EDM Finish Qualty Question

Chad,
It sounds like Tom's saying the machine he's getting uses an orbital motion to make a hole that's larger than the electrode. Compensating for wear.

Butch Lambert said:
Are you sure Bat doesn't wire their raceways?
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Straight from Bruce, they use a broach for the raceways, then lap.

I think there's a misconception that a broach always makes a hole that looks like a woodchuck chewed it in, and that's not the case. I sharpened one at work a few months ago to do a part and it was amazing how nice a slot it made even without any lapping. Tool angle = everything. (also changed the cut depths and made new keys...)
 
Chad,

I have measured chambers done off the same reamer by the same guy and you would not belive the difference! EDM electrodes at least in my case are being done by an ANCA tool grinder that is accurate to .00005".
Is that overkill? yes, but if you can EDM and there does not appear to be any disadvantage..... Can EDM hold repeatable sizing? You bet because you can "sneek up on it" using an orbital motion. With a reamer you have one shot to get the correct size and finish.(you could always go deeper for finish but not for for size)

Tom
 
RoyB said:
Reminds me about a story told by old guy employees of Morse Twist Drill down here in New Bedford, MA...........Back in the 60s, MTD developed a drill for drilling holes in micro circuit boards. It was claimed as the thinnest drill in the world. About the diameter of a human hair...............A Japanese company bought a couple and sent them back to MTD with a hole drilled down the center...........That, was the beginning of the end!
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What I think is funny is that I heard this apochryphal hoohaww about 1975 for the first time as, "an American ...... sent to Germany...." etc, with of course the claim being that the Germans were 'wayy ahead of us.

I'm not exactly sure what sort of moral applies, nor what sort of mindset this story appeals to.....

BTW Japan was just a blot on the map back in the 60's wasn't it???

I thought it was in the mid-eighties that the stories all changed to "Japan is better than us" etc.....

LOL

al
 
SOOOOOO, after the perfect? chamber is cut, we chamber a cartridge that has .002-.004? clearance. There's some impressive records shot with a plain Ole reamer, the perfect shot is impossible, as long as there is atmosphere to shoot through.

Making Bullet dies with an EDM is a no brain-er, Chambers on the other hand??????????

That chamber still has to align with the bore of the barrel, and an EDM is no assurance of that.

I believe that the whole barrel process needs revamped, IE, chamber, and bore, rifling all done at the same time

Seems, grinding a chamber would make more sense.
 
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chamber, and bore, rifling all done at the same time
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I believe Sako or some other European company is hammer forging the whole deal, chamber and rifled bore in one process.

BTW, the Japanese story was just an attempt at levity. Nothing more.
 
alinwa said:
What I think is funny is that I heard this apochryphal hoohaww about 1975 for the first time as, "an American ...... sent to Germany...." etc, with of course the claim being that the Germans were 'wayy ahead of us.

I'm not exactly sure what sort of moral applies, nor what sort of mindset this story appeals to.....


LOL

al
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Apparently many are "better than us" now. That's where the ultra precision work is going today-out of the US.

As to a small hole story, at the place I retired from, we regurally drilled holes down to 0.0012" diameter, and hundreds of them in each stainless steel plate.

Don't believe that? Take a cigarette filter apart and mike one of the filaments. At one time we made about 90% of the worlds cigarette filters. Each filter stream made the filter pack from one spinarette.

When we got into the "hollow-fill" textile market (1970's), we would drill a 0.0012" hole, thread a wire through it and EDM a clover leaf looking hole that was only 0.007" across the petals. That is how hollow-fill fiber is made that goes in many of your insulated clothes and sleeping bags.
 
EDM chambers

Several years ago I posted about cutting chambers with an EDM. When I was at the community college we had several EDMs. Take it most were passed down from industry and were not modern machines. I made several Carbon burners for one of the plunge machines that had a vertical tank. I cut some very nice chambers with the EDM. The problem was that it took about 6 hours to do a 308 sized chamber.

Time and machinery equal money. I could not aford to buy a EDM machine set up for machining chambers. And the time including set up far exceeds the time including setup with a lathe and reamer. If one wants to cut chambers fast and with a greaqt surface then all they need to do is use a flush system.

Shapers line the floors of many warehouses because vertical mills took their place. Many plunge EDMs have been replaced with wire EDMs and CNC vertical mills with carbide tooling. Water jet tooling is going to replace a lot of EDMS. They are faster and less expensive.

Nat Lambeth
 
We frequently hear talk of the need to knock the shine off a new chamber with a little emory etc. to get the case to grip the chamber during firing to minimize bolt thrust. Another truism is the need for absolutely oil and lube free chambers and ammo toward the same end. So what's up with this micro-finish chamber talk? Are we to now rely on stiction of an ultra smooth chamber to give us what we're looking for? Wassup?

Greg
 
TRA, why not do the stock in the same operation. What did you decide that machining did, more stress or less stress?
Tom,
I believe the variations on the reamed chambers are either a bore not indicated properly or a tight reamer button following a bore that is crooked. Your reamer would not cut evenly on all the flutes.
Butch
 
Butch Lambert said:
I believe the variations on the reamed chambers are either a bore not indicated properly or a tight reamer button following a bore that is crooked. Your reamer would not cut evenly on all the flutes.
Butch
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I think you will find that where a particular gunsmith is having varying chamber diameters when using the same reamer, he is using one of those so-called "floating" reamer holders. With many of the floating holders used today one can easily get as much as 0.005" variation in chamber body diameter from one barrel to the next.
 
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