Headbasket mesh punch die

Hi all,

Well I am at the point where I am actually ready to make some mic parts. I designed a male and female die set to form head basket mesh. This is my first stab at it. Does anyone know if there is anything special to be designed in to get a clean cut?

What I have now is a lip on the male die, that will meet the edge of the female die and (hopefully) break the mesh clean. Pic attached where you can see the two pieces (middle of image).

Anyone done this before?

There is a video out there somewhere of the Neuman factory manufacturing one of the Large Diaphragm mic's and the video shows the cutting, forming and assembly of the headbasket screen.  I saw it somewhere on this site, but not sure where. 

Did a quick youtube search and came up with this, that does show the tackwelding of the fine mesh to the coarse mesh, then forming and cutting etc.

Might help you visualize one process that works

http://www.youtube.com/watch?v=mTfG6gKeb18

Yep, I did watch this video, which is the basis for my dies. I am just not sure if there is any technical requirement to get a clean break on the edge. I left .25mm relief where the male die cutting lip meets the female. I am not sure if that will be enough, depending on tolerances.

riggler said:

Yep, I did watch this video, which is the basis for my dies. I am just not sure if there is any technical requirement to get a clean break on the edge. I left .25mm relief where the male die cutting lip meets the female. I am not sure if that will be enough, depending on tolerances.

Click to expand...

Not sure if you'll find any infos about that, and you might be caught in the process of fine tuning this value for yourself  :-\, won't be a cheap process i guess.
I could be wrong, but seems like a precise info, and maybe a little "secret"????
Since this will also depends on the Mesh thickness and the numbers used, worse case scenario would maybe be just a half cut, but i guess 0.25mm could do, that's seems tight enough.

Yes Zayance. It is not the end of the world if I don't get a clean cut, more of a lesson in learning how it is done. I estimate the mesh thickness will be about 2.5mm.

For a clean shearing effect, you may need to get an almost 0 tolerance fit there. (like a metal shear), and also think about angling the cutting edge so the cutting force is concentrated on a couple points, then slices along the mesh, like a green-lee punch dye. Otherwise, you might find that it just binds up.

Dunno if you saw this one, but it shows how they do it in AEA ribbon microphones.

http://www.youtube.com/watch?v=SHkOkqnJjy0&feature=player_embedded

Wow, I like how AEA does this. Much easier for the DIY-er. I can remove my cutting edge, just form the mesh. Pull it out, trim with Dremel!

holy crap those are not your average fridge magnets!

We use hardened steel diesets for grille forming. An integral trim will typically leave a burr since the waste must bend down so a shearing crosscut can be done.

Punch press tonnage is quite low for most grilles. We do use punch presses rather than AEA's antique blacksmith press. It's a neat old machine though.

To trim we mount the pressed grilles on a little fixture and a thin abrasive cutoff  wheel (run in a router table) neatly trims them with no burr.
We can do this in the cnc as well, but it's silly to waste class 7 spindle bearing use and wear...hence the semi manual station. It's about as fast.

We do punch round flat grille material for capsules. Punch and die are 01 tool steel hardened and tempered to 58-60 RC. Die clearance is 10%
of the mesh wire thickness...typically about 0.001". We use a spring extractor since the parts tend to bind in the die. Stripper plates are not needed with most mesh sizes. We do these in a 3 ton kick press.

Les
L M Watts Technology

Hi Les,

Do you know of any low cost way to DIY a forming die? In your experience, do you think a 3D printed part or a hardwood part would last to form about 60 pieces? Getting a steel die made is ridiculously expensive. I think that you are right and that I will have to forego the cutting edge in my die.

I would imagine a hardwood die would last through that small of a run. If not, make two!

A wood form would not work well with that particular shape I think.

But it depends on the material.

We use two different types of mesh...260 brass and 304 stainless steel. The 304 is much more difficult to form but has nice corrosion resistance.
The brass forms easily if you anneal it (which we  do). Forming  re work hardens it. We then Electroless nickel plate. We could do that for you.

Yes the dies are super expensive to have made. We make them in house. The large ones are milled from 1018 steel and then case hardened.
A smaller one for our pencil mics is a simple round cup....those dies are just lathe tuned from 01 tool steel and hardened .

An unhardened steel die can be used for proofs, but has significant wear even after a couple dozen formings with SS. Much less wear with brass.

There's a way I think you can make that die without extensive cnc tooling though. It's a method we have used for quick protos.
In your case rough mill the upper convex portion from mild steel, then hand file to shape. With care this can be done quite accurately.
Then apply strips of flexible tape to simulate the mesh thickness and use it as a mold to CAST the lower half in filled epoxy resin.
Line the top with steel strips. That's the only area that has big wear...it's where the mesh deforms 90 degrees fron flat sheet to basket edge wall.

The rest of the bottom mold doesn't wear much because it's subject to hydrostatic like pressure. In fact in many forming dies rubber material is used. It uniformly applies pressure to the material which then forms around the steel upper die.

You can in fact hydroform things like this with just one die. But that's another story.

It would be good to case harden the upper die (we use Kasenite) but if you are forming annealed brass unhardened steel would probably last several hundred impressions.

Now...if you have a cnc mill all this becomes easier...just mill, polish and optionally harden just as any other die or injection mold.

You'll need a press of some sort. Cobbled up things with automotive jacks could work...or vices...we use a punch press.

And then there's the easiest way...have us do it for you! :^)

Les
L M Watts Technology

Hi Les, I tried sending you a PM, did you get it?

riggler said:

Hi all,

Well I am at the point where I am actually ready to make some mic parts. I designed a male and female die set to form head basket mesh. This is my first stab at it. Does anyone know if there is anything special to be designed in to get a clean cut?

What I have now is a lip on the male die, that will meet the edge of the female die and (hopefully) break the mesh clean. Pic attached where you can see the two pieces (middle of image).

Anyone done this before?

Click to expand...

Excuse me, would you please tell me your this plan succeeded, I also hope to have a Headbasket