# Repairing ZAMAK Gears???



## Bi11Hudson (Aug 1, 2020)

Recently, watching a U-Tube video (Keith  Rucker) on brazing up a cast iron gear and my creative juices flowing (rare) got me to wondering about repairing broken teeth on Atlas, or in my case Craftsman, change gears. Steel gears can be welded, and "old school" repairs to cast iron are done with brazing rod. Aluminium has several methods of repair but my thoughts revolve around the ZAMAK gears on Atlas machines. Zamak is, of course, a trademark for a Zinc-Aluminium alloy with trace elements of Magnesium and Copper. While containing aluminium, it has different characteristics than pure, or almost so, aluminium.

My thoughts involve the fairly recent development of a "welding rod" for aluminium. Such a rod is actually more related to soldering, as it doesn't melt the base stock. I am wondering if it can be used with ZAMAK similarly to brazing cast iron. I have, years ago, used an aluminium rod that was used with a "buzz-box" welder. I don't know how much was the low melting point of aluminium and how much was *my lack of skill*, but the end result wasn't very good. It held together, but I wouldn't trust it to hold *my* weight, my standard for welding. And sure as hell wouldn't trust it to hold up on even change gears.

I have some broken(replaced) gears for the Craftsman and intend to one day try it. But thought someone in more of a hurry than me, or someone facing a broken change gear, might give it a shot. Or someone with a little more experience in metallurgy might have a comment. positive or *negative*. From my perspective, it is an unknown. And likely to remain so for quite a while as the idea has a very low priority. It will get done eventually, but eventually has a loonnngggg life span to me.

Bill Hudson​


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## Ulma Doctor (Aug 1, 2020)

i'm no expert in repairing ZAMAK, but i know it is highly unlikely that end result would be favorable, especially on change gears.
you may do better to try to recast, rather than repair.
Zamak was chosen due to its low cost, ease of casting, and lack of post casting machining
it was not chosen due to its ease of repair or superior wear characteristics.


if you are interested in trying an experiment, i could hunt down some 3D objects and 3D print some gears to try


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## pontiac428 (Aug 1, 2020)

I would be curious how that low-temp aluminum-like wonder rod would work.  With that zinc and copper in ZAMAK, "real" hot repairs are unlikely to work.  Interested in the results of any future attempts to repair these.


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## savarin (Aug 1, 2020)

Personally Bill I would cast new stock and cut then.
A very basic vertical slide will suffice. Heres mine https://www.hobby-machinist.com/threads/tumbler-reverse.10122/#post-87735   somewhere in there.
I got the idea from this guy. 



Very handy and not difficult.


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## Bi11Hudson (Aug 1, 2020)

Just to set the record straight, I *have made* replacement gears out of aluminium for my Craftsman lathe. Even made a couple out of plastic, though not very good, they do work. . . sorta. Even the 127 tooth for metric threading. Although, for most metric threading I use the "almost" gearset. The plastic 127 tooth gear was mostly to see if I could do it.

I have the change gear box (101.27440) on mine. Several 30 tooth gears inside that box. I have made replacements, that's where the "broken" gears came from. I am wondering mostly from a theoretical perspective, if the idea would even work. I have a small mill, Atlas horizontal, and can (and have) made gears for my lathe. That's why the idea is so low a priority with me. I do intend to try it, one day, just to see if it works. But it's not a priority. . .

I have seen, although *I'm not that good*, a welder repair a crack in a gas engine carburator. He was using a torch and a piece of welding rod to manipulate the molten metal. I think he was also trying it to see if he could do it. Took him half a day in a commercial shop, where time is income. They were working on my trailer (commercial) so I was at loose ends, just watching.

Such metal is not "pot metal", I *think *it is similar to ZAMAK. If it works for ZAMAK gears, it should work for carburators and other automotive castings as well. Possibly a very useful contraption.

.


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## savarin (Aug 1, 2020)

I have 2 rods of that soft aluminium repair rod but have never used it.
The guy who gave them to me said they were very good to repair ally items.
I really must give them a go sometime.


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## derf (Aug 2, 2020)

Those "wonder rods" you see vendors showing off at the fairs and trade shows, is actually zinc.


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## savarin (Aug 2, 2020)

Now thats interesting to know.


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## Bi11Hudson (Aug 2, 2020)

derf said:


> Those "wonder rods" you see vendors showing off at the fairs and trade shows, is actually zinc.


Like Savarin, I also find that possibility interesting. On the other hand, Zinc is the basis for galvanizing. And galvanizing gives off toxic fumes when heated. I have done a lot of "tubular" work with both Rigid and EMT conduit and have been very aware of such "out-gassing".

When using the rod, one is told to heat the metal, not the rod. When the metal is hot enough, the rod is "flowed" on, just like proper soldering. That would be enough heat to cause "out-gassing" if they were Zinc. Since they are not restricted in any way, they must not be Zinc. Unless they come out of China, who is allowed to produce and sell such materials without a warning label in the States.

.


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## derf (Aug 2, 2020)

Zinc does not put off any toxic gases until it's way past it's melting point. The melting point is around 700-725 F. If you heat it with a torch rapidly, it will get past the melting point and give off the white smoke and the gas. If you melt it in a pot with controlled heat, it melts like lead.


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## MikeInOr (Aug 3, 2020)

I tried to repair the broken ZALMAK crank handle on my 12 Craftsman lathe... it didn't go so well!


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## Diecutter (Aug 3, 2020)

The ones I have  were made by Bernzomatic item #96268, aluminum brazing/welding rods. Have not had a chance to use them however. Instructions say  "Ideal for sealing holes in aluminum.  Useful in repairing outboard motor castings and most kirksite and zinc base die castings."  Working temperature is listed as 700 to 750 f.  Think I bought them from Lowe's.


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## BGHansen (Aug 3, 2020)

Following the thread as I have an Atlas MFB mill with mounting ears on the gear box that were cracked when I bought it.  They've since broken off.  I figure it's made from Zamak like the gears, handles, etc.  Have "visions" of making an aluminum gear box and reuse the Atlas face plate, axles, etc., but a welded repair would be better.  

So how do you control the heat to under 700 F so I don't liquify the gear box?  I'm guessing heat it in a heat treat over (have one) to 600 - 650 and melt something in the joint?  That's what Bill is suggesting above which seems plausible.

Bruce


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## pontiac428 (Aug 3, 2020)

I figure a big rosebud tip and an IR thermometer (or heat crayons) might oughta do it.  Always easier to control flame-on heat than it is to control arc heat from welding.  200 degrees should be plenty of range between filler melt temp and base metal melt temp.  Besides, that magic aluminum-fixem rod balls up and rolls off when overheated.  If that's not a warm fuzzy feeling, you could try the weld with propane.  It takes a lot of moving air to get propane up to 700 degrees.  600F is more like it for a propane hand torch.


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## MikeInOr (Aug 3, 2020)

JB weld then machine to shape?

Or some other type of reinforced epoxy.


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## Bi11Hudson (Aug 4, 2020)

BGHansen said:


> Following the thread as I have an Atlas MFB mill with mounting ears on the gear box that were cracked when I bought it.  They've since broken off.  I figure it's made from Zamak like the gears, handles, etc.  Have "visions" of making an aluminum gear box and reuse the Atlas face plate, axles, etc., but a welded repair would be better.
> Bruce



The important point to keep in mind is that the rod isn't a "welding" rod. It does not melt into the parent metal. I think of it as a "hard" solder, between silver soldering and brazing. To use on something like the mill, I would be skeptical of the strength. Prefer to make a replacement part out of Al stock. 

There have been a number of "tests" on YouTube as to holding strength. In most of the tests, it holds about as strong as soldering with copper, as in pipe. It will hold for something like I have going, using aluminium angle back to back so the holes are drilled consistant side to side. (3/8x3/8x1/16) Cutting two pieces and soldering back to back, drilling, and heating to release. Solder doesn't take on aluminium, so this is a replacement for that process.

That's why I was asking after folks perceptions about repairing a ZAMAK gear as one would braze an iron gear. Repairing the "gear box", I suppose the first step is to *use a magnet* on the piece. I have an MF-C and can't picture in my mind what needs repairing. But my machine is mostly iron castings, with ZAMAK gears and knobs. If it's iron, it can be brazed.

.


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