Help a non-metalworker?

C'mon Don give him some slack...He said he was a non-metalworker.

I betcha he jut got misled because those who flog high end audio stuff brag about gold plated connectors and he just thought it was because gold had lower resistivity, when it's really put there for corrosion resistance.

Yep, you can easily guess what I'd do....

Use conductive epoxy to glue in a stranded wire pigtail and get some mechanical bend relief, and then solder a binding post to the free end of that wire. Further messing around mechanically or thermally with what's left of that post may lead to the internal disaster he was worried about.

Who sits around staring at the backside of their speakers anyway? Once again I say, "Pretty is as pretty does."

Jeff

Reply to
Jeff Wisnia
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I meant no disrespect. Ya don't have to be a metalworker to look up resistivity in a book. I was surprised when I looked up the resistivities. I thought I was going to say that gold isn't enough better than copper to make any difference in a speaker termination.

Then I discovered that Wilson (not Wilsong) uses stainless terminations. That happened because Mr. Wilson saw some audio gear in Mazatlan with terminations so corroded they were green.

Imagine what partial rectification might do to your $4400 sound... Tawk about distortion!

If a guy had more time than money (like me) and further had audiophile zeal for the best possible repair ..... I may have an idea.

It would take some experimenting to get the process right, but I wonder if one could make a fixture to spin-braze the joint. Liberally "tin" the end of the new (stainless) post with a strong silverbrazing material like H&H Easy-Flo 45. After tinning, machine the new post round in the lathe so there's a "slug" of silverbraze material fused to the end. Then, with fixture holding the parts parallel and concentric, spin the pin with axial pressure so friction at the point of contact melts the silverbrazing material. Then abruptly stop the spin. Result: a strong butt-braze that is probably very nearly as strong as the parent material, with only very localized heat due to the rapidity of the operation and the specific heat and relatively low thermal conductivity of the materials being joined. Electrical properties of such a joint would be excellent.

One could then brush-plate the new pin (or spade) with gold if desired.

I really don't know if this would work, but I do know that spin-welding is done as a production process.

Reply to
Don Foreman

"Don Foreman" wrote: (clip) It would take some experimenting to get the process right, but I wonder if one could make a fixture to spin-braze the joint. (clip) ^^^^^^^^^^^^^^ I think your idea could be made to work, with adequate preparation. My idea is an outgrowth of yours, and could possibly be a little easier. Instead of "spin-brazing" how about "spot-brazing?" Use an electrical spot welder to melt the filler material, instead of friction. It would not require the alignment jig, nor the rotary input power. You would have to find someone with a spot welder and a cooperative attitude, however.

Reply to
Leo Lichtman

What do you connect the other electrode to? The broken pin is down in a hole.

I would worry about blowing the voice coil and/or affecting the magnet with the current pulse.

Reply to
Don Foreman

I got an email response from the customer support. The guy said the spoke with production and they told him it was possible to get to the pin in question by using a dremel tool on the expoxy potting. The pin seems to be broken within the wall of the speaker (about 5/8 inch thick, corian like material). I've carefully dremelled enough material away(about 1/2 inch depth) to see a bit of the rest of the pin.

Now I'm taking a break before I screw things up. I understand that one can really f**k things up with a dremel tool.

I've ordered a replacement pin through a dealer so I can see what I'm dealing with.

What I think I might do is get some more of the pin exposed and find a place where I can place a proper solder point. I would then cut the original pin at that point, cut the replacement pin to match and solder them together. I'm sure this will be stronger than what I'm doing now since when I pull the pin out in it's current state of disrepair there is solder bonded to the external portion which I heated; it appears the solder is not well bonded to the stump embedded in the speaker, probably since that part isn't hot.

Reply to
vernon.huang

OK. I've finally uploaded pics to the dropbox. They are labelled starting "broken speaker...".

There is a text file explaining the pics as well.

The item in the picture that is not a speaker post is a 4/40 x 3/8 headless hex screw that I considered using as an internal fixating device assuming I could find someone to drill and tap the existing ends of the broken post.

Thanks for all the input!

Reply to
vernon.huang

Ooops, make that "vh broken..." for the filenames.

Reply to
vernon.huang

Now you're getting somewhere!

Can you tell if the broken pin is made of stainless steel? If not, do you have a broken off piece that someone could examine?

You'd probably get a stronger joint if you have a bushing or collar made that would enclose both the stub and the new pin -- or have a pin made that has a larger section with a hole that surrounds the stub.

If you can accurately measure the diameter of the stub (with calipers, not a ruler) and make a sketch, I would be glad to machine a part for you. Contact me by email if that is of interest.

If the material is stainless steel, then I would recommend a tin-silver solder for joining them. I could send you a bit of that. It melts at 430F, not greatly different from ordinary lead-tin solder, but it is a lot stronger and it wets just about any ferrous or copper-bearing metal -- steel, stainless, copper or brass.

Reply to
Don Foreman

I looked at the pictures. Looks like the material is copper. Are there any threads on the stub at the bottom of the hole? If you can dremel out enough material, a new part could be made that has a drilled and tapped hole to engage the threaded (?) stub. Three threads would be enough.

If the replacement part were knurled on the outside and the hole was then backfilled with epoxy after the part were screwed onto the stub, I think you'd have a repair that would be sound both mechanically and electrically.

I would make the replacement part of brass, rather than copper. There's enough cross-sectional area that the resistance would still be negligable, and it would be somewhat stronger than copper.

This could have a spade lug rather than be a binding post, if you like. I could plate it with tin or nickel -- or gold, if you wanted to buy the juice.

Reply to
Don Foreman

From the photos, I'm thinking there's a nut back there, one of two securing the double binding post to that "Corian like" stuff he mentioned. Could well be something just like the "Vampire BP2" a ways down on this page:

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And, screwed into the nut is the remaining male threaded part of the busted post, with a wire soldered to it's back end in typical binding post fashion. Or, maybe they used a solder lug under the nut, with the speaker/crossover lead wire soldered or crimped to it, in which case removing enough of the plastic ought to let you access the surface of that solder lug.

If they didn't use a solder lug and he drilled into and peeled out the existing threaded stub to to be able to screw something into the threads of that nut, he'd likely disconnect the back end of the stub from the nut. I don't like that.

I'll raise my voice again and scream CONDUCTIVE EPOXY! I think I showed a couple of days ago that the added series resistance would be insignificant.

I (who can spend three hours fashioning and splinting on a replacement foot of an antique ivory asian "medicine lady", missing when I bought it) can appreciate why the OP eants to keep the original appearance of his speaker by connecting a pigtail lead with conductive epoxy as I suggested, even though I think that's the best way to avoid fracturing the conductive epoxy when connecting a lead to the speaker.

My "second best" suggestion is to reconnect the present broken binding post back onto whatever metal is there *without* trying to drill into it, and use conductive epoxy to make the connection.

I'd suggest Dremeling a couple of "keyways" into the existing plastic binding post base because it's likely to be made of some thermoplastic epoxy won't like to stick to, and there's a fair amount of torque exerted when the binding post finger nut is tightened. (Maybe even enough to be what caused that busted post in the first place?) I'd use enough conductive epoxy to make the connection and squeeze up around the post, removing whatever bubbles over.

Whatever method he ends up using, he'd better be gentle about tightening the finger nut on that post. Using bannana plugs on the end of the speaker leads might be the safest choice.

Jeff

Reply to
Jeff Wisnia

Gold is wanted for several reasons on many items.

  1. it is a noble metal - that is, not much dissolves it.
  2. It flows on contact with more gold or a metal it likes (most).
  3. It forms a gas tight fit - so the chlorine in the air doesn't etch copper...
  4. It can be plated on so thinly.
  5. It looks nice.

Martin

Reply to
Martin H. Eastburn

Me either. My suggestion was not to drill the stub, but to have something made that screws onto it.

Unless it cracks over time, due to different rates of thermal expansion of metal and epoxy.

Good idea. I'd knurl the insert too. Then there's no dependence on adhesion of the epoxy, it forms a mechanical lock by interference fit when it cures. I might also mill some flats on the outside of the post where it emerges, so a little wrench could hold it while leads were being torqued.

I'd include wrench flats to hold the post while tightening. Problem with banannas is that they project, providing a lever to bonk and break. Wires are more flexible.

Reply to
Don Foreman

I find it hard to believe that he was lucky enough to have that post break so that there was still some of the threaded part sticking out before the nut. In my experience stuff like that tends to break about three quarters of a thread turn down inside the nut. But, if he was, then your idea of screwing a threaded piece over it is preferable to just relying on conductive epoxy, but I'd use that epoxy too, it probably couldn't hurt.

Hasn't happened to me yet. Besides, how big a temperature swing is an indoor louspeaker liable to see?

Guess it wasn't just his finger torque, in the text file he posted with the three photos he tells how it happened when he was using "a tool" to tighten the post.

I'd use

Looks like from viewing his first photo that the part is already knurled. Likely that's likely the section around which the plastic dual binding posts "base" was molded, for obvious reasons.

Yeah, but what are the chances that wrench will get used every time? I wouldn't depend on it, even if it was me who owned that speaker. Well, maybe if I left a dedicated little wrench hanging on a string at the back of the speaker to wake up my memory.

Now we're back to my wanting him to use conductive epoxy to fasten in a flexible pigtail.

Jeff (Who is thinking, "Jeez, if we got paid by the hour for all this thinkin' time we'd fer sure be 'fartin on silk', as they say down Maine.)

Reply to
Jeff Wisnia

Bet you would, if you'd written the check for the speaker and then had to fix it or get it fixed.

I wonder if they sound better if the little wrench is gold plated.... (ducking)

Reply to
Don Foreman

Thanks to all in the group for all the great advice and generous offers to help. It's incredible how helpful the metalworking community has been.

I have placed my order for conductive epoxy as I see this as the least risky and least destructive means of getting a repair. I will also try to use some silver/tin solder and see if this works better than the lead based solder I've been using.

I can't tell what the posts are made of. Looks like a silver metal with a gold plate.

In the long term I will also continue to slowly dremel away epoxy to get to the post. When I get the replacement I'll upload a pic. I'm sure that there is more post to work with since it broke off within the wall of the speaker. Maybe if I'm careful and lucky with the dremel I'll be able to expose enough threads to work with. Exposing enough post to cut and then join ends together with a threaded sleeve sounds like a great long term solution.

Any tips on what type of dremel head will cut epoxy but not damage the post? Should I try to use any solvents when I get really close to the post?

Reply to
vernon.huang

I can't think of a rotating cutter which would guarantee your not damaging the remaining part of the post if it touched it, but have you tried "thermally excavating" the epoxy with a hot soldering iron tip? Something around 3/16" diameter with a chisel shaped end ought to do it if you dig carefully.

I do hope you get lucky and you find you can expose enough of the threaded portion. Judging from the 4-40 setscrew in your photo, I'd guess that the thread on the broken part (If it's US made) is likely to be 6-32, in which case the chances of drilling and tapping it for anything which could give you much strength aren't slim and none, and Slim rode out of town yesterday. You'd be far better off using Don's suggested threaded sleeve, once you identify just what the thread specs are.

I wouldn't recommend using chemicals to clean off the post, I just don't know what the long term effects might be. You could probably get most of the epoxy of the threaded part just by poking at it with a small sharp tool, and if there is stuff left in the threads you could probably make a small diameter erzats "die" to clean it up by taking a matching threaded standoff (see below) and hacksawing a slot about 1/8" deep across the diameter on one end.

You could probably buy a "reddy maid" brass standoff from one of many places like this:

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And you could shorten a long one easily enought if you needed too, but it's probably easier just to let one of us make one out of brass for you and pop it in the mail once the thread specs and length are known. That's only "the work of a moment" for Don, or even me, and (speaking for myself) the satisfaction of knowing you helped somebody duck a horrificly expensive commercial repair job is ample reward.

HTH,

Jeff

Reply to
Jeff Wisnia

From the looks of jpg3 it appears the quick terms' are mounted on a plate, attached to the speaker by four screws. What did you find when you pulled the screws and plate? If that area isn't potted maybe the terminal can be replaced as a unit.

Bob rgentry_at_oz_dot_net _AT_ = @, _dot_ = . to eMail

Reply to
Bob Gentry

Bob,

The entire chamber housing the circuitry is potted with black epoxy. I'm dremelling in where the potting is up against the wall of the speaker where the pin inserts. It appears that the pin has broken off inside of the wall of the speaker and extends a way into the potting. I'll know more when I get a stock post to compare it to.

I've found the post (the sparks gave it away) and now I'm going to dremel around it and pick away carefully using something like a dental tool.

Reply to
vernon.huang

The plate can't be removed. I tried removing the screws, a heat gun and some prying. The mfg says that the potting makes it impossible to remove. They probably installed it along with a gasket and then poured the potting in.

Reply to
vernon.huang

Most commercial binding posts are made of brass. It would be nickle-plated under the few microinches of gold. However, Wilson says they use stainless steel hdwe, so it might be gold-plated stainless steel. Gold can be plated directly onto stainless.

About any dremel bit will cut metal about as readily as epoxy or plastic.

I might make a little trepanning tool, like an end mill with a hole in the middle. The hole would go over the stub, which would serve as a guide. That would leave epoxy or plastic in the threads but remove the material around the stub. I'd then try gritblasting the plastic out of the threads with a airbrush-like blaster or "air eraser" as

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maybe glass beads. That would aggressively attack the plastic without doing much to the metal other than clean it.

Chemicals that will attack epoxy are rather nasty and can leave a gummy mess.

I wonder what would happen if one poked at the epoxy with a red-hot wire or pick while shooting a jet of oxygen into the hole with a jeweller's torch. I'd try that on a practice piece first, with CO2 or baking soda at hand to smother things if they got too vigorous. I'd also do it in a very well-ventilated space.

Reply to
Don Foreman

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