Dowel Hole Burning

Could use some help. Using wire to complete a 0.500" dowel hole in about a 3" thick piece of steel. The hole starts at about 0.460" and I do not want to drop a slug. I have tried a no-core method to erode the hole open but that fails often for contact faults and wire breaks, especially when completing the finishing passes. I have also tried doing a no-core to within 0.010" of final but that has similar results. Lately I have given up on no-core and done successively larger rough passes to within 0.010" and then a final cut with roughing and 4 finishing passes. This works better but I am still having problems. There has to be a better way. I appreciate everyone’s help.

Starting with .040 stock in the hole is annoying for the wire. Usually when this happens to me I will use a no-core with .005 step over using 0.010 wire, if you are getting wirebreaks, your cut might be to hot or poor flushing. I let the no-core take me within .004-.006" of my finishing size, then being that your piece is 3" thick, I would take 3-4 more passes finishing. Also try running your 3rd condition again after your 4th.

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I agree with this method, I usually step .008 using .010 wire with lower power, rough cut feedrate, and low flush.
When you get to the normal Rough Cut offset, use lower power and low flush for that also, then skim normally.

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Have you been able to improve your cut at all? Just curious, I know how frustrating it can be sometimes.

Thanks for the thoughts on this. I appreciate the help. I have had some decent success. I did the no-core pass with a 0.005" step and it worked reasonably well. I had a few breaks, but made it through. I then did 4 skim passes and the end result was a perfectly fine dowel hole.

As always there is more to the story. I completed another project with a similar feature and it went flawlessly so I compared the differences in the two and I believe where my first project was frustrating may have had less to do with the dowel hole and more to do with “consistent thickness” of the starter hole.

I am thinking that I will throw this out on another thread which I will be posting shortly. Thanks again for the help and I am interested to hear what you think of this new thread.

I Wire EDM precision dowel holes all the time.
I usually don’t care if the slug falls. I program a M00 at the completion of the circle. This way the slug usually falls as the machine stops.
After slug removal, skim for finish size.

If I do need to retain a big slug or core, I program a stop about .020 from program end. Then I use a thin brass shim with a small 90 degree bent flap at the bottom that fits into the eroded wire track.
I straighten the flap, push it down until the flap clears the bottom of the workpiece and the flap pops out. I gently pull up the shim to tighten the flap, then bend the top of the shim parallel
to the top of the part. Then EDM until the slug is cut free. I raise the upper head and pull up on the shim to remove slug. Faster and cheaper than doing no core.
To prevent wire breaks on no core: increase SV, decrease tension, decrease on time, slightly increase Wire RPM.
Will cut slower… but you will spend less time
re-threading broken wire.

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Don’t forget that it’s also your wire and water quality, tension, a stable environment and more, there are so many things to take into account but overall we can get it done.