I am trying to cut an arch in 2x lumber. (not too steep, about 4" rise over 2' and back down again)
I haven't used a jigsaw a lot, especially curved work that has to look good. I believe I have a good tool, but not sure if blade selection is right - just using a DeWalt wood balde about a 1/4 wide.
I find that I can't stay with the line, and maybe this is just a matter of practice - but when you wander even a little it shows. Also the blade would bend some and make the cut edge out of plane. Sanding makes it a lot better, but still not satisfactory as finish work.
I tried making a jig plate for my router and mounting it to a board to swing a radius (radius needed is 73 1/2 inches, with a 4' swing) (I knew I was going to need to make several passes,increasing the depth each pass), but I abandoned that method as the jig was not firm enough and it did not cut a crisp radius.
Next I used the same board against my jigsaw foot, and followed the jigsaw with the board as I swung the radius. This did ok on my trial 3/8 plywood, but when I tried on my 2x the blade would bend - as it did when free handing 2x material, only worse.
your advice will be greatly appriciated. these problems are really frustrating !!
This kind of cutting is better suited to a bandsaw. As you've discovered jigsaw blades just bend to much. If you don't have one, or don't know somebody who has one, it can still be done. I use a compass type tool to make my arch first. With a width of 2' & a rise of 4" the "compass" would be set at a distance of 19 15/16" (point to pencil). I would swing that arch on a piece of 1/4" mdf first. The mdf should be easily cut with the jigsaw. If needed you can clean it up by sanding. Then pin the template onto the 2x4. Using a router with a long flush bit with a bearing I route the arch. It's a little more work, but it gets the job done. Hope this made sense. ;) Good luck.
I think you are very close to getting the results you want, from the tools you have. Maybe the trick here, for the tools you have, is to use both the jigsaw and router.
Either lay out the arc as you have been doing, or make a pattern as suggested above. Use your jigsaw to cut away most of the material, staying just far enough away from the line to make sure the jigsaw doesn't bend its blade or wander into it.
Then with either a stiffer (or better supported) swing arm, or the pattern, use the router to trim away the remaining material.
I say better supported for the swing arm because I routinely use that goofy 5.6 MM lauan ply for jigs used with the router to cut arcs and as long as I have it supported along it's length, it's just fine. It is also much safer to have the work supported adequately. Using a power tool is no time for surprise movements of anything!
Draw the arc on both sides, cut to the outside of the line, flip the stock and repeat. The blades tend to want to flex to the outside, flipping the work will minimize your "cleanup" efforts.
Strange as this may sound, it feels stranger, if your a righty try cutting this arc as a south paw, amazing what the other half can do, the brain that is.
another alternative...........rough cut with jigaw.........tape down a pattern and cut approx 1/2 thichness with top bearing bit.........flip stock over and cut remaining with a bottom bearing bit following the cut from 1st
I don't know what kind of jigsaw your Dewalt is, but if it's the kind that uses generic blades, no wonder. I agree with the others who talk about cutting on the waste side of the line and then cleaning it up, but you may also need a new jigsaw. Try a Bosch with stiff blades, and go slow.
Do you have a spokeshave? If not, they can be purchased at a very reasonable price ... if it's a one-time deal. If you have wanted one, and don't want to get an el-cheapo, here's your chance! ;) Others here will have more experience and can tell you if this approach is feasible.
However, I think Dick has the best approach. The router will give you the perpindicular face you want and it'll be really clean. Use thin ply or hard board for your template.
I use a Bosch with Lennox 450S blades in it for this kind of work and I'm able to get fair curves that easily clean up on an OSS (big Grizzly). Anyhow, try a different blade. I don't know what type of blade your Dewalt takes but try the equivalent to the Lennox 450S. A bandsaw is also good at this but I prefer to use a jig saw. If blade deflection is a problem then create a template using your jig saw and sanding to get it fair (or a spokeshave - try Lee Valley) and then use the template to mark the cut, cut close with the jig saw and then mount the template and use it to guide your router.
Note: the first two pictures, top to bottom, show the sample woods I bought to match: mahogany, walnut, oak, the bottom is the side of the table. The remaining 3 pictures are of the wood in question...