Hi amchristophe:
The problem is that you need to make the trode small enough that it can slip into the pre drilled hole.
It is then orbited out sideways to burn the threads.
So the trode is skinny...much smaller than a tap of equivalent nominal size.
The major diameter of the trode must be even smaller than the minor diameter of the thread so it can drop in the hole.
As the thread gets coarser the problem gets worse as the trode minor diameter gets so small the trode gets hard to make.
In addition, the trode will not survive to burn a complete thread.
Sinker trodes wear in the corners first and most aggressively.
This affects the major diameter and the area round it first and worst.
So you have three problems as a vendor:
1) you need to time the second trode so it sits in the same radial orientation as the first trode did.
There are ways to do that, but when the trode is tiny, it all gets harder.
2) you can't drop a thread gauge down the hole until all the trodes have been run.
If you screwed it up on the first burn you have to throw away the part, and you don't get to find that out until the last burn is done.
3) unless you have experience with the material, you have no idea if it will burn decently...some will, some won't.
This silicon carbide stabilized aluminum doesn't sound promising...remember, the material must be conductive to burn and so far as I know, silicon carbide is not electrically conductive...it is a semiconductor at best and in pure form, it is an electrical insulator.
I wouldn't dream of taking this on until I knew for sure it could actually be burned on the sinker with any kind of control.
Related to gauges and gauging; the EDM process leaves abrasive grit all over the part in the form of a fine sand-like substance suspended in dielectric oil...think lapping paste..
It's almost impossible to clean it perfectly while the part is in the work tank.
If you leave some behind, it will seize your thread gauge and jam it in the hole while fucking up both the hole and the gauge.
This is why nobody in their right mind wants to quote it...it's a much more challenging set of problems than is immediately apparent.
If somebody actually pulled off a 2-56 thread in this material...they get my respect for even trying.
If they missed a bit on the first kick at the can, you need to cut them some slack and have a conversation with them about how they can improve their process.
If they cost a lot...too damned bad...it's a hard job fraught with uncertainty and difficulty...I wouldn't touch it without a cost-plus contract and lots of time to play with it.
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
