OT-burning threads...mirror finish?

[El Scotthead]

I had an argument yesterday with the engineer(yeah, it's happening alot lately).

 

I burned some molded threads, using copper tungsten. It's the first time I've actually burned a job with CuW. They came out pretty good. Of course they had an edm mat finish (6 Rmax), which is comparable to the finish in the rest of the mold. However, he got on my case because they didn't have the mirror finish that HE expected. I tried to explain that I don't think you can get a mirror finish on burned threads. How can you when you can't move in Z? BTW, the threads are 1/4-20, scaled up for 0.018 shrinkage. I used a circular orbit and locked Z. Is there a way to burn threads with a mirror finish? I have a call into Mits, but of course they haven't called me back yet.

 

thanks,

scott

Mitsubishi EX-8

[Kannon]

good luck!

I use CuW all the time for threading and the finish is never beautiful. I am lucky cause the purpose is to just get threads in heat treated material, and they are happy.

I use the same method, burn the hole to the minor, then undersize the threaded electrode to go down and orbit to the major locking the Z. I think the finish is rough because everything in the threading is being drivin from your delta R. Your delta Z's in your Masterpack are all zeroed, along with SV method to fixed. I believe that the flank gaps are to close in your roughing epacks to your finish size. What would happen if you would increase your flank gaps in your delta R, telling it to stay further away from finish size? I always wanted to try it but never got the chance. This would give your finishing epacks more material to burn. That I would have to believe give you a better finish.. not mirror, but better. Along with that, obviously would be machine time. Ask your engineer if the finish is bad enough to add more hours of sinker time.

just a thought and am anxiously awaiting your response from mits...might even want to ask them if my idea will work or not.

I get pretty tired of calling tech support 20 times, and having the receptionist ask me my phone number each time. Its the same number I left you with the last 19 times!

good luck..

Kannon

2 Mitsubishi Ex-8

[Jorgen]

Hi

 

No experience with Mits but you should be able to get a really good EDM finish even with constand Z as long as you don't have a flat surface. What you need to do is to leave more stock between your power settings. It will take longer to burn but you should be able to get the same finish as on all other burns. How much stock depends on the angle you burn, I been doing well with leaving 60% extra for threads

[DC Gorn]

Your Engineer is mold design engineer or a product engineer? I am guessing he is not a manufacturing engineer. He is use to seeing parts after they have been "Cherried" up by a toolmaker. I have seen some pretty neat stuff done with EDMs but they always have EDM finishs not mirror.

[El Scotthead]

thanks for the quick response guys.

 

DC,

he's a mold designer. He thinks, because he was a "toolmaker"(termed loosely) for a few years, that he knows all about the trade. Also, because he can sort of run the old manual sinker(very big overstatement), that makes him a sinker guy. We don't sugar-coat anything. If it comes out with an edm finish and we polish it, we tell him we polished it. But if he thinks something should be a certain way(mirror finished threads right out of the worktank, for example), then there's no rationale in the world that will change his mind.

 

Brian and Jorgen,

I did actually cheat my flank gap a bit. I used the FAP technology for a trode undersize of 0.0050. Then I orbitted 0.0100, so there should have been 0.0050 stock for the finisher to clean up. The finish was one of the best I've gotten on threads. Maybe if I'd have been able to orbit more, it would've helped...not really sure, though. I'll have to play around with it. I'll let you know what Mits says, but I'm not holding my breath that they'll even call me back today.

 

In case you're wondering...why FAP and only a 0.0100 circular orbit? The engineer ordered the trodes without any input from me He's lucky I could still use them. They were only undersized 0.0100, so I had to put a 0.5000 spacer between my (2) inserts and do a tennis-racket style burn(basically a side burn, but with orbit in the xy plane, z locked, and full fixed mode) in each direction. FAP is the only way I know to do a burn like this. Made for a tricky program. But I didn't scrap any, and it certainly boosted my confidence, no matter what egghead says.

 

BTW, DC, you have groupies?!? I'll have to call my reseller and find out where mine are

[gavetta]

If your "engineer" really was a "Toolmaker" then he would already know that a "mirror" finsih won't be acheived with EDM. It's been a while since I ran EDM (5yrs) and unless someone has come out with some new technology since then I don't think you can make it happen.I know when I worked for Motorola, they had Mits' that could leave a really good finish with a special EDM solution (big money for it and the machine to use it)and lots of time but it was still far from mirror. There was still a light recast layer that if you chose to you could polish to a better finish. Maybe he had run into this and that's what he was hoping for. My .02

[Kevangel]

There is some new technology (EDM fluid made by them) out by Charmille where they have graphite so fine its "suspended" in the dielectric and helps give incredible finishes , something about it helps reduce size of sparks so craters are smaller. Just for reference.

[gavetta]

Yeah,it was something like that with the Mits but I still wouldn't call it "mirror" finish. It was darn good though. Took alot of time too but like I said it was 5 yrs ago so I guess maybe they have improved on it. I guess I also souldn't have been so quick to jump at the "engineer" thing but....we've got a few "Einsteins" around here that love to tell me how I should do my job when they have no knowledge of what's suppose to be done and think every job "should be a 5 min job, simple right" .......ahhhh.....yeah

[El Scotthead]

I actually heard back from Mits yesterday. You're absolutely right, gavetta. Mirror finishes can be acheived, but not on threads. According to Mits, you can only get a mirror finish on the bottom surface, not the side walls. And its not accurate, because it uses the crud in the gap like jeweler's rouge to "lap" the high spots down(actually melts them into the low spots). It doesn't work on sidewalls because gravity pulls the "rouge" down out of the gap. However, if you're carefull, and control the environment around the machine, you can acveive accurate burns with a fine mat finish.

 

He did mention the new machine they have with the particulates in the oil. Sounds like it works real nice, but its buku $$.

 

BTW, I won't fault you at all for jumping on the "engineer's" back. When I gave him the above info, he actually said this: "Scott, I've seen it done myself. I know it can be done, they must not know what they're talking about." I just handed him a piece of paper with Mits phone number on it, said, "call them yourself, then. Rich is the guy I talked to," and walked out(before I did something rash).

 

Nice new avatar, btw. I could use one of those martinis right now

[gavetta]

Yeah, that's sounds about right from what I remebered. The guys at MOto were looking to get better finishes on the deep ribs and hard to polish areas.

Good luck with your "engineer/toolmaker" guy. Some people won't listen even when it's in black and white right in front of them.

 

Martinis for all.