Excel files to help you design Gear Trains for wooden clocks

Spreadsheet to calculate the length of clock pendulums

If you have decided to design and build your own wooden clock then the following charts should give you some idea of how to tackle the tricky mathematical bits that are needed to make sure that the clock can run accurately throughout the day. Some of my earlier posts should have introduced you to some of these formulae that are used in this process. The idea here though is that we try to automate the process using Excel to do the heavy lifting and at the same time give you the opportunity to try out different combinations needed to me the constraints of the design you have in your head.

This first chart is used to calculate the length of the clock's pendulum which in turn uses various combinations of gears to achieve this, with you inputting tooth numbers into the appropriate box.

Basic concepts

• Minute shaft makes 1 revolution every 3600 seconds
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• You are using a Graham Escapement that stops the rotation 2x for each completed swing(Tic Toc)
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• metric units
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• g= 9.8m/s/s
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• T= pendulum period of time for a Tick and A Tock
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• pi= 3.14159
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• length of pendulum = g(T/(2 *pi))2
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• If you aim to have a second hand then the Escapement wheel should rotate once in 60 secs.

The chart provides inputs for a maximum of 3-wheeled Gear Train and if you only use 2 then fill the appropriate boxes with the number 1, it also requires you to provide a pair of gears with a Wheel and a Pinion for each pairing. You must only input figures into the Green coloured boxes as the orange ones contain the Formulae to calculate the value.
If you want to add other combinations to the green area either clear an unwanted row or use the normal Excel technique to copy the whole Green and Orange bottom row of boxes and paste them to the row below.

Click on the picture below to download the Excel File.

Spreadsheet to calculate Gear tooth Profile.

I have always used a modified version of the standard gear tooth profile so as to give me more clearance between teeth and a bit more leeway when cutting the teeth by hand or on a scroll saw. The most important thing with regards to tooth profile is consistency in the pitching of the teeth. The charts below reflect this and the details are given for both the large gear and the Pinions in the most used tooth sizes.

Again if you want to add other combinations to the green area either clear an unwanted row or use the normal Excel technique to copy the whole Green and Orange bottom row of boxes and paste them to the row below.

Click on the picture below to download the Excel File.

PCD is the Number of TeethX Mod

Outside Diameter is (Number of teeth + 2)X Mod

Root Diameter PCD-(ModX3)

Spreadsheet to calculate centre distance between a Pair of Gears

This is probably the simplest of the charts as it simply calculates the distance between the two mating gears by adding the two Pitch Circle Diameters (Ø50 mm in this case) together and dividing by 2. If you experience difficulty with distortion of the gears that causes problems with assembly then you might want to increase this by 0.5 mm.

Useful File types for wooden clocks builders - Step File

I have included STP or STEP files with most of the clocks that you can purchase as these files provide you with exact 3-D models of the clock that you can use in your 3D CAD program to modify any of the parts.

That is useful if you own and use 3D CAD software but if you don't then the files can be used in conjunction with an STP file viewer program to provide you with a great deal of extra information about the parts of the clock and the way that they fit together.

There is a considerable number of these available on the internet, some free and some not so much. I have only looked at the free ones as, to be honest, you should be able to get all you need from them. The programs fall into two groups, On-line where you upload the files you want to view and PC or mobile Android or iOS based.

What I was looking for in a viewer was first and foremost how easy and intuitive it was to use and manipulate the parts or assemblies when loaded. Secondly was whether it would produce a list of parts in an assembly and whether it would highlight a part within an assembly when clicked either in the model or the parts list. This is important as it is sometimes difficult to find parts and identify them when you click on either the part or the part in the list. 

Autodesk Viewer

Starting with the Online STP viewer my clear favourite here is the viewer from Autodesk, simply called the Autodesk Viewer which will open over 80 file types including STP,  STL and Solidworks, etc.

 

Once you have registered and signed in, use the Model Browser to find the part of the assembly you want to view. once loaded as shown below the assembly can be opened up in the Model browser where you can click on individual parts or groups to make them either visible or invisible. It would benefit you at this stage to either read the instructions or set up some of the settings, I advise you to do
this as it makes it easier, later on, to manipulate the model and interrogate it for more information on the parts.

Now you are ready to use the viewer, one of the rather nice things you can do with the loaded assembly is to explode so that the parts can be more easily identified, this is simple simply click on the Explode symbol at the bottom and then slid the blue ball to the right to see all the parts fly apart. 

To see individual parts without the clutter of the other parts around it simply click on the part in the parts list and the other parts disappear, to bring them back right-click on the same part and click on the Show all message to bring them back. finally, on this I would recommend you go into Configuration - Display settings and turn off 'Ghost hidden objects' as this makes the visible part more difficult to see clearly.

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eDrawings

This next one can be downloaded to run on your PC or Mobile no Online option here. This is similar in many ways to the Autodesk Viewer but can load Solidworks files as well if you need that functionality. It is also slightly faster to load larger files as there is no internet connection needed.

Functionality on this one is pretty much the same as the Autodesk viewer with a Parts tree showing all the parts in their sub-assemblies with the same abilities to hide and show individual parts or sub-assemblies. Identification of those parts is easily done as highlighting in the parts tree also highlights the part on the model. 

Exploding of the assemblies is also similar to the Autodesk Viewer. Not much to choose between these first two and may come down to a preference for either PC or Online-based.

CADassistant

CAD assistant has similar functionality to the above and is either PC or mobile-based which may well be useful to iPad owners. It lacks the ability to explode assemblies but does have the functionality to change or add colour to a part which may well be the function that you are looking for.

I found it slightly more difficult to use than the others but to be fair that may be just me and certainly the ability to add colour could well make it worth looking at. If you click on the image below you should be able to download the STP files for this project.

So those are the ones that I consider worth using when you are trying to find more information about the wooden clock design you are going to build. Each has there merits and no reason for you not to try each one before you decide.