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Eliptical element... this should be easy


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I'm working on a job that requires two of these (1" x .5" the easy way):

elipticalelement.jpg
That comes out to nearly 24" of stock.

They need to flatten at the ends slightly (where the rivets go) and then follow an eliptical, symetrical curve.

I am kinda challenged when it comes to tools. I am working in a coal forge, and its hard to get a very long heat, and I don't have a jig of any sort.

I have tried so far to do it free hand with benders or over the horn, but I keep ending up asymetrical or slightly twisted.

I will eventually get it, but I'm at my day job right now, so I thought I'd holler for help and see if I could get any good tips before I get back at it.

Thanks in advance,

Don

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Don, do you have a metal table, ie. a welding table? You can make a simple jig by marking your desired arc on the table and weld some short stubs standing up, on the inside of the arc. heat the piece and clamp it to the end upright and bend around. Heat the next section and continue until you have the complete piece curved. I have done this several times and it works out pretty well. Hope this helps. :)

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I would do that by hammering over my hardy hole. Gently tighten the curve until it fits your drawing. This can be done cold easier than hot. If you need a bit more curve than you are able to get over the hardy hole move to the step for the last few adjustments. Lots of light hits will allow you to adjust gently and with great accuracy. You'll find that you have FAR more delicate control than you do when using bending forks.

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Sometimes you can make two different bends and they look elliptical. My project ended up as one bend on each end first, then a bend at the middle section. Took less time to do than to explain it.

Make the first elliptical shape (slightly smaller) and then use that as a jig to make the rest. Hot iron moves easier and then cools to the shape. Cold iron always has some spring back.

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Sometimes you can make two different bends and they look elliptical. My project ended up as one bend on each end first, then a bend at the middle section. Took less time to do than to explain it. Make the first elliptical shape (slightly smaller) and then use that as a jig to make the rest. Hot iron moves easier and then cools to the shape. Cold iron always has some spring back.


Good point, in drafting class (mechanical drawing), freshman year of high school, I recall approximating an ellipse by using circles to form the ends, then using a different sized circle that is exactly tangent to the first two circles to form the sides. Way easier to state it this way than to draw it.

This looks like the method used
http://jep-s.blogspot.com/2010/07/how-to-draw-ellipse-by-four-center.html

Phil
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open the jaws on the vise. Start the stock in from the top and pull towards you. Do from both ends evenly. You should have a model (either a drawing or a wire/rod model). After hand bending cold you can open the jaws a bit and strike from the top into the curve to close it. Open it by laying over the face of the anvil and striking on top.

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You may already know how to draw an oval , but if I can describe this method clearly enough you might find it easy ; On my steel layout table I draw a straight line and draw another making a right angle cross one horizontal line and one vertical line. On the vertical line, I measure a distance above the cross and measure the same amount below the cross. These points I centerpunch and drill a 9/64" hole in each mark so a 1/8" pin can be inserted in both. then tie a string into a loop that you place over each pin and your pencil stretches the loop to make a triangle, holding the pencil so it will mark the oval as you circle the two pins keeping the string tight, to make the oval larger make the string longer, to make it smaller shorten the string. With a little experimenting you will come to the size oval you want, and will be able to make a bending jig by tack welding pieces of plate or angle iron along the line you have drawn.

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Well, I got 'em done, and they turned out nice.

Drawing the elipse wasn't the problem (I work with AutoCAD in my day job). The real problem was getting 1" x ½" stock to bend smothly with no flat spots.

Here's the jig I came up with:

1000723w.jpg

The shape extended well past the half-way point, so when I formed the opposite side, everything matched up nicely.

Yeah, there was a considerable cloud of smoke and cursing, but it got the job done. If I were gonna go into production on these pieces, I'd have the same jig water-jetted from some 1" plate. But wood worked fine for the two pieces I needed for this job.

Thanks for all of the good advice.

Don

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I didn't comment earlier because I thought you wanted the two separate elements. If you want the complete ellipse it's often easier to cut it in half along the minor axis (You've halved it along the major axis.) that way your sharpest bend is in the middle of each piece. This gives you something to hold onto while doing the most demanding bending and it means that the welding and grinding are in the gentle part of the curve and easier to align and clean up.

Also, for future reference, this is the technique I use to draw an ellipse with pins and a string. It allows you to place the pins in the right spot and get the right length of string to get the right size on the first try. By using a consistent technique you can make sure they have the same shape in all sizes.

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