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Hi,

FIrst, Happy New Year to all--

I just put a Bulova 10BZAC on my bench and it has an interesting thing-a-ma-jig on the stud screw that I'm wondering if it is used for adjusting the beat error?

I've included a picture from the internet and circled what I'm talking about--the screw that holds the hairspring stud to the balance cock has some sort of cap on it that I'm assuming can turn the stud?

Anyhow if anyone has any experience with this movement would appreciate hearing about it before I attempt to play with it.

Levine98

10BZAC1961.jpeg.823955c4aaab33b555fa4f6e08446893.jpeg

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38 minutes ago, Levine98 said:

Hi,

FIrst, Happy New Year to all--

I just put a Bulova 10BZAC on my bench and it has an interesting thing-a-ma-jig on the stud screw that I'm wondering if it is used for adjusting the beat error?

I've included a picture from the internet and circled what I'm talking about--the screw that holds the hairspring stud to the balance cock has some sort of cap on it that I'm assuming can turn the stud?

Anyhow if anyone has any experience with this movement would appreciate hearing about it before I attempt to play with it.

Levine98

10BZAC1961.jpeg.823955c4aaab33b555fa4f6e08446893.jpeg

That would help centering of the hairspring if it did. Can you post a close up of it.

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40 minutes ago, Levine98 said:

circled what I'm talking about--the screw that holds the hairspring stud to the balance cock has some sort of cap on it that I'm assuming can turn the stud?

What purpose would turning the stud serve?   Did you mean to say "turn the stud arm" ? or stud carirer?  or Beat adjustor arm? 

Rgds

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9 minutes ago, Nucejoe said:

What purpose would turning the stud serve?   Did you mean to say "turn the stud arm" ? or stud carirer?  or Beat adjustor arm? 

Rgds

I don't know, why I'm asking. However on closer examination under my microscope, I noticed that the stud arm may be adjustable. I'll find out when I clean it and reassemble tomorrow.869418719_Photoon1-2-23at2_30PM.thumb.jpg.57e72492179ec14eda812b103d84fb43.jpg

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5 minutes ago, Neverenoughwatches said:

Is it just not part of the stud carrier. Does it actually turn ?

Seems a bit of a new fangled design for a 60 year old watch.

9 minutes ago, Levine98 said:

I don't know, why I'm asking. However on closer examination under my microscope, I noticed that the stud arm may be adjustable. I'll find out when I clean it and reassemble tomorrow.869418719_Photoon1-2-23at2_30PM.thumb.jpg.57e72492179ec14eda812b103d84fb43.jpg

I cant see how it would change the beat, if it does turn it must have some other purpose. Looked at a few other examples and all are like this. They seemed a high grade movement for the time with 6 adjustments and temperature controlled isochronism. So is this another adjustment feature ?

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I've worked on a bunch of Bulova 10BPAC and 10BOAC. Those two movements share 99% parts and have fixed stud on the balance, making adjustment a real pain.

This is my first 10BZAC and although the base movement looks to be the same as the two above, the stud configuration is different (and I'm hoping adjustable)--maybe it was considered an improvement since according to pink pages the 10BZAC seems to be the a successor to the 10BOAC and 10BPAC movements. 

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You'll notice your stud holder looks like it's made out of a different material Then the rest the balance bridge. It probably can be pushed and used to put the watch in beat usually when there a different Material that's what happens. It just happens to be a strange design.

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1 hour ago, Levine98 said:

Just an update--it is an adjustable stud arm. However I still don't know what the donut shaped thing is for that is part of the stud holder, but not going to worry about it 🙂 

Like John said just a strange feature of the movement.  I was initially thinking that if it turned to center the hairspring it might be some kind of predecessor of an Etachron stud adjuster.

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21 hours ago, Levine98 said:

Just an update--it is an adjustable stud arm. However I still don't know what the donut shaped thing is for that is part of the stud holder, but not going to worry about it 🙂 

After assembly and regulation. BTW this was a non-runner bought on eBay for $20. Amplitude dial u/d is closer to 260 with 60 year old orignal mainspring. 

1FBC1354-9761-4560-91F3-F3B47B68D980.jpeg

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Correct, Jan/23 is my one year anniversary--started with Mark's online classes last January then invested in tools and put together a dedicated workshop in my house over 2022.

I had to give up two other lifelong hobbies a couple of years into my retirement, so endded up with lots more time than planned. Wife encouraged me to take the plunge when she noticed me following several watch repair youtubers for a couple of years.

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