how many skim passess????

We do a lot of bores,key ways and some other applications were we need +- .0003 ,in these cases how many skims would you normally take.I understand that all vary on material type, thickness setup etc etc. We use lot of different material but for example 4140 HT 3" thick EDM'ing a 2" square in the middle,using brass .01 wire. How many skims will you take? and also just in case if you wanna know, we own Makino.

Depending on finish requirements and flushing conditions 1 rough and 3 - 5 skims. Using Mitsubishi. Progressive Tool @ MFG. INC. Greensboro, NC

asraraleem said:

We do a lot of bores,key ways and some other applications were we need +- .0003 ,in these cases how many skims would you normally take.I understand that all vary on material type, thickness setup etc etc. We use lot of different material but for example 4140 HT 3" thick EDM'ing a 2" square in the middle,using brass .01 wire. How many skims will you take? and also just in case if you wanna know, we own Makino.

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We have several fanucs and a makino duo 64. If your somewhat new to the particular machine, or if your just making 1 part go safe with multiple skims maybe 3. Honestly all the machines we have run will hold that in 1 skim easy checking with gage blocks and a bore gage. We use wireedm in a job shop environment every minute counts. If the machine was a tool room at fortune 500 company then I would give a mirror fininsh

Wire newby here, with a question. If you have to hold tenths, what depth are your skim passes? Is there a rule of thumb relative to wire diameter? Or stock allowance for skim cuts? Our shop bought an Agie Charmilles Cut P-20 wire machine for a particular part we make in large quantities, previously farming out the wire work. Tolerances are a few thousanths, speed is of the essence, and the situation doesn't lend itself to us gaining expertise through experience with this particular job, but surely other work will present itself.

Hi John:
Most of it is pre-canned; you pull all the cut settings from a table in the machine as a package, and with it the offsets appropriate to the material composition, the part thickness, the desired outcome (accuracy, speed, surface finish): all is done for you.
Most times this works fine.
It doesn't work though, when the part warps so much it won't clean up all of the roughing with the finishing toolpaths.
This is almost always due to stress release in the material.
Roughing the part out oversize then becomes necessary, which makes the first skim cut take way more than it's designed to do and it has to take more in some places than in others.
Sometimes the best way forward is to take a second roughing pass with the flushing turned down and the wire tension turned up.
Sometimes two semi-finishing skims is the better way; it seems to depend on the machine.
The goal though, is to leave very little (the correct amount) for the final skims, and to make them take off the same amount everywhere.
My machine typically roughs about 0.0035" oversize, then semi finishes 0.0005" oversize, then skims for final finish and size with one or two skims of 0.0001" to 0.0002" each but I don't select these offsets manually; I pull up the cutting condition package based on the wire size, the material and its thickness along with the number of passes, and accept the canned package unless I'm doing something really screwy.
For example, I've found I can go around a profile and re-cut it taking a tenth at a time for up to 0.0005" without touching the offset; I still prefer to fit things like close tolerance ejector pins this way, opening out the pin bore a tenth at a time until I like the fit.
Cheers

Marcus
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