Using EDM to Cut Bullet Mould Cavities

[Southron Sanders]

Durng one of those general discussion sessions on bullet moulds, casting, etc., a buddy of mine asked me if I knew of anyone cutting bullet mould cavities using EDM.

I had to admit, I had never heard of such a thing. So my question is for those on this BB that are familiar with EDM:

Would it even be possible to cut a bulet cavity in a mould using EDM? Wouldn't it be very expensive if it was even possile?

Inquiring minds want to know.

THANKS!

[45nut]

For a one-off it is certainly possible and viable, for production runs the electrode would be worn too quickly is the word I got.

I know the Patent holder for EDM Chambering and have discussed this, he does EDM chambering for his own wildcats and chambers barrels using measurements from 2 dummy rounds from your set of dies, or will even make dei sets for the true wildcats people have sent in.

For the folks not wanting to settle for a chambering reamer from a vendor relying on SAMMI specs which may or may not be at a extreme of the tolerances the option of a chamber fitting the dies you have on hand offers many benefits. Tighter control over the cartridge fit to the chamber is first.

http://img.photobucket.com/albums/1003/45nut/100_1162.jpg

In that picture are the dummy rounds and the chambering electrodes for my 50 Alaskan and 458 Win encore barrels, the carbon electrodes are fragile and would be easily damaged trying to use them for production runs, but the maker has cut molds for his own use.

I believe Dubber has had a mold cut using EDM, I hope he chimes in.

[beagle]

My machinist buddy just cut a .25/20 chamber in a "dummy" barrel blank for his Martini. It worked out well. Now, he'll get the good barrel and do it for real.

We've discussed making moulds with EDM but have never gotten together long enough to do one. It's definitely possible for a custom job but as has been pointed out, not cost effective for a production run./beagle

[yeahbub]

I work for a company that does EDM on jet engine parts using a number of different electrode compositions in graphite and copper alloys. There are low-attrition electrode types used to reduce the number of electrodes necessary to EDM cavities to a finished shape and tolerance. These are usually copper alloys and the expense depends on the amount of material that needs to be removed, the finished surface requirements, machine time and electrode qty.

A mold would be relatively easy to finish if some of the material was removed from the blocks by conventional drilling leaving enough material to clean up to the finished size via EDM. The electrode would be best spun to evenly distribute wear while creating the initial detail in both blocks simultaneously. A finish operation could be used to produce desired sharpness of detail and surface texture. The contest would be whether molds by EDM would prove worth the cost of the R & D to get them into production. Once the technique is worked out, producing them en masse would reduce their costs even further, but would they be materially better than those produced by conventual means? At this stage of the game, probably not.

After seeing photos of molds from the 1600's carved from stone, I had an idea that molds could be "molded" from alumina slurry or similar ceramic given the needed heat-conductive qualities. The raw material would be inexpensive, durable, largely heat-proof, and have very little waste. The delicacy of the finished item would require some forethought and care, same as iron and aluminum, but throwing up a burr in a cavity resulting in boolits that won't fall out would be a thing of the past, as would rust or corrosion. The place to start would probably be milling an experimental set of blocks out of commercially available machinable ceramic material and see how they work as proof of concept.

[dubber123]

Kens right, it was me. If you use the search function, you should find a thread on this. I had 1 made, it worked very well, but if I didn't have a "contact", it would probably be cost prohibitive.

1 benefit is, the mould halves are closed tight when the cuts are being made, making the cavities super round. I goofed with my specs, (a guess) and had to lap mine 1/2 thousandths, but that was my fault. The mould showed "0" out of round as cut.

[NHlever]

I work for a company that does EDM on jet engine parts using a number of different electrode compositions in graphite and copper alloys. There are low-attrition electrode types used to reduce the number of electrodes necessary to EDM cavities to a finished shape and tolerance. These are usually copper alloys and the expense depends on the amount of material that needs to be removed, the finished surface requirements, machine time and electrode qty.

A mold would be relatively easy to finish if some of the material was removed from the blocks by conventional drilling leaving enough material to clean up to the finished size via EDM. The electrode would be best spun to evenly distribute wear while creating the initial detail in both blocks simultaneously. A finish operation could be used to produce desired sharpness of detail and surface texture. The contest would be whether molds by EDM would prove worth the cost of the R & D to get them into production. Once the technique is worked out, producing them en masse would reduce their costs even further, but would they be materially better than those produced by conventual means? At this stage of the game, probably not.

After seeing photos of molds from the 1600's carved from stone, I had an idea that molds could be "molded" from alumina slurry or similar ceramic given the needed heat-conductive qualities. The raw material would be inexpensive, durable, largely heat-proof, and have very little waste. The delicacy of the finished item would require some forethought and care, same as iron and aluminum, but throwing up a burr in a cavity resulting in boolits that won't fall out would be a thing of the past, as would rust or corrosion. The place to start would probably be milling an experimental set of blocks out of commercially available machinable ceramic material and see how they work as proof of concept.

The investment casting process that Ruger, and others use for their gun parts uses a ceramic mold. A wax is made of the part in an injection die ( could be machined from wax too) and then is dipped in ceramic until a thick layer is produced. The wax is then melted out of the ceramic "shell", and the steel is poured into the shell. Of course one mold only makes one part....... :-)

I have had custom chambers cut on a CNC lathe, and I'm sure molds can be produced that way, and I suspect that the Moutain Molds are. The program for cutting the mold is made from the drawing you produce in their provided "CAD" program. The nice thing about using a CNC is that one can produce a chamber, loading dies, and chambering reamers from the same CAD file.

[Marine Sgt 2111]

I used to make electrodes in a mold shop specializing in plastic injection molds. We used the 3M mounting system which means the carbon is cut on the same mounting block that you use to burn the cavity with.

Using a CNC lathe to turn the electrodes (because you can mass produce the same form over and over) and in a good sinker (type of EDM machine) make consistant cavities. If you use a hard, fine grade of graphite, use one or more worn "trodes" to rough the cavity then go in with a freshly turned finisher it is possible.

This all takes a lot of time and money and it's far faster to just use a CNC lathe to rough and finish a cavity and being cnc you can mass produce the same cavity over and over.

That's my two cents and 36 years in a machine shop....

[Willbird]

OK now for a plot twist, what about just making the MOLD itself from EDM graphite ??

EDM electrodes are often only used once. A past employer made dies for Federal Mogul(they own champion spark plug) each die insert gets EDM'd with 3 electrodes, which are recut after each use...they make them 6" long to begin with, hex shaped, and recut them in a small turret lathe, each recut shortens them about 1/4".

One thing you could do with an EDM'd cavity that you could not do with a cnc lathe is make say lube dimples instead of lube grooves :-)....or a pattern like a straight or diamond knurl to hold lubricant.


Bill