Why is my lid jig a miserable failure?

[Bolster]

I want to make a lightweight lid of aluminum flashing (.010 thickness) for an aluminum mug (an Imusa mug which is 3.9" ID). I'd like to take the mug and lid backpacking, and be able to boil a bit of water in the mug for rehydrating meals. The lid is the sort that sits down into the mug about a quarter inch, then toward the edge bends vertically up, and then bends back to horizontal at the edge, to sit on the rim of the mug. Here's a photo of someone else's lid--perfect, exactly what I want to make. (If I can't make one myself I may have to buy one from this guy, who apparently possesses an IQ about quadruple of mine.)



I thought about how I might bend the desired ledge into a circle of aluminum flashing, with the tools I have, and came up with the idea of (left to right in photo) a "fulcrum" with pivot screw for holding the lid at its center, allowing it to rotate; and an "anvil" and "presser foot" which would bend the edge into shape. The orientation of the lid is upside down during fabrication, and the mill is turned off--nothing is spinning here(!), except for the lid blank, which I turn by hand on the pivot screw as I work around the edge.



The anvil is radiused (along the Y axis, you can see it) a little under the dimension I need, at 1.75 in. The presser foot does not have a similar radius (a problem?), I left it square, as you can see. I use the quill of my mill to move the presser foot up and down (Z axis), gently, while slowly rotating the blank. There is a horizontal (X axis) space between the hammer and anvil of about .1 inch, which I've been keeping wide, in hopes it will allow gentler bending.

Regarding the sharpness of the working edges themselves (both anvil and presser foot) they are only slightly filed.

Feeding the blank around in a circle, I'd take maybe 20 very small presses (the slightest bend appears), then on the next rotation, 20 more light presses (a little more bend), each time pressing only the amount that the metal seemed willing to give. I worked at an agonizingly slow pace.

Result after maybe 15 rotations: Miserable failure!



Even when I try to gently massage the desired rim onto the blank, I get all kinds of problems. First thing is that the blank starts to warp or bow, popping into different non-flat curves as I go around. If I keep up the work, I start to get wrinkles at the lip. And if I forge onward, I eventually open up a circular rip in the lid, like a can opener would do.

Clearly I'm doing at least one, and possibly, several things wrong. I think I am stretching the metal so there is "more of it" around the rim, which must be causing the warping and bowing. I'm considering radiusing the presser foot to see if that might help. I think there'd be less metal stretching, as I can see the square edges of the presser foot making imprints around the lid as I work.

Very frustrating, after taking the time to make the jig, to have such an unpleasant result. Help appreciated.

[S. Heslop]

I figure the reason it's going all crinkly is because the areas the arrows are pointing to in the picture below are being stretched.



If you own a lathe you could have a go at spinning it (google metal spinning).

You could also try hand raising it. Raising thickens the metal. Like most artsy craftsy things, most people who raise will try pretend it's harder than it actually is, but it doesn't really take long to pick up the skill. With a soft material like copper or aluminium you could use a wood or plastic hammer to raise with. I could go into more detail if you think you might give it a go.

I remember finding these videos useful back when I was looking for information.

[Brass_Machine]

Hiya Bolster

I am not sure I can help much as I have made anything remotely similar.

I think I would try a 2 piece die. Sorta like I see the guys who make boilers user for their end caps. I will see if I can find some pictures as I am sure I will not do a good job describing. You may also need to anneal it, again, I am not 100% sure as I have never done anything like this.

Link to PDF on annealing

The other method would be to spin it. This is an add for a company, but it gives you an idea on what can be done.

Eric

[Bolster]

Pretty amazing you were able to graphically illustrate so quickly, Heslop, and you must be right, because it seems the more I work the rim, it seems the more metal I have to work with! So my boneheaded jig stretches metal--swell. I suppose there is no saving the jig, then. Scrap aluminum.

Sadly, I do not have a lathe. Brass, I am curious what a 2-part die would look like. Would it be the entire circumference?

[S. Heslop]

Pretty amazing you were able to graphically illustrate so quickly, Heslop, and you must be right, because it seems the more I work the rim, it seems the more metal I have to work with! So my boneheaded jig stretches metal--swell. I suppose there is no saving the jig, then. Scrap aluminum.

Sadly, I do not have a lathe. Brass, I am curious what a 2-part die would look like. Would it be the entire circumference?

Here's a timestamped youtube video. The fella has videos on his website without the audio muted, but youtube lets you link a specific time.

&t=57s

Whats happening at that point is he's bringing down those crinkles around the corners. That's the real secret to raising. You push the metal in, and then you whack the crinkles down (and this leads to the metal thickening over-all rather than stretching).

If you get yourself some sort of domed anvil, any reasonably dense piece of material with a smooth-enough surface (i've seen people using wrought iron fence post toppers, large trailer hitches, cannon balls, or even a bit of reasonably thick pipe,), you could have a go at bringing them down by hand. Then planish the surface smooth to get a cool hammer-finish.

I mean it isn't the ideal way to do it, i'll admit that, but it's a way that won't require fancy equipment or that much thinking.

[Bolster]

This fellow who made the lid in the top photo appears to have made a heavy, all-at-once die, see the video at about :50.

I don't have the ability to make one of those! And, I wanted an option that would allow me to make lids for various pots, by simply adjusting the distance between the pivot and the anvil.

Looks like metal spinning would be my best bet, and I'm guessing there's no salvaging of the mill jig shown above.

 

[Bolster]

Wait, here's a better video. The magic happens at around 7:00.

That's a pricey, non-adjustable die.

[S. Heslop]

You could maybe cut out an inside circle of a bit of hard wood with a hole saw, or a jigsaw (I like to hold my jigsaw upside down in a bench vise and use it like a rubbish scrollsaw), and glue that onto a bigger block of wood. You could then use the cut out hole to make the matching die.

I'm not sure if you'd get enough pressure using your mill as a press when doing the whole thing, although it is thin aluminium. Maybe you could just put it on the floor and jump on it.

Edit: In fact if you have a bench vise you could just use that as a press.

[Bolster]

So...the recommendation is to make the rim all-at-once, rather than a little bit at a time, because the all-at-once die method stretches the metal less?

Yes, I could see making a wooden jig with my router and one of those plastic circle jigs that attach to router bases. Feel rather foolish about all the time I spent making my nice aluminum mill jig, tho.

I guess it's "practice."  I should have known better about the metal stretching.

 

Thanks for explaining it to me.

[S. Heslop]

So...the recommendation is to make the rim all-at-once, rather than a little bit at a time, because the all-at-once die method stretches the metal less?

Yes, I could see making a wooden jig with my router and one of those plastic circle jigs that attach to router bases. Feel rather foolish about all the time I spent making my nice aluminum mill jig, tho.

I guess it's "practice."  I should have known better about the metal stretching.

 

You should see all the terrible jigs and fixtures i've built. It's rare when the first attempt works.

[Stilldrillin]

Sadly, I do not have a lathe. Brass, I am curious what a 2-part die would look like. Would it be the entire circumference?

Don't forget. A mill is a lathe, standing on end......   

Good luck! 

David D

[Bolster]

Don't forget. A mill is a lathe, standing on end......   

An end-standing lathe with no carriage...!  Have you figured out how to add the carriage?

[Stilldrillin]

The table, is the carriage.......

Install a block, with a tool mounted on top. 

David D

[DMIOM]

The table, is the carriage.......

Install a block, with a tool mounted on top. 

David D

or even just pop the tool in the vice!

[Stilldrillin]

or even just pop the tool in the vice!

That's MK11 developed, already....... 

David D

[tekfab]

You could also try annealing it before you start and for safety's sake perhaps during the process.
A simple way to anneal is to heat the metal until a piece of softwood such as a match leaves a scorch mark.
Mike

[Fergus OMore]

I would think that you'd be best advised to forget all this mill stuff and go back to basics which is a 'Bob and Aunty' which is a pair of formers which like the couple in question fitted together- with just a little bit of clearance. I'm sorry but that is how old time blacksmiths described it.

If you want to do it the way of industry, you could copy the way drinks cans are made- and that is with a slug of aluminium being spun with a former in the middle of it until it forms the base and then continues onto the making the sides!

If you want to make it the way that my old firm made 'caps' and 'closures' you have to make up progressive hardened dies and use stamped blanks from sheets. We used to put screw threads on- and never damage the coatings and decoration.  Far too involved for a one off?

Again, you could do the whole thing with a raising hammer as everyone that has made a model loco boiler does with copper.  If you must try some variant of spinning, you will need very hard and very polished tool ends(  ).

I'd stick with Bob and Aunty who seemed to produce one item at a time

Regards

Norman

[PekkaNF]

If you have a good shop press, you could make form from steel (simple turning) and do some "Rubber pad forming".
http://metalmeet.com/forum/showthread.php?t=3129&page=3
http://content.answcdn.com/main/content/img/McGrawHill/Encyclopedia/images/CE619200FG0020.gif
http://www.answers.com/topic/sheet-metal-forming
http://en.wikipedia.org/wiki/Rubber_pad_forming
http://www.jmpforming.com/applications/aerospace/rubber-pad-forming-for-aerospace-industry.htm

Pekka