Step 5: Designing The Gears

When designing gears, there are many parameters that can affect the size. I took some of the standard values for the variables when making the calculations. I used a pressure angle of 20 degrees, and a Diametral Pitch of 8. These combined with the number of teeth of each gear, I was able to calculate the Pitch Diameter, Root Diameter, Outside Diameter, and Base Circle Diameter.

Now that I have the Diameters of the gears, I can start drawing them. I found instructions on drawing gears with CAD and followed them to draw these gears. It was written by Nick Carter. A link to his page is in the last step in the References Section.

The free2Design file has the Gears and Pinions with a layer that shows the lines drawn to create the teeth. While researching clocks, I came across Gary's Clocks. He mentioned that there is a big difference in what you can draw with CAD and what you can actually cut using a scroll saw. I learned this the hard way. Cutting the gullet between the teeth is a bit tedious. To try to speed things up I decided to add circles between each teeth to be drilled out with the drill press. That saved time trying to round out the valley between the teeth, but I think it caused some problems with the teeth meshing with each other.

Along with the gears are the Escapement and the Ratchet Mechanism. As stated earlier the Escapement is a mechanism that allows the energy to escape slowly. This is done using a gear, lever and pendulum. What hasn't been talked about yet is the Ratchet. We said that a weight is wrapped around an axle with string, and it slowly lets out to drive the clock. We need a way to re-set this, or wind the clock. The Ratchet will allow us to do that. It fits loosely over the axle of one of the gears, and pushes against the gear with a pin and lever. When the clock needs to be wound, the Ratchet can be turned counter-clockwise without moving the gear. Then when the weight pulls it clockwise again, it catches on to the pin fixed to the gear, and continues to power the clock.
<p>Can we use something else instead of wood?</p>
<p>I was going to try 3D printing mine with plastic components.</p>
I was wonderong I could use cardboard (layers glued together), as I still don't have the proper tools. If it works finely, I'll tell you --- if I remember ;)
<p>It will be really hard to get the precision required with cardboard and no laser cutter, which I assume you don't have either, but then again Benjamin Banneker hand made a clock.....</p>
<p>Great job</p>
<p>&quot;Common Tools&quot; is a wonderful goal. Watching a machine make something is not always a lot of fun, even if you made the machine to begin with. </p>
<p>Hi Marvay, how accurate did your pendulum clock turn out? Can it measure in seconds/milliseconds, or could it somehow be made to? How accurate are pendulum clocks overall?</p>
<p>Would it be possible to provide the fundamental key gear parameters to the body of the plans? The reason I ask is that I already have a CAD package that has a <br>Gear&quot; function but I may be missing it but if there was a simple list of each gear that stated key metrics (OD, # of teeth, Center bore diameter, Pitch Diameter, Base Diameter, etc.) then it would be possible to &quot;create&quot; the gears in any particular CAD package without necessarily using file viewers, etc to see the key metrics. Thanks for the consideration - would love to make the clock - I own a small CNC and a good software package to create the gears.</p>
<p>I read through your article with interest, anticipating the section about the design the escape gear and escape levers. Any reason for this? </p>
<p>Hello there - I was wondering what you used for axles on this. I'm considering doing a gear clock, but I can't decide what to use. I was thinking brass rod in a brass press-fit bushing might make for a functional and decent looking axle, but I have no idea what other people have used.</p>
Hi! How do you adjust the hour and minute hand? When you wind it, does it cause the gears to spin too?
I just found this instructable. Thanks for sharing. I'll have to spend more time looking at this. I've always wanted to make my own clock, especially since it was something that my great grandfather did. I liked that you use open source software aslo. Thanks again for sharing.
rennysoncemann,<br>Please reread the teachings of Galileo Galilei. It's Physics 101.<br><br>Since Galileo discovered the isochronic property of the pendulum, they have been the world's most accurate timekeeping technology until the 1930s. This could NOT be so if the angle of the swing would vary the frequency.<br><br>Wider swings do NOT take longer, unless you are comparing a swing of 1 degree v. 179 degrees. Then, the variation in period or frequency is really influenced more by friction in the bearing and air friction.<br>Clocks, use relatively low angle pendulum swings, so these factors are kept at a minimum as there is less movement. The only reason a clock's pendulum may have a higher mass, is to take advantage of Newton's First Law of Motion to overcome as much of the friction to keep it moving as long as posible. The addition, or subtraction of mass will NOT change the frequency of the pendulum. <br><br>The period of swing of a simple gravity pendulum depends on its length, the local strength of gravity, and to a small extent on the maximum angle that the pendulum swings away from vertical, called the amplitude.<br><br>It is independent of the mass of the bob.<br><br>If the amplitude is limited to small swings, the period T of a simple pendulum, the time taken for a complete cycle, is a function of the length of the pendulum and gravity.<br><br>For small swings, the period of swing is approximately the same for different size swings: that is, the period is independent of amplitude.<br><br>This property, called isochronism, is the reason pendulums are so useful for timekeeping.<br>Successive swings of the pendulum, even if changing in amplitude, take the same amount of time.
Um - strictly speaking, the amplitude of the arc does change the period, because a basic pendulum is not truly isochronous, only very nearly. This is basic horological theory and well known amongst horologists and is due to the differing effect of gravity on the pendulum at different points of the swing. A truly isochronous pendulum would swing not in a perfect circle, but in a slightly modified curve called a cycloid (check out &quot;the tautochrone curve&quot; on Wikipedia). This discrepancy was perceived as a problem in early clocks where the pendulum had to have an enormous swing to unlock the escapement. As rennysoncemann says, Huygens invented &quot;cycloidal cheeks&quot; to try and combat this by modifying the way the pendulum swung. The trouble was that in practice, nobody could make them work. <br> <br>The advent of the anchor (recoil) escapement effectively solved the problem by massively reducing the required arc of the pendulum thereby making the discrepancy so small, it could be ignored, certainly in domestic clocks. There is still an error however, and to reduce this as much as possible the best quality clocks used by astronomers were designed to have the smallest arc of movement they could get away with. You, in your response also quote that the amplitude of the pendulum must not be large, so I'm not certain why you thought rennysonceman was incorrect? <br> <br>Similarly, in theory the mass of the pendulum bob is unimportant, but in practice, it is desirable to make it as heavy as possible, but with the smallest surface area possible in order to minimise the effects of air pressure and friction. The smallest surface area would be provided by a sphere; horologists compromise and use a cylinder because it is easier to make. The disc shaped bob invariably found on domestic clocks might seem desirable to reduce air resistance but apparently confers no great advantage. <br> <br>Sorry, I've drivelled on too much.
Sorry, but a wider swing takes longer, and it's not because of friction. Christiaan Huygens, who invented the first pendulum clock, realized this fact. His primitive escapement necessitated a very wide swing, so he added so-called &quot;cheeks&quot; to his pendulum suspension, to alter the path the bob takes from a circle to a &quot;cycloid&quot;, which is the curve needed to have true isochronism. Read more here:<br><br>http://en.wikipedia.org/wiki/Christiaan_Huygens<br><br>For small swings, the effect is quite small and could be ignored in a weight driven clock, whose pendulum swings are reasonably constant and therefore unvarying. For spring driven clocks, where the swing gets smaller and smaller as the spring unwinds, the effect was bad enough that a fusee was added to the finest movements to keep the driving force, and therefore pendulum swing, as constant as possible. Cheaper spring driven clocks weren't very accurate anyway, and the recoil escapement used in those movements tended to drive the pendulum faster when wound tight, which partially compensated for the wider (slower) swings of the pendulum. Not that it really mattered in that era, as people set their clocks daily anyway, to a sundial or the town clock bell.....<br><br>Cheers,<br><br>Chris
&quot;&quot;One of my goals with this was to use common tools that are more widely available to most people. I didn't use any expensive hard to find wood working machines, or costly software packages when designing this.&quot;&quot; <br> <br>there should be more people with this opinion here! <br>this is very nice! well done.
Are there any cad files for this? I have access to a laser cutter at my school it uses cad. When ever I try to open any files on this instuctables it gives me .tmp files.
I apologize to everyone that have asked for DXF files, or another format from the free2Design program or more information about my Instructable. I have been in and out of Instructables for the past year or so, and haven't kept up with my messages. <br>The free2Desing program didn't have an export function. I also didn't realize it wouldn't be around for much longer after I used the program. They shortly canceled the project. The reason I used it was that I was looking for a free, easy to use program, that had certain functions that made designing the gears easy.<br>My main purpose of this Instructable wasn't to make something that everyone could duplicate(you could, but honestly it's an ugly design). It was to teach anyone interested in building a clock, how to figure out their own design. Yes you can buy plans, kits, and other clocks to make, but putting it together doesn't teach why you need certain ratios. It just teaches you how to assemble something.<br>I hope to make another clock sometime, and if I do, I will make sure it's in a program that most everyone can use.<br>Thanks for viewing this Instructable and all the comments.
Please: could you add your designs as DXF files so that everyone can open them in pretty much any program? My father and I are trying to make this clock for xmas and we can't work with E2 files. Thank you!
the link to the file is broken. It links to a .tmp file instead.<br><br>Nice instructable.
rennysoncemann, You are incorrect about the properties of a pendulum. The &quot;width of arc of the pendulum swing&quot; does not affect the period... <br><br>&quot;The frequency of the pendulum is dependent on the length of the string or wire. The shorter the wire, the greater the frequency or how fast it goes back and forth.<br><br>The frequency is independent of the amplitude of the swing, provided the initial angle is not large. At larger angles, there is a slight change in the frequency.<br><br>Also, the frequency is independent of the mass of the bob. In other words a pendulum with a heavy bob will move at the same rate as one with a lighter weight bob. But this only makes sense, since the acceleration of gravity on a falling object is independent of the mass of the object.&quot;<br><br>See:<br>http://www.school-for-champions.com/science/pendulum.htm
Really cool ratchet system for your weight axel, I may do something similar. Why do you have the second lever though? I can't seem to work out what it does.
On the ratchet the second lever appears to be a type of spring to keep the other lever engaged into the ratchet system.
Hello ! OK I know that I'm a newbee. And I know that I speak French and I'm not fluent in English but !!! <br>I just become a member. And it's very cheap but : <br>I cannot open any of your files. <br>Your ods file is not recognised by my Open Office Calc and free2design is not found by my explorer. <br>Then could you please say me what I'm doing wrong ? <br> <br>Thank you for your quick answer. <br>Best to all.
nice work.I'm trying to make small gears.I think I can put some designs nto my website http://tilmen.s5.com/anasayfa.html soon.
Here's one tip on cutting gears with a scroll saw. Since clocks only run in one direction, there's no need to cut the 'back side' tooth profile. That speeds up the process.<br><br>Ed
Unfortunately, the freeware version of free2design is unavailable. Are there any other substitutes?
Be a student and get a student licence for AutoCAD.<br>Or join their beta program and get their beta software.
A9CAD is fairly easy to use and totally free.<br/><br/><a rel="nofollow" href="http://www.a9tech.com/a9cad/">http://www.a9tech.com/a9cad/</a><br/><br/>Unfortunately, it does lack certain advanced features that would make your design work a lot faster.<br/><br/>For example, in the case of designing these gears, it would be handy to have a &quot;Polar Array&quot; feature. That's where you select an object or group of objects, Pick a center point, tell the program how many duplicates you want and how many degrees you want it to cover. The program would then automatically rotate and place the objects for you. So, you could draw one tooth of the gear, tell the program how many teeth you need and where the center of the circle is and it would draw the whole gear for you.<br/><br/>Alas, with A9CAD, you would have to draw each tooth individually. :(<br/><br/>Still, it is free and it is effective. I was trained on AutoCAD at work, but couldn't afford a license for home. A9CAD is a good free substitute.<br/>
the free version of allycad will allow you to copy a gear tooth x number of times in a polar fashion around the center! Or if you don't mind metric and using module instead of diametric pitch then use the included tool for drawing involute gears. It's a great program, I've used it for going on 7 years now, and built over 13 clocks using it. One tip. Wood clocks need more clearance and backlash than metal. Part of the fix is to set the centers 0.04&quot; further apart, which with involute gears will not affect their speed.
Can it open the &quot;e2&quot; files in the instructable?
The best free computer drafting program out there is at www.allycad.com!
Thanks This was a big help <br> <br>In Step 4, there is a spreadsheet with each gear, <br>the number of teeth, and the ratio that the gear train creates. <br> But for a quick reference, <br> here are the Gears and their teeth: <br>Each line represents an axle <br>Pinion 1 - 12 teeth Wheel 1 - 36 teeth , <br>Pinion 2 - 10 teeth Wheel 2 - 40 teeth, <br>Pinion 3 - 8 teeth Wheel 3 - 40 teeth, <br>Pinion 4 - 12 teeth Wheel 4 - 40 teeth, <br>Pinion 5 10 teeth Wheel 5 - 36 teeth. <br>The escapement gear has 30 teeth and is not in the list above since it does not factor into the calculation of the gear ratios. <br>
Thanks for the work here <br>I like this &amp; trying to make one <br>wish i could open the files <br>or that jpg files cound be downloaded
Go to abbeyclocks.com or maybe its abbyclock.com. It's a great page by a guy named Mark Headrick. Escapement animations will help ya alot. Plus he has a downloadable (FREE) paper on designing escapements!! It is super!!
I've tried to send you a Private Message but it doesn't seem to work. Can you send me one so i can respond?
am I missing something. When I try to download I get a tmp file. do I need to be a pro member to download?
Email me for a pdf I made showing a way easier method than Nick's. No offense intended to nick1
Ya know. The hardest part I ran into 6 years back when I started designing wooden clocks was how to draw a gear tooth. I came up with a easy way to do it and also designed a spread-sheet in open-office to calculate all the necessary info to do it. After clock #2 I gave up on cycloid gears and went to involute gears. I also found that lantern pinions work far and away better than cut pinions plus are easier to make! After building 13 clocks (everytime I put one on the wall someone wanted to buy the thing) and no problems thus far I think I have most of it down pretty good. It is way too addictive!LOL
Wow!<br>I am extremely amazed!<br>I hope i would have time to try this out.<br><br>Thanks Marvay. Great work!<br><br>- <a href="http://jackdi.blogspot.com/">Jack</a> -
Im releasing very shortly new software which can help in things such as clocks or geared mechanisms. You can see the tutorials and such now at www.gearotic.com , its inexpensive and should aid in making all things geared much more easy to make and envision. <br> <br>Thx <br>Art <br>
Cool! Now I know how to build someting like this
I like this one better. (Sry marvey). Can you do an instructable for it?
<br />

About This Instructable




Bio: Favorite Show: How It's Made
More by marvay:Wooden Gear Clock
Add instructable to: