# Brazing together bronze nuts



## spike7638 (Feb 23, 2018)

Full disclosure: I'm an utter amateur machinist, and have basically no idea what I'm talking about when I use (most) machining terms. Please bear with me. 

I need to make an assembly that looks like a tall nut (a "connector nut" might be the proper name) in silicon bronze (for underwater use on a boat). The last roughly 3/4" of one end of the tall nut would be turned down to be cylindrical; the other end would actually be doing work as a nut. Here's a crude attempt at a mechanical drawing to show what I mean: 


The part labelled "A" is hex; the part labelled B has been turned down to be a 1" diameter cylinder (with threads in the middle, but those don't matter at the "B" end). 

I could start with rod, bore it out, cut internal threads, mill flats on the "nut" end, etc., but frankly...I'd probably screw it up three or four times, at great expense (both in materials and frustration). 

So now I'm thinking that I could just stack up three nuts (perhaps threading them snugly onto a rod as a starting point) and braze them together. I'd have the threads I need right from the get-go, and the remainder of the assembly doesn't need to be terribly strong...but it *does* need to be electrically connected to the front part, or I'd be considering using something like epoxy to assemble things. 

Is it possible to do this? Would I find that the brazing material wicked into the space between adjacent nuts, ran all the way to the center threaded rod, and thereby messed up everything by turning the whole assembly into a kind of weak rod?   Is there some obvious way to do this that I'm missing? 

[For those who care about details: I need to put a donut-zinc onto the back end of my propeller shaft; the geometry of the propeller cutout, the rudder, and the deadwood make putting it in the front not really feasible. The "nut" end of this thing is the second nut for the propeller; the cylindrical tail is there to give the zinc something to grab onto. The current version involves copper tubing brazed to a nut, but the OD is 7/8, and I need a larger zinc, which means going to a 1" center.]


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## francist (Feb 23, 2018)

I have been tempted by similar scenarios before, multiple times actually, and one feature I always discover is that nuts will not all clock the same when you tighten them onto the rod prior to brazing. In other words, the flats will not necessarily all line up. And in order to get the flats aligned, you find that some of nuts are too tight, some are too loose, etc. It can be done, but there is much trial and error fitting.

As for the other logistics of this, I'll leave to others. 

-frank


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## bfd (Feb 23, 2018)

why don't you just make a nut. 3/4-10 easy to get a tap. bronze/brass McMaster carr. a better material choice might be stainless steel (316) not (304) there might be other stainless but I am familiar with these 2 around salt water. just a suggestion bill


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## brino (Feb 23, 2018)

Hi Spike,

A couple thoughts......

If you put three nuts together on a threaded rod the flats will not all align, is that a problem?
I wonder if a lower temperature (silver?) soldering process would be better.
You could wax the threaded rod first, or apply soot from a candle or oxy torch.

Is there any reason why a stainless steel coupler nut wouldn't work:
https://www.amazon.com/Coupling-Nut...=2025&creative=165953&creativeASIN=B00FASWCLM
https://www.fastenal.com/products/details/0172552
https://www.mscdirect.com/product/details/02164754

The end for the cathodic protection disc could be turned down.

-brino


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## spike7638 (Feb 23, 2018)

francist said:


> I have been tempted by similar scenarios before, multiple times actually, and one feature I always discover is that nuts will not all clock the same when you tighten them onto the rod prior to brazing. In other words, the flats will not necessarily all line up. And in order to get the flats aligned, you find that some of nuts are too tight, some are too loose, etc. It can be done, but there is much trial and error fitting.
> 
> As for the other logistics of this, I'll leave to others.
> 
> -frank



Right...good point. In this application, only the flats (and indeed, the threads!) on the first nut matter at all (I could turn down both the second and third nut to 1" and it'd still serve its purpose), so that's not a real consideration in this case (although your experience matches my own in other situations).


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## spike7638 (Feb 23, 2018)

bfd said:


> why don't you just make a nut. 3/4-10 easy to get a tap. bronze/brass McMaster carr. a better material choice might be stainless steel (316) not (304) there might be other stainless but I am familiar with these 2 around salt water. just a suggestion bill



I'm not at all certain that I can confidently make a nut like this with my machining skills, as I said. 

As for stainless: experience has shown (or shown ME, at least) that using stainless nuts on stainless shafts in salt water generally isn't a great idea --- galling is a constant risk. If the prop shaft itself were bronze, I'd definitely consider a stainless nut.


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## f350ca (Feb 23, 2018)

Second what Frank said the nuts won't line up. Brazing bronze is tricky, they both melt at about the same temperature, silver solder might be a beter bet. When you weld nuts together they tend to pull and result in the thread binding.
1 1/8th hex material should be readily available, just need to drill, tap and turn the end down,


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## spike7638 (Feb 23, 2018)

brino said:


> Hi Spike,
> 
> A couple thoughts......
> 
> ...



Thanks for those ideas. The lower-temps process sounds nice, but mixing a third metal into things where I'm trying to reduce electrochemical corrosion seems like the wrong direction to head. As for stainless nuts: I'd use that on a bronze shaft, but my shaft is stainless, and the potential for galling worries me. But your remarks, along with those of f350ca and others, make me think that I should re-think things a bit and see if I can come up with something different/simpler/whatever.


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## brino (Feb 23, 2018)

spike7638 said:


> but mixing a third metal into things where I'm trying to reduce electrochemical corrosion seems like the wrong direction to head





spike7638 said:


> the potential for galling worries me.



Okay, I see.
Is there any reason you could not connect the sacrificial zinc right to the stainless threaded shaft?
https://www.thechandleryonline.com/product_info.php?products_id=8201
That one woulnd't tighten onto a 3/4 inch shaft, but zinc is soft so taking a little off the mating faces to make the thru hole smaller is easy.
Just don't breathe it if you sand/grind it off!

I guess you still want a second nut to jamb the first one.....maybe the shaft isn't long enough?

-brino


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## mikey (Feb 23, 2018)

I'd like to throw in my vote with @bfd and @f350ca - I would buy some bronze hex stock and turn the round end. Then use a 19mm drill or bore it to about 0.7482" ID, tap it and you're done. Simple job, and you CAN do it, Spike.


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## RJSakowski (Feb 23, 2018)

If brass will work, https://www.mcmaster.com/#brass-coupling-nuts/=1bp5r39


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## spike7638 (Feb 23, 2018)

brino said:


> Okay, I see.
> Is there any reason you could not connect the sacrificial zinc right to the stainless threaded shaft?
> https://www.thechandleryonline.com/product_info.php?products_id=8201
> That one woulnd't tighten onto a 3/4 inch shaft, but zinc is soft so taking a little off the mating faces to make the thru hole smaller is easy.
> ...


The shaft is tapered: it's 1" stock, which has a slight taper onto which the mating taper of the prop fits (with a key as well); then there are two nuts, the first of which snugs up the prop on the taper, and the second of which pushes on the first, and is typically either castellated or has a through-hole, and gets a cotter pin into a small hole on the very end of the shaft (which is turned down to about 1/2". So there's not really any shaft left behind that second nut. (Sigh), and it's certainly not 1" material. 

If you ever want to hear a fun debate, ask 2 boaters whether the nut next to the prop should be the thin or the thick one. If you ask any two boaters, you'll get three different answers (often with diagrams and fancy discussions of shaft elongation and other entertaining --- but not quantitative --- things.) 

As for your earlier suggestion of clamping the zinc directly to the shaft --- that's what's usually done, typically just ahead of the prop. There isn't clearance for it on my boat. (Sigh again). Another possibility is to chisel a hex cutout into a 1" donut, and clamp that down onto the big nut. But then there's the cotter pin to deal with (and having to remember to make TWO modified zincs, so that when I need to replace it mid-season, diving under the boat holding my breath, I don't end up swearing a whole lot!)


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## spike7638 (Feb 23, 2018)

RJSakowski said:


> If brass will work, https://www.mcmaster.com/#brass-coupling-nuts/=1bp5r39



Silicone bronze works pretty well in salt water; the zinc is meant to reduce the already-fairly-low-corrosion-rate of the propeller (which is slightly raised by it sitting on a stainless rather than a bronze shaft). Brass, on the other hand, in most alloys tends to act like a battery, and first gets pink spots as the zinc in it disappears, and then begins to look like Meunster cheese. Not at all the right material to use in any critical application underwater. It's a pity, because that'd be a great starting place to work from.


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## markba633csi (Feb 23, 2018)

Does even naval brass have this problem? I know silicon bronze is expensive
Mark


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## spike7638 (Feb 23, 2018)

markba633csi said:


> Does even naval brass have this problem? I know silicon bronze is expensive
> Mark


I don't know exactly what "naval brass" is, but if it's the stuff that's used for naval clocks and other such things, then the answer is "yes." On deck, it rapidly develops verdigris. It's the sort of thing that used to keep sailors in the British Royal Navy very busy with their polishing rags. Fortunately, stuff on deck may sometimes get sprayed, but rarely suffered prolonged immersion of the kind that leads to serious corrosion. If it does, your ship's upside down, and you've got bigger problems to worry about.


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## markba633csi (Feb 23, 2018)

Well, fortunately the part you are talking about would not be to hard to do, just costly to buy the material and the large tap required. Maybe have to buy a taper shank drill also unless you wanted to start with say a 1/2" twist drill and use boring bar to size.  It could be done on most any small lathe.
Mark


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## RJSakowski (Feb 23, 2018)

spike7638 said:


> Silicone bronze works pretty well in salt water; the zinc is meant to reduce the already-fairly-low-corrosion-rate of the propeller (which is slightly raised by it sitting on a stainless rather than a bronze shaft). Brass, on the other hand, in most alloys tends to act like a battery, and first gets pink spots as the zinc in it disappears, and then begins to look like Meunster cheese. Not at all the right material to use in any critical application underwater. It's a pity, because that'd be a great starting place to work from.



Being a fresh water boater, not a problem here.  

Here is an article that claims brass is superiuor to bronze for prop nuts.  The catch is, he doesn't specify what alloy.  There are more than two diozen brass alloys.  https://www.passagemaker.com/channels/propeller-nut-myth-busting

I dd some searching and it doesn't appear that a bronze coupling nut is readily available.  Making your own would require starting with a 1-3/16" round minimum. Technically, it shouldn't be too difficult to machine from scratch.  If you follow Kieth Fenner on You Tube, he is as close as you can get to a boating machinist guru.  He may be able to give you some advice.

If you decide to try the three nut approach, I would suggest TIG welding with the silicon bronze rod.  Good luck!


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## FanMan (Feb 23, 2018)

If you only need the threads at the hex end, why not just use a single nut with a longer cylindrical bushing (1" OD, 3/4+" ID)?

Trying to braze three nuts together while keeping them aligned inside and out is more likely to be screwed up (no pun intended) than machining it from solid bar or hex stock.  But you don't say what kind of machine tools you have available.

A drawing of the  assembly would help us understand the application.  Where is the hole for the cotter pin?

You're correct that you _don't_ want a stainless nut on a stainless shaft.


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## tertiaryjim (Feb 23, 2018)

While I don"t have the temperature information I have seen examples of bronze bushings and gears that got hot when people heated a bore for expansion and then pressed the bushing in or heated the gear to expand it. The bronze can harden and become very abrasive. 
It will eat shafts!


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## Mitch Alsup (Feb 23, 2018)

FanMan said:


> If you only need the threads at the hex end, why not just use a single nut with a longer cylindrical bushing (1" OD, 3/4+" ID)?



And if you must guarantee electrical conductivity, any kind of soldering at the joint will do that.


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## kd4gij (Feb 23, 2018)

Well I make boat shafts. The full nut goes to the prop. As it is the one with all the force. The half nut is a lock nut. On a 1" shaft there is 3 choices Double nut, castle nut. Or nylock nut. All bronze of cores.  I am not sure what You are trying to do.


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## bfd (Feb 23, 2018)

yes galling can be a problem, if the shafts are put together with a good thread lube, ( the one we used is called n-5000 , it was a colodial nickle and I used it on stainless steel pump shaft couplings that ran in the pacific ocean for years driven by a 500 hp motor they came apart years later with no galling) you do what you want but I have some bronze , brass or stainless you can have if you send me your address bill


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## brino (Feb 23, 2018)

Thanks all and especially @spike7638 for asking for this very interesting conversation.
Never too old to learn!

-brino


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## kd4gij (Feb 24, 2018)

I am a machinist in a prop shop.  Best thing the op can do is paint his prop with zinc chromate primer. I see rudders all the time eaten up with electrolysis every where except under the zinc anode.  Putting a large enough zinc anode on the prop nut would interfere with the flow.


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## Ulma Doctor (Feb 24, 2018)

Hi Spike,
i'm a landlubber, and i don't know squat about maritime engineering.

i can offer a trick to weld nuts together and still have them useful as a nut
blacken a mild steel threaded shaft with carbon soot from an acetylene flame and thread the nuts on in the orientation desired
put the assembly in a vise for stability and check to see that the threaded rod still turns in the captive nuts
tack the nuts on the corners and tig the nuts together with silicon bronze
remove the threaded rod and finish as desired
if the threaded bore is tight, run a standard tap through the bore.
i wish you the very best of luck


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## spike7638 (Feb 24, 2018)

Mitch Alsup said:


> And if you must guarantee electrical conductivity, any kind of soldering at the joint will do that.


True...but once again, more metals leads to more potential for electrolysis, so brazing (with silicon bronze) has its appeal.


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## spike7638 (Feb 24, 2018)

kd4gij said:


> Well I make boat shafts. The full nut goes to the prop. As it is the one with all the force. The half nut is a lock nut. On a 1" shaft there is 3 choices Double nut, castle nut. Or nylock nut. All bronze of cores.  I am not sure what You are trying to do.


You might want to take a look at the article that someone else referenced, which shows that the ABYC and other engineering groups say the opposite about the order of the jam nut and the bit nut (https://www.passagemaker.com/channels/propeller-nut-myth-busting). Then again, with your experience, you may say "Forget the engineers -- I know what I'm doing!", and I'm sure it's worked out fine for you over the years. 

Personally, I suspect that in almost all applications of the sort that matter to *me*, it's completely irrelevant: I've got a 1" shaft, a 15 x 15 prop, and it turns at about 1200 RPM, tops, driven by a westerbeke 40, which puts out (depending on which literature you read) 40 HP, 37 HP, or 28 HP.  Regardless of which it is, it's too little to matter a whole lot, esp. because it's on a sailboat where I seldom use the engine to push us along.


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## spike7638 (Feb 24, 2018)

kd4gij said:


> I am a machinist in a prop shop.  Best thing the op can do is paint his prop with zinc chromate primer. I see rudders all the time eaten up with electrolysis every where except under the zinc anode.  Putting a large enough zinc anode on the prop nut would interfere with the flow.



The chance of my rudder being eaten up with electrolysis is very slim: it's made of fiberglass.  

My prop is bronze, and the donut-zinc has been working on it pretty well for the last 30 years. I just want to be able to move up one size, so that I replace it once a summer rather than twice.  

The prop is in an old CCA-rule cruising boat, with the prop in a too-small aperture, sitting about 2 inches behind a 3-inch-wide deadwood. The donut near the center of rotation isn't the thing screwing up the flow ... or if it is, it's only providing about .01% of the screwup.


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## spike7638 (Feb 24, 2018)

bfd said:


> yes galling can be a problem, if the shafts are put together with a good thread lube, ( the one we used is called n-5000 , it was a colodial nickle and I used it on stainless steel pump shaft couplings that ran in the pacific ocean for years driven by a 500 hp motor they came apart years later with no galling) you do what you want but I have some bronze , brass or stainless you can have if you send me your address bill



Wow...that's very generous. Let me get back to you if I can't figure out some other way to get the job done. 

That n-5000 looks like amazing stuff. It _should_ be for $75 a tin.


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## RJSakowski (Feb 24, 2018)

Which way to install the nuts wouldn't  be an issue if you used two nuts of the same thickness.


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## spike7638 (Feb 24, 2018)

RJSakowski said:


> Which way to install the nuts wouldn't  be an issue if you used two nuts of the same thickness.



Which, to be honest, is what I've done in the last few years because of my peculiar zinc arrangement.


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## CluelessNewB (Feb 24, 2018)

Other than the crazy price they get for them why not just use a "C" size prop nut and zinc?  It's 3/4-10 thread.  Typically the shaft is drilled for a cotter pin.  
	

		
			
		

		
	




http://www.boatzincs.com/prop_nut_s...MIkoCp8e6_2QIVxiSBCh1BtwX7EAQYASABEgL24PD_BwE


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## spike7638 (Feb 26, 2018)

CluelessNewB said:


> Other than the crazy price they get for them why not just use a "C" size prop nut and zinc?  It's 3/4-10 thread.  Typically the shaft is drilled for a cotter pin.
> 
> 
> 
> ...



Answer: lack of clearance between the aft end of the prop and the leading edge of the rudder. And that's even after I enlarged the rudder aperture with a Sawzall, which was a somewhat terrifying activity.


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## CluelessNewB (Feb 26, 2018)

Ok how about this:

The "Perry Nut Zinc"  
http://www.boatzincs.com/p-3.html


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## spike7638 (Feb 26, 2018)

CluelessNewB said:


> Ok how about this:
> 
> The "Perry Nut Zinc"
> http://www.boatzincs.com/p-3.html



That's what was on there before the current arrangement. It's far too little zinc for the job, and has to be replaced multiple times per summer, which involves extracting the cotter, loosening one nut, replacing the zinc, reinstalling the nut, snugging it up just enough for the cotter to fit again...all underwater holding my breath. 

I don't want to seem ungrateful, but I really *do* know lots about boats -- just not much about machining, which is why I came to you folks. I appreciate the thinking-outside-the-box that lots of folks have done here, and I'll now go back and noodle a bit more, and maybe even include a picture or two next time, showing the current arrangement, etc.


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