tricky tooling question for you sinker EDM gurus

[hkfanatic]

first off im going to start out by stating i have NO experience with a sinker machine and how its tooling is made. but im in need of someones experience, we are trying to get a project completed here at our shop that requires some edming to be done and EVERY contractor we contacted does not want to touch it. so im looking to get some advice.

we need to burn 12 flutes onto the inside on a rifle chamber in a barrel. flutes have to be from .020 to .030 deep and .020 to .030 wide

here is a pic of one of the barrels cut in half so you can see what needs to be done.




its my thoughts that the tricky part is that it CANNOT extend all the way back the the breech face, let me know what you think

[easymike29]

Burn one flute, then index the part or the electrode.
Gene

[MrWild]

you say flutes, but you mean rifling i'm assuming. The flutes get a twist, am I right? If so, you need a free wheeling swivle head, and a lead. The swivel head is allowed to swivel/spin (of course) as the ram extends downward. A lead (maybe not the right term) is above the bore and gives the electrode the twist you need as it goes down into the bore. The lead needs to be longer than your riflings, and the electrode should have all your flutes.

Basically you need the same set up more or less as if you were machining threads. The difference is that the ram floats as the head spins for threads, but for this you will want the head to float (free wheel) as the ram sinks. The lead causes the head to spin or twist giving the rifling. Total PITA and will take several electrodes to accomplish. Have you thought about broaching the rifling instead?

[hkfanatic]

Originally Posted by MrWild you say flutes, but you mean rifling i'm assuming. The flutes get a twist, am I right? If so, you need a free wheeling swivle head, and a lead. The swivel head is allowed to swivel/spin (of course) as the ram extends downward. A lead (maybe not the right term) is above the bore and gives the electrode the twist you need as it goes down into the bore. The lead needs to be longer than your riflings, and the electrode should have all your flutes. Basically you need the same set up more or less as if you were machining threads. The difference is that the ram floats as the head spins for threads, but for this you will want the head to float (free wheel) as the ram sinks. The lead causes the head to spin or twist giving the rifling. Total PITA and will take several electrodes to accomplish. Have you thought about broaching the rifling instead?

the fluting i require done is different to rifleing, the barrels are alredy rifled and chambers cut. these barrels are specific to the Heckler and Koch rifles in that they have 12 horizontal flutes cut into the chamber (where the shell sits) to facilitate in cycling the weapon. without these flutes the rifle would fir once and not cycle.

if you look at the pic i posted you can see the flutes in the chamber. the factory EDM's them in i know this for a fact. all of the other barrel MFG's out there broach cut the flutes.

i had thought about doing them one at a time but i wanted to see if there was any way to do them all at once. i may just have to do it that way, or at least tell the shop im going to try to get to do it that.

thanks guys!!!

[rwkjr]

Does the flutes extend up into the necked down area to the smaller dia.? job does not look to difficult for a CNC sinker maybe 3 electrodes, do you have a print or cad model? How many do you need done? a couple could be costly, dozen or more maybe not. I have sinker capabilities.
RK

[hkfanatic]

rwkjr, yes it extends into the necked down part a little if you look closely at the pic i posted in my first post you can see it a little thats one of the units im copying that i cut up to see inside.

i need about 75 barrels done, in the first batch and depending on sales more in the future. the only thing i see being an issue is that the longest barrel is 26" long and i would imagine that a REALLY deep sinker machine is required.

at this time i do not have a print or cad file but could have one drawn up. if your machine can handle the length of the part. i could send you over a cut up unit and a intact barrel so you can see what might be involved. my barrels are about 2 months away from delivery so i have a little time to work this EDM issue out.

let me know, PM me your contact info if you'd like to discuss things over a phone.

-HK

[rwkjr]

PM SENT
RK

[easymike29]

In addition to my first suggestion (indexing electrode or barrel) there is another possibility, although complex.
It may be conceivable to design a fixture to hold the electrode "blades", lower it into the cavity, then extend the blades to do the burning. Not unlike an expandable lap for instance. Of course the devil is in the details.
Gene

[HKgunslinger]

That looks like either an HK 91 type, or a SIG AMT barrel. Yes that is fluting, not rifling, both are roller-delayed blowback operating rifles, and require that some of the expanding gasses get blown back into the chamber to "float" the cartridge case so it will smoothly extract from the chamber.

Work-tank ofthe machine doesn't need to be as deep as the barrel, the ram-to-table max distance is what is crucial here. Just setup loc-lines supplying dielectric to where it is burning.

HK probably has highly specialized tooling for doing this that would be prohibitively expensive to replicate for small run, then there is also the problem of finding someone with an EDM with a big enough Z-envelope to burn these, there is a reason none of the contractors will touch this project.

The only way I see to burn these is to do a couple of flutes at a time.

Barrel locked into rotary indexer, set for six divisions, barrel canted at a 5 degree angle or so (and your electrode canted with the inner profile at 5 degrees also) 2 flutes per electrode, copper or copper-tungsten electrodes, depending on your power supply. Burn, and Turn

Depending on surface finish/power supply, each burn (2 flutes) will probably take only a couple minutes, even on an older machine. Once electrodes are cut and you have the machine set up for the job, you could probably get away with 20 minutes per barrel, start to finish.

'Slinger out.

[hkfanatic]

Originally Posted by HKgunslinger That looks like either an HK 91 type, or a SIG AMT barrel. Yes that is fluting, not rifling, both are roller-delayed blowback operating rifles, and require that some of the expanding gasses get blown back into the chamber to "float" the cartridge case so it will smoothly extract from the chamber. Work-tank ofthe machine doesn't need to be as deep as the barrel, the ram-to-table max distance is what is crucial here. Just setup loc-lines supplying dielectric to where it is burning. HK probably has highly specialized tooling for doing this that would be prohibitively expensive to replicate for small run, then there is also the problem of finding someone with an EDM with a big enough Z-envelope to burn these, there is a reason none of the contractors will touch this project. The only way I see to burn these is to do a couple of flutes at a time. Barrel locked into rotary indexer, set for six divisions, barrel canted at a 5 degree angle or so (and your electrode canted with the inner profile at 5 degrees also) 2 flutes per electrode, copper or copper-tungsten electrodes, depending on your power supply. Burn, and Turn Depending on surface finish/power supply, each burn (2 flutes) will probably take only a couple minutes, even on an older machine. Once electrodes are cut and you have the machine set up for the job, you could probably get away with 20 minutes per barrel, start to finish. 'Slinger out.

you hit the nail on the head, im having a batch of .308 HK PSG-1 / MSG90
barrels made (quite a few actually) most of the other manuf. like JLD broach cut the flutes in. i want them as close to factory as possible so im going the EDM route

im quite sure its able to be done, im sure i'll find somebody to do it.

[HKgunslinger]

Like I said, the only way to conventionally burn this with a straight sink is to angle the barrel, the 5 degrees is just a guess. But trust me I know how it goes, you might go to 10 different shops that have the capability, but will turn it down because they're too lazy to try to figure it out. Show up with your end product and say "I want these made" and you're likely to get a dumb look. But show up with drawings of the electrode profile, tell them what angle to burn, with rotary indexer, etc. and you're much more likely to get them to take the job

I'd help you but my shop does not have an EDM yet (actually going to acquire a Charmilles likely before the end of the year) I have friends at the shop I used to work, ...carbide work, lots of EDMs, but they're more contractors for Kennametal than they are a job shop so they would not be able to help, meeting Kennametal deadlines is top priority and I never saw them take in a job that wasn't Kennametal or a subsidiary.

Best of luck

'Slinger out.

[rwkjr]

Where is the 5 deg. you are refering to? is this the lead in where the flutes start, or are the flutes angled from start to end, I dont have much info yet just pic posted.
I would create all the geo. of flutes on small dia shank trode, major dia. of trode being .005-.01 under the chamber dia. CNC mill and index similar to gear, reamer, spline or other shape. drop trode into cavity and vector or orbit out to depth, depending on # flutes may be able to put all on trode at once would have to check to see if flute on trode next to one burning say at 90 deg. in a vector move would distort the shape to be burned next, this geo. is so small may not matter, or like previous post, burn with 2 or 3 blades on trode vector out every 120 deg. this could probably be simulated in cad to see other then that most difficult part is the trode development, and deep tank EDM is not needed. I do blind end work on 24" + shafts regularly, just takes some creative fixturing.
RK