Mechanical Clock Escapement with Balance-Wheel

prusaprinters

<p>Since I saw a mechanical watch for the first time I wondered: How do they work? Why does it tick and why is it ticking with a constant frequency? And why is there this thing, which keeps tilting from one side to the other?</p><p>To answer my questions I was watching quit some YouTube-Videos and staring at a mechanical watch. It was quite hard to imagine all the fine details, which make the hands of the watch turn, since you simply couldn't hold the mechanism in your hands and turn it around to inspect it.</p><p>Therefore I designed this fully 3D-printable clock-escapement including a little power-reserve. You should keep in mind, that I'm a student and that I gathered my little knowledge about this mechanism on my own. Therefore, some information might be incorrect. If so, please leave a comment and I will correct it.</p><p>&nbsp;</p><h4>Required materials and tools</h4><ul><li>some PLA-filament</li><li>ca. 112mm of 2mm-diameter metall rod (I used welding filament)</li><li>10x M5 nut (it's additional mass for the balance wheel)</li><li>a pair of sidecutters</li><li>a hard surface to press against OR a vise to push the rods in the printed parts</li><li>a drill with a drill chuck (if you have a lot of patience, you can also use some pliers)</li><li>a pair of protective gloves to prevent the rods from accidentally hurting you</li></ul><p>For a version, that requires less uncommon parts and tools, click <a href="https://www.prusaprinters.org/prints/69812-mechanical-clock-escapement-with-balance-wheel-m3-">here</a>.</p><p>&nbsp;</p><h4>Print instructions</h4><ul><li>Material: PLA</li><li>Perimeters: 2</li><li>Infill: 15% (I used the Gyroid-pattern)</li><li>Layer-Height: 0.2mm</li><li>No supports needed!</li></ul><p><i>You can just use the standard Prusament-PLA setting in Prusa-Slicer!!</i></p><p>Depending on how much of an elephantfoot-effect you get from your printer, you should consider printing the "powerReserveTransmissionGear_ElephantfootCompensation" instead of the regular “powerReserveTransmissionGear”. Note, that the gear in “set1_mechanicalParts_MINI” is the one without the elephantfoot compensation.</p><p>&nbsp;</p><h4>Assembly instructions</h4><p>Print all parts. You can either slice them on your own using the stl-files or the 3mf-files (the 3mf-files are sets to print multiple parts at once) or you can use my pre-sliced gcode-files for the Prusa MINI.</p><p>All parts beside the frame-parts and the spiral-springs have a centre hole that needs to be bored out to size using a pice of the 2mm rod. You can simply load a pice of the rod into the chuck of your drill and enlarge the mentioned centre holes. You might want to squeeze one end of the rod A LITTLE BIT with the side-cutter to have a faster effect when boring out the holes. Enlarge the holes until the parts spin freely on the rod. Enlargening it too much can result in the mechanism not working properly!!</p><p>Next, take the "frameBottom" part and locate the three most outer roudn-shaped holes. Cut three pices of 32mm length of the 2mm rod and push those into the before mentioned holes. <strong>Don't push in a rod in the middle hole yet!</strong></p><p>Now, cut of a piece of rod with ca. 11mm length. It can be shorter, but it cannot be longer! Push this piece of rod into the remaining round hole in the middle.</p><p>If you want to lubricate the mechanism, now is the last chance to get access to the rods!</p><p><i>If you want to assemble the mechanism on your own, use these explosion pictures for reference:</i></p><figure class="image"><img src="https://media.prusaprinters.org/media/prints/69711/rich_content/79e10fa8-788e-4b43-8eb4-564215f2f5ab/explosion.jpg#%7B%22uuid%22%3A%22b12ba3b3-85c6-43d5-9a61-d1198120bf6e%22%2C%22w%22%3A2056%2C%22h%22%3A1554%7D"></figure><figure class="image"><img src="https://media.prusaprinters.org/media/prints/69711/rich_content/53cd4263-0ef5-4b41-bc03-6c2eab317aaf/explosion2.jpg#%7B%22uuid%22%3A%22cfd58231-5b54-45e2-9ed4-ecd9f327636a%22%2C%22w%22%3A1606%2C%22h%22%3A1518%7D"></figure><p><i>If you want to follow the detailed instructions, here are they:</i></p><p>Pick up the anchor and slide it onto the short rod in the middle. Pay special attention to the orientation of the anchor, otherwise it wouldn't work (use the pictures for reference).</p><p>After that, take the balance wheel and insert the ten M5 nuts into the appropriate holes. It's a tight fit on purpose - you don't want them to fall out!</p><p>The balance wheel has a hexagonal shaft-end. Press on the small spiral-spring. The little stud on the spring must face away from the nuts and the rest of the balance wheel. The orientation of the stud in relation to the second pin on the balance wheel is really important! If you look on the balance wheel from the side where you can see the metall nuts, the stud on the spring should be facing 3 o'clock when the pin on the balance wheel is facing 6 o'clock.</p><p>Now you can slide this assembly onto the rod near the quadratic hole. If the frame lays flat on the table, you shouldn't be able to see the nuts, when looking from the top. Now gently push the stud on the spring into the quadratic hole. The anchor might be in the way of the spring or the balance wheel. If that's the case, simply tilt it until you can slide it on. Make sure, that the pin on the balance wheel is placed in the little slot in the anchor.</p><p>Slide the escapement wheel onto to rod in the corner of the rectangular triangle of the frame. Make sure it's oriented correctly so that the spiky teeth of the escapement wheel can interact with the anchor.</p><p>Now you could test the mechanism by applying little pressure clockwise on the escapement wheel. The balance wheel should start to swing and the escapement wheel should move in little steps.</p><p>After that, it's time to build the power reserve. There is a larger and a smaller gear left. The larger one should also have triangular teeth instead of “normal” shaped ones. The smaller gear also has a hexagonal shaft. Push the big spiral spring on it. The stud on this one should be facing away from the gear you are currently working with. The rotational position of the spring in relation to the small gear doesn't matter.</p><p><i>If you notice an elephantfoot-effect on this gear, try printing the version “powerReserveTransmissionGear_ElephantfootCompensation.stl”. This one has a small chamfer around the teeth and therefore should prevent the elephantfoot-effect.</i></p><p>Take the biggest gear and slide the stud from the big spiral gear into the quadratic hole of that gear. Slide this sub-assembly onto the remaining metall rod. The smaller gear with the “normal” teeth should face down.</p><p>To finish things, press the frameTop-part onto the free ends of the metall rods.</p><p>Congratulations, you have finished the assembly of the clock-escapement-mechanism! Now it's time to inspect it and learn the behavior!</p><p>&nbsp;</p><h4>Further tips and tricks to make assembly easier</h4><ol><li>If the press-fit of the nuts in the balance wheel is too tight to push it in by hand, use a M5 screw to locate the nut. Take the screw out and press the nut in using a hard surface or a vise (be gentle with this one ;-)).</li><li>If the press-fit of the rods is to tight to push the frame parts on, you can also enlarge the holes in the frame. Be carefull, this might be causing the mechanism to fall apart later. You can also use a big allen-key as a small hamer to tap the parts on.</li></ol><p>&nbsp;</p><h4>How to use this mechanism explanations</h4><p>While securing the escapement wheel, you can wind up the mechanism by rotating the biggest gear with the triangular shaped teeth counter clockwise. Watch how the spiral spring compresses more and more!</p><p>If you let go of the escapement wheel, it should start to tick. If it doesn't, give the balance wheel a little push. Furhtermore you can adjust the distance between the frame parts to reduce friction.</p><p>In a real clock, there would be a lot more gears. Most of them are connected to the escapement gear (the one with the picky teeth). They reduce the rotational speed of the escapement wheel and thus drive the hands of the clock.</p><p>The mass of the balance wheel and the spring-stiffness are the two important factors when it comes to the periodic time. The periodic time is the time it takes for the balance wheel to swing one full period. In other words: To swing back and forth once. This periodic time is approximately independed from the amplitude of the balance wheel ("how far it swings"). This periodic motion then moves the anchor and therefore also controlls the speed of the escapement wheel. Because of the constant periodic time, the escapement wheel is always moving with the same constant average speed. That's the reason why clocks can keep time!</p><p>&nbsp;</p><h4>What to watch out for when studying the mechanism</h4><p>Try to understand how the force of the power reserve is transmitted. Also watch how the escapement wheel gives impulses to the anchor and how the anchor transmits the impuls to the balance wheel.</p><p>You can stop the mechanism by hand, if you want to have a "slow-motion" look at it!</p><p>You can also experiment with different amounts and placements of the nuts inside the balance wheel. That will have big impacts on the behaviour of the mechanism!</p>