copper electrode

[ngkim]

i wonder anybody knows how to mill the flat surfaces of all the steps of a 3d electrode by leaving spark gaps on all flat surfaces of steps without having to do a 2d contour.can't use a flat endmill cos negative stock not allowed for a flat endmill!a surface contour won't work,bcos of flat surfaces doesn't leave a negative stock.it seems mastercam don't have much literature on milling copper electrodes.

[cadcam]

To add for over burn on a dunker scale the file.

[ngkim]

Mr. Cadcam,how do you scale a drawing for spark gap of 0.05 mm?i have tried that but it's not accurate.and what is a dunker??

[tm311]

I think jay is talking about a sinker e.d.m

[Scott Bond]

Hi

"I think jay is talking about a sinker e.d.m"

Sometimes called "dumb sinker"(jmho)

Hi

I think M.C. will make any cuts that the user wants to make. The user has to know what he/she will be cutting.

If you contact your reseller for MOLD PLUS ,he could demo the electrode maker.

If you would like ,i will look at your file .Please zip it and put on the ftp sight.

[cadcam]

Yes sir i was talking a about a sinker EDM.

Some of us silly mold makers call them a dunker.

Ok so you are stating it in metric I see.

When i used to make eletrodes for molds in most cases .001 to .003 for over burn.

[JAMMAN]

quote:

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Some of us silly mold makers call them a dunker.

---

I was in shock when I learned what silly electricians called strain reliefs. He even sent me to the supply store to pick up two different sizes. Both variations of large.

[Guest]

I have never cut a copper electrode, but can't you put a negative value in the stock to leave fields. This will over cut the stock by that value.

JM2C

[Ketil]

Hi !

I am also wondering how to scale a file and get a

constant gap?.

I always use graphite in my electrode (easy to cut), but the principle is the same.

I try too use a spher mill or a bull mill,then you can set the stock to leave to negative

(-0.05mm).

If you like to use a flat endmill(10.0mm) try to define a new tool (9.9mm)but remember to move the z.axis -0.05mm in the mill. This method is not precise.

[bryan.davis]

Ignore the scale file advise its actually an incorrect way of solving the problem and WONT give you a constant spark gap on anything other than regular polygons (CADCAM gets a slap on the wrist!!!!)

BTW if you are using regular polygons then the formula for the scale factor is

1-gap/radius

where the radius is that of the circle thats tangental to the sides of the polygon.

The correct way as previously mentioned is to use a -ve stock allowance,

Another way is to create the electrode by using offset surfaces, but once youve tried this a couple of times you will probably revert to the -ve stock allowance method unless you have a specific reason for setting differing spark gaps on your surfaces.

[ 01-25-2002: Message edited by: bryan.davis ]

[ngkim]

but the trouble is,if you are milling multisurfaces,with lots of pocket depths as well as tapered angles with a small radius at the bottom of each pocket depths e.g r=0.2,0.1,0.3,what type of cutters are you going to use?ball-nose?flatendmill(remember can't specify negative stock in parameters or else resetted),bullnose?if you use flatendmill and gave it a smaller dia.eg.(9.9)for spark gap -0.05 of nominal dia. 10 mm.,then how about a small radius r0.2,r0.25,r0.08etc.it is rather not precise.

[Jerry Bichsel]

I have used MC since v3 mostly for injection molds and here is how I address this.

Lie.

Enter a corner radius equal to whatever spark gap you're cutting to. This will let you comp with a flat endmill. But you will actually use the flat endmill. This works fine as long as you are trying for square corners between wall and floor.

Good luck.

[Ketil]

Hi

I would use a ball mill(the smallest i can find is dia. 3mm R0.15mm ), but R0.08mm??? if you use a flatendmill and you have gap 0.05mm i belive it would vill be 0.05mm radius after E.D.M ? 0.03mm wrong??.

What are you making??, i call R0.08 a sharp corner.

Now i am going home for the weekend .

[cadcam]

Bryan. Davis,

Hi Bryan I know I don't know every thing. And I a willing to say I am wrong when I am wrong or give bad advice.

But to say,what I am saying is no good I have to say other wise.

I am not pulling this out of air.

This is how I have done it for the most part for a long time.

I even talked to a friend that has a plastic injection mold shop about it. This is how he accounts for making trode's.

There are more then one way to skin the cat.

But I am sorry to say I am not off in left field.

I can say that my way may not be the best or even the proper way.

I am going to follow what you folks come up with because I know I can learn some thing new or a proper way to do this.

Thanks for reading this rant.

JM2C

[bryan.davis]

What you advised is a common misconception, and at the end of the day isnt completely incorrect in that it will give you a spark gap.

However the method you prescribed dosnt produce an even spark gap, consider an electrode 3mm x 200mm (we make big mould tools!) if you scale it to give a 0.1mm spark gap each side and use the 3mm width to calculate the scaling factor then you will calculate a scale factor of 0.9333, however this factor will give you a spark gap of 6.6667mm on the 200 mm dimension!!!.

Mastercam does have the option to scale each axis differently, but why, when at the end of the day the correct solution is to apply a -ve stock allowance.

[cadcam]

Thank you,for your reply.

All this helps me and others.

I will take what you have given me and keep it.

[JAMMAN]

Maybe I'm outside my box... but Im curious as to what -ve means.

[Greg Williams]

Hi Guys,

What this thread shows is that there is no absolutely correct way to manufacture electrodes.I have always done it by using -ve stock to leave. If by some chance I cant use this method I apply the spark gap to the tool (use a 10mm Bull endmill and tell mastercam that I have a 9.9mm with a radius of 0.01). At the end of the day it only really matters if you are trying to hold a very tight tollerance. Hopefully someone from mastercam is reading this thread.

[bryan.davis]

-ve = negative

+ve = positive

[Tim Holston]

The – stock is a good way of putting overburn but I think he is not wanting to machine large flat area and with a ball mill it takes to long. Some time you need to go back to the days of ver 3 where I started as well and do some 2d tool path they even have a – Z as well as XY in contour and pocket. I cut copper tungsten all the time for swaging dies. You can use a taper bull nose end mills and pocket out the bottom leaving the small rad. And taper walls.

Tim

[ngkim]

Mr. Greg,

So in order to use a flat endmill to mill on multisurface of sharp corners or small radii(r0.1,r0.2,r0.3),eg spark gap 0.05mm,we input 9.9 dia.R0.01 in the parameter page of surface machining,is that correct?So in general we just need to D-2(spark gap),R0.01(is the radius the same for different spark gaps?).I hope you could enlighten me on this.thanks

[JAMMAN]

quote:

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-ve = negative

+ve = positive

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Ok........ I'm beginning to feel stupid. I guess the "ve" portion is what I don't understand.

[mold100]

This is one of those more than one way to skin a cat things.I know of three ways to do this,2 have been brought up.1)cut 2d contours or pockets,2)my favorite,Bull mills,3)From back in my unsmartcam days,Lie tell it you diameter of your cutter is undersize the total amount of negative stock you are using Ex.if you want .003 per side with a .25 e.m. you tell it your tool diameter is.244.,the only problem is if it is in a program with 3d you have to run them seperate or change your tool offset in the machine,because the z needs to be offset .003 deeper(or 1/2 your total overburn.)Hope 1 of these can help.

[JAMMAN]

Isn't it possible to comp in computer at the center of the ball nose and accomplish X,Y and Z stock "Lies"? Take it easy on me, I don't own mill level 3.

[Lucky]

In Summary:

Scaling is Bad - works for shrink allowance in mold but not for electrode undersized. To make an elecrode for a mold using part geometry, first apply scaling to allow for shrink then apply surface offseting or negative stock for undersizing. Order is important - Do not offset for undersize/spark gap then scale for shrink.

Negative Stock is the preferred method resulting in a consistent undersize normal to all surfaces.

Fudged tool descriptions give correct results and work around the undersize cannot be greater than tool radius issue.

To obtain correct dimensions in the EDMed cavity using electrodes produced this way requires a spherical orbit. Various EDM manufacturers have names for this (AGIE=equimode, Charmilles=3D-ORB, etc.). These 3D Spherical orbits make the cavity larger than the electrode as measured normal to the surfaces (the same way Mastercam undersized it). Other orbits such as circular, cylindrical, 2D vector, 3D vector, polygon, etc. will not yield correct cavity dimensions.

Some new CNC Sinker EDMs Do not have a spherical orbit, most old CNC machines do not and ALL manual machines retrofitted with orbiting heads do not. Keep this in mind if you know you are doing it right in Mastercam but your cavities are not right.

Cutting a 3D shape with a non-spherical orbit requires the shape of the electrode to be distorted. For example a circular or cylindrical orbit requires all electrode geometry to be undersized or moved in the top view (X-Y Plane)only. No easy way to do this most of the time. The part has to be completely remodeled. Ouch!