How Does a Watch Work? (Watch Escapement Desk Toy)

This has been a bucket list item since I got my 3D printer, and with over 16,000 likes on Thingiverse I'm not alone! If you are like me, and learn better with hands on demos, then follow along to build this project and see what makes it tick (literally).

This Instructable uses the mainspring and hairspring mechanisms that revolutionized the clock making industry in the 17th century. Devices like this were able to keep time within 10 minutes and actually were responsible for adding the minutes hand to watches. Previously watches used only a mianspring, and could be off by hours by the end of the day. But how does such an old device actually work? It's design is still used today, but you may not actually know.

I'm going to go over getting the pieces, assembly of the device, address some fine tuning, and cover some of the physics involved in this deceptively complicated 'simple machine'.

The first thing you'll need to do is visit Thingiverse (Watch Escapement Desk Toy) by: LarkysPrints If you haven't visited Thingiverse already what are you doing with your life? Oh, you must not own a 3d printer. That's ok, you can pay somebody else to print the parts for you, or find a maker space to use. Even my local library is offering to do prints at cost now days. Realistically just ask your uncle real nice if he'll do it for you (he will).

Full credit goes to LarkysPrints for all 3d printed parts. You should be able to mouseover any part to identify it on the picture above. I would love to do a smaller snap fitment of this someday, to make it more within reach for a large audience. Until then here we go!

3D Printed Parts (in order of assembly - STL file name):

Mainspring Assembly (left set of parts)

• Spring Frame Bracket
• Ratchet Spring
• Barrel Ratchet
• Ratchet Barrel (Red Gear)
• Ratchet
• Main Spring (Grey)
• Winding Stem
• Spring Frame Front
• Winding Key
• Bracket

Gear Train Assembly (middle set of parts)

• Train Frame Back
• Gear Train (Yellow)
• Escape Wheel (Light Blue)
• Train Frame Front
• 2x Bracket

Balance Assembly (right set of parts)

• Balance Frame Back
• Hairspring (Orange)
• Balance (Dark Blue)
• Impact Pin Housing)
• Pallet Fork
• Balance Frame Front
• Bracket

Note 1: There is only one file for Brackets, but you'll need 4 of them. Don't forget! Also, you'll want to print them in the orientation that from the top down they look like this: |--|--------|--| this will give best layering and strength

Note 2: Many of the files aren't oriented for printing. You'll have to turn many of them on their flat face. They I only missed the barrel ratchet, and had to print again because you'll get a lot of the parts floating.

Note 3: This is BIG! I compared with my head for reference (and I'm 6'4"). The GIF on Thingiverse was deceptive to me. With a 200mm x 200mm printer it will take 4 trays of parts. This means you'll have to get a good head start if you're hoping to have it ready next day that's probably not realistic for most printers. It was about $10 worth of filament is all though, so don't let that scare you. I did 30% infill. You could probably go less if desired.

Hardware (official):

• (13) M4 x 16
• (2) M4 x 20
• (2) M4 x 40
• (1) M4 x 50
• (3) M4 x 60
• (24) M4 Washers
• (19) M4 Nuts
• (4) M4 Locking Nuts

• (2) M3 x 12
• (1) M3 x 25
• (3) M3 Washers
• (3) M3 Nuts

Note 1: Many of these could use longer or shorter bolts. I bought these: M4 variety pack (small), M4 variety pack (large), M3 Variety Pack. With that you can use what you think is best. You'll still need to source washers and locking nuts. Some could even be left off completely as you'll see.

Note 2: I didn't actually get washers and locking nuts, and it worked. I'm not missing the washers. You'll definitely want to use Loctite as they do come unthreaded. I tried adding an extra locking nut, and it wasn't holding, but I didn't tighten it with a wrench.

Tools:

• Wrenches for nuts (didn't actually use it, but it will make life much easier)
• Sand Paper (you might not need this if you don't paint)
• 3d printer and everything that goes along with it.
• Drill (Not required unless you don't get all the materials... I'll explain later)

Ready, lets GO!

1. Place the Spring Frame Back down with an M4 x 40 (can be shorter) bolt through it. (I forgot the bolt in mine until the end as I was getting pictures set up)

2. Place the Ratchet Spring on the Spring Frame Back place the Barrel Ratchet on the Ratchet Spring, and secure with a locking nut. (My Ratchet Spring broke, and I placed it in the wrong location in my GIF. I know I'm looking incompetent already. Stick with me. I don't know that steps 1 and 2 were even necessary. Mine cranks up just fine without this mechanism. You may have a different experience).

3. Place the Spring Barrel (red) down.

4. Place a M4 Nut inside the Ratchet.

5. Place the Ratchet inside the Spring Barrel with nut securely in place.

6. Place the Main Spring on top of the ratchet with the Winding Stem going on top of that.

7. Place an M4 x 60 bolt through the Spring Frame Front and slide the bolt through the rest of the assembly up to the Spring Barrel (red) then place that whole assembly onto the Spring Frame Back with bolt in line. Ensure you've secured the Main Spring on the underside of the Spring Frame Front. (This was the only other piece that broke on me. You might consider doing the spring frame front at 100% infill to combat this problem. It's working fine without a reprint, and is kind of nice shorter as I can put it on/off more easily)

8. Secure the Bracket to the bottom using 2 M4 x 16 Bolts and Washers, with the Nuts on top. (Make sure you align with the proper holes so the bracket is adding more security to the frame.)

9. Add the Winding Nut. (A great remix opportunity would be to add holes to this and the winding stem to secure with a bolt as it has the propensity to fall off.)

This next section is the easiest of the three. Keep it up!

1. Place 2 M4 x 60 Bolts through the Train Frame Back with Washers on them, and secure with Nuts. (One bolt can be shortened that supports the yellow gear. I think I went with a 40mm, and the other doesn't actually secure into the other side, so don't worry if it doesn't seem long enough. You've already secured them, and the other side is just a support. Another remix opportunity!)

2. Place the Gear Train (yellow) on the left bolt and secure with a Washer and Locking Nut.

3. Place the Escape Wheel (light blue) on the right bolt.

4. Place the Train Frame Front on the right bolt. (Remember I said it won't be secured. Just resting on top.)

5. Secure the frame with Brackets on each end using 4 M4 x 16 Bolts with Washers on them, and secure with Nuts. (I found it was easiest to place the nut in and hold in place with a finger then use the included allen wrench to screw the bolt in.) (This time you'll need to ensure the bracket is positioned to overlap with the other frame pieces. NOT LIKE THE BRACKET IN THE FIRST STEP.)

6. Secure the two assemblies together using 2 more M4 x 16 Bolts with Washers, and Nuts.

Last section! Get 'er done!

1. Place your M4 x 50 Bolt with Washer and M3 25 Bolt with Washer through the Balance Frame Back and lay down. (I had to drill the M3 out to a M4 because you'll notice the set I purchased didn't have 25mm M3's.)

2. Secure bolts with Nuts. (I couldn't fit a nut into the M3 slot because I didn't expand that portion, and just lived with the one nut in the next step. Works fine.)

3. Place Hairspring (orange) on both bolts, and place Nut on M3 bolt.

4. Place the M4 x 16 Bolt through the Impact Pin Housing from the back side. (It's not secured)

5. Secure the Impact Pin Housing to the Balancer (dark blue) using 2 M3 x 12 Bolts and Washers with Nuts on the back side of the Balancer. (Don't worry about the position. We'll tune this later.)

6. Place Balance (dark blue) assembly on the Hairspring (orange), and secure with a M4 Locking Nut and Washer.

7. Place 2 M4 x 20 Bolts through Balance Frame Front with Washers, and secure with Nuts and Washers. (Don't worry about the position on these now either. I actually ended up not needing them on mine Place M4 x 40 Bolt through Balance Frame Front with Washer, and secure with Nut and Washer. (I dropped this on down to 25mm.)

8. Place the Pallet Fork on the back side of the M4 x 40 Bolt, and secure with a Washer and Locking Nut. (Make sure the short end of the Pallet Fork is on the top end.)

9. Place the Bracket on the right end of the frame using 2 M4 x 16 Bolts with Washers, and Nuts. (Ensure the bracket is on the... eh, you're tired of me telling you what to do... You've figured it out. Use the last 2 bolts to secure it all together)

All right, crank it up and let that baby roar!

My biggest recommendation... DON'T PAINT ANYTHING. I did it thinking it would help make instructions easier, and I'm sure it did, however, the paint is sticky, and gums up the gears, and more importantly made the whole system have too much friction to function properly.

If your clock doesn't start up right away after cranking it try the following tips for success (not necessarily in order).

[x] Wind up the Main Spring a little more. It should coil tighter - not looser as you wind it up.

[x] Give the Balancer (dark blue) a little flick to get started.

[x] Ensure you springs are secured. They're the power plants for the whole mechanism.

[x] Ensure your gears are not binding. The Mainspring produces quite a bit of torque, and the gears may not be seated correctly.

[x] Ensure you haven't overtightened anything that's supposed to rotate. The gears, pallet fork, and balancer should be able to rotate freely.

[x] Check that the pallet fork (silver) is not hitting the Escape Wheel (blue) on its teeth. It should catch the Escape wheel like a hook on the top, and blocking the teeth on the bottom. If you're hitting the ends of the teeth with the fork clear the jam and continue troubleshooting.

[x] Ensure the pallet fork's retaining bolts are not too close together. Too close and you won't clear the teeth on the Escape wheel. Too far and you'll loose energy by hitting the escape wheel. I didn't have any problems with either, and actually don't see a need for these. One of mine fell off and I just left it.

[x] Tune the impact pin. If your system frequently has trouble pushing up on the pallet fork turn the impact pin clockwise and re-secure so it has more of the springs potential energy to push up against gravity. If it has trouble pushing down on the pallet fork rotate the impact pin counter clockwise and re-secure so the spring is more neutral or even assisting the downstroke.

[x] Sand all pieces where friction is encountered. Start with the pallet fork and the escapement wheel, then move to all the gears if needed.

[x] Change the slope of the pallet fork. I had to elongate the pressing surface for each side to get enough energy out of the system to throw the impact pin in each direction. I also had to clean out the impact side of the pallet fork so it didn't bind.

[x] Check for other places of binding. I've seen things catch on bolts, and between the impact pin housing and the pallet fork.

[x] Retighten connections. They may have come loose and you've introduced too much play into the system.

Whew, you got it working in less work than me?! Good job on not painting your parts, and using different colored plastics to get the same effect.

Can you identify all the simple machines in the system? I've highlighted some of them here for you.

The heart of the system really is the pallet fork. It is the Escape Wheel pressing on the inclined plane at either end of the fork that adds energy to the system to keep it running. It took a lot of looking at the GIF to figure this out, but only a little playing with it to see that's the key. This is also the piece that prevents energy from leaving the system prematurely, so your spring doesn't just unwind immediately. Remarkable engineering!

The mainspring is acting like an inclined plane or screw (which is really just like an inclined plane wrapped around an axle). You store potential energy by winding the mainspring up just like you would by rolling a ball up a hill.

The ratchets ride up an inclined plane to advance.

The gears seem like a wheel and axle (which I might call the Winding Stem), but they're most like a lever. They transfer energy around a fulcrum and provide mechanical advantage at the expense of travelling a further distance.

Can you spot any others?

Hey, if you like learning stuff you should check me out on YouTube. I'm just getting started, but you can subscribe here to see what I'm up to next!

Modern watches aren't generally wound, and therefore rely on small electromagnets and a battery - or are just all digital - instead of using this mainspring setup. Nevertheless, this worked way better on a ship than a sundial or pendulum. Also, did you know that using gravity and water could be used to propel a clock mechanism with surprising accuracy?

Thanks for reading, and thanks to Instructables for featuring this on the mainpage!