View Full Version : Need help with a JIG
04-29-2004, 12:24 PM
Hey you guys,
I need a jig to create a perfect arch with 3/8" or 1/2" mild steel round bar. It is going to be the leg for a sofa table (kind of). I have some idea on how to make the jig, but since this thing has to be a perfect arch and I need to create a mirror image for the other leg I prefer to go to the experts; YOU GUYS
04-29-2004, 12:48 PM
Making 2 identicle arcs, given the imperfections in steel, is close to impossible.
If the arches will be closed by a bar across the open end, you can hold the radius. Without something holding the radius, 3/8 or 1/2" bar would also deflect just holding the weight of whatever you put on top of it.
04-29-2004, 02:46 PM
Franz is right on the money. To get close will require more luck than skill. Well, either that or a CNC bender. :D Either way it's a tall order.
Probably the best you can do is trial and error, and leave extra bar on each end to trim off after bending.
04-29-2004, 03:38 PM
I can do it with wood and maybe the same technique will work with metal. With wood you bend the wood into an arc by pinning the ends and let the arc happen naturally. Then you laminate (glue) another piece on top, then another and so on until they hold each other in the bent postion. You may be able to weld thin strips together to do the same thing but they would have to be flat to start with.
I hope this makes sense. It works well with wood.
04-29-2004, 04:07 PM
I got yer jig right here...
04-29-2004, 06:53 PM
I AM VERY SORRY JOSEJUMP, BUT I DO NOT SEE ANY POINT WHATSOEVER IN YOUR ANSWER. IS THAT SUPPOSE TO BE FUNNY. HUMMMM...
04-29-2004, 08:19 PM
Amalgam, this is how I would do it, but I'm sure it's not the only or best way. Either make yourself a wooden fixture or draw your arch on a piece of carpenter paper. If you use the fixture, bend until both pieces fit in the fixture the same. Or, if using the paper, both as close as you can get to your drawing. Weld them to whatever will be above the legs holding the table. Then, place them on a flat surface and find the leg that is highest and weld a support to it so it can't move under weight. On the other leg, use a bar clamp to pull the two ends of the leg together until the the whole thing is level and weld your brace on it. Because of the spring in the steel, it's gonna be a trial and error project.
04-29-2004, 08:42 PM
uh.. sorry, it must be an irish thing....
You know, a jig.. dancing.... Ha, Ha...
Geeze, it isn;t as funny when you have to explain it...
04-29-2004, 11:38 PM
If you have a steel plate table you can draw the arck minus aasy one inch radius then tack weld tabs on the arc line arond every two inches. You can calculate how much material you will need by the circumference formula using the middle of your bar as the diameter line. add an extra threee or four inches one both ends for a flat spot and then pull it wound your jabs on the table.
04-29-2004, 11:41 PM
Another way is to use a cheep harbour frieght bender of a hossfeld if you have it. You can cut an undersize ring of large pipe and then using the arms of the bender feed the straight bar against the pipe ring to force it to the circle.
04-30-2004, 04:00 PM
Don't know if I'm missing the point, but why can't you roll the material into a circle & then cut it in 1/2?
04-30-2004, 05:47 PM
In most cases a circle is holding itself together, either by compression of an unwelded seam, or it's welded together to keep it from flying apart. I'll bet it will be very rare to make a circle with no stresses in it that would lend itself to making two perfect hemicircles.
05-01-2004, 07:16 AM
hmmm, something on the line of a coil spring, maybe just wrap the piece of iron around something that is a little smaller than what the finished piece needs to be& see how close to the size it ought to be & go from there.
That will work, I've done it alot of times for different size rolls & rings of flat & round stock. I don't know what dia. or radius you are shooting for, but go ahead & add some extra for the ends because you more than won't be able to bend them all the way.
The ring is going to expand a little, so start out smaller than you need. You may have to attempt this 2 or3 times. I normally use pipe for my jigs & sometimes I will cut plate to the correct dia.
It's easier than you might think, just buy extra material.
Remember, custom built things cost more & takes longer.
05-01-2004, 10:13 AM
Thank you guys very much. As always lots of good people helping out seriously.
05-02-2004, 09:01 PM
Route a circle or arc in 1/2 inch plywood the size of the arc required using a center pivot hole and a compass arm on the router. Fasten the pattern to a larger sheet of plywood and form the bar using the plywood to check the shape and size. Then hold the bar to the pattern with blocks screwed to the plywood. Weld the bracing to hold the arc to size. If the two bars are not identical, but symmetrical, unfasten the pattern and flip it over.
05-03-2004, 11:55 AM
Stingers, good suggestion. I hadn't yet had my paradigm shift for the day. In fact, a large circle cut from plywood is how I made 36" diameter arches in 3/4" 16-gauge square tubing for a 3-arch room divider. I slightly undersized the plywood hemicircle, bent the tubing, let it relax slightly to the specified size, clamped, and then welded the other structural and decorative pieces into the inside to hold the finished product. It was before my digital camera days, and I've been looking for a scanner because words can't describe this project. It was for a lady who's favorite color is gold, and this entire thing I painted in metallic gold paint for her. She was very happy. I later built a double-leaf security door in almond trimmed with gold. She basically ignored the home-owners' assoc. on that one.
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