# Repair a broken antique coffee grinder bolt



## KMoffett (Dec 6, 2019)

A coworker asked if i could join the two parts of an antique coffee grinder bolt. The cat knocked it off the mantle. I'm not sure if siver brazing is the best choice and what alloy braze.  I have access to an XFR, to analyze the metal content. Attached is the bolt and the XFR analysis. It can't see anything lower than sodium, so no carbon. I'm wondering if this is enough to tell what it is.  If we really need the carbon content I'll see if I can get an SEM scan.


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## chips&more (Dec 6, 2019)

I would turn down the shank of the head part. This saves the look of the carriage bolt type head. Make a new lower part with the square and threads and a hole for the shank of the head part. Then Loctite the two together. XFR analyze/report…SEM scan…WOW!


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## machPete99 (Dec 6, 2019)

Given that the original apparently snapped it must be under some tension, maybe too much.
Silver solder or braze might not be strong enough.
You could TIG it back together with steel and it might be as strong as new, and then keep the Gorillas away from it!
If TIG does not work fallback is fabricate a new one from appropriate bar stock.


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## brino (Dec 6, 2019)

If final length and strength is not critical, I would:
1) on the lathe chuck, face and drill each piece,
2) tap the holes,
3) join with a suitable piece of threaded rod (maybe #10-32) and lock-tite
-brino

EDIT: test with a dry fit; if the two squares on the top and bottom shanks need to align, just face a little off one side until it's perfect.


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## cathead (Dec 6, 2019)

Or use some welding skills and gas weld or TIG weld it back together............Or even make a new one, heat it up to 1000 degrees
and immerse it in oil for that "old time"look....


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## b4autodark (Dec 6, 2019)

I would center it like brino say's, bevel the edges and tig it with silicon bronze filler and turn it back to diameter.


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## matthewsx (Dec 6, 2019)

I’d either weld or make a new one. Looks like the kind of project that could easily be overthought. If it sits on the mantle I have to assume not too much stress on it  

john


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## Tim9 (Dec 11, 2019)

PERSONALLY... if you have lathe and mill, I’d just make a new one out of something like 4140 steel.
  Silver solder braze just not strong enough for a tensioned bolt and also silver braze really needs to be super clean. So you’re going to need to grind both ends.
  It doesn’t look hard to make a new one in my opinion.
  By the, just guessing here but due to the square sections plus the adjust type of nut, I’m guessing this bolt is for the crank handle and the level of grind is regulated by tightening that nut.....kind of like pepper grinders, you tighten the nut to make the grind finer. Seems more troublesome to repair than making a new one. Easy enough to make it look old. Like mentioned above oil burning does a decent job of aging steel.


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## Winegrower (Dec 11, 2019)

Is that XFR from Harbor Freight?    I could use one of them.


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## KMoffett (Dec 11, 2019)

Winegrower said:


> Is that XFR from Harbor Freight?    I could use one of them.


No. They got a deal on the a used one. Only $140,000.00 

Thanks for all the advise. I wound up silver soldering it.  Ground both faces flat. For alignment I mounted the bolt's head-end in a 3-jaw chuck in a lathe. Mounted the threaded end in a tailstock chuck. While separated, I fluxed and tinned each face. Then fluxed, reheated, and pushed together. Looks like this will work. I don't think I mentioned that this coffee grinder is only used as a ornament.


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## pontiac428 (Dec 11, 2019)

KMoffett said:


> I don't think I mentioned that this coffee grinder is only used as a ornament.



You kinda threw that sentiment out the window when you ordered x-ray fluorescence (XRF) to identify your alloy...


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## KMoffett (Dec 11, 2019)

pontiac428 said:


> You kinda threw that sentiment out the window when you ordered x-ray fluorescence (XRF) to identify your alloy...


I happen to do low end work for a Geology Department that has high end analysis equipment.


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## middle.road (Dec 17, 2019)

KMoffett said:


> I happen to do low end work for a Geology Department that has high end analysis equipment.


*LMAO*! I was about to say "on a coffee grinder handle?"  
Can I send you my old Stanley plane that I bought at auction (30 yrs ago) and the handlers dropped as they were handing it off and broke it at the throat?
At least it went from $36 to $1 in a blink of an eye, and I've been hauling it around ever since.


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## StanR (Feb 21, 2021)

Plow bolt?
4 machined flats?
Threads smaller dia than standard plow bolt?
What I have learned about decorative machinery, there seems ot be no shortage of someone who wants to "give it a try"

Cheers

Stan


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## ericc (Feb 22, 2021)

Old fashioned mild steel.  This looks old.  Silver solder should be fine.  With small gaps, it is very strong.


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