I'm hoping that the metalworking community can help me out. I no nothing about this subject but would like some advice.
I broke the speaker binding post on a very expensive and very heavy subwoofer (A Wilsong Audio Puppy) The post is about 3-4mm diameter. I can't remove the piece that is still embedded in the speaker because it is soldered in and the circuitry is inaccessably potted. To ship to the manufacturer and have them fix would be very expensive.
I'm thinking that my solution may be to drill a core and tap both ends of the broken pin and connect them with a (conductive) headless bolt.
Would my local machine shop be able to do this and how much should I expect to pay? I'm on the San Francisco peninsula.
I still get electrical contact when I insert the pin but I'm not happy with this solution.
Any help would be greatly appreciated. email replies greatly appreciated.
So there's a stub sticking out? I'd make a brass sleeve that just fit over it and get a matching threaded piece and put it in the other end of the brass sleeve and crimp it on. You can get small brass tubing short pieces from hobby shops, and you can likely cut it yourself if you have a Dremel tool (with one of those superthin abrasive wheels) or maybe the hobby store guy would take pity on you and cut it. A better fix would be to solder the sleeve, but then you run the risk of the heat doing something bad at the other end of the stub.
If you don't have a stub sticking out, what do you have?
The post broke off about 1/2 cm inside the speaker. I have the broken off piece and a hole with the other half inside. There is no way to extract the other piece since it is soldered in and the circuitry is potted.
Conductive glue would be great. How conductive is this stuff?
Soldering doesn't seem to be an option since it's down inside of the hole.
And if the broken piece is too short to work with, go to the store and buy an 8-32 or 10-32 brass machine screw (whatever fits in the hole) and use that as the replacement stud...
" snipped-for-privacy@ncap.net" wrote: (clip) Any help would be greatly appreciated. email replies greatly appreciated. ^^^^^^^^^^^^ How about dropping a small coil spring in the hole, and then inserting the broken off post? Perhaps a spring from a ball-point pen, or similar. Then hold everything in place with some ingenious solution you come up with, such as: 1.) string 2.) Hot glue 3.) C/A glue 4.) Tie wrap 5.) Very small clamp, etc.
Could you run in a small self-tapping screw until it makes contact with the broken, hidden stub, and then attach your speaker wire to that?
Or, drill and tap the hole to accept an appropriate length of all-thread. Then tie your speaker wire to it with two nuts.
Help these folks out with a couple pictures, would be my advice.
Here's how. Tape a ruler next to the part in question (and the part that broke off) and snap two or three pictures (various angles).
Upload the pictures to the metalworking dropbox using the procedure shown in:
formatting link
Repost your question, referring to the photo's URL (for instance):
"Hi all.
Could you please look at:
formatting link
and tell me how to fix this myself?"
From what you've said so far, I expect that you need to use freeze mist, some penetrating oil and a 'left hand drill' to shrink and back the broken part out of the assembly. Match the threads with those from a cut-off piece of brass machine screw and a nut.
Don't laugh, look at the bottom of page 2281 of the McMaster catalog for the proper size bit that you use with the drill motor *in reverse*.
I'd grab my Dremel with a small dentist bit in it and start cleaning out around the stud so that I could get at it. Epoxy later can fill the hole. Be carefull as the binding post may be soldered to a printed circuit board rather than a wire. Then, after finding the wire, solder to the wire a new binding post. The binding post is probalby a 5 way post that Radio Shack sells. Short of that, you probbaly don't have enough meat inside to do a good job of drilling and tapping a new hole as just inside there is usually a smaller section where the soldering is actually done onto the post. Don't bother with the conductive epoxies as their conductivity isn't good enough to do a good job of conducting the current that the speaker will be using. Take the number of watts that the speaker is rated for and divide by
8 for the amps of current that the speaker uses and you may be supprised at how much current that the speaker uses and consider that you go and buy low resistance wire just to make the speaker sound good. Any resistance in the path decreases the volume and increases the resonant points of the speaker which makes it sound bad. I'll note that the potting is to keep others from copying the design and this really doesn't work all that well as there are edpotting chemicals available for alll of the various hard potting compounds. It just means that the copyier needs to be a little more persistant.
-- Why do penguins walk so far to get to their nesting grounds?
I was about to strongly suggest he use conductive epoxy to join the broken parts when I read your comment. Conductive epoxy has saved my chops quite a few times when I didn't dare apply soldering heat to someting, and once when the magnet wire I needed to reconnect turned out to be made from aluminum. (I just reminded myself of the Korean war era when I used to run into TV deflection yokes and power transformers wound with enameled coated aluminum magnet wire, because copper was needed for the war effort.)
Conductive epoxy is expensive, but I've had the same two little tubes of the stuff sitting in the kitchen freezer for at least a dozen years now, and usually just "a little dab will do ya".. It still works as good as it did when I bought it after about ten minutes warming up the two tubes in my pants pocket.
Before packing it in I Googled up some specs on conductive epoxies and found their volume resistivities are claimed to be around .001 ohm-cm.
Now, copper is about 1000 times lower in resistance than that so at first what you said about adding too much series resistance in the speaker circuit almost scared me off.
But, I don't give up that easily, and decided to work it out. Suppose the broken post is about 5mm in diameter and he can butt join the two broken ends together with a layer of conductive epoxy averaging say
0.5mm thick.
If I just did the math right the series resistance of that layer of epoxy will be only about 0.25 milliohm.
Number 12 copper wire has a resistance of about 2 milliohms per foot, so it seems like that layer of conductive epoxy will have no more effect than adding another couple of inches of that kind of wire to the speaker leads, hardly a major worry, 'eh?
I don't claim to be an expert on this stuff, and I never even played one on TV, and maybe there's some "contact resistance" factor or something else I don't know of that sneaks up to grab you at the epoxy-metal interface. But if there isn't, than I don't see why conductive epoxy won't do the job for him safely, particularly if he can buttress and protect the part he's joining back on so that it's not likely to bust off again.
If the OP can satisfy himself that it's safe to drill a hole a short distance down the center of the remaining piece and drills a similar hole in the broken off piece, then he could splint the epoxy joint with a short piece clipped off a No.4 brass machine screw and add strength.
"Bob May" wrote: (clip) Take the number of watts that the speaker is rated for and divide by 8 for the amps of current that the speaker uses and you may be supprised at how much current that the speaker uses (clip) ^^^^^^^^^^^^^^^ In order for that to be true, 8 would have to be the volts at rated power. Where did you get that figure? By any chance, did you use 8 because it is an 8 ohm circuit? That wouldn't be right, then. If you want to work with the power formula with the figures that are known, use P = I^2Z, where Z is the speaker impedance of 8 ohms. So P = 8I^2, or I = square root (P/8).
A machineshop certainly should be able to do this, as could many amateur machinists. There are several readers of this group in the bay area, TBD whether any would like to go for it for maybe a case of beer or ???. I would, but I'm in Minneapolis -- when I'm not gone fishin' this time of year.
Being a non-metalworker, you will very probably screw this up without the right tools and skills. That isn't meant to be a put down by any means, merely that we metalworkers have learned from the screwups on our own projects. Exactly how to do your job isn't clear without good photos or a first-hand look, but it doesn't sound like a difficult job. I suspect I'd use a vertical mill or a shop-made jig.
Thanks for all the replies. I'll try to post some photos later today.
I took some advice from the forum and put a ball of solder on the end of the stub. I then inserted this into the hole and held a soldering iron to the post. I had practiced before doing this and learned that the solder on the tip (about 1 cm away) melts after about 36 seconds.
So I held the soldering iron onto the pin in place for about 45 seconds and things seem to work now. I'm not altogether happy with this solution and would like to find someone who could join the two pieces together with a highly conductive post. This is an audiophile grade system and I don't like my band-aid solution. I don't relish the idea of shipping a 130lb speaker back to Utah for repairs though.
Anyone in the bay area want to take on this project or recommend a place? Let me know what it would take.
" snipped-for-privacy@ncap.net" wrote: (clip) things seem to work now. I'm not altogether happy with this solution (clip) ^^^^^^^^^^^^^^^^ If you had left it for repair at a professional "audiophile grade" shop, they might have done the same thing, and charged you $85. And you WOULD be happy. So, just send me the $85, if that is what it takes. I would have done it for less, but as the psychiatrist said, "The fee is an important part of the treatment."
The problem is that with only solder holding it together it breaks with any type of stress on the pin, if I move the speaker, the solder breaks. I would also like to use a spade connector instead of the banana clip connector. If I tried to use a spade connector now it would pull the pin out.
Ultimately I think I want to splint the pieces together with a post or headless bolt placed in a hole drilled concentrically down both pieces.
I'm willing to pay to have the post fabricated out of gold or whatever. This is a very high end speaker.
Why would you want gold? You are aware that gold has higher resistivity than copper, right?
Matter of fact, I think Wilson uses stainless steel hardware.
formatting link
That may be why you're not having good luck with ordinary solder. It doesn't wet stainless well at all. You might have better luck with a tin-silver solder of similar melting point but considerably more strength and far better wetting of stainless.
I would suggest that you separate the matters of electrical conductivity and mechanical strength. You are not going to get the strength of the original part with a "splint", so if you broke the original it's nearly a certainty that you'll eventually break the repair unless it's mechanically reinforced.
Make the electrical connection with silver-tin solder, conductive epoxy or whatever, provide mechanical strength by other means: a flange with screws into the body or whatever.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.