Date: 11/18/08
Subject: Burning Dowel Holes

Question:
Currently we burn our dowel holes .0005 undersize and lap them after burning. We have found on larger die sections this method reduces the chance of a hole being too large and scraping the entire die section. Have you seen or heard of this practice from other companies?
Thanks,
Bob

To reply to Bob, use the Subject:
Burning Dowel Holes

Answer:
Bob,
Are you burning your dowel holes single pass? I would suggest burning the dowel hole with multiple skim technology after all the openings have been roughed (and skimmed). Most machines have technology for multiple skims. A 4 skim technology will hold size and location w/.0001". Since the overcut on the final skim is only a few tenths/side, it's virtually impossible to blow the size and ruin the block.

Yes other people do hone the dowels for final size, but I don't recommend it. You can skim the hole to size in the time you can hone it. Besides, honing can change the hole location if there is a start-end glitch from a single pass cut. Also, if the block is large, honing can affect the squareness of the hole.

In the "old days" before highly accurate skim technology, we used to leave stock in the dowel holes and actually pick up and balance key features on the die openings in the Jig Grinder. Then we'd finish jig grind the dowels. This allows you to see any machine error or distortion in the block. For certain critical jobs with only .0001"/side clearance, numerous die openings, and no tolerance for error, this can still be a useful technique today. However, it is very time consuming and costly.

Roger Kern
rjk@gedms.com

Answer:
Bob,
 
Leaving lapping stock on dowels holes is just not cost effective. It is best to take the extra time and skim the dowel holes to size. Also, check size before pulling the block out. Doing this will help the rest of the shop to be more efficient.

Todd Turkster
Cole MFG.

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Date: 10/20/08
Subject: Copper or Graphite Electrode

Question:
Good day to all,
I have a requirement to sink a cavity into copper.
Can this be done using a copper electrode, or should I use graphite for this?
Are there any special considerations when sparking into copper?
 
Your comments and answers will be most appreciated.
 Theo Marnewick

To reply to Theo Marnewick, use the Subject:
Copper or Graphite Electrode

Answer:
Hello Theo,

You should be able to use either copper or graphite to burn the cavity with your choice being determined by metal removal rates vs surface finish.  In both cases you can expect high wear on the electrode. I have technology sheets available for both options that I would be happy to share with you. This information is on paper so if you provide me with your mailing address, I will copy and mail these pages to you.

Although the technology I have is for a specific brand of machine, you should easily be able to adapt the settings to work with your EDM.

Best 3Regards
Jack Sebzda Jr.
Regional Manager
System 3R USA Inc
915 Busse Road, Elk Grove Village, IL 60007
Phone 847-439-4888 Direct Fax 847-439-5099

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Date: 10/20/08
Subject: Manual / Charmilles Form 220 NC

Question:
One of our customers in India purchased a used Charmilles — make Form 220 NC machine from Europe. Unfortunately, the machine was supplied without Operator and Electrical manuals.

The customer is very badly in need of this manual. Can anyone help to get a copy of the manual?

Thanking you. 
Best Regards, 
S.N.Mallanna

To reply to S.N. Mallanna, use the Subject:
Manual / Charmilles Form 220 NC

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Date: 10/7/08
Subject: Bearing Replacement Tips

Question:
Does anyone have any experience or tips for replacing a bearing in my grundig motor on my Charmilles Robofil 230F.

Thanks
Timothy

To reply to Timothy, use the Subject:
Bearing Replacement Tips

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Date: 10/7/08
Subject: Wire Capacitance and Polarity

Question:
Does anyone happen to know how to calculate a wires capacitance and polarity?

Thanks,
Jason

To reply to Jason, use the Subject:
Wire Capacitance and Polarity

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Date: 10/7/08
Subject: Challenges in EDM

Question:
I recently found EDM Today Magazine online. I think your articles are very informative and easy to read.

As a student of master of technology, I have a project on EDM, so I am intrested in doing some innovative work in this field.

I would be greatful if anyone could provide information regarding challenges in the EDM process.

Thank you,
M.B.W.

To reply to M.B.W., use the Subject:
Challenges in EDM

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Date: 9/8/08
Subject: Dielectric Disposal

Question:
Has anyone ever burned the fluid in a waste oil burner…I ran some through a small oil burner detached from the unit…and it burned very clean, does anyone know if this acceptable or has anyone disposed of the fluid in this manner.

Thank You,
Craig

To reply to Craig, use the Subject:
Dielectric Disposal

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Date: 9/8/08
Subject: Code Transfer

Question:
I need help regarding Agie CNC 100/3 code and transfer from PC to wire EDM.

Thanks,
Nikolay

To reply to Nikolay, use the Subject:
Code Transfer

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Date: 7/14/08
Subject: AGIECUT 50

Question:
Hi,

I am currently using an AGIECUT 50. We bought it second hand, years ago, and we have only learned enough of the machine to get us by. We are starting to look at making dies and punches and need to learn a lot more of the machine. We are using 0.2mm brass wire on 8-20mm thick tool steels. If anyone is familiar with this machine or generation of machine, early 80's, I would be most grateful for your help.
• I am interested in things like the program code (syntax), the machine uses a code called CNC100/3 but I have yet to find any specifics

• The effects of changing each setting and what it is responsible for doing, power, current, % of idle pulses, etc

Thanks for your help,
Andrew

Andrew Sidey
Student Mechanical Engineer
Alcoa Fastening Systems
Clayton Business Park
1508 Centre Rd Clayton 3168 Australia

To reply to Andrew, use the Subject:
AGIECUT 50

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Date: 7/11/08
Subject: Surfcam post for Charmilles 310

Question:
Hello:

We recently added a ’97 Charmilles 310 WEDM to our shop.  The difficulty I’m having is to get a post that will work with Surfcam.  The tech from my software vendor is trying his best, but surely there has to be someone who has gone through this before.  Generating the toolpath radiuses using I & J values seem to be the major sticking point.  We haven’t even ventured into automatic threading or tapered cutting which will have it’s own issues.

It also seems that Surfcam does not share posts from techs nor does it have a sponsored site to post and get answers to questions. In my opinion, Surfcam works great for 2&3d milling but still needs some work on the WEDM side.

Thanks for your time and I look forward to your reply.

Roland Hermann

To reply to Roland, use the Subject:
Surfcam post for Charmilles 310

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Date: 7/11/08
Subject: Cutting conditions and electrode material for cutting zinc

Question:
Sirs:
I have a zinc workpiece and am unfamiliar with cutting conditions and the best electrode material to use for this job.
We have Sodick ram machines, Mark 11 and Mark 21.
Ideally, a chart showing settings, spark gap and wear would be the best solution.
I am thinking aluminum and magnesium would have similar conditions.
Any suggestions would be very much appreciated.
 
  Wm Short
FisherCast Global

To reply to William, use the Subject:
Cutting conditions and electrode material for cutting zinc

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Date: 7/11/08
Subject: Copper Impregnated Graphite Application

Question: I have a Charmilles Roboform 350, and I would like to try using copper impregnated graphite electrodes, what technology do I use on the machine?  Do I tell the machine the electrode material is copper or graphite?
 
Thanks,
Tyler Royce

To reply to Tyler, use the Subject:
Copper Impregnated Graphite Application

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Date: 6/26/08
Subject: EDM Sinker Workload

Question:
I don't know if you can help me with this situation or if you know someone that can. I work for a plastic injection mold shop dealing with mostly automotive. Over the last few years, our EDM (Sinker) workload has dropped off tremendously. Due to the fact that our CNC machines are capable of cutting more fine detail than ever before. I would like to find some kind of work that we can utilize our machines and make some profit and not worry about losing the work to CNC machines. I don't know if there are any metals out there that can be EDM'd and not machined due to there hardness?...Etc...
If anyone has any ideas, please let me know.
Thank you,
Scott
Electrode Department

To reply to Scott, use the Subject:
EDM Sinker Workload

Answer: Scott,
Your plight is shared by a number of sinker houses. Two areas to be considered are medical and aerospace.
Both utilize metals that are very difficult to machine:
• Titanium
• Inconel
• Waspalloy
• Hastaloy
• Stellite
For example, Sinker EDM is the only method for putting in the driving slots in bone screws and Sinker EDM is used for putting in the seal slots in gas turbine blades. For these applications, copper graphite is often the electrode material of choice.
Good luck in your search for new sinker applications.
Roger Kern

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Date: 6/16/08
Subject: Wire EDMing Graphite

Question:
I would appreciate reading your thoughts on wire EDMing graphite.  I’ve had my share of problems doing it.
Thank you,
Bert

To reply to Bert, use the Subject:
Wire EDMing Graphite

Answer:
Bert,

While the Wire EDMing of graphite can pose some challenges, it is readily accomplished by many EDM'ers on a daily basis.

The key to successful Wire EDM'ing of graphite is in the selection of the correct graphite grade.

The most common problem encountered when Wire EDM'ing graphite is that of pitting of the graphite surface and blowing off the external sharp corners. This problem occurs due to the relatively weak bond between the graphite grains in the less expensive materials. It has been my experience that these problems generally disappear when fine grain, high quality, graphite grades are utilized, since these grades are characterized by significantly enhanced structural integrity (small grain size and low porosity) leading to enhanced transverse rupture strength. Specifically, I recommend the following grades (or their equivalents) for Wire EDM:

Fine Grain Graphites (most cost-effective solution for general purpose work):

Poco EDM-3
Toyo Tanso TTK-4

Copper Impregnated Fine Grain Graphite (Recommended for Carbide and Aerospace materials or where delicate sections benefit from the added strength resulting from the impregnated Copper):

Poco EDM-C3

Sub Micron Grain Graphite (Ultimate for fine detail, but most costly)

Poco AF5

I have also found that coated wires produce superior results in cutting graphite.

Finally, be sure to consult with your machine manufacturer for the most appropriate cutting technology and cutting strategies for graphite.

When the correct graphite grade, wire type, and cutting technology are combined, productive Wire EDM'ing of high quality graphite electrodes is readily accomplished.

Roger Kern

Answer:
Hi Bert,

Roger did a great job of covering all of the pertinent points of wirecutting graphite… follow his lead.  Meanwhile, I'd like to elaborate on his point: “I have also found that coated wires produce superior results in cutting graphite.”

One of the best-kept secrets in EDM is using CobraCut-B wire against graphite.  CCB has a zinc oxide coating over a copper core instead of brass.  The zinc oxide coating is "rough and porous" compared to pure zinc and will cut faster and flush better with fewer wirebreaks.  The copper core has higher conductivity than brass which is needed to wirecut graphite successfully.

Note that CCB's tensile strength is only 600 n/mm2 (hard brass is 900 n/mm2), reducing threading reliability and possible increased difficulty in skim cutting.  Despite these two issues, CCB is my choice against graphite.

Regards,
Bud Guitrau

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Date: 6/16/08
Subject: EDM Wire Cleanliness Testing

Question:
Hello Roger;
I recently found EDM Today Magazine online. I was going through your Table Manners article, and noticed a procedure that you perform. What is EDM wire cleanliness testing and what are you looking for when your testing the wire?
By the way, your articles are very informative and easy to read.
Thank You,
Spencer

To reply to Spencer., use the Subject:
EDM Wire Cleanliness Testing

Answer:
Spencer,
Cleanliness testing is performed on EDM wire to determine the amount of contaminant (which can consist of powder, flakes, drawing lubricant, and paraffin) remaining on the surface of the wire after the manufacturing process. "Dirty" wire can have serious ramifications with regards to the reliability and maintenance of the Wire EDM guide and threading systems.

While there are no internationally recognized standards for wire cleanliness, GEDMS has developed two systems for the evaluation of the cleanliness of the wire we purchase from our suppliers.

The first method is a quantitative test developed by Dr. Dan Tomalin, a metallurgist. This test accurately measures the amount of contaminant deposited on a pair of standardized cleaning pads after 1,000m of wire is passed through them under controlled conditions. The result is measured in mg/1000m.

The second method is a qualitative method I have developed in which 1,000m of wire is passed through an actual guide system on a Wire EDM (upper and lower cartridges containing pre-guide, power feed, and diamond guide). In this method, each of (7) guide system components is "rated" for contamination and entered into a spreadsheet which determines a "cleanliness score" for the wire under test.

We are still researching the correlation between the two methods.

Please refer to the two PDF documents below.

Cleanliness Test Status

Wire Inspection Procedures
Best regards,
Roger Kern

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