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"Welded" comm connections


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#1 havlicek

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Posted 30 November 2016 - 09:37 PM

I've been asked to do this again, so I hope it doesn't get buried, or at least that someone bookmarks it.  

Anyway, what I do is not really "welding", it's more "brazing" or high temperature soldering using a silver alloy that's a little more than half pure silver and the rest other metals, designed to melt/fuse at around 1200F.  Resistance type welding IS done for many armatures, and is probably the most widely used method, but doing it well/consistently/reliably requires some expensive equipment.  Using a silver alloy for high temperature soldering or "brazing" produces a very strong and electrically sound connection and can be done on the cheap.  I like that because, I'm cheap.

For a power source, you need a lot of current.  Low voltage is best because it reduces the chance of striking an arc and vaporizing the com tab, but the car-starter type thing I use is cheap...just like me.
IMG_1847_zpsxsbc0fpe.jpg

 

For a way to control when and where you deliver all that current, I use a boat ignition switch I got from some website.  It's contacts are rated to handle all that current, which is important.  It's a momentary switch, meaning it only "trips" while you press it, and is normally open, meaning that when you press it, it closes the circuit it's attached to.  I mounted it in a plastic project box and just ran the two contacts to a pair of brass bolts that act as terminals on the top of the box.

IMG_1843_zpsj2aweuhx.jpg

 

The positive wire from the car charger goes to one of the box's terminals.  When you trip the box's switch, the current runs through the other terminal to an alligator clip I use to hold a piece of gouging rod held against the com tab...and that will heat it up PRONTO.  The negative from the car charger goes to a smaller alligator clip that's attached to the com.  When the circuit is tripped, the current flows through the gouging rod to the tab and back to the charger.  The gouging rod gets hot fast because of it's resistance, causing the silver to melt and make the permanent connection, a connection that should be good to 1200F.  Copper melts at around 1800-1900F, so the silver should melt before the copper com tab.  ***The reality is that the difference in melting points gets small when you trip the switch because it takes only a few short blips to melt the silver.  If you feed only a bit too much current, the copper will melt and you can strike an arc that will instantly ruin the com.  The best way to have at this is to quickly pulse the thing on and off with your foot until you see the silver fuse.  Just holding the circuit closed will melt both the silver and the tab.

Here's the gouging rod in the package:
 

IMG_1839_zps9ihyoazv.jpg

 

Here it is out of the package:

IMG_1840_zpsnwzgiumo.jpg

 

I cut it down to small 2 1/2" or 3" pieces that I sharpen, but not too sharp, or they produce too much heat in too small of an area too quickly to control.  I also put a small "groove" on the tip to help prevent it from slipping off the end of the com tab like so (the tip shape gets tuned-up after every couple of coms):

IMG_1841_zpsrdtfsad5.jpg

 

The silver alloy I use comes from a nifty jewelry-making website called Rio Grande, and you can buy it by the foot.  A little goes a long way, so it's cheap...did I mention I like cheap?

IMG_1838_zpsyte8iio9.jpg

 

I also use the same alloy in a syringe that comes as a powder mixed with brazing flux:

IMG_1837_zpsrozoj5lh.jpg

 

I put a very small amount of the flux/silver goop on the tab and then put a teensy weensy bit of the silver wire on that.  The goop holds the silver in place and helps the silver flow, as well as adding a bit more of silver.  When ready to hit the current, the tab looks like this:

IMG_1842_zps0m7h0k2r.jpg

 

With the negative from the car starter attached and the gouging tip touching:

IMG_1845_zpspksxut5t.jpg

 

NOTE: I have the back jaw of the clip insulated with some high temp tape just for a little more insurance that the current flows through the tab I want it to.  If you're not careful, the current might not do that...no bueno.

When done, you get something like this.  I usually get a smoother joint, but the arm meters perfectly (*it's a #27 for the "A Walnut Is Born" thread) at .138 ohms per pole, so I know it's good:

IMG_1846_zpsy56w8ci3.jpg

 

You just have to lather/rinse/repeat for the other two poles and you get this:

IMG_1848_zps4mlnfcgm.jpg

 

The arm is ready (after testing on a meter after welding) for being tied:

 

IMG_1849_zpssjq1uo68.jpg

 

Then it gets epoxied.  After all that, it gets a fresh com cut, and then balanced and ground.  This one is a hot little #27 wind and will spin very fast, so it needs all the good stuff!

 

-john

 


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John Havlicek




#2 SlotStox#53

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Posted 30 November 2016 - 10:18 PM

Very concise and clear John :) Thanks again for detailing the process & tools *bookmarked*


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#3 havlicek

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Posted 01 December 2016 - 08:30 AM

***I should mention that, while all this involves high current DC, it's relatively low voltage and apparently "safe", at least as regards personal health.  I've never been burned, electrocuted, or otherwise harmed as far as I can tell.  That is not to say that there isn't some way a person might figure out how to harm themself doing all this.  This is all a "jury-rigged" system I was able to figure out/cobble together from piecing web-information together, so the above is just how I do things...informational.  ***You can easily destroy a commutator as I mentioned and the heat produced is substantial, even though it's confined to a very small area.  That heat does produce a small amount of smoke from burning the flux, so don't breathe that stuff, the same way you shouldn't breathe the fumes from soldering.  There isn't any lead involved, so that's a good thing, but whatever the composition of those fumes is, no doubt it isn't good to inhale.  This is all just common sense, but it bears repeating here, just as you need good sense when using power tools, or when working on say an automobile.  The carbon gouge will get warm and then hot, so I hold it at the back only...duh!  be smart and have fun!

 

-john


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#4 wbugenis

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Posted 01 December 2016 - 09:24 AM

Great work, John.  

 

Really clever simplification of a process that has been an obstacle for some.

 

A very  small addition to the information out there:

 

          Solid copper alligator clips like the one you are using is made by

   

                                                   Meuller    part no       BU 60C  (this is a common controller part)

 

                       Also check out    Meuller      BU 27C       (for more current capacity)

 

Thanks  

 

Bill


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William Bugenis

#5 olescratch

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Posted 01 December 2016 - 02:19 PM

Thank you very much!  A pic is worth a thousand words, with your description of each step places this into the million bracket.  Now to go out and collect all the pieces to try and duplicate your results.  You really don't seem to have any "secrets" that you're not willing to share and I thank you for that!  Wifey just showed me how to bookmark, and this is my first item!


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#6 havlicek

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Posted 01 December 2016 - 03:58 PM

Thanks Bill and John

 

 

 

Really clever simplification of a process that has been an obstacle for some.

 

Well, I'd be less than honest if I tried to say I wasn't in a complete fog about how to go about this Bill.  This was much harder to find information about than the powder coating...that was more about how in he** does one actually get the powder.  The welding thing was really mostly about guesswork and...yes...ruining commutators.  Even after experimenting on some non-critical parts, I still ruined coms...it's just that the ratio of good coms to ruined ones has gone up over time ;)  Now, I'm at the point where if I ruin one...it's because I got lazy.

 

 

 

You really don't seem to have any "secrets" that you're not willing to share and I thank you for that!  Wifey just showed me how to bookmark, and this is my first item!

 

Not at all John.  Well, there may be a few winds I keep to myself, but as far as the actual processes, just the opposite.  I've burned up countless posts...no, make that pages of posts and gigs of bandwidth/data documenting things here (hopefully not to the point where Greg gets ticked at me!).  While nobody shared anything about anything when I was a kid, there's still at least a little of that on the production end of things today, but far less.  Some have given me helpful hints about things (like Bill for example) when they could, but when it comes right down to it, you have to actually "do it" to figure out "how to do it".  The painful lessons are the ones not forgotten!

-john


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#7 grooverunner

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Posted 23 April 2017 - 02:08 PM

Hi John,

 

What is the part # for the flux you use , I used the #'s off of it but they did not work and they make a few different ones.

 

Thanks in advance

 

Ken


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#8 havlicek

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Posted 23 April 2017 - 04:47 PM

Hi Ken,

 

     Here's a direct link so you can get the #.  Again, this is a powdered silver/flux combination paste, and I use the "Extra Easy" alloy for both this and the silver wire:

https://www.riogrand...tra-easy/103101


 


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#9 grooverunner

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Posted 23 April 2017 - 06:03 PM

John,

 

Thanks again, I'm going to rewind more like repair a Cox FT16D for my Dad's ISO Chassis 2E,  I figure it's a good place to start. Anyway I was reading this thread with interest and realized what your setup is just like or my Black Beauty Induction soldering unit I have for electronic things I do. So I got a few powder coated arms and coms from Bill. I have a LaGanke winder. 

 

Wish me Luck!

 

Thanks Again

 

Ken


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#10 Brian Cochrane

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Posted 23 April 2017 - 06:25 PM

John, are you stripping off the coating on the wire where it raps around the comm tabs?



#11 havlicek

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Posted 23 April 2017 - 07:25 PM

John,

 

Thanks again, I'm going to rewind more like repair a Cox FT16D for my Dad's ISO Chassis 2E,  I figure it's a good place to start. Anyway I was reading this thread with interest and realized what your setup is just like or my Black Beauty Induction soldering unit I have for electronic things I do. So I got a few powder coated arms and coms from Bill. I have a LaGanke winder. 

 

Wish me Luck!

 

Thanks Again

 

Ken

 

Excellent!

 

 

John, are you stripping off the coating on the wire where it raps around the comm tabs?

 

Always and diligently.  Any insulation left at the com tab connections will become carbon and can noticeably affect the connection.  I also routinely clean the tabs until "bright" before brazing, and then also clean them after brazing to make sure whatever burned residue might be on there can't later cause problems.


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