Ideas for short small drawn enclosure?

I work for a company that makes heavy draw dies for the automotive industry. Corners are hard to draw. What do you mean by "more or less square"? What radius are you looking for on those corners?

How many pieces do you need? Does it have to be made of sheet metal? Draw dies take a lot of work. They have to be highly polished (mirror) to get good flow and you're going to have a hang of a time with the square corners. You'd probably be better off making this component using another process. Dies aren't well suited to small quantities.

All of this will depend on the material you're using, its condition (hard, semi hard, soft, etc.) and its thickness.

The above is worth exactly what you paid for it.

Good luck.

Regards,

Robin

Does that plug into the Frankenhouse amp? ;-) (Under Electronics projects in my sig.)

Tim

-- "I have misplaced my pants." - Homer Simpson | Electronics,

- - - - - - - - - - - - - - - - - - - - - - --+ Metalcasting and Games:

So just cut open a soda can! Or you might try some aluminum flashing of the sort that roofers use. It's a little thicker but thin enough that you can cut it with ordinary scissors.

That's also how custom bodywork for sports cars used to be made and maybe still is somewhere. An English wheel; large canvas bags full of lead shot; a rubber hammer; a sheet of aluminum and an artisan who knows what he's doing. There was a time when most of the bodywork on Ferraris was made that way.

But for guitar pickups, isn't shielding important? Wouldn't sheet copper work better, since it's not only malleable but also easily soldered? How about brass shimstock?

I made something very similar to the box you want out of copper. I made the dies out of oak as I had some on hand and milled the recess with an end mill. So the corners were more or less square, but rounded. It took me a couple of tries before I got something nice. If I had to try many more times, I would have had to make another set of dies. I used my vise as the press.

Dan

I had a look. That's one of the ones that use those big dim light bulbs. When the time comes to plug somthing in, I will probably make an artistic decision based on what amp is in the basement and operating.

Kevin Gallimore

This is not a production item for me. I might make half a dozen, and the amount of scrap I might generate would horrify a commercial shop. Like most of us here, part of the fun for me is finding a way to do it. The items are available (China's finest) inexpensively. I just want to make some that look different.

Thanks,

Kevin Gallimore

It doesn't have to be that thin, but thin is good. The (probably unmeasurable) eddy current losses will be higher in thicker material. That is the reason I wouldn't simply mill a cavity in a block of something. Some outfits flash an aluminum coat on the inside of a plastic cover. Many pickups ignore an electrostatic shield altogether. One of my other options is to wrap the coil in copper or aluminum tape, and cast an attractive shape around it in epoxy. Mostly it's a exercise in making something that looks different. As a collision between transducers (you have no doubt noticed that any kind of audio transducer tends to draw a fringe element out of the caves) and musicians, I want to have some fun with it. Not only will the dials on the instrument go to 11, But I'll tell 'em that the pickups have to wound underwater at midnight using low xenon copper wire, made by pounding copper nuggets flat. I'm still working on the virgin sacrifice story.

Thanks,

Kevin Gallimore

The higher conductivity wouldn't make a difference for the purposes of an electrostatic shield in this application. I was looking at aluminum to be able to anodize and dye them in a spiffy color. But since everyone has mentioned it, hammered copper would be an interesting unusual effect.

Thanks,

Kevin Gallimore

I have some copper flashing downstairs and will give it a try. Thanks!

Kevin Gallimore

I think that you will need more than just an *electrostatic* shield. You will also need an electromagnetic shield. These are normally made of multiple layers. IIRC, it is alternating layers of mu-metal and copper, drawn together as a unit. (At least, that is the kind of shields which used to used around magnetic tape recorder heads, especially the professional ones where coupled in magnetic fields were a serious no-no.

I'm not sure how much more or less sensitive a set of pickup coils for a guitar would be, but I think that the magnetic shielding still should be considered important. I seem to remember that at least some were especially designed to reject external fields -- called "humbucking" pickups.

Good Luck, DoN.

Now -- I have *dealt* with producing coils which had to be wound under a bath of silicone oil. (The reason was that these produced a rather high-voltage pulse in a quite small size.) Switch to that from the water, and you may even *convince* someone. Perhaps claim that the Silicone oil has to come from removed breast implants, recalled by Dow Corning some years ago for health reasons. :-)

Enjoy, DoN.

I read a description in an aluminum fabrication book by alcoa that I really want to come up with an excuse to try - forming with rubber in a press. Make a form from wood to serve as a die, put it on a sheet of wood or metal, make a box just bigger than the base plate and several inches deeper than your part is tall, get a sheet of rubber somewhat thicker than your part is tall and put it in the box. Put base plate on hydraulic press, put die on base plate, put sheet of material on die, put box on with rubber in contact with material, and press away. A calculation I did some time ago suggests that you would only need 5-10 tons for your little box, assuming you don't set up multiple dies. The base plate needs to fit the box within about 1/32" to keep the rubber from being extruded out, and the box and base need to be several inches bigger than the die in each direction so the edges don't limit the forming. The rubber can be layered up from thinner sheets, and adding smaller dies around the main one helps direct the forming if needed. I don't know if you could get a really good corner this way, but it would be fun to try, hmmm? :-) The process is supposed to be good for low volumes because only one die is needed, not a matched pair, and the die can be cheap wood. If you are really interested I'll dig out the book and post the actual title and name of this process.

-- Regards, Carl Ijames carl.ijames at verizon.net

DoN. Nichols wrote: You will also need an electromagnetic shield. These are

Wrapping the pickup in mu metal probably wouldn't work out very well. What generates the voltage are the steel strings cutting the flux lines. If I magnetically shielded the pickup it would only serve a cosmetic purpose. But it _would_ be quiet. I have considered an experiment using a gapped core to concentrate the flux in a given area, but as far as I know this is not done commercially.

I seem to remember that at least

Humbuckers have two coils, one with the magnet slug, and one without. The coils are wired out of phase. A field impinging both of the coils is bucked out. What it costs is winding capacitance, moving the resonant peak of the assembly down.

With any of this stuff, it all depends on the noise you like. My pickups will be special because I'm going to wind them with Monster cable.

Kevin Gallimore

I wouldn't be able to hold my breath long enough to wind a pickup. I'll tell them the reason it takes so long to make them is that I have to come up for air.

Perhaps claim that the

But think of the warning labels!

Kevin Gallimore

As I recall the end mill I used was a ball end mill so there was a radius in the corners and at the bottom. I may also have formed it part way and then annealed the copper before forming it all the way. I can't remember if I did that or whether that was when I was trying hammer forming.

Dan

That was more what I was thinking -- block the hum source from most directions, but allow easy access to the strings modulation of the field -- just as there is a gap for the tape to pass through to reach the heads, and sometimes a secondary cup shield which closes down once the tape is in there (e.g. the Ampex 300 series and 440 series machines).

But one technique which I have not yet seen tried involves making connections to the two ends of the string, and just putting a permanent magnet near the strings where the pickup coil would otherwise be. With this, you could even use bronze strings or titanium, or other esoteric choices, and still get pickup.

Good Luck, DoN.

I see a problem with that. The string and associated wiring would form a loop which could pick up a significant amount of hum.

When I was teaching a hardware course, I wanted a "grabber" demo of time domain reflectometry. I got several feet of monster cable and the same length of hardware store #12 side by side (not twisted pair) "lamp" cord. I then compared the propagation and impedance characteristics of the two in the range of DC to several tens of MHz. There was no perceptable difference into either a matched load or an 8 ohm termination. Monster cable is a marketing ploy for those that fit, "A fool and his money are soon parted."

Ted

--Howzabout using cartridge brass? Real common, dirt cheap and you can pick your "caliber" to match, yes?