Intaglio and Electric Discharge Machine

[Mustafa Umut Sarac]

Small electric discharge machines plans are available from micro scale engine builder sites or forums.

Electric Discharge Machine is especially for uncuttable , unprocessable alloys when cutting or shaping or drilling. Its has extremelly high precision.

I found when I was thinking , it would be possible to prepare intaglio masters without burin work.

All injection mold makers prefers low strenght curved work with edm , they also correct bad cad file and bad cam work with edm at injection mold , mold preparing to jet engine pals.

I think I need your opinions , this idea is new for me and I dont know any company uses that for banknote engraving.

Mustafa Umut Sarac
Istanbul

 

[AgX]

As far as I know only etching, diamond embossing, electron-ray and laser-ray Erosion has been commercially employed for drummaking so far.

But as you indicated electric discharging may be more accessible to the amateur. One might modify a printer, by giving it a discharging head.

Keep in mind that even with an analog steered discharger you would be quite far off the Apug field.

 

[Michael Guzzi]

As it happens to be I work in its sister process: Wire EDM, which, instead of using a copper electrode "negative" to form the part, uses a brass alloy wire that works much like a bandsaw, just with much much higher precision (accuracy over a 5 inches thick part can be as high as 0.00008" - yes THAT accurate).

But, your idea involves, I reckon, a quite elaborate electrode(or many small ones that form the final image) to be machined in a CNC milling machine (possibly a high speed model, to cope with the minuscule mill sizes needed to get to all the corners in the electrode needed to produce the smallest details). Or, a hand engraved electrode, which I believe defeats what you are trying to achieve here.

The idea would be good to make many nearly identical masters (nearly because the electrode wears out just as the part does, just at a reduced rate - graphite electrodes are better in this regard, but can cost as much as 10 times more than a regular copper one), but for one-offs it would be quite expensive I think. And you would still need to hand the shop a CAD drawing showing exactly what you want them to machine. The masters would last practically forever though - make it from a Stainless Steel alloy such as 440C, or a tool steel, such as D2, H13 or such high hardness steels. But this seems like overkill to me, IMHO.

 

[AgX]

Mustafa is not considering a 3-D eletrode, that erodes a whole area at the same time as in tool-making, but a needle-electrode which is guided in lines over the area (flat printing plate) by incremental steps.

Thus one Tungsten micro-needle would be necessary. Doable.

 

[Mustafa Umut Sarac]

Hello AgX and Michael,

As you know the real trick in intaglio process is the 3D nature of hand movement and burin or graver.
The track is not only a track but it has virages .

So I was thinking to use a robotic arm like robot head which inspired from 1980s US Submarine Propellers grinding head patent.

think you are orchestra chief and you stabilized your hand and move the baton. It draws a sphere in 3d.

I am thinking to use that kind of head and move the engraving plate in 2d.

Would it be successful ?

 

[Mustafa Umut Sarac]

As it happens to be I work in its sister process: Wire EDM, which, instead of using a copper electrode "negative" to form the part, uses a brass alloy wire that works much like a bandsaw, just with much much higher precision (accuracy over a 5 inches thick part can be as high as 0.00008" - yes THAT accurate).

But, your idea involves, I reckon, a quite elaborate electrode(or many small ones that form the final image) to be machined in a CNC milling machine (possibly a high speed model, to cope with the minuscule mill sizes needed to get to all the corners in the electrode needed to produce the smallest details). Or, a hand engraved electrode, which I believe defeats what you are trying to achieve here.

The idea would be good to make many nearly identical masters (nearly because the electrode wears out just as the part does, just at a reduced rate - graphite electrodes are better in this regard, but can cost as much as 10 times more than a regular copper one), but for one-offs it would be quite expensive I think. And you would still need to hand the shop a CAD drawing showing exactly what you want them to machine. The masters would last practically forever though - make it from a Stainless Steel alloy such as 440C, or a tool steel, such as D2, H13 or such high hardness steels. But this seems like overkill to me, IMHO.

Thank you Michael , I havent known the eroding effect. This is important.

 

[Michael Guzzi]

Depending on how accurate you want the final product to be, and the needle thickness, that may work. Slow, but it may work. The smallest EDM work I saw was about 0.2 mm round, 0.5mm deep, and each hole took about 15 minutes to be made, under oil, and consumed about 70Wh of power.

 

[Mustafa Umut Sarac]

Hello Michael,

I think 0.2mm is too thick for intaglio but I am not sure , may be its enough. Please enlighten.

Umut

 

[Mustafa Umut Sarac]

The smallest EDM work I saw was about 0.2 mm round, 0.5mm deep, and each hole took about 15 minutes to be made, under oil, and consumed about 70Wh of power.

If we increase the wattage to 700Wh , is precision been lost ?

 

[Michael Guzzi]

AgX suggested a Tungsten micro needle. That escapes the realm of normal EDM, the gap (distance from the tip of the electrode to the part) would have to be increased, needing a higher voltage to establish the arc, and accuracy and stability of the arc would suffer, especially if eroding in the air, as there would be a buildup of contaminants on the needle caused by the small particles of material melted away form the part. As seen in poorly done TIG welding, when you hold the electrode too close to the pool of metal, and/or poor gas shielding (I believe they use Argon, maybe other noble gas - too expensive for home use though).

Hello Michael,

I think 0.2mm is too thick for intaglio but I am not sure , may be its enough. Please enlighten.

Umut

I'm not sure either, I guess it depends on what you want off it but I suspect the finest engravings on say, the Dollar bill, are about 0.02-0.05, by looking at them.

If we increase the wattage to 700Wh , is precision been lost ?

You would lose some precision-generally, the slower you work the better the accuracy and finish.

Home made EDM's aren't impossible to make, but may not be economical once you reach a certain accuracy. Especially the power controller unit and the axis movements, these are the heart of a EDM.

As a little offtopic, I studied under a man that designed the power source and erosion heads for a custom machine, that he told us, was used to EDM some part of the jet nozzles for one of the late NASA Apollo rocket engines. The drawings were something to behold.

 

[Mustafa Umut Sarac]

Well , with your post Michael , I remembered welding. When you cover the place to be welded with flux powder, the welds would be extremelly clean.

With wire edm , will there be a chance to cover electrified area with flux ?

Is this good idea ?

NASA is great.

 

[Mustafa Umut Sarac]

I'm not sure either, I guess it depends on what you want off it but I suspect the finest engravings on say, the Dollar bill, are about 0.02-0.05, by looking .

Can I reach that precision with miled electrode , hand made electrode or commercially sold graphite one ?

 

[Michael Guzzi]

The NASA bit is just a little offtopic, I am nowhere near the knowledge of that man!

Well, TIG welding does away with any kind of flux as far as I know, but that is because they use shielding gas which works much better. Some kind of flux may work for the application, but I have no experience doing that. And, well, you are trying to remove material instead of adding it, so I don't know how that would work with flux.

In regular EDM machines one uses a special dielectric oil that helps cool the part/electrode, carries away the particles melted away, and stabilizes the discharge by providing a stabler medium for it. Wire EDM uses deionized water for the same purposes.

Wire EDM is not possible at all to be used here, we are talking "ram", or "sinking", traditional EDM here.

Can I reach that precision with miled electrode , hand made electrode or commercially sold graphite one ?

I guess the only route would be hand made. But that is really fine detail, the electrode will wear those out very fast. One would need thus 2 electrodes, the second one just for the detail burns. I guess at this level of detail the whole idea gets very hard to pull off. And the graphite is just another material to make electrodes from, they have to be shaped somehow just like regular electrolytic copper. It is softer to work with, and may be more suitable to hand work. It's a special, fine grain graphite (there are actually various grades) and costs quite a bit.

Is there anybody else on APUG that works with EDM to give more input here? AgX? I am giving my opinions based on what I know, but more opinions would be welcome, as anybody that works with this stuff knows that there is more than one way to make things in this field.

 

[Mustafa Umut Sarac]

Dear Michael,

Thank you for everything. Let me ask an important question , If I make my fine graphite 0.02mm thick Sinking EDM burners , would I be needed to lower the head after each burn ? I am thinking stamp size engraving and For each little line , how much the wire loss its lenght. Thinking loud , may be this would be the same as depth burned . I think this would be very labor intensive job for making each burner for few lines.

I think graphite burner production can be simplified as bassoon reed making. An cutter , a jig can be modified to produce 30-40 burner for couple of hours of run.

Now another question , how many watts must be the burner , 70 wh or lower or higher ?

I am thinking highest precision and cleanest cut .

Additionally , what kind of liquid to sink is most suitable?

 

[AgX]

You would need a feed of that burning graphite eletrode I guess.
In a eroding process that is interrupted when moving to the next nap.

 

[Mustafa Umut Sarac]

AgX , Wonderful idea , I think I must borrow idea from graphite pencil makers , mold the powder , press and bake.

 

[Mustafa Umut Sarac]

By the way , do graphite needs clay to be molded , set shape and baked to final. I saw someone was molding pencil sculptures by that technique but I dont know whether pure graphite could be processed as above.

Second question arises , At internet there are many EDM plans available especially sinking ones. Do they come with moving table or what is the best way to make a moving table. May be piezo ones , but I dont know.

Third question , I want to build a moving table and how I would be needed to describe its precision ? How precision been called at CNC business ? And I heard PLC circuits. Are they needed ? Nano precision might be expensive but may be not , I dont know

 

[Michael Guzzi]

Many questions here.

Thank you for everything. Let me ask an important question , If I make my fine graphite 0.02mm thick Sinking EDM burners , would I be needed to lower the head after each burn ? I am thinking stamp size engraving and For each little line , how much the wire loss its lenght. Thinking loud , may be this would be the same as depth burned . I think this would be very labor intensive job for making each burner for few lines.

I think graphite burner production can be simplified as bassoon reed making. An cutter , a jig can be modified to produce 30-40 burner for couple of hours of run.

Now another question , how many watts must be the burner , 70 wh or lower or higher ?

I am thinking highest precision and cleanest cut .

Additionally , what kind of liquid to sink is most suitable?

The electrode would most certainly erode away at a fast rate.

What depth are we talking about here?

The power needed is dependent on a number of factors, the most important one is the area of the electrode. 70Watts would be probably enough, at full power the Wire EDM's I work typically run in the 200-250Wh.

And you understand the power supply isn't just DC, it actually pulses many million times per second (think 10us on, 30us off, repeat for the whole burn), and this brings some complexity to the design, but not much, mostly good RF shielding and such.

The most suitable dielectric fluid would be one of the special oils used, these are flame retardant, last a long time among other things. In the past, kerosene was used, it is OK but is obviously very flammable. In wire EDM we use filtered, deionised water. This would be OK for slower work, but I don't recommend it. Ultimately some fluid must be used, "dry" EDM is impossible due to fast carbon buildup on both the part and electrode, causing all sorts of problems.

You would need a feed of that burning graphite electrode I guess.
In a eroding process that is interrupted when moving to the next nap.

That could work, never seen anything like it though. But thinking on this, maybe use two electrodes, one made from tungsten for the "roughing" of the coarser details, and the the ultra fine graphite one for the fine detail.

By the way , do graphite needs clay to be molded , set shape and baked to final. I saw someone was molding pencil sculptures by that technique but I dont know whether pure graphite could be processed as above.

Second question arises , At internet there are many EDM plans available especially sinking ones. Do they come with moving table or what is the best way to make a moving table. May be piezo ones , but I dont know.

Third question , I want to build a moving table and how I would be needed to describe its precision ? How precision been called at CNC business ? And I heard PLC circuits. Are they needed ? Nano precision might be expensive but may be not , I don't know

1. We normally buy blocks of a special graphite that are then machined to shape. That is because the graphite needs to be free from porosities and defects so that it has maximum strength and conductivity. "Normal" graphite may work, but Im not sure until I try it.

2. You would have to show me what you are talking about, I've never seen proper plans for a EDM online. They are probably fixed tables or at most manual ones.

3. The precision is important, not only the positioning accuracy and repeatability but also its interconnection with the CNC unit to provide stable, efficient EDM operation. PLC's are great in respect to robustness needed in the industry but harder to implement in hobby use. I recommend a PIC microcontroller (maybe more than one, in dedicated modules properly interfaced to one another). Precision as read in the panel of a CNC EDM is often 0.001mm, and in wire EDM, 0.0001mm. In practice, 0.005 is plenty precision. For a hobby use like engraving, I think 0.01 should be enough no?

Are you thinking about building a CNC machine? Post the dimensions etc that you need the machine to have and I'll take a look. A gantry type machine would be ideal to you IMO. Sort of a plotter with a EDM head on it.