oversized blanks on the band saw, and cleaned them up with an oscillating spindle sander, and sandpaper on a curved block of wood. They turned out OK, but not perfect,and took a LONG time.

I just finished a cherry dining table (48" diam expands to 10 ft) and want to make 6 cherry chairs to go with it. Have considered steam bending (never done it) but the tenoning process seems like a potential problem to me (among the other imagined problems)...

the bandsaw/oversized blank idea is pretty wasteful of wood, but is probably how I will go...Considering getting a compass plane to help smooth things out. Any ideas on that, or any of the above?

I have since installed the Carter style BS guides on my saw, so hopefully I can get closer and smoother with the bandsaw.

advice much appreciated!

david

[Andy]

Have you checked out the recent threads here about this exact topic? A compass plane would probably work, but the grain would almost certainly be going different directions on each side of the convex curve. Therefore you could plane with the grain "downhill" on each side, but you'll still have to do some sanding/scraping in the middle where the grain direction changes. My advice: spend some quality time tuning your bandsaw to reduce vibration to get smoother cuts to start with. If you don't have a bandsaw book (i.e. Mark Duginske or others), get one. Tuning/tweaking might take a while, but it should pay off during this project alone if it reduces sanding on 12+ curved chair rails. Your new blade guides certainly won't hurt either. Also, if you weren't already planning on it, cut the tenons on your stock before you cut the curves. Good luck, Andy

[Al Holstein]

Reply to curved back chairs:

Have you considered using your bandsaw to resaw the back of the chair into narrow slices and then glueing them back together as a lamination when bending them in mass with a template. I did that with a section of fir for a chair and it worked fine. I made a template of the curve that I wanted and glued up all of the slices 3 in my case and then used clamps to make the bends in the template. After drying there wasn't any spring back and the surfaces were the smooth ones that was on the board that I started with. You do lose the thickness of the bandsaw cuts, but if you get a good clamp job the seams are not really detectable.

Something to think about.

Al

[Lowell Holmes]

I use spokeshaves. Veritas is the brand I use.

I cut the curve with the bandsaw and then use the spokeshave on the concave side. I use shaves and hand planes on the convex side. On the first chair I made, we relieved the wood in the curve with a back saw and chisels and then used the shaves.

You cut lines across the grain, defining the curve, break the wood off with chisels and then smooth it with the shaves. It is quick and very safe to do it in this fashion.

[Lew Hodgett]

Since you are trying to fair out an inside curve, take a couple of pages out of the boat building community where fairing is a common practice.

1) Make a couple of profiles from 1/4" hardboard or 1/8" aluminum, if you can find it and machine it.

2) Saw the blanks as close as possible on the band saw.

3) Knock off the high spots with a 4" right angle grinder equipped with a rubber sanding pad and 24 grit discs. Use profiles to check your progress. (Aluminum will leave black marks on the high spots)

4) When close, say about 1/16", switch to a 2" dia x 2" lg, 40 grit flap wheel. You can use an electric drill but a low cost air drill is my favorite.

5) When you are within about 1/32", switch to a rubber block and 100 grit to finish.

Using the above, I watched a guy fair out airplane propeller blades to within 0.001".

I hired him to fair out my boat.

Nobody says it id easy, but it works.

Lew

[david blumberg]

I did an archive search a coupla months ago, might have missed that...

hadnt thought of that...

excellent idea; I think our library has that book and video

yes, did that on the other chairs.

[david blumberg]

thanks, Al...

That was/is an option I am considering. My concern was having the plies show (like plywood). Your 3 slices made how much final thickness? I wonder how many plies I would need for a 3/4" back in cherry?

david

Al Holste> Reply to curved back chairs:

[david blumberg]

lowell, thanks for the suggestion. I had not heard of that technique before...

david

Lowell Holmes wrote:

[david blumberg]

Lew, thanks very much for the response. I will consider that...

david

Lew Hodgett wrote:

[Lowell Holmes]

Issues 90 and 91 of Woodwork magazine feature articles on making a Craftsman style rocking chair. The techniques are shown in those articles. Sometimes hand tools are easier and quicker to use. I use both hand and power tools.

I never mentioned that we use scrapers as well. A well prepared scraper will remove a lot of wood, leaving a smooth surface.

It's nice to have the option of which technique to use. :-)

I'll post a photo of a recent chair I made in abpw newsgroup.

[Stephen M]

I recently did some work in 16/4 cherry with both convex and concave curves. It had a little tighter radii than you chairs but I experienced the same problem.

I'll second the Veritas shave idea. IME, shaves to a surprisingly good job of ensuring a smooth curve (not to be confused with a smooth surface) which I think is what is eluding you. You would think that you need all of that sole of a compass plane to control the curve, but I'm not convinced its necessary. The Veritas shave with a convex sole, is very much like a small compass plane and it performed well.

Another approach that occurred to me however:

The problem with the OSS is that the drum diameter is too small. If you have a lathe, you could fabricate an 8" or 10" diameter sanding drum. Although the surface speed might be but crazy. Just a thought.

One other thought on the abrasive approach: Start with the biggest and nastiest grit you can find. My initial attempts with the 3" OSS were with medium grit. It tended to ~divot~ because it was too tempting to apply more than the lightest pressure. A light touch helps achieve the smooth continuous motion you need with the OSS.

In the end, I used a combination of shaves and abrasives, shaves really shine when smoothing (shaping) the curves. My technique is not good enough for a final surface, so the OSS was effective at smoothing the surface (but I did have to work through the grits)

-Steve

[Tim]

Are you talking about a solid curved back, or just curved rails? If the former, all I can do is wish you good luck; I wouldn't tackle a job like that. If the latter, I went through it and can give you the benefit of my experience.

[david blumberg]

I am a scrapaholic...scraped every bit of the dining table, hi chairs, and other furniture in the house. I have web access on FW; i'll check that out, thanks..

david

Lowell Holmes wrote:

[Andy Dingley]

Make your own - rework the base on a cheap S/H woodie. Most of mine are coffin smoothers, either rounded off to cut concave or with extra bits attached to cut convex. I'm no fan of cast iron adjustable compass planes. A #113 is expensive and fragile, a #20 is a big heavy clog of a thing.

[Al Holstein]

I lost the width of two or three bandsaw cuts. I plies show less than plywood because the grain is all in the same direction and is consistent with the next piece only off set by what the curve changes the angle. You would need to start with pieces that were longer than the finished to cut off when you trim them. You might want to start with the back piece being thicker than 3/4" to get 3/4" as the finished thickness.

Good luck with your project.

Al

[david blumberg]