Machining Wheels from cast brass

Discussion in 'Clock Construction' started by rgmt79, Oct 3, 2017.

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  1. rgmt79

    rgmt79 Registered User
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    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?
     
  2. Jim DuBois

    Jim DuBois Registered User
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    Cast brass as Wild suggests machines nicely and easily. That said, unless it is hammered out and flattened, it can be quite weak in places. There is often some degree of porosity with bubbles having left pits or cavities in places in any casting, unless the process goes extremely well, start to finish. A lot of period American tall clocks demonstrate poor castings with pits still in plates, gear teeth let in apparently at the time of original finish work to replace failed teeth etc.

    The hammering process will expand and thin the piece being worked substantially. Unless someone is doing really first rate restoration of fine clocks, or doing very large work, such as tower clocks, having parts cast in standard brass is an unnecessary complication in my mind.

    I don't know what formula brass the tower clock companies used in production stateside, but it seems to be a bit more robust than some smaller cast brass clock parts. It is not hammer hardened brass in tower clocks....but is machined and then used as cast in most parts. I use ultra machinable 360 or 363 and or 1/2 hard engravers brass for at least 95% of my work.

    Photo is of parts cast in yellow phosphor bronze, material I use from time to time when conventional brass is inappropriate.

    2017-08-17 13.38.04.jpg
     
  3. novicetimekeeper

    novicetimekeeper Registered User

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    Peter Hagemans is currently casting his own brass for a verge bracket clock, he has a thread on it that has been very informative though many of the pictures currently have a few problems since the switch.

    Like him my interests are in late 17th and early 18th century clocks where modern brass alloys look completely out of place
     
  4. sharukh

    sharukh Registered User
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    Can you provide a link please ?

    Sharukh
     
  5. scootermcrad

    scootermcrad Registered User
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    This is another great topic that somewhat relates to some wheel reproduction questions I have.

    With large scale clocks that started with large cast brass and had to literally beat them, how on earth do you even know where to start? Is the casting itself just extremely oversized and a ton of machining is done to bring it back to its true dimensions before cutting teeth?

    Also, since we're on the topic, if starting with a NON cast part, are the raw brass materials forged brass plates then machined to spec, or is the material an extrusion of sorts? Seems like small parts and wheels are ideally machined from raw materials of the billet type.
     
  6. rgmt79

    rgmt79 Registered User
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    As I understand it, brass is an alloy of copper and zinc and they are combined in a molten state before being cast into a solid, so all brass starts life as a casting in some shape or form. Sheets are cold rolled to the desired thickness...the act of rolling also work hardens the material. Vintage clocks produced before cold rolling was invented, were made from 'yellow' brass (around 70/30 copper/zinc) and plates and wheels were hardened by hammering. Modern brass does not have that yellow (or gold) appearance and, for example, to replace a wheel in a vintage clock it's better to obtain an oversized yellow cast blank and hammer it down to almost the desired thickness and then finish by machining.

    At least that is my understanding of the theory, I have not attempted it yet...I started this thread because I need to replace a great wheel in a vintage grand sonnerie movement and wanted to know if there are any machining issues...one machinist I approached said he would not do it for me because he says machining cast brass would ruin his cutting tools...so I'm interested in Jim's comment above. I actually have a yellow cast brass blank, which I purchased from Malcolm Wild and I assume is of such a quality that the sort of imperfections Jim talks about will not exist to any significant extent.

    Thanks for all the comments and would welcome more input to this thread.

    Richard
     
  7. Jim DuBois

    Jim DuBois Registered User
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    #7 Jim DuBois, Oct 6, 2017
    Last edited: Oct 6, 2017
    Large cast brass parts such as tower clock wheels are not hammered nor rolled, they are machined "as cast". Some processes may scale up or down and yield better results one way or the other. In the case of brass castings the pores and pits, when present, tend to remain similar sizes be it in a tower clock wheel or in a conventional clock wheel. In the smaller scale a casting flaw/blemish may yield an unusable part while in a tower clock wheel it is not a functional fault but perhaps no more than a blemish with no impact on function. And some machinists don't like working with cast metals as there is usually a bit of residual sand in the pits of the casting and it does chew up cutting tools. But, from my perspective, cutting tools are consumables and should be treated as such. Most are moderately priced and with so many made of carbide today they dull much less with sand cast parts. Machinists know, or should know all that. I would guess the machinist you mention just doesn't want to do the job.....

    The strength of brass cast tower clock wheels, as cast, is generally sufficient for their purpose, but it should be noted that later and larger tower clocks frequently have cast iron wheels instead of brass, it is cheaper material wise and substantially stronger as cast than is brass. I don't know how large your wheel is for your clock but I suspect all will be fine just to finish the casting you have...Wild sells/sold good product....
     
  8. novicetimekeeper

    novicetimekeeper Registered User

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    All metals used in engineering are molten at some point, but I don't think that would mean we would call them all cast. Billets are produced and then rolled or extruded or forged.

    In the late 17th century clockmakers realised that additional hammering of escape wheels would produce a harder wheel with extended life. Until then the hammering was in order to thin the product, even dialplates were cast, in Northern England they were cast with gaps that went behind the chapter ring to save on brass which was very expensive. Pillars would be robbed out of movements during maintenance3 and those and old movements melted down to produce new parts.
     
  9. rgmt79

    rgmt79 Registered User
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    #9 rgmt79, Oct 6, 2017
    Last edited: Oct 6, 2017
    Thanks guys, I'm learning a lot from this thread:) For your information Jim, I enclose a couple of pics of the damaged wheel...it's aprox. 1.75" dia and .15" thick
    To avoid some complicated machining, my idea is to turn off the old teeth to just below the root and machine a ring from the cast blank and press or glue that onto the resultant hub and then machine the teeth into the ring. Malcolm Wild suggests Loctite 638 as the best option. I would welcome your thoughts on that idea. I think the original wheel was some sort of fabrication, otherwise I cannot fathom out how the click spring could have been formed.
    IMG_0262 2.jpg IMG_0263.jpg IMG_0264 2.jpg
     
  10. Jim DuBois

    Jim DuBois Registered User
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    So, it looks like the wheel is made up of at least 2 pieces of metal, riveted or soldered (or both) together. One part would be the wheel with teeth and the other being the circular piece that makes up the spring?

    Firstly, I would never attempt to "ring" a wheel with cast brass. The likelihood of it crumbling apart is very high. Secondly, I personally would make a entire new assembly as it appears this one has been to more than one dance already. When you mentioned tower clock wheels and casting I immediately thought of spoked wheels 10-15-20" in diameter, not a fairly complex little piece under 2" in diameter. My mistake, sorry.

    I would machine the entire assembly, in two pieces, using 1/2 hard engravers brass. I would cut the teeth, then assemble the two parts. Using brass as the spring material is a bit problematic but it obviously worked for some time...so.....just my recommendation. Thanks for posting the photos, most helpful....
     
  11. rgmt79

    rgmt79 Registered User
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    Thanks Jim, did I mention tower clock wheels? No need to apologise, I'm sorry for any confusion, I should have posted pictures from the start. I agree with you, on closer inspection it would appear that the ring that forms the click spring is a separate piece and looks to be a push fit inside the wheel...maybe I can use it again...
     
  12. Jim DuBois

    Jim DuBois Registered User
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    My problem entirely. Discussing tower clock parts on another thread and someone got confused (me)
     
  13. gmorse

    gmorse Registered User
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    Hi rgmt79,

    This looks to be constructed in exactly the same way as the great wheel in a fusee pocket watch. The brass click spring is turned as a complete ring which is then cut and filed to form the spring and riveted into the recess in the wheel.

    Regards,

    Graham
     
  14. rgmt79

    rgmt79 Registered User
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    I don't see any sign of riveting Graham, but your comment relating it to the great wheel of a fusee pocket watch is interesting...

    Richard
     
  15. novicetimekeeper

    novicetimekeeper Registered User

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    The pictures are not in focus but I can see at least one round that looks like it was a rivet hole now filled with solder, I think I can see another rivet too.
     
  16. rgmt79

    rgmt79 Registered User
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    You are right Novicetimekeeper, on closer inspection I can see 3 small brass rivets (almost invisible)...the obvious one you can see is a steel rivet for the click (which is part of the click and rotates with it), the solder is from a previous teeth repair. Sorry for the poor quality photo's...

    Richard
     
  17. novicetimekeeper

    novicetimekeeper Registered User

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    As the rivets are usually from the same cast brass they can be virtually invisible when done well and not disturbed. You see it on clocks all the time where you know a pillar must be riveted in because you can see it the other side.
     
  18. scootermcrad

    scootermcrad Registered User
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    What a great thread! Learning a ton! Great topic!

    Sorry guys! That's my fault. I'm muddying up the waters while trying to learn about reproducing a 13"+ wheel from acceptable replacement materials. Jim and I had been talking in a thread running in parallel that I had started right before this one popped up. Learning a ton from both. The larger wheel, mid picture is what we were referring too.

    img_2551-jpg.jpg
     

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