Question about center distance

AmateurFixer

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Hello,

I am fairly new to horology and am interested in designing and constructing my own watch movement. I know that most people I met or talked too said that it's impossible for me to construct my own movement, but I would still like to try and challenge my self.

I'm reading "A Practical Course In Horology" book and stumble across a statement that I found hard to grasp. I was reading about gear construction and sizing and the book states that, "The center distance is determined by means of a depthing tool." So I was wondering whether using a depthing tool is necessary or not, because we can find the distance between the 2 meshing gear and pinion by adding the 2 diameters and divide it by 2, can we not? And my second question is, how do we know the center distance when we are designing a movement without first knowing what the diameter of the wheels and pinions are?

Can someone please share their knowledge on constructing a movement if you don't mind. It will be greatly appreciated.

Thank you

Best,
Rus
 
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Skutt50

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You are in for a very interessting jurney. I have tried to build a wooden clock but time has not allowed me to complete it. In my early days I also tried to build a watch with all gears in a straight line, just for fun, but again repair and service jobs took over... Perhaps one day in the future.....

One thing I learned is that a depthning tool is very useful. I set the gers in the tool and adjusted to a position where they moved smoothly and could then scribe a line on the brass plate. I now know where to drill the hole to get a good interaction between the gears. To find the spot for the next gear just start somewhere on the line and dra a new OR if you have two holes and need a new hole for a gear inbetween, just drw a new line and where the lines cross is where to drill.

On some older (Swiss) movements one can still today see the scribed circles from when the movement was made so a depthning tool has been used even for "mass produced" watches.

You should be able to pick up a used depthning tool from an auction site at a resonable price. I think you will find that it is worth it.

As for your question regarding using the radious Yes, that will work to if you, ofcourse, use the radius of where the teeth interact. But I believe you will drill some extra holes before you are satisfied. You could also do it that way and drill a bit too close. Then by cutting/trimming each gear slightly you could find the right position but I think that will take much longer.....

As for your second question, I really don't know but I would guess that one would start with determining the size of the movement and then, on paper, size and position the gear train, mainspring, winding mechansim etc, to make them fit the given movement size.
 

John Runciman

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I suppose you really don't need adapting tool. Suppose you designed your watch with the computer made all the proper calculations conceivably could just CNC the watch and you never would need adapting tool.

another way of interpreting a question is their formulas out there if you're missing a gear for instance at a clock. You can measure things do calculations and cut a replacement gear and pinion.

if you don't have at the book found that the link below is a must have for making watches. it has a nice simple title like watchmaking because the book tells you how to make a watch.


Watchmaking: Daniels, George: 9780856677045: Amazon.com: Books
 

Skutt50

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do you think they ever put them in a depthing tool just to make sure there right?
I wouldn't be surprised if they do, but I belong to the genertion growing up with slide rulers, and math tabels so I am not familiar with computer designs and what they can perform. The first IBM PC was introduced after I graduated from the university.........
 

gmorse

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Hi Rus,

The other book you should read as well as the Daniels recommended by John, (which is superb if you already have some understanding of watchmaking), is 'Wheel and Pinion Cutting in Horology' by J. Malcolm Wild, (ISBN 1-86126-245-0), which covers the practicalities of wheel and pinion cutting with just enough theory to tie it all together.

Regards,

Graham
 

karlmansson

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Apr 20, 2013
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Hello,

I am fairly new to horology and am interested in designing and constructing my own watch movement. I know that most people I met or talked too said that it's impossible for me to construct my own movement, but I would still like to try and challenge my self.

I'm reading "A Practical Course In Horology" book and stumble across a statement that I found hard to grasp. I was reading about gear construction and sizing and the book states that, "The center distance is determined by means of a depthing tool." So I was wondering whether using a depthing tool is necessary or not, because we can find the distance between the 2 meshing gear and pinion by adding the 2 diameters and divide it by 2, can we not? And my second question is, how do we know the center distance when we are designing a movement without first knowing what the diameter of the wheels and pinions are?

Can someone please share their knowledge on constructing a movement if you don't mind. It will be greatly appreciated.

Thank you

Best,
Rus
Hey Rus!

I'm on the same path as you are. My approach to it has been to start by servicing watches from difference decades and looking at how different manufacturers have solved different problems. I do this to get an understanding for the mechanics in watches, as cumulative errors in the watches I have serviced is starting to amount to me adressing every part of a watch, from screws to balances and their springs.

My next step is to build a wall clock out of an existing set of gears as an exercise partly in construction (as I intend to make a retrograde hand system for it) but mostly to understand depthing.

Like you, I was for some reason heavily attracted to the concept of making gears and pinions when I started out. I guess this has something to do with my preconception of clockwork being gear based. It is after all what you see when you open up a watch movement. While gear and pinion cutting will be of importance for making a watch, from experience I can say that there are a lot of other skills that will probably prove more useful earlier on as you proceed. The understanding of materials and hardening properties as well as turning precise parts with a graver are two.

To adress the question you are asking: the theoretical center distance of two gears can be used provided that you manage to create a perfect tooth form and are able to cut it at exactly the correct depth. This is rarely the case, and if you calculate your gear mesh based on perfect epicycloid gear profiles, you will find that even the predominating cutter manufacturers such as PP Thornton do not use true epicycloids for their cutter design but rather a circle approximation of it. This will cause a gear to behave ever so slightly differently and it may have run smoother had you increased or decreased the center distance ever so slightly. I'm not sure about you but my goal is to make a well functioning watch rather than a watch that is perfect in the sense of theoretical measurements. The latter may be important it you are planning to design a movement that will be mass produced on CNC machines. I view my own efforts on the same level as the turn of the century watchmaker shops in England, just with lesser skill and better lighting. I will try and match parts to each other rather than getting them to certain dimensions straight away.

I would also encourage you to read up on gear theory for a better understanding of the different diameters involved for different tooth profiles. The diameter you are refering to is the pitch circle diameter. This is not the same as the tip diameter, which is the one you can measure and consists of the pitch diameter plus the addendum. I'm not sure just how new you are to horology so please excuse me kicking in any open doors. If you are not familiar with the concepts of epicycloid gearing and involute gearing I would urge you to start you gear theory reading in reading up on the difference between the two.

Regards
Karl
 
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gmorse

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Hi Rus,

One major difference between the gearing used in clocks and watches and that in almost all other applications, is that all horological gearing, (with the exception of motion work and a few other places), uses the wheels as driving elements and the pinions as driven. This reversal of normal practice, especially in the very small sizes necessary in watches, results in compromises in tooth forms.

Regarding depthing tools, older second-hand tools should be carefully checked for alignment; at any given setting, the runners must be parallel and read the same at both ends, otherwise the results will be misleading. If the runners aren't truly parallel, how will you tell which pair of runners is correct? The radius of the arc scribed by the tool when the two wheels are engaging at their most efficient point, (the centre distance), will be the sum of the two pitch radii.

Regards,

Graham
 

karlmansson

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Apr 20, 2013
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Hello,

I am fairly new to horology and am interested in designing and constructing my own watch movement. I know that most people I met or talked too said that it's impossible for me to construct my own movement, but I would still like to try and challenge my self.

I'm reading "A Practical Course In Horology" book and stumble across a statement that I found hard to grasp. I was reading about gear construction and sizing and the book states that, "The center distance is determined by means of a depthing tool." So I was wondering whether using a depthing tool is necessary or not, because we can find the distance between the 2 meshing gear and pinion by adding the 2 diameters and divide it by 2, can we not? And my second question is, how do we know the center distance when we are designing a movement without first knowing what the diameter of the wheels and pinions are?

Can someone please share their knowledge on constructing a movement if you don't mind. It will be greatly appreciated.

Thank you

Best,
Rus
Reading your first post again, I see where your hang up is. The center distance isn't per definition determined by the use of a depthing tool. It is determined by the gear ratio and the pitch circle diameters of both driving and driven gears. The center distance can however be found conveniently by using a well made and precise depthing tool. George Daniels describes a method of checking a depthing tool in his Watchmaking.

Regards
Karl
 

Jerry Kieffer

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Hello,

I am fairly new to horology and am interested in designing and constructing my own watch movement. I know that most people I met or talked too said that it's impossible for me to construct my own movement, but I would still like to try and challenge my self.

I'm reading "A Practical Course In Horology" book and stumble across a statement that I found hard to grasp. I was reading about gear construction and sizing and the book states that, "The center distance is determined by means of a depthing tool." So I was wondering whether using a depthing tool is necessary or not, because we can find the distance between the 2 meshing gear and pinion by adding the 2 diameters and divide it by 2, can we not? And my second question is, how do we know the center distance when we are designing a movement without first knowing what the diameter of the wheels and pinions are?

Can someone please share their knowledge on constructing a movement if you don't mind. It will be greatly appreciated.

Thank you

Best,
Rus
Russ
When I first started in Horology many years ago, one of my goals was to construct a movement.

For years that goal was basically laughed at of course by those who had not attempted it.

In the end, my most useful information came from two gentlemen (Now deceased) who had actually constructed properly functioning movements.
My approach was to request movement photos to separate wind bags from reality. I then made appointments to examine the movements and discuss construction procedures. After spending thousands of hours, not all but most will be happy to share experiences. If your truly interested I would suggest a similar approach. If there is no evidence or work examples that a Author has constructed a movement, then their comments have to be considered opinions in regard to this subject.

To answer your question, I have found that a depthing tool is useful in Clock size construction but not consistently accurate enough for watch work or construction. While they are a very simple contraption at first glance, there are many points of construction contact where errors can be multiplied or interpreted.
My personal method of starting movement construction is to machine the center wheel and fit it to a blank movement plate attached photos.

I then machine a pinion that the center wheel will drive that is long enough to be separated in two pieces. One part will be used for the actual pinion while the second piece is used for depthing. For depthing I center drill a piece of stock to be mounted in the Milling machine spindle per photos. For movement construction, I use a Machine lathe and Milling machine and not a jewelers Lathe. This allows me to duplicate production procedures utilized in horological parts production.

On the second pinion I machine a pivot that fits the work piece snugly but still rotates freely. From this point the wheel and pinion are mounted in the mill and adjusted for depthing that provides for friction free operation as shown in the photos. Once this is achieved, the spindle is now positioned for drilling/reaming a hole utilized for jewel or setting installation. This procedure provides accurate predetermined and assured outcome unlike a depthing tool.

In todays word you can draw something and produce it by CNC, however it unlikely to work to perfection as intended. At this point the end result is considered a prototype that is adjusted by trial and error until it works to perfection. It is then redrawn and duplicated by CNC in production.

By using machine tools I am able to duplicate CNC procedures on a manual machine. Since a Horological movement is mostly one off items, not much is lost since each part requires its own setup and tooling required for both CNC and Manual.

Jerry Kieffer

fullsizeoutput_54c.jpeg fullsizeoutput_54d.jpeg
 

DeweyC

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Hello,

I am fairly new to horology and am interested in designing and constructing my own watch movement. I know that most people I met or talked too said that it's impossible for me to construct my own movement, but I would still like to try and challenge my self.

I'm reading "A Practical Course In Horology" book and stumble across a statement that I found hard to grasp. I was reading about gear construction and sizing and the book states that, "The center distance is determined by means of a depthing tool." So I was wondering whether using a depthing tool is necessary or not, because we can find the distance between the 2 meshing gear and pinion by adding the 2 diameters and divide it by 2, can we not? And my second question is, how do we know the center distance when we are designing a movement without first knowing what the diameter of the wheels and pinions are?

Can someone please share their knowledge on constructing a movement if you don't mind. It will be greatly appreciated.

Thank you

Best,
Rus
Rus,

It appears you are thinking the ODs of the wheel and pinion define the depthing distance. It is the pitch circles (the intersection of each member where the teeth and leaves actually engage. This is smaller than the ODs. Most people will make their wheels and pinions and than use the actual components to mark out the pivot locations using them in the depthing tool.
 
Last edited:

AmateurFixer

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Jun 16, 2021
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Hello,

Thanks for the replies, I was out of town for a couple of days hence the late reply.

I started repairing vintage watches almost a year ago, and have worked on multiple different movement designs. Now I just want to challenge myself to design my own watch movement, because I met a guy who fixed high end watches for a living and he laughed at me when I told him I wanted to design my own movement and case 1 day. He also pointed out my age and say that I will lose all the motivation one day and should just give up early.

I actually made a hand drawing for deciding the wheels and pinions sizes like Skutt50 suggested, I am also planning on modelling the movement on CAD to check for the alignments, free rolling of the gears and etc.

Again, thank you so much for all the great advices.

Best,
Rus
 

karlmansson

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Apr 20, 2013
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I started repairing vintage watches almost a year ago, and have worked on multiple different movement designs. Now I just want to challenge myself to design my own watch movement, because I met a guy who fixed high end watches for a living and he laughed at me when I told him I wanted to design my own movement and case 1 day. He also pointed out my age and say that I will lose all the motivation one day and should just give up early.
Sounds like a very negative person. I can see how it would seem like a fruitless and futile endeavour from the perspective of someone having watchmaking as their daily grind though. I think that from an economical perspective it IS a pointless excercise and chances of making any money from it are slim and will require sacrifices few might be willing to make. But as a hobby, if it brings you joy and pleasure, why not? I think industry folks and hobbyists go into these things with very different approaches. I know that I will make many mistakes in my designs and executions of them, but mistakes is one way I learn. And I like learning and getting better at things. So people who scoff at you are probably missing the point...

Keep on keeping on I say.

Regards
Karl
 
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