Machining cast brass wheels

[rgmt79]

In J Malcolm Wild's excellent book Wheel and Pinion Cutting in Horology, he talks about cutting wheels from "yellow cast brass to match the colour of the old clock brass." He says also that before machining, the cast blank should be hardened by hammering on an anvil or steel block. However, he does not talk about it being difficult to machine cast brass (he recommends 70/30 copper/zinc). I would like to know if anyone on this forum has any any experience with this?

[Bob Tascione]

Hi Richard,
I haven't experimented with change the copper to zinc ratio but have melted down and cast antique brass many times. Cast pieces such as a missing or broken pillar doesn't need to be hammered/planished but any working part or part that requires machining probably should be. Work hardening metals like steel can be harder to machine as well as tough on cutters but work hardened brass although stronger than non-work hardened, is still easy to machine and easy on cutters. The addition of a small amount of lead in later years made machining of brass easier but still easily machinable without the added lead.

Hope this helps,
Bob

[rgmt79]

Thanks for the reassurance Bob

[rgmt79]

The reason I started this thread is I have a damaged great wheel that needs replacing/repairing (see photo's). It belongs to the going train of a grand sonnerie movement I'm working on. I made contact with a guy in the uk who advertises a bespoke wheel cutting service, but declined to quote for the job on the basis that he will not work with cast brass because it damages his cutters...an excuse I think (in view of bob's comments) because he clearly is not interested in doing the job.

So, I'm now considering doing it myself and look to advice from you guys as to how best to proceed. To avoid a lot of work to produce an entirely new wheel, my idea is to retain the existing hub by turning the damaged teeth down to below the root of the teeth and then having machined a ring from the cast brass blank and attach it to the hub by press fit or glue (when I suggested this, Malcolm Wild suggested loctite 638 as the preferred option) I think the tensile stresses resulting from a pressed fit would make the ring vulnerable to failure. I propose cutting the new teeth after the ring is attached.

It appears that the wheel is made up of 2 parts with the click spring formed from a ring pressed inside the hub. If I were to machine a complete new wheel, then I guess I could reuse the click spring ring, but then left with a challenge when it comes to the click itself.

I would appreciate comments from members of this forum.

Thanks in advance,

Richard

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[Bob Tascione]

Hi Richard,

Maybe I should have used the word 'easier' (referring to machining hammered cast brass compared to cast steel) rather than 'easy'.
The UK wheel cutter guy 'doth speaketh the truth' if he is thinking of a raw sand casting. A casting straight out of the mold can be rough on a cutter. Brass sand castings generally have lots of internal imperfections like occlusions and air pockets as well as extreme surface hardness caused by oxides formed when brass interacts with oxygen while passing through the molten to cooling phase. Antique brass cast back in the old days didn't go through a whole lot of quality control. These days metals available to us were poured into molds in a nitrogen (oxygen free) environment eliminating the effects of oxygen's interaction with the metal. It also goes through a bunch of hot rolling processes that eventually lead into a succession of cold rolling processes. Yawn! Finally out pops a beautiful sterile piece of perfect brass.

Hammering is akin to the cold rolling process used today only much less controlled. It hardens and strengthens the brass by making the grain structure smaller. The hardness isn't what kills the cutter but rather the imperfections and surface hardness are.

Hammering the brass not only hardens and strengthens it but also deforms the microstucture of the brass relieving stress a bit as well as reducing the effects of the imperfections. Also very important when working with any casting that will be machined is to remove that small amount of hardened surface material where any machining will be made by making a skin cut along that surface. Definitely still far from today's quality metals but far, far better than machining a raw cast part.

I personally wouldn't be too hard on that guy. Again he most likely is thinking of raw castings and how badly they will eat up his wheel cutters. At the price of cutters these days who can blame him?

True restoration of any antique horological or other demands the closest match possible to original materials and design. If that means a casting of the part is required then so be it. After all, clock and watchmakers made them this way for more than a couple of centuries so why can't we do it now if a good restoration requires it?

There's much more that can be said about this. The fact is that often times it's just an issue of economics. For example a customer may not be willing or able to pay for the extra time it takes to do the job correctly. When it's a personal timepiece then finding the time to do it might be a real problem. In that case it's probably best to set it aside until the task can be tackled and enjoyed. It's always a personal choice I suppose.

Take care over there for now Richard,
Bob

[rgmt79]

Thank you Bob for your detailed clarification and for letting the Uk guy off the hook , although, I did go back to him and say he could use whatever brass he felt comfortable with, but no response...there is a bit more to this than straight forward teeth cutting, so I think that is the real reason.

You say "a customer may not be willing or able to pay for the extra time it takes to do the job correctly". Although there is no customer involved here, I assume you are telling me that the correct way to do this repair is to start again and machine a new wheel from scratch? On reflection, I think I will do just that and machine from 1/2 hard engravers brass rather than cast brass. Once assembled back in the movement, the outer circumference of the teeth is all that is visible and even then the whole movement is hidden from view inside the clock case.

On closer inspection, I can see that the click spring ring is in fact riveted with 3 small brass rivets (almost invisible) and the steel click itself is also riveted, where the rivet is part the click and rotates with it...I will have to work out how to deal with that.

Thanks again Bob and take care,

Richard

[Bob Tascione]

Hi Richard,
I was going to wait to see if someone else wanted to jump in and address the ring idea. Didn't want to hog the entire conversation which I sometimes have a tendency to do. But...guess I should clear what I said up a bit if I can. I wasn't really suggesting that you make the entire part over making the ring. I was more or less supporting your choice to use original cast brass if you wanted to and was saying that when someone wishes to go through the extra work as you are willing to do to turn out the best restoration job possible they should be commended for making that choice; not discouraged.

My feeling is that in the case of your clock the part is already more or less destroyed so no permanent harm done if you can make a suitable repair. You can always make the entire part later if you wish. There are many times though that a repair may result in damage that can't be undone. This should always be avoided.

New brass is what most of us use when making parts for most common timepieces. If it's something that doesn't cause any permanent damage and can make the timepiece operable then that's often the route that's taken. Again it's usually a choice motivated by economics.

There are lot's of choices out there when it comes to brass. Common yellow brass used for making parts on antique clocks and watches here in the U.S. would be C35300 or just C353. i think its near equivalent in the U.K. is CZ131 ?? Someone please correct me it that's wrong. It's a yellow brass with added lead giving it a great machinability rating. Its' zinc content is higher than the old brass but is a pretty good color match to the antique brass. C360 is another free machining brass used quite often over here. I think William is using C360 for his clock that he's making??

Dayrn up here on the forum is the guy to talk with about available brass in the U.K. used for matching old brass used in horology. He does incredible restoration work over there and knows a great deal about restoring antique European clocks. I know that he's been extremely busy lately so dragging him up here right now might not be possible...but miracles do sometimes happen!

Anyway, the ring might work well for you. Can't really hurt to give it a try as long as it's secure and can't slip. A key made from a small diameter plug passed through both pieces might help secure it. Let's see if anyone else up here has some ideas.

Adios for now Richard,
Bob

[rgmt79]

Thanks again Bob, you make a very good point about not being able to damage the wheel anymore than the damage that has already been done, so there is no harm done in giving it a try...useful experience for a beginner like me

Thanks also for your recommendation for 'modern' yellow brass...I think that's the way to go and save the cast brass blank for some other time. Since Malcolm Wild is English, I assume the references he gives in his book "For modern clock the material most suitable is CZ120 compo engraving brass, with the addition of lead to aid free machining." Maybe that's not the UK equivalent of C353, since you refer to that as being "yellow brass used for making parts on antique clocks in the US" You mention CZ131 as possibly it's near UK equivalent...Malcolm mentions CZ121 which is extruded brass bar which can be also used by parting off the appropriate thickness...as you say, maybe Dayrn or someone can chip in on this

It was Malcolm who suggested Loctite 638, so I assume he has some experience in using this...if I cut the teeth after attaching the ring to the hub, then I guess if the machining forces don't dislodge the ring, then it's secure enough

Thanks again Bob,

Richard

[Bob Tascione]

You bet Richard,
Yes Loctite is extremely strong and is used a great deal in horology now. We used it a lot in the tool & die industry. My only concern with using it is some future use of a cleaning solution with a solvent that breaks down Loctite. I'm probably over concerned.
CZ120 is also recommended along with CZ118 and CZ119 by Thornton cutters so looks like you're all set.
Please let us know how it turns out Richard. Should be a fun job.
Take care for now,
Bob

[willofiam]

Hey Richard, looks like you guys have it all covered and it definitely looks like a fun job. I do use the loctite at times though I have not used it enough to trust its strength and completely understand it ( applies to most things ) although I once was putting something together with loctite, didnt get it just right, all stuck together wrong and it was extremely difficult to get it apart again!!! I ended up soldering the pieces together which gave me the ability to have it put together first and I think it would have been easier to change it if it went together wrong. I have done a few barrels by cutting off the teeth, making a small recess, soldering on a ring and re-cutting the teeth again. If the fit is right it is very difficult to see the joint.

It looks like 70-30 copper-zinc is defined as "cartridge brass" very hard and difficult to work with. If you have not seen the post in the clockmakers forum I did a bit on brass.

Have fun, William

[rgmt79]

Thanks for your input William, which gets me thinking about solder as another option for fixing the ring...I'm not familiar with solder being used in such a structural way, more the electrical connection type of soldering. Can you give me any tips, type of solder, type of gun, temperature etc?...if not this job, I have other clock work which will require structural soldering. Incidentally, you can undo a Loctite 638 joint by heating up to something like 250degC

You bet Bob, I will follow up with my progress

Cheer,

Richard

[willofiam]

Well....soldering can be one of those things ......I have several types of solder I use and several way to heat things...here are a few ideas.
I like a solder called Tix, it has a low melting point and uses a liquid flux though it is not as strong as some other solders it is easy to use with the low melting temp...I also use what is called silver solder, higher melting temp. and much stronger than the Tix..I cannot seem to remember the composition of the silver solder I have though...this has a paste type flux. I have several irons with different temps and tips depending on the job...one thing I do use alot is a pencil type torch with a adjustable flame ( butane ) cheap one from a big box store. When buying the solder is should have material composition and heating temperatures of it.

If I were to solder that ring on a wheel like you have I would use the silver solder, coat both pieces with the paste flux and cut up small chunks of the solder, just set them on top of the joint all the way around the seem. I would probably use a larger mapp gas torch and very slowly introduce heat just until the solder melts and spreads, depending on the setup I may want to use a thick plate of brass or steel (2.5 mm or so) as a heat transfer, meaning heat up that piece and let the heat transfer to your parts, allows for a more even heating of your piece. careful not to solder everything to it ....

Sorry I cant be of more help on this subject...Best thing to do ...I think...is get some cheap supplies and do a bunch of experimenting for heating, strengths and techniques...one tip...you have to have your soldering surfaces absolutely clean...Have fun

[rgmt79]

Thanks William, that's very useful information. The one question that comes up in my mind when considering both methods adhesive v solder, is how close fitting do the mating parts need to be? Looking at the technical data sheet for Loctite 638, it says "Loctite 638 is designed for the bonding of cylindrical fitting parts, particularly where bond gaps can approach 0,25mm and where maximum strength at room temperature is required. The product cures when confined in the absence of air between close fitting metal surfaces and prevents loosening and leakage from shock and vibration" It also says "For slip fitted parts, apply adhesive around the leading edge of the pin and inside the collar and use a rotating motion during assembly to ensure good coverage." Will silver solder work with "slip fitted parts"? My understanding is that it creates a good joint only with sufficient clearance (whatever that might be) between the mating parts to ensure capillary action drawing the solder into the joint. Maybe I should research a similar technical data sheet for silver solder and maybe I should rig up some kind of test before committing myself. More food for thought

Cheers,

Richard

[Bob Tascione]

Hi Richard,

I know William has been on the road the past few days so I'll jump in here real quick.

My feelings on using solder and/or adhesives in horology is to try not to rely on them but rather use only to add strength when needed. A slip fit in this case wound mean total dependence on solder. When you have lateral and longitudinal strain mixed with temperature variations which cause expansion and contraction, humidity etc. eventual break down of the bond integrity leading to mechanical failure is inevitable. Take a look at a piece of wooden furniture that has separated at a seam held by glue to see an exaggerated example. We see it all the time. That's why a good cabinet maker will always add things like dowels or special joinery to help share the load. This is also why I suggested using a pin (dowel) passed through the two pieces to place most of the strain on it rather than on the bond. This as well as a light press fit will help in sharing the forces.

The bond may be strong at first and withstand the machining of the teeth but 'over time' that bond may begin to break down. If the surfaces are roughed up a bit with a piece of course grit sand paper, cleaned, flux appied and then lightly pressed together solder should find and move into the crevasses. If Locktite is used and applied prior to pressing it will move into these scratches. Also heating the part by placing it on a brass plate like William suggested will heat the part more evenly and in my opinion is the way to go.

There are times that shellac or commercial adhesives are used with clearance between the two parts such as with pallet and roller jewels. When possible though sharing the strain between the parts is a good thing. At least that's my thought.

Hope this helps,
Bob

[rgmt79]

Hi Bob,

That all makes perfect sense, thank you again

Richard