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Wire EDM - need some education


Feb 19, 2002
Peralta, NM USA
I have a couple of parts that need to be cut from hardened steel. They have inside and outside dimensions and I need some idea of just how to prep the material for wire EDM. Obviously some through holes are necessary but it would seem to be that they need to be referenced to the drawing so the EDM comes out square. I'd also like some pointers for the drawing - what's required and what's useful to have. I'm assuming something like a DXF would be the base for the

If it matters this is a part for my next steam locomotive - it's the valve link that connects the eccentric with the valve. I'm figuring on making it from 1/4" A2 since I've got that on the shelf. There's a radiused slot (section of an arc) in the middle that's kind of important for location, radius and finish, the outside doesn't matter as much.


Jul 23, 2019
When I was subbing out wire EDM I made DXF drawing with annotations explaining also if I was after male or female piece and how many passes I require. Marked up datum and edge to clock. If I drilled holes before heat treat I would also dimmension them from the datum (unnecessary if they have cam software). If you are after male/punches part then it is also worth marking on which face would you like the tab being left.

If tapers or 4 axis were required I marked up top,middle and bottom profiles with different colours and annotate on the drawing. Next to it or on another page I would put side view showing heights for each plane as this is important.

That is for injection mould tools.

For one off I would send a plate with few 3mm holes drilled 5-10 mm from the edge and send DXF of your part. Give them a call and explain what you are after in terms of accuracy finish and tab. Much quicker.



May 31, 2011
upstate nj
If you have a feature that is important having a start hole properly dimensioned is important. The setup is going to be determined by the programmer, tolerances help. If this is a multiple setup part having some relatively to other parts greatly increases accuracy. If this is the case I prefer to work off a 3d model, a bunch of 2d drawings can get messy.

All in all it's not too difficult, you can post the drawing here for us to look at if you want.

5 axis Fidia guy

Aug 17, 2006
I will give you some very quick advice based on my in house experience and also that of an outside shop. You need material around the entire piece to drop out, many times we need a minimum of .25 inch because the workpiece sits on rails in the machine. It's cheaper and more accurate for the wire guy to pick up an ACCURATE thru hole compared to working off an edge or center of the block.(No need to thread and break the wire). It's always best to have the wire house put in the start holes, unless you have a conversation with them first. They get all red assed when you just willy nilly put in a hole where YOU see fit. Let the wire guys know where to "tag" the part, this area will have to be worked out, by the wire or some means other than the wire. Give them a tolerance and surface finish needed, this will give them an idea how many skims you need, if any. Also material is cheap, give them some room for an extra part or two, if one gets scrapped, it sucks trying to play catch up with material later.
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