Small Punch Tool

[Joules]

Was set a challenge, can I make a disc with a 0.2mm hole in it that is round.  First try was using a pin and ground it down to 0.25mm, however the steel was too weak and broke once the hole was made.   Found a broken 0.75mm HHS drill and ground a new punch aiming for just under 0.2mm.  Due to the radius on the resin wheel used for grinding, it ended up with less than 0.5mm usable before the taper went out of tolerance.  This time the tool survived punching a hole and looks like I can go smaller in diameter, but not by much.

The bottom hole in this example is the 0.2mm and the hole above was opened out to 0.5mm trying to get rid of the ragged edge.   The shim stock punched is 0.12mm beer can, the application for such a hole is in a pinhole camera with a 25mm focal length. (hole needs to be 0.18mm ideally)

Just something a little different.

[BillTodd]

Impressive 

I wonder if an improvised EDM might do the job . I've worked on a couple of sparkers ,they don't appear to be too complicated.

[Joules]

Funny you should mention EDM, as that was an option discussed, but dismissed as I could grind a tool faster than build an EDM.

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This however did catch my attention and will be following with interest.  Not so sure about the bigger machine at the end, water and this type of mechanics.

[philf]

Bill, I like the look of the wire edm. I want one!

I've made form tools for making small pinion cutters (for clocks) by machining with small (0.8mm dia.) carbide milling cutters. I'm then automatically limited to a 0.4mm radius. With a 0.3mm dia wire this is reduced to 0.15mm which is acceptable. As well as the reduced corner radius, milling tool steel with 0.8mm end mill is a bit testing.

(I'm using a Eureka relieving attachment for the pinion cutters.)

The only real concern is the finish - would it be good enough for a form tool?

Phil.

[Joules]

Hi Phil, the finish is quite rough on a small scale, so would say any tool still needs grinding, and or polishing to get a good finish.  The EDM does look a great tool for small part work.  Will have to see what the reviews come in like once it gets released.  The second machine they show has a steerable wire for angled cuts.

[BillTodd]

The most accurate machine we had at work was a swiss made Agie (?)  it could handle 100um wire  . They are bloody expensive to run but capable of astonishing accuracy.

The wire edm electrolyte was deionised water from a massive (as big as the edm) filter units.

 The sparkers , die sinkers, used an oil similar to paraffin, with automatic fire suppression systems (that would occasionally go off without prompting).

Yes , the finish is fine but granular, it would need lapping to a cutting edge.

[philf]

We had an Agiemaspark (not sure how it's spelt) die sinker. As you say it used a paraffin like coolant. It probably went for £100 or so when our toolroom closed! A very useful machine.

[awemawson]

My Eurospark H425 die sinker is almost identical to the Agiemaspark, in fact many were badge engineered. Here's an ancient thread describing mine:

https://www.madmodder.net/index.php/topic,9319.msg103084.html#msg103084