EDM Chambering

TRA,
I can see what you're saying and it seems logical. Maybe you're having a problem with the way it's been worded, maybe you disagree with the idea, and maybe you're just making conversation. That's all good. Now, if it's the wording you disagree with, maybe it should be stated that the stress that has been relieved from the part is that which was in the material that got removed. The rest of the stress is still there. Is that better?

With that thought, here's another example. Recently I bought some 1x6x8's for making some window sashes. I cut them to around 65" and ripped them (for the sides). Of 6, 2 sets warped all to bits in a couple days. I did all the work on them, boring for doweling and routing for glazing. These stood here for a couple weeks before I began and they were straight as a die when I began. 3 Days after ripping, they warped sideways a worst of a 3/4" over 65"s. The 2 sides warped opposite directions. Pretty much mirroring my hypothetical metal example above. Now, all I removed was a 1/8" saw kerf, and no heat of any significance was put into the part. (all the heat came out in the chips so to speak). Just using that as an example, how would you explain that? And would you say it's similar to the situation with metal or no?
 
4mesh

Now were on the same page, my disagreement came from the statement that machining a part removes "it's" stress and that's not true, it only removes the stress that resided in the, now chips and the forces of stress that resides is now enhanced...to me that's inducing stress....whatever.

The wood, that would be "no", as wood is affected by it's moisture content, and has an unpredictable grain structure. By cutting it you open the surface to absorb moisture at an uneven rate. I know that's an extremely lame description on why it warped, but I hope it serves the purpose.
 
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TRA,
It ain't too tough for me, you just did not read my posts. You are stating that I posted something that I didn't post. You originally stated that heat of machining induced stress. How much heat does it take? OK, you said the part would be warped, stress or no stress. I guess you better get out the ouija board and explain to me as to what you have decided.
I'm going to bed.
Butch
 
Butch
I don't recall saying you said anything.....You need to work on that vanity issue your having.

It seems you know more about this than I do, so I'll refrain from trying to comunicate with you.

I can snipe just as good as the next guy, IF that's the way you want it.
 
TRA said:
4mesh

Now were on the same page, my disagreement came from the statement that machining a part removes "it's" stress and that's not true, it only removes the stress that resided in the, now chips and the forces of stress that resides is now enhanced...to me that's inducing stress....whatever.
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I thought that's where you were going. We were obviously typing at the same time 3 posts ago.

On the wood example, I'd buy the loss of moisture (unevenly now with the newly exposed cut), but, there was ample time for drying before I cut it. Why didn't it move at all till that cut was made? Really, these are rhetorical questions cause we both know the answer. I think we're more on the same page than were gonna admit.

Could you give an example of putting stress into a part? Obviously the steel doesn't dry out. I can think of one example being the quenching of an alloyed steel from high temp, as in heat treat. Some steels have so much stress in from that that they will explode if they are not put through a draw cycle within a short period of time. It'll look like a piece of tempered glass that's smashed. Other than with heat, I can't think of a way to induce that much stress in steel, or anywhere near that much.

I wouldn't say that there is "no" stress put into a part when it is machined, but I'd say it is an insignificant amount. As a tool burnishes a part a little during machining, you'd expect something. But, can you suggest that is enough to deform a part? It seems unlikely.
/edit
Forget that last question. I guess that's not what you contended to begin with. Sorry.
 
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While the debate rages between Butch and TRA I'll just say that after years of running a mold shop I cannot for the life of me see any reason for chambering a barrel on a EDM machine. First of all I don't see the accuracy being as good as doing it on a lathe and the finish won't be as good as a lathe polished chamber. So to me the whole exercise is pointless. I did hear someone say that he cut a chamber on a CNC lathe with a single point tool that turned out as well as any chamber that he had cut with a reamer and in about half the time. But that's another story and since I didn't do it it just reminds me of the old "ignorance pooling" thing and I won't take that one any further.
 
Cheating is good!

But, take that title for instance and consider it more closely.

Machining induced residual stress in structural aluminum parts
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Are they not saying that the stress is already there (residual) and that machining now makes it obvious?

Fyi, those books do not look like Pulitzer prize winning reading... Those excerpts in the second one do look interesting, but wow, I'm not sure I'm interested in knowing that much about it!
 
clowdis said:
I did hear someone say that he cut a chamber on a CNC lathe with a single point tool that turned out as well as any chamber that he had cut with a reamer and in about half the time. But that's another story and since I didn't do it it just reminds me of the old "ignorance pooling" thing and I won't take that one any further.
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Well, it's safe to say it wasn't me saying the above cause two things are true in my case. First, doing a chamber in a CNC is definitely not faster. Second, I've never done one with a reamer. All the advantages I can think of come from the ability to make dies that are precisely what you "want", then, after you find out that you got exactly what you "wanted", you can change your mind and try again for what you now "want"!
 
I'd be interested in hearing, how you determine that after you machined a part, that the stress was induced or relieved. All I hear you saying is after you removed the stress by machining a part that it now requires "Stress Relieving"[/QUOTE]


Would you quote where I posted this?

Butch
 
Butch

Where did I say that you posted it, at all? "WHERE" do I say "BUTCH LAMBERT" said any such thing. You seem to have a problem, with accusing people of things just so you can dominate them or to show how superior you are.

I disagreed with the statement that machining removes stress, you quipped, that I should show YOU a real reason that machining could cause stress and I have offered up plenty of references to validate my statements. One of them being heat.

I'm not going to attempt to explain Quantum Mechanics to you, but I will defend myself and what I say is based on fact. I answered your question and referenced it. Those that I referenced are rather basic, but they should at least prove to you that "Machining" does "NOT","REMOVE" stress.


If it's over your head, then I apologize.
 
Thin skinned, I guess I got your GOAT. Can't you even read your own quotes? Are you able to understand Quantum Mechanics?
I'm gonna watch the Bowl Games. Lot more entertaining.
Butch
 
Butch
When I'm talking to you, I reference you by typing

Butch
I DID NOT SAY YOU SAID IT..........Your fantasies are overwhelming you.

Butch
To answer your questions , from post #32 in order
Yes
Yes
 
Lets try this another way. We'll start from scratch.

Metal (and I mean in general terms encompassing everything from the finest "unobtanium" to the lowly chunk of lead) starts life in a pot that's heated until the material becomes a liquid. It's then cast, forged, whatever into it's basic forms. Bar, plate, etc. Mills that produce this stuff spit it out as fast as they can make it. It's shot with water, oil, etc to faciliate cooling.

What you end up with guys is essentially a ball of rubber bands. There is tension (stress) within that material everywhere. If we for instance were able to make a long rod out of rubber bands and then begin snipping away at the ones on the outside (chips in the conveyer) what's going to happen to what's left over? It's going to be pushed around and will 9-10 times end up looking like a banana. We didn't add more stress to it by taking stuff away on the outside. All we did was expose it's influence.

This is where "normalizing", (stress releiving) comes into play. By heating (or freezing, or both) the material in a controlled state and in a controlled atmosphere, holding it at that temperature for a predetermined amount of time, and then carefully controlling the rate back to the ambient temp, a great deal of the "inner turmoil" is removed. Are there any sort of assurances that the material will not warp or distort during this process? That's answered with a firm NO. In fact it likely will warp/distort. That'd be because the material is moving towards its "dead" (stress releived) state. This is where the "voodoo" comes in. Just how much material do I (as a machinist) leave on the part so that I can bring it back to tolerance after this process?

Here is a real world example that I can speak of based on eye witness accounts:

I spent my early adult life devoted to the notion of one day owning and building racing engines for NHRA dragsters. I worked for a few different high profile guys while in S. California. Old school rule for circle track engines: "Old dragster blocks make the best circle track blocks." Now why is that? It's because the cylinder case has been heat cycled a 1/4 mile at a time-meaning it's allowed to get hot, then cool over and over and over again. This "seasons" (another old school term) the material. When the endurance racer gets a hold of one in good shape he treats it like gold. He can work that block over -meaning bore the holes, hone them, and square everything up and have an added assurance that it will stay that way over the lifespan of the engine.

The cylinders won't be as inclined to bell mouth, barrel out, or shift on the centers. The main caps and line bore/hone isn't going to warp or wrap up and cause goofy wear patterns on the mains. It's all in the pursuit of horsepower and longevity.

Richard Conley, Paul Rossi, and Bill Craddock were the three guys I worked for. All of whom are industry experts in their own respective fields and all of whom have multiple national event wins out there in "go fast land". (NHRA Competition Eliminator, SCCA, and NHRA Pro Stock/Top Fuel Cylinder Head development) I was just a lowly maggot. I wasn't allowed to do much other than get sodas down at the quicky mart and push a broom. Don't think for a second though my ears weren't open and I wasn't asking questions.

More proof:

We'd take a brand new Chevy Bow Tie blocks straight from GM and build a Comp motor on it. We'd run it on the dyno trying out cams and have them stacked like chord wood when we were done. Then after doing this almost a hundred times we'd tear the engine down and give the cylinders a kiss in the hone again.

EVERY single time we made more power after kissing the cylinders.

Now why is that? I can assure you it had nothing to do with seating rings. It's because the bores wiggled a bit due to heat cycling and the hone straightened them up again. This promotes better ring seal and better ring stability. Considering these little savages would wind up to over 13,500rpm it becomes very important.

2.52hp per cubic inch normally aspirated on carbs and gasoline back in the early 90's was no easy feat. It's still tough to do, yet Richard's engines did that very thing. Honing the bores after they cycled a bit was an easy 30-40 hp. When everyone is making nearly the same power level these kind of small small increases become very significant.

Whether guys want to argue about induced stress or stress relieving, my point wasn't to turn this into a vocabulary debate. It's to show that when you chew on stock, it will likely want to move on you. It becomes important to appreciate this on things like a rifle.

Enjoy your new years day.

Chad
 
NesikaChad said:
They leave absolutely no burrs, and induce zero stress into the parent metal.


Machining a material does not induce or create stress. It relieves it.

We can demonstrate this easily with a material that has a great amount of "inner turmoil"; Delrin. Take a block of the stuff and bore a hole in it. Then slot one side of the bore. What happens? The hole and the slot clams shut. We relieved the stress that was already present within the material. We did not create more "drama" within that piece of material.

Take a flat plate of cold rolled that's a 1/2" thick and fly cut a 3rd of it off. When you pop it out of the vise it'll likely bow up like a banana. Again, the stress was taken out of the material and it warped. You didn't add to what was already there.

Take that same piece of material and have it stress relieved. (an oven process generally) It'll likely come back looking like a banana and now you have to fly cut it flat again. Only difference is now it lays there dead as a post when you take it from the vise.

So, whether you cut a chamber with a sinker, a reamer, or a post hole digger if there is stress in the material you are going to have an effect on it. A barrel doesn't know or care what tool makes the chamber, if the material condition is bad (meaning the stress relieving process sucks) it's going to have a greater potential for distortion when whittled on. That being said a reamer will be just as accurate dimensionally as the graphite plug. (assuming both are done using appropriate machining procedure)

As for burs.

In general terms most modern high performance centerfire rifle cartridges operate in the 50-60k pressure range. That pressure combined with flash chamber temperatures of over 5000 degrees means the probability of any little burr or booger loitering past the 1st or 2nd pull of the trigger is quite small.

Have a great new years.

C
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Ok, I see where you headed, and your right. But not completely right.

A lot of what your saying only applies to certain forms of machining. A gib from a machine gets ground an curls up on you from the stress induced. Yet you take a piece of hardened gauge stock that is warped, and hit it with a hammer in the right places (this relieves stress). But you take the same piece and put it on a surface grinder, and grind it (fliping it every other cut). Why did it not relieve itself? Because the grinder induces a compressive stress just like an end mill will. We send steel thru a normalizing process to relieve stress induced by rough machining. They usually change very little, but if you really check they still due slightly. But the real factor is that the part does not change when finish machining. Where did the stress come from? Machining of course (prime example is a block of CRS verses the samething in 8620). I mean to say were mostly talking slight changes here, but you really catch them when you start to scrap the ways on a machine. If you know what your looking for, you can actually see things change over night. A gib out of your lathe needs to be scraped. It's not warped or anything, so you just goto work on it with your hand scraper (I'm old school but have been known to drag out a Bix from time to time). Why dosn't it change when your scraping something like a total of 10 thousandths? You are adding a compressive stress at a very low cutting speed. Now you get lazy and have your buddy mill the same gib about .008". The gib curls up on you (this is the relieving of the stress you refered to), but actually the stress relieved is only a surface stress (does not go deep). You then take the gib and lay it on something dead flat and get your pencil torch out to relieve the stress again ( I'm not good at this part). If you put the heat in the wrong place you got a mess, but if you do it in the right place the gib flattens out. You relieved stress in one place to counter act another place. Like I said it's a black art.

Now back to the EDM and stresses. I've been to more than a few places that build and sell EDM equipment, and the idea of stress free cutting is one of their big selling points (as well as zero tool pressure and no distortion in the part). This came from Elox, Hitatchi, Fanuc, Cinn. Milicron, and it seems like one other.
gary
 
nhkuehl said:
Could a cartridge case or dummy round be used as the electrode? Talk about chamber fit! - nhk
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that's kinda similar to what they are doing with a sinker. But they are using graphite, copper innert tungstin, and maybe something else that will look like the case. I've cut hexes and tapers and gear profiles. If you can make the plug, and have a good enough power supply; it will cut most anything that will conduct electricity. To me it's a sales gimmick! Just like most bass plugs!
 
4Mesh said:
The examples were given above. If you want to dispute/discuss them, that's ok. But, I think it's a pretty safe bet the stress is in there and needs relieved. Here's another example.

Piece of metal stock 3" wide. Has stress in it (assumed). Stand it up in front of you and look at it. Left 1.5" has stress pulling the part into a banana toward the left. Right 1.5" has equal stress pulling the part into a banana toward the right. Part looks straight to you.

Cut some material off either side but not both, the part will pull toward the side without material removed. That's what Chad is saying.

What you are saying is that if the part has heat put into it, it could either gain or loose stress (I'm paraphrasing from what I took of your post). I would partially agree that if you do metalwork on that part and your tooling causes the part to get hot, you will ALTER the state of the material and if there is stress involved, odds are you will have a part that is no longer shaped like it was when you began.

But your idea of putting heat in adding stress is counterintuitive (says I). Let's say I turn a part in a lathe with no coolant and it gets up to 250F. That's pretty darn hot. I take the part out of the lathe, lets say it was a long narrow round of some crappy steel. It most likely is not a long narrow STRAIGHT round any more. Ok, now, if I had taken the same part, put it in an oven and heated it ONLY to 250F and then let it cool again, do you think it would have changed in shape as dramatically as some parts you've probably seen come out of a lathe? I bet not. I bet it would barely move, if even measurably. So, one could conclude that the heat did not do the alteration, but the material removal did.

As an experiment. grab a piece of relatively straight 3/4" Cold rolled round stock. Put a center in one end of it. Chuck up quite tightly with 2 or 3" in the chuck. Now bring your live center into the part. Hopefully, the bar is straight enough the center fits up perfectly without help. Now, turn the part down to 1/2". Stop the lathe, and pull the center but let the part in the chuck. If you CAN put the center back in, that is some pretty nice stock you have there cause I'm betting there's times you won't be able to get it back in there. If you could convince me that heating that part to the same temp would have bent it that far, then I'd say you're right. But I don't think it'll ever move that far. I've seen examples of this very thing and the part center sprung ~1/2" from the live center when the tailstock was pulled away.
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Here's what I was always taught, and it's worked well for the last forty years. (so don't laugh too hard):
* if the cutter rotates in a circular fashion it induces a stress in the part it's cutting. How much of course is debatable, and I'll leave this for all of you. If the part kinda curls up in a fairly strait fashion (like a leaf spring on a car) it's usually from relieved stress (Chad's right about this). Now if the part has a twisted shape after cutting; it's usually cutter induced stress (like a gib on a lathe taking a twist after cutting). Some metals do this much more than others by the way.

* OK we're past the end mill idea. Ever run a planer or a shaper? I have, and one of the first things you notice is the parts never take a set, warp, or twist. I asked about that when I was about a hundred years younger, and was simply told that the cutter was going in a strait line at a very low cutting surface speed. This was easier on the metal being cut and induced less stress (or maybe relieved less if your in that camp). Parts came out flat, and were much easier to scrape (like machine ways). Later on after I was set free by my master I kept a nice shaper hooked up for plaining machine gibs. This process often saved me days of work because the parts were flat and strait. But there's some more here. When you had a gib that had been milled you had to take over twice as long to scrape it because it was constantly changing on you. Twnety years later I was visiting a well known and large machine tool builder, and these guys had this planer that was bigger than my house! They had nine lathe beds setting on the table to be plained. Yet they had a big machine center fifty feet away that would have been able to take the basic frame much further in one setup. They told me that there was much less stress in the cast iron after plaining than there was in cutting it with a machine center. But you didn't notice it till you started scraping the bed in (I already knew but didn't think of it).
gary
 
squeakie said:
If you can make the plug, and have a good enough power supply; it will cut most anything that will conduct electricity.
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That's really what I was asking and was wondering if something like a brass cartridge case, thin and hollow, would work as an electrode. Could the brass withstand the heat? Thanks. - nhk
 
4Mesh said:
Well, it's safe to say it wasn't me saying the above cause two things are true in my case. First, doing a chamber in a CNC is definitely not faster. Second, I've never done one with a reamer. All the advantages I can think of come from the ability to make dies that are precisely what you "want", then, after you find out that you got exactly what you "wanted", you can change your mind and try again for what you now "want"!
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If I remember correctly it was Bruce Baer that was commenting about singlepointing the chamber. I don't remember if it was done on a machine that he had or one that someone was trying to sell him. Said it only took a couple of minutes to cut the chamber. Now I don't know if a couple is 2 or 10 and I don't know if it was 6PPC chamber or a 458 Win Mag. That is what prompted my "ignorance pooling" comment, no facts just remembering what someone told me.
 
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