Burning out a tap

First one I burned no problem, in just a few minutes...the second one just did not want to burn. I tried changing settings increasing power, frequency but after a couple hours I got almost nowhere. I am using a 0.070 carbon rod on what looks like a 6-32 tap (I didn't break it so I don't know what kind or material it is made of). When I shut the machine down I did not have a nice clean hole but more of a pocket less than 0.100 deep.
Any guidance as to what to look for would be appreciated - not sure if its a machine problem or if something strange is going on with the tap. It seems that the energy is not being properly directed or ...?

Could it be a carbide drill? I get parts from time to time from a customer to burn out taps. Once in a while there is a broken carbide drill rather than a hss tap. Verrrry slow trying to edm carbide on steel settings. I now check with a magnet (parts are ti) to save fustration.

Btw, I have good luck with copper tubes with the center divider for burning out taps. Good flushing.

It would help the learning curve, as to what settings others are using for tap burnout.

less on time, more off time.

lavrgs said:

First one I burned no problem, in just a few minutes...the second one just did not want to burn. I tried changing settings increasing power, frequency but after a couple hours I got almost nowhere. I am using a 0.070 carbon rod on what looks like a 6-32 tap (I didn't break it so I don't know what kind or material it is made of). When I shut the machine down I did not have a nice clean hole but more of a pocket less than 0.100 deep.
Any guidance as to what to look for would be appreciated - not sure if its a machine problem or if something strange is going on with the tap. It seems that the energy is not being properly directed or ...?

Click to expand...

If the tap is loose in the threads it may be shorting out and causing the machine to back up. look at the electrode very close and see if there is any pitting or "iceicleing" on the electrode. It could also be that the tap broke(more than one piece) and some small piece is in the hole you are trying to burn. clean the threaded hole out and make sure the electrode is clean as well. (blast air in the threaded hole and clean the electrode with some fine emery....)
I'd try that and less on time and more off time.
Ryone

CougarMountain said:

Could it be a carbide drill? I get parts from time to time from a customer to burn out taps. Once in a while there is a broken carbide drill rather than a hss tap. Verrrry slow trying to edm carbide on steel settings. I now check with a magnet (parts are ti) to save fustration.

Btw, I have good luck with copper tubes with the center divider for burning out taps. Good flushing.

It would help the learning curve, as to what settings others are using for tap burnout.

Click to expand...

Very good point - I occurred to me that this "broken tap" may not be a tap because it looked too solid- no flutes. I will check it with a magnet as you said as well as cleaning and checking for broken pieces and inspect the electrode.

Less on time and more off time - I have very limited experience with EDMs what does this help with?

Thanks for the quick responses

Bill

Could still be a tap even if it has not flutes, could a be a roll tap that forms the threads rather than cuts them. A real bugger to get out in my experience, have to spark out to something like the thread minor diameter for the tap to break up.

It looks like there is one part where a different tap was used, I burned out the tap in the last of three in the usual amount of time. On "the difficult one" I am able to turn the part over and attack what is close to a flat surface but the progress is slow as it was originally. I do see it going a bit faster and that may be because of the suggestions offer earlier are more prevalent on the other side - this side is clean, unbroken etc.but it took about an hour to burn a 0.70 hole 0.100 deep.
As Matt suggested this may have to be a "pecision" burn to get all the bits out but for now I will be happy to get through it! I'll be back at it tonight and report back.

Bill

Sorry for not relaying what I found... when I went to the shop and asked if they had used a carbide tap...they said no but after a short pause I was informed that since the tap broke with only a few threads cut they had made a punch out of carbide and it broke...bottom line is that attacking it from the tap side caused all kinds of strange arcing - fortunately I could turn the part over and attack the carbide using a 0.070 carbon electrode. Once I got through that it also went through the tap and I pushed out the carbide...
Burning more carbide tonight...rough out a lathe grooving tool, its slow but it seems to be going.