Fusing brass to steel, issues with pin holes

[Screwmachine]

I need to make a bimetallic balance wheel (this is watchmaking stuff), but there's very little info out there. I have one text that in a paragraph explains the process, cut groove in steel blank, make brass ring to fit and stand a bit high, "coat groove, ring, and the rest with borax mixed with clean water", then heat until the brass melts.

I have tried borax and boric acid, heating with a torch (propane, large, don't have oxy acetelyne or other), and heating in a oven that reaches a high enough temp. So far boric acid and torch have given the best results, oven (surprisingly) the worst. Borax seems a little less good than boric acid. I do have some black brazing flux from Carbide Processors which has some promising sounding nasty stuff in it, but it has dried out; I can grind it in a mortar remix with, water?

The steel is a standard steel used here, not too different from O1 (no lead, easy heat treat). The only brass I can get a hold of is similar to 360, which contains lead, so I'm wondering if that could be an issue. Anyone with any experience here? It has to be fused, brass melted, brazing is out as the whole thing gets reheated after machining to heat treat the steel. About 10 tries in- worst part is cutting the 0.6mm x 2.20mm deep groove, haha. Total diameter of the blank is 16mm.

 

[john.k]

I have investigated a somewhat similar effect ,and IMHO ,my issue was caused by hydrogen solution in high carbon steel ......the hydrogen comes out of solution before the brass hardens..........if your oven can be made inert atmosphere ,the brass may be OK without any flux .....I dont know...............alternatively you might try the copper brazing process,no flux required.

 

[MrStretch]

Doesn't Gazeley (sp?) Describe the process of making a bimetalic balance wheel in one of his books?
Are you sure the steel needs to be hardened afterwords?

 

[memphisjed]

brass brazing wire, you can get it pre fluxed- very handy if you do not use often. Torch is easier on small items. No water needed. Just heat and try to get some flux on steel before going to brazing heat.
I wouldn't even try and fit the groove, just glob (very technical name) braze into it, sand off when done.

 

[Peter from Holland]

This is not the solution I know but instead of water I use alcohol
Worked better for me

Peter

 

[Screwmachine]

Doesn't Gazeley (sp?) Describe the process of making a bimetalic balance wheel in one of his books?
Are you sure the steel needs to be hardened afterwords?

Yes, it's Gazeley's book! One paragraph. Definitely gets hardened afterwards.

This is not the solution I know but instead of water I use alcohol
Worked better for me

Boric acid is soluble in alcohol, borax in water. Boric in alcohol is getting me close, but not there yet.

I have investigated a somewhat similar effect ,and IMHO ,my issue was caused by hydrogen solution in high carbon steel ......the hydrogen comes out of solution before the brass hardens..........if your oven can be made inert atmosphere ,the brass may be OK without any flux .....I dont know...............alternatively you might try the copper brazing process,no flux required.

No inert oven, unfortunately. But these things have been made for a few hundred years, so while I'm sure it would help, it must be possible without.

 

[jim rozen]

Probably the lead or zinc is coming out of the brass - most likely the zinc which has a higher vapor pressure.

1) use a minimum of temperature to do the job
2) consider usinf bronze, no zinc in that.
3) if you happen to be quenching the part to cool it, don't.

 

[jscpm]

Normally this kind of application requires a casting. Brass is traditionally used because it is much easier to cast than bronze or other metals due to its easy fluidity. The natural thing to do would be to create a mold, preheat the steel and place it in the mold, and pour molten brass into the mold. Brass can be molded in plaster which typically gives high quality results.

 

[L Vanice]

As an alternative to Gazeley, I looked up Saunier's method. It also involves melting brass to fuse it to the steel, but with a steel disc in an open crucible rather than a groove in the steel. But then the brass is partly machined and the brass rim hammered or rolled to harden it. There is no further heat treat of the steel, since that would anneal the hammered brass. See pages 741 ff (section 1365) of Claudius Saunier's 1887 book:

A Treatise on Modern Horology in Theory and Practice​

A Treatise on Modern Horology in Theory and Practice - Google Play

play.google.com

Zinc oxide fumes from overheated brass are hazardous. Saunier says, "The fusion will be complete when the vapour of zinc is distinctly seen to rise."

Larry

 

[bob]

Press fit with Loctite not easy but if done right it will never come loose
Bob

 

[Screwmachine]

As an alternative to Gazeley, I looked up Saunier's method. It also involves melting brass to fuse it to the steel, but with a steel disc in an open crucible rather than a groove in the steel. But then the brass is partly machined and the brass rim hammered or rolled to harden it. There is no further heat treat of the steel, since that would anneal the hammered brass. See pages 741 ff (section 1365) of Claudius Saunier's 1887 book:

A Treatise on Modern Horology in Theory and Practice​

A Treatise on Modern Horology in Theory and Practice - Google Play

play.google.com

Zinc oxide fumes from overheated brass are hazardous. Saunier says, "The fusion will be complete when the vapour of zinc is distinctly seen to rise."

Larry

Thanks Larry, I knew Saunier had something on it but don't have access to a copy at the moment. Sounds like Gazeley's approach is a little "cleaner", and follows other descriptions I've read (just can't remember where!). When I was in school here there was a nice framed set of actual parts at each step on the wall of the kitchen, groove, brass ring, fused, machined, hardened and tempered, finished.

Press fit with Loctite not easy but if done right it will never come loose
Bob

I know the wonders of Loctite, not at all applicable here; the outside bit of steel gets turned off, the inside turned, arms cut, and the rim cut. Image of a finished bimetallic balance wheel below.

 

[Freedommachine]

ME: "Wow, what the heck is this guy making? I bet it will be nearly impossible to find an answer to this question."

The Rest of PM:
"Oh, a bimetallic balance wheel, of course. I've had good results with method 'X'."

Yesterday I learned that an acetylene generator is actually a thing. Today, bimetallic balance wheels... I wonder what tomorrow will bring?

@Screwmachine You said the torch yields better results than the oven. Is the problem a failure of the brass to properly fuse? When the base metal is heat treated, wouldn't the high temp have a negative effect on the fused brass insert?

Please keep us posted, I'm intrigued!

 

[MrStretch]

Will you be doing all the steps to adjust for temperature at the end?
According to Peter Bonert (sp? Co-author of the Carriage clock book), nearly all the "compensating" balances on Carriage clock platforms are fakes- the rims are not cut all the way thru so it just looks fancy. I heard this from him many years ago in school and have never seen one that was cut thru, just like he said.

 

[Screwmachine]

Too add a little more info- These were hammered after turning off the steel to " close the grain" of the brass. Of course subsequent heat treatment for the steel would anneal any hardness imparted to the brass. These were also mass produced by both the American and Swiss (and English to a lesser degree) "mass" by the Americans from mid/late 19th century, "mass" by the Swiss from a couple/few decades later. They had to have a dependable repeatable way of doing it... And I doubt there were any inert gas ovens in the 19th century.

I figure this is an issue of one or a few small details. I've sort of discarded the idea that 2-3% lead in the brass is hurting anything. I have 5 more blanks ready to go, but my ex-chemist computer scientist mathematician friend who's very lucidly in his 70s walked into the shop as I finished them and reminded me of the definition of insanity, hahaha.

Will you be doing all the steps to adjust for temperature at the end?
According to Peter Bonert (sp? Co-author of the Carriage clock book), nearly all the "compensating" balances on Carriage clock platforms are fakes- the rims are not cut all the way thru so it just looks fancy. I heard this from him many years ago in school and have never seen one that was cut thru, just like he said.

Yes, this is a special project for a really special and cool customer. It's an adaptation of a particular marine chronometer balance (but in a watch), and the goal is to get it through Besancon.

Plenty of pocketwatches (and wrist) out there with partially cut rims too! One reason I heard is they got paired with newer alloy hairpsprings, but I have to say I never noticed one with an alloy spring. Just cheap quality. I have seen some very nice carriage clocks with proper balances and springs though, Rossel Fils and LeRoy for sure (but I've seen some astonishingly bad LeRoys too, yikes).

 

[jim rozen]

" I've sort of discarded the idea that 2-3% lead in the brass is hurting anything."

How much zinc is in the brass. Which has a higher vapor pressure, lead or zinc.

 

[John MacArthur]

I'm not looking at it right now, but I'm pretty sure Daniels "Watchmaking" has a section on just this procedure.
Johnny

 

[john.k]

On the subject of zinc fumes......I used to work in a blue haze of zinc fumes from arc spraying zinc ,I could taste the zinc ......yes ,you do get affected by the zinc,but seem to get used to it...........I doubt ZnO has any effect tho.

 

[jim rozen]

Zinc fume fever is caused by volitalized galvanized coating going into the air as ZnO and is not well understood medically.

Point was that zinc blowing out of overheated brazed joints or overheated brass components during silver soldering IS well known and can cause pinholes and voids as seen in the photos above. Probably the zinc is volatalizing out of the joints.

 

[EPAIII]

There must be a way to reliably mass produce them.

Yes, I am sure there is. But I have to wonder if the people who have figured that out have actually shared all the details. Perhaps they just describe enough to let someone get in trouble and leave off the secret solution to that problem point.

Works better than a patent when you want to keep an industrial process to yourself.

Just a WAG, but could/would a vacuum in the oven help?

 

[Bill D]

I know for epoxy and such they can place the whole assembly in a curing chamber and pressurize it to shrink any bubbles. Can an inert furnace be pressurized? That would prevent vapor pressure from causing problems wouldn't it?
Bill D