confusion on spark gap on top most level and all flat level

[foolsh]

when i went for a course on copper electrode milling,the teacher said to leave all flat surfaces without spark gap as well as top most level and reference plane z for edm machine setting to zero.while cutter diameter is deducted 2 times the spark gap and ball nose cutter radius becomes radius minus spark gap.but i suspect somethings wrong,what if the ball nose cutter goes over the top most point?wouldn't it becomes smaller than actual height?

[Müřlıń®]

quote:

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wouldn't it becomes smaller than actual height?

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No, the electrode is up the distance of the gap.

[Brad St.]

Foolsh, in my experience it's how you and the edm person pick up and set up everything. If you mill the top then you have to mill everything in relation to it the same also. It becomes a matter of what works best for you and your machine and operations thru your shop. You really need to take the time and establish a system that **ALL** are familiar with in house. You don't want to be having one edmer picking up a trode one way and another picking up a diferent way when especially your picking up a third way to manufacture the part. They need to follow how you orientated the cut and pick up the same as well as the fact that you need to use an appropriate method that they can utilize on the sinkers.

 

This may sound like a lot but it is the fundamentals that allowed me in my previous experience to go from a 5 man shop with manual sinkers to over 30 people and 3 charmilles with 40 tool changers with a robot tool changer on one of our high speed graphite centers.

 

Take a hard look at the geomtery your cutting and where it needs to be when your done. If you can see that then you can cut it many diferent ways, finding the most efficient way is the key to your next raise on your paycheck.

 

[El Scotthead]

Another big thing you have to consider is if the electrode will be used on a manual or cnc edm. And if its a cnc, then what type of orbit will be used? It'd be tough to try to explain it on here and have it make sense.

 

A great help to me was talking to some friends who run sinkers and have them desrcibe how they would make electrodes in certain situations. I even had them sit down and sketch the final cavity(with finished dimensions), and then sketch the electrodes. This is really the best way to understand what the EDM is doing during the burn process.

 

I would suggest talking to the EDM operator(s), if you can. If not, I'm sure there are resources out there that can explain this stuff more clearly than I could.

 

The Mitsubishi training manual is pretty good, if you can get your hands on one(you have to go to class to get it, but maybe you can borrow one, or find it on the internet).

 

If you have a certain electrode you're having trouble with, may put a sketch on the FTP site so we can take a look and make suggestions.

 

HTH

scott

[Fig sign]

I make electrodes many years and work on EDM too.

What actually happens on edm without orbitting is simple enough :

you mill everything less size of spark.

May be exept lower reference plane ,if you use it in setup

Dimensions like width and length would be less 2*spark ,BUT HEIGHT WILL BE THE SAME .CAUSE

0-s-(4-s ) IS SAME -4

AS 0-4

iN ORBITING ,WHEN ELECTRODE MAKE PLANETAR MOVEMENT ,the picture is different

HTH

[foolsh]

what about the highest point,wouldn't it be milled off minus the spark gap?if we use ball nose cutter,i.e. cutter dia.-(2 x spark gap),tool radius - (spark gap)?especially if the top surface is a radius surface but not flat?

[Fig sign]

sURFACE OFFSET WITH NEGATIVE SPARK VALUE FOR ANY 3D

TOOLPATH .surface offset -0.035

for any 2.5 toolpath you add spark size to height ,if you mill height z0 with pocket toolpath it became z-0.035

HTH

[Matt Berube at Ferron Mold]

We use 2 basic cutting strategies for electrode milling.

 

On items that are not critical, I lie to Mastercam about cutter diameter. For example, if my tool is .250 dia Ball End Mill and spark gap is .005 / side, I will define the tool as .24 dia. This results in electrode that has spark gap in X and Y but not Z. Using this strategy, we typically employ "down and orbit" cycle in EDM.

 

On critical items,(mold shutoff) I define the cutter as what it really measures and to achieve spark gap, I specify NEGATIVE "stock to leave".

 

The second strategy will remove stock from the top of electrode if your surfacing toolpath includes the top. If the top is flat, I usually add a toolpath that rips it off to Z - S.G. If the top is contoured, I make a "set block" to set height in EDM and figure the burn depth from it. For this strategy we use "spherical orbit" in EDM. This is the only way I've found to get accurate 3-D shutoff surfaces.

 

The most important thing is to make sure that you are leaving your step heights intact. If you are milling "s.g." from top surface, you better take it from all steps. If you leave the top at Z origin, you leave all the steps alone.

 

This stuff is easier to do than explain... I hope this helps a little...

[foolsh]

got it!i will mill off all spark gaps at the top and all flat levels!that ensures that all surfaces have spark gaps except the reference plane foe edm setting

[Müřlıń®]

In the "Old Days" of manual EDM, you would have to measure your cavity depth in order to achieve any kind of tight tolerance.

 

We figured overburn and crater depth for polish.

 

So in order to keep from making more electrodes than you really need, we just kept up with how much our electrodes were wearing and played our tolerances.

 

I always made just the sides - stock for O/B.