How to bend wood like this - Outdoor furniture project

[Maurice Mcmurry]

A clever thing that banjo builders do is to use iron brake drums for forms. I have a wheel from a line shaft pillow block that I have bent around. It is too small for those chairs but it is an excellent form.

IMG_2013.jpg

[Alan Lightstone]

So working on a different approach. I cut out some 1-7/8" thick, 6" or so wide white oak blanks, long and wide enough for half of the bend of the chair back. My thought was to make quarter circle pieces, glue them together (with dominos or dowels for reinforcement along their long axis, and then attach the long end pieces, which would be easy.

So I made a pattern out of 1/4" MDF, traced out the pattern on the first blank and cut pretty close to the line on my bandsaw. The only pattern router bit that I had that was long enough was a 2 flute, 1/2" shaft, straight bit with 2" cutter length.

Here's what the oak looked like before routing with the pattern on top (just placed there in the picture, not 2-sided taped down yet:
Chair Back Piece with Pattern 1.jpg
Well, besides this being a little scary on the router table, I got a significant amount of tearout in a few locations. I'm tempted to buy a spiral upcut router bit to do this, but will this eliminate the tearout, considering that I am going around the grain during the cut?

[Derek Cohen]

Alan, the key to avoiding tearout is a light cut. Several light cuts are better than one deep cut.

Joining the pieces is easier with dowels using centre finders ...









Getting there (lots more shaping still needed) ...



Regards from Perth

Derek

[Alan Lightstone]

Alan, the key to avoiding tearout is a light cut. Several light cuts are better than one deep cut.

Joining the pieces is easier with dowels using centre finders ...









Getting there (lots more shaping still needed) ...



Regards from Perth

Derek

Thanks for the advice, Derek. The dowel option looks like a great way of doing it.
How do you do light passes with a pattern / flush trim bit? I sawed as close as I could to the line without going too far in with the bandsaw. Once that is done, aren't the passes with the router bit kind of fixed?

Clearly you've accomplished the task I'm looking to do. How did you make those curved back pieces?

[Derek Cohen]

Thanks for the advice, Derek. The dowel option looks like a great way of doing it.
How do you do light passes with a pattern / flush trim bit? I sawed as close as I could to the line without going too far in with the bandsaw. Once that is done, aren't the passes with the router bit kind of fixed?

Clearly you've accomplished the task I'm looking to do. How did you make those curved back pieces?

Alan, my apology - I was describing two separate strategies for two separate tasks, and they would have appeared to you to be the same.

Firstly, the legs were marked out with a template I created, and then bandsawed out. The first time I tried this, there was about 2-3mm waste, and the result was Tear Out (scary stuff!). It had been a while since I had worked Hard Maple, and forgot how fragile it can be. Following this, I bandsawed to 1mm, and then decided it would be easier to just use a spokeshave, which I did.



The legs are oval, and the process was started on the router table with a large half-round bit. Rather than attempt to take it off all at once, this was done progressively. In other words, a few fine cuts ..



Now the part that applies to you is this - building the arms.

Templates for three sections.



Fitting three sections. They are blocky at this stage:



This is probably what you are looking for:



After joining the sections with dowels and epoxy, you can clean up with a sander. I am using spokeshaves ..



The reason for the (3/8") dowels was that, using pointers, they are easier to position on a curve than a domino. All I needed was a block of wood as a guide to drill square ...



Hope this helps.

Regards from Perth

Derek

[Alan Lightstone]

Very useful information, Derek. And your build is very similar to what I am attempting.

I really don't know if I am good enough to bandsaw to 1mm without accidentally going into the pattern. I do have a edge sander so getting the outside curve close after the bandsaw wouldn't be very difficult. The inside curve is more of an issue. A spokeshave, or I saw a YouTube video of Ramon Valdez adapting his belt sander to do different diameter curves that looked interesting (I have a very old belt sander that I basically never use, that might make sense to modify in this way.) https://www.youtube.com/watch?v=sx5xM5vSHTc Not sure it would work for me, as I need a 16-1/4" inside radius, and at least for his belt sander, the smallest he can get is 16" radius. But very interesting, nonetheless. I could get close on the curved portion of my edge sander and perfect it with a spokeshave, perhaps.

Also wondering if a Shaper Origin can do this. It's maximum depth would come into play, as well as having to make multiple jigs, but it's another thought. Anyone tried anything like this on one?

[Derek Cohen]

Hi Alan

Regarding the question of lighter cuts using a straight pattern bit, it occurred to me later than you could use a step process of progressively deepening the cut via decreasing sized bearings, such as these (which I purchased for cutting rebates) ...



Regards from Perth

Derek

[Mike King]

Alan, working on your bandsaw technique is a key to being able to follow the line. Michael Fortune taught me his technique, which relies on using the back of the blade as a fulcrum for passing the front of the blade into the cut.

https://www.finewoodworking.com/2011...on-the-bandsaw

Another option is use pattern bandsawing.

https://www.finewoodworking.com/2008...complex-curves

I often use pattern bandsawing to rough the part, then pattern shape the result on the router table or shaper.

When I pattern shaped the legs for my chairs, I made my jigs so that I could flip my part end for end. This means that you have two jigs for each side being shaped. You shape the part going downhill with the grain; when the grain switches, you flip the part onto the other jig, and start shaping from that point.

But, in my experience, there's no substitution for hand tool work. Pattern shaping, whether with a bandsaw, router, shaper, will only get you so far. Then it's time for drawknives, spokeshaves, rasps, and sandpaper. Maybe even round bottom planes, travishers, and scorps. Even better, the reward that you get from shaping by hand is the real payoff, in my opinion.

So, machines can help to remove a lot of the work, but hand tools are often quicker and more flexible that trying to achieve a perfect result with a machine. And the marks of handwork indicate that a craftsman built the piece rather than it being mass produced in a factory.

Mike

[Alan Lightstone]

Thanks Mike, Derek. That pattern bandsawing trick sounds like a great plan. And I do have a set of different sized bearings, so just in case could start on the router that way too.

I think I do need a better pattern bit for the router, though. Infinity tools sells a nice spiral one with sufficient cutter length, and they are in my neck of the woods, so I might get that too.

Watching Michael Fortune cutting that close to the line on the bandsaw just proves that I'm no Michael Fortune. And yes, he could have also done with by steam bending, bent lamination, probably a billion other ways. He's very, very impressive. So is Brian Boggs, whose chairs are also very impressive as is his technique in Fine Woodworking.

[Alan Lightstone]

So, looking at the articles, Brian Boggs technique of making parallel curves with perfect arcs looks like the best for me:
https://www.finewoodworking.com/proj...andsawn-curves

He suggests using a 4TPI, skip tooth blade, which I don't have. I can't find any for my Felder FB710 (needs 201-5/8" long blade). Sawmillbladesdirect.com doesn't have any in stock, just 3tpi Lenox Tri-Master Carbide blades.

Any good sources that would carry them? Timber Wolf sells them, but those are just steel blades. I'd much rather get a carbide blade for durability.

[Derek Cohen]

Alan and all

Look at this!



Regards from Perth

Derek

[Alan Lightstone]

Pretty amazing.

Now if I only lived in London...

Would look fine painted, and considering it's like MDF, I assume couldn't survive outside. Especially in a humid climate like mine. But for inside work, wow!

[Mike King]

I've bought bands from https://www.industrialblade.net/ -- cheaper than bandsawbladesdirect.com

[Kevin Jenness]

If you are running a quarter circle blank along the curve in one direction some tearout is almost almost guaranteed. Find a way to cut with the grain, either flipping the blank end for end in the jig, using a box jig with templates top and bottom or using a trimming bit with both top and bottom bearings.

Going back to your post #36, the semicircles shown in your model are segmented in 4 pieces. This is stronger, with less grain runout and waste, than a 2 segment assembly. I don't know if you could get out those full height segments from 8/4 material though. With your stacked approach you can increase strength by vertically offsetting the joints in your "bricks". More segments decreases the risk of tearout when routing against the grain.

Your jig is scary. At the least, add some handles to keep your fingers away from the cutter. Even safer would be to have separate, more substantial jigs for the inside and outside curves. Also, the jig should be longer than the blank so you can start feeding it against the pilot bearing before the cutter engages the blank. There's a reason why some old school shaper hands were known as "Stubby".

[Alan Lightstone]

If you are running a quarter circle blank along the curve in one direction some tearout is almost almost guaranteed. Find a way to cut with the grain, either flipping the blank end for end in the jig, using a box jig with templates top and bottom or using a trimming bit with both top and bottom bearings.

Going back to your post #36, the semicircles shown in your model are segmented in 4 pieces. This is stronger, with less grain runout and waste, than a 2 segment assembly. I don't know if you could get out those curves from 8/4 material though. With your stacked approach you can increase strength by vertically offsetting the joints in your "bricks".

Your jig is scary. At the least, add some handles to keep your fingers away from the cutter. Even safer would be to have separate jigs for the inside and outside curves which could be more substantial. There's a reason why some old school shaper hands were known as "Stubby".

I agree about the scary part. I won't be doing that again. I agree about inside and outside curve jigs. But even using a 1/4" plywood or MDF jig with the wood piece clamped to it would exceed the cutter length on my router bit.

I was hoping to have less joints, so was trying for the curved portion to be segmented in 2 pieces. Might not be the best approach. I would think with a total height of 5-1/2" - 5-3/4" for the chair back (3 individual pieces glued together vertically) it would be plenty strong.