Introduction: K'Nex Grandfather Clock


This Instructable shows how to create a working K'Nex clock from scratch. A few liberties have been taken as described below. If you are only able to rigidly follow instructions, then this is not for you; some creativity will be required because It does not cover the complete construction of the grandfather clock in the first video; rather, it covers the essential elements (the escapement, the pendulum, the gear trains, the assembly for the hands, etc) which enables that kind of clock to be built - the first video shows an implementation of the clock elements which are covered in this Instructable. The dial and case are left to the builder according to their taste. The second video shows a working cut-down version of the clock (with a shorter pendulum so that it ticks faster in the video) which this Instructable does cover. The clock in the first video ticks for just over 24 hours on a single wind. It does not have a striking mechanism. It uses two weights, one on each side of the clock. This Instructable covers only part of one side, the other being a mirror image of it, and so there is only one weight in it.

The Inspiration

The serendipitous discovery of a K'Nex yellow gear with 84 teeth was the inspiration for this clock. There are three types of K'Nex gear: the small blue captive gear has 14 teeth; the red gear has 34 teeth, and the large yellow gear normally has 82 teeth. These cannot be directly used to create the 12 to 1 ratio that a clock's minute and hour hands need, but the yellow gear with 84 teeth changed all that - a 6 to 1 ratio was now available, which was half way there! The K'Nex user Shadowman39 pointed out that it might have come from a solar set. It also appears in one of the educational sets.

The Goal

The goal was to create a K'Nex-based clock which would tick for 24 hours on a single wind. This does not mean that the clock is wound just once each day, because in practice the time of winding can vary by a few hours - that is why an old-fashioned alarm clock was referred to as a '30-hour clock'. The clock has a main wind in the morning, and a 'top-up' in the evening. The goal of 24 hours was achieved by:

* Having an escape wheel with 16 teeth instead of the K'Nex-implied eight.

* Using two weights (3kg each) instead of one so that, effectively, one heavy weight could be used which otherwise would have bent K'Nex rods. This enables a higher gear ratio than would otherwise have been possible.

* Making the clock as high as was reasonably sensible, with the weights starting at the very top of the clock and moving to the very bottom.

* Using a pulley system so that for every inch of line wound round the spool, the weight moves only a quarter of an inch.

* Making sure that the clock had a slow tick so that a single wind would last as long as possible.


The terms 'rod', 'shaft', 'axle' and 'arbor' have been used interchangeably.

The term 'plate' refers to the front or back side (normally made of brass) of the movement which has the pivot holes in it.

A traditional grandfather clock has the weights supported by gut - it is very hard-wearing, lasting up to 60 years. The clock in the videos uses braided nylon, but the current version of the clock uses very thin and very strong fishing line. It is therefore referred to as 'line' in this Instructable.

The Use of K'Nex

K'Nex is a great construction toy but the pieces are made of a fairly soft plastic. In order to build a clock which incorporates heavy weights, some non-K'Nex pieces have been used. A few screws have been used to clamp some pieces together to avoid destructive torsion in rods, and some lead weights have been used (a heavy one to drive the clock, and two light ones to balance the hands). Some pieces (not many) have been cut, and so K'Nex purists may wish to abandon this Instructable now! There is some electrical wiring in the clock in the first video, as well as a couple of micro switches and an electric bell. It is fair to say, though, that over 99.9% of the components of the clock are K'Nex.

The Design

A pendulum clock works by using a swinging pendulum to allow an escape wheel to rotate at a constant rate (the teeth of the wheel 'escape' the pallets). The escape wheel is at the end of a train of gears; at the other end is either a barrel which contains a mainspring, or a spool which is turned by a heavy weight. Whichever method is used, the escape wheel is given a rotational force which gives the pallets, and therefore the pendulum, an impulse each time it swings to the left or to the right. Use Google for more details.

The intention was to make a clock which ticked once a second, just like a real grandfather clock. The escape wheel has 16 teeth and so it needed to turn once every 32 seconds, i.e. 112½ times each hour. A red gear in mesh with a blue gear gives a ratio of 34/14, and so three of these in series will give a ratio of 343 / 143 = 14.32... This is about 1/8th of the target, and so an approximate one-second tick can be achieved with three lots of red/blue gears and a pseudo 8-1 gearing (which can be done by using 8-way connectors). The precise duration of the tick would therefore be 3600 / (343 / 143 x 8 x 32) = 0.98177 secs. This is pretty close to one second and is the best that can be achieved. In practice it sounds like a one-second tick.

Problems Encountered

The clock was built a year ago and various problems have arisen, some of them causing causing it to stop. It is problems like these - the finding and fixing of glitches - which make such a project so interesting.

* Once or twice, embarrassingly, the clock has stopped apparently for no reason only to find that it had not been wound! It is very easy to start looking for an obscure fault instead of starting with the obvious.

* During the early stages of the build the clock would stop because one of the weights had got caught on something in its path (another embarrassingly obvious cause that should have been spotted earlier).

* Attempting to turn a K'Nex gear on one end of a rod when there is a gear on the other end which drives further gears creates torsion in the rod. Over time the rod gradually becomes weaker, ultimately resulting in shredding. This is why, three months after the initial construction, two of the yellow gears had long screws passing through them (see Step 5 - The Gear Train).

* When the clock is wound, the ratchets are moving for 25 minutes. Over the course of a few months, some movement of the pieces on the rod which has the ratchet on it has taken place. In particular, the tan clip which slots into the inner part of the ratchet has tightened against it. This has not only made the winding noisy but has also made the yellow gear next to the ratchet become wobbly and not mesh with the blue gear very well. Because there is very little power reaching the escape wheel, the slightest resistance can cause the clock to stop. The ratchets need to be checked every few months and loosened if necessary. The whole gear train - from the winding spool to the escape wheel - must be very free-running.

* The word 'wind' has two connotations with this clock. it is necessary, of course, to wind the clock twice a day, but once or twice the clock has stopped because of wind, as in strong breeze! The clock was standing next to an open window and the wind blew against the pendulum, causing the clock to stop. It took a couple of weeks to find the cause because it was an external influence.

* All moving parts need to be liberally oiled in order to minimise resistance.

* The original escape wheel (as seen in the first video) was sloppier than the current one. This caused the teeth of the escape wheel to bounce briefly against the pallets, thus sapping some of the energy. The escape wheel in this Instructable is much more rigid, but because it is heavier the clock's weights had to be made slightly heavier (so maybe it wasn't worth changing the escape wheel after all - but the tick does sound healthier).

* When making the case it was difficult (here in the UK) to find enough red triangular panels. There seems to be a dearth of square panels of any colour too! Sites such as eBay are useful, and the K'Nex User Group is a very useful source, but even they have very few of the required panels. From 2010 to 2015, car boot sales were a very good source, but strangely K'Nex is hardly seen at them now.

The Steps in this Instructable

Step 1: The Escape Wheel

Step 2: The Pallets

Step 3: The Crutch

Step 4: Combining the Escape Wheel, Pallets and Crutch

Step 5: The Gear Train

Step 6: The Winding Spool

Step 7: The Pulleys and the Weights

Step 8: The Pendulum

Step 9: The Transmission to the Hands

Step 10: The Hands Assembly

Step 11: Winding the Clock

Step 12: Regulating the Clock

Step 13: Maintaining the Clock

Step 1: The Escape Wheel

The escape wheel needs to be a solid block; any flexing in the teeth will sap energy from the escapement.

When attaching the eight rotational connectors in the 8th and 9th pictures, make sure that they click into position - it is very easy for one to look in place when it isn't.

In the 10th picture, rotational connectors have been added around the outside of the escape wheel. The purpose of these is to make sure that the slots to the left are tight, so that when the 'teeth' are inserted (see the penultimate picture) there will be minimal flexing when a tooth hits a pallet.

The last picture shows that the escape wheel teeth are staggered, but it won't matter because the pallets will be three connectors deep.

Step 2: The Pallets

Like the escape wheel, there must be no flexing of the parts, otherwise some energy will be lost. By the time the weight's energy has reached the escape wheel it is very weak, but that is all that is required to give an impulse to the pendulum to maintain its swing (as long as it doesn't get depleted through unnecessary flexing somewhere).

The fourth to sixth pictures show the assembly of the pallet block. This is one of the few places where some K'Nex pieces had to be cut. The top front of the orange pallet was found to have struck the teeth of the escape wheel, only slighly and hardly noticeable, but it is better avoided. The 6th picture shows exactly where the cuts were made.

Step 3: The Crutch

The crutch is the part of the escapement which slots into the pendulum.

In the picture above, the assembly will be attached to the pallet block and the blue rod will hook into the pendulum.

Step 4: Combining the Escape Wheel, Pallets and Crutch

The first two pictures show, respectively, the front and back of the structure which will hold the escapement assembly.

The front side of the escape wheel has on its axle two silver spacers and a blue spacer. On the rear side is a tan clip gripping the escape wheel and three silver spacers.

The front side of the pallet assembly has on its axle three silver spaces, and on the rear side are two silver spacers and a blue spacer.

The pendulum will be done in Step 8.

Step 5: The Gear Train

In the first picture it can be seen that the escape wheel shaft has on it an empty section equivalent to the length of three silver spacers, a tan clip attached to a blue gear, and another tan clip attached to a blue gear; a blue spacer.

The large yellow gear shown in the 1st and 2nd pictures has a K'Nex ratchet attached to it.

The axle shown in the 3rd picture will have a lot of torsion on it between the red and yellow gears because of the heavy weight driving the red gear. The assembly has therefore had to be strengthened with four 4.5 x 60mm screws.

Part of the side of the clock has been added, but the important aspect of the next few pictures is the train of red gears which will connect with the winding spool (which will be higher up).

The last picture shows the spacers, tan connectors and red gears from the side.

Step 6: The Winding Spool

Eight yellow rods need to be slotted in to three white connectors. The first one is easy; the adjacent ones are harder. All goes well until there is one left. This is a pig, because there is no longer any flexibility in the adjacent (occupied) slots.

The best way to do it is to lay the eight yellow rods along the slots and then lay a red rod on the top of the yellow one. Now use a vice (or a pair of strong hands) to push the red rod down onto the yellow rod, thus clicking it into position.

The spool is another example of where the K'Nex pieces need to be reinforced. Two 4.5 x 60mm screws have been used, shown in the 4th picture.

A structure will need to be made to support the weight, as shown in the 5th picture.

Note that in this mock-up there is only one weight and just a single pulley on top of it. In the grandfather clock in the first video there is a more complex pulley system - see the next step.

Step 7: The Pulleys and the Weights

A pulley is normally used to gain a mechanical advantage where, say, a 1lb force can be used to lift a weight of 4lbs, but with the pulling end of the line moving four times as much as the weight end.

In a traditional grandfather clock the mechanical advantage relates to the winding: for every inch of line wound onto the spool, the weight only rises half an inch.

As depicted in the PDF above, in the clock in the first video there are two pulleys (actually, 25mm K'Nex wheels) on top of the weight and a fixed pulley at the top of the clock directly above the weight (see the 3rd image). One end of the line is fixed at the top of the clock on its side. The line then goes down to the first pulley on the weight, up to the fixed pulley, down again to the second pulley on the weight, and up to the winding spool via another fixed pulley at the top of the clock. The result is that for every inch the weight falls, four inches of line are unwound from the spool. This mean that when the weight falls the full height of 80 inches, the line unwinds 320 inches. This, combined with the fact that the escape wheel has 16 teeth rather than the obvious 8, is how the clock can tick for so long on a single wind. Another factor is that the line (which is very strong fishing line) is very thin so that there is very little overlapping on the spool (this would increase its effective circumference and thus use more line for each revolution).

In the construction in this Instructable there is just one weight with a single pulley on top of it (see the last image).

Step 8: The Pendulum

One of the advantages of a grandfather clock is its excellent timekeeping, mainly due to the long, slow-swinging pendulum.

For a one-second beat the centre of gravity of the pendulum must be around 39 inches from its top.

The first picture shows the basic design of the one for this clock. In the first video, at around 1m 33s, the full pendulum can be seen. It's a little more elaborate than the ones shown in the picture because it has a couple of wheels on it to make the tick even, and there is a regulator on it.

The fourth picture shows how the pendulum is supported, and the fifth shows the spacers required on the pendulum's arbor.

Step 9: The Transmission to the Hands

The power from the weight is transmitted to the hands via a gear train.

The first picture shows the red gear which lies directly above and is in mesh with the blue gear of the escape wheel shaft. Let's call this the transmitter.

The second picture shows a spindle which has on it a white connector with eight prongs on it. Let's call this the receiver.

As the escape wheel rotates, once in every revolution the transmitter will knock the receiver. This arrangement creates the 8 to 1 ratio that we need as part of the near-one-second beat, but it also has another very important function: when the transmitter and receiver are not in mesh (which is most of the time), there is no direct link between the escape wheel and the hands, meaning that the hands can be moved freely.

The third picture shows the red gear which is in mesh with the blue gear of the receiver assembly, and the fourth picture shows the next step in the chain. The fifth picture shows them all put together.

The sixth picture shows the view from the front and the seventh picture shows another view from the side.

The minute-hand shaft is shown in the eighth picture, the ninth picture showing a side view.

Finally, the last picture shows a view from the front.

Step 10: The Hands Assembly

It is here that the 84-tooth yellow gear comes into its own. In combination with a blue gear there is a 6 to 1 ratio, and so if it is combined with a 2 to 1 gear ratio the required 12 to 1 ratio will be achieved.

The 2 to 1 ratio has been achieved by using a pseudo-8-leaved pinion (see picture 3) in combination with a pseudo-16-tooth gear (see pictures 8 to 10)

The pinion has to be built onto the black minute-hand arbor because there are two rotational connectors inside it (see picture 3). It is shown fitted in pictures 4, 5 and 6.

Picture 7 shows the black minute-hand arbor with two blue spacers and two rotational connectors on it.

Pictures 8 to 10 show the construction of the pseudo-16-tooth gear, and picture 11 shows the minute-hand arbor which it will be fitted to.

Picture 12 prepares the assembly for the hour hand.

To fit the minute hand a tan connector is fitted to the black arbor with the prong outwards, and a black connector is pushed onto it. It is held in place by a blue clip.

In practice the two pseudo-gears work very smoothly.

It is very important that the hands are balanced. Only a little force is imparted by the escape wheel teeth, and if a hand is heavier or lighter at 9 o'clock than it is at 3 o'clock, it could cause the clock to stop. The hands' counterweights are made from lead - there is no K'Nex piece that is heavy enough to be elegant.

The penultimate picture shows a red gear with a ratchet on it. This red gear is on the end of the arbor of the 'receiver' as described earlier. It prevents the receiver from being jogged out of position as the clock ticks (which could cause a jam).

The last picture shows the clock with the hands fitted.

Step 11: Winding the Clock

In the picture, the red gear on the bottom right needs to be turned anticlockwise in order to wind the clock.

In the first video, at 2m 38s, the clock is being wound. There is a red gear at the bottom with a white connector in front of it. It is the red gear to the top left of it that is being turned anticlockwise.

The clock is wound using a 12v K'Nex motor. The shaft with the red gear / white connector on it has another red gear behind it in mesh with a blue gear. It is the shaft with the blue gear that has the motor's white gear on it (this is driven by the motor's worm gear).

The motor's worm gear must be engaged with the train of gears before winding, and then disengaged afterwards.

In the video, at 2m 5s, a lever is moved to start the winding. This turns on a micro switch and engages the worm drive at the same time.

When the weight has risen to the top, a micro switch is activated which diverts the current from the motor to a bell to give a warning that the lever is to be returned to its original position.

In the grandfather clock in the first video (but not in the mock-up in this Instructable), there is a crude power-maintaining device which keeps the clock ticking while it is being wound. It consists of a small weight (c200g) on the end of a K'Nex chain which is manually raised before the winding is started. It simply drives a large yellow gear (which is manually engaged after the weight has been raised) which is in mesh with a pinion (a blue gear) on the end of the escape wheel shaft. When the clock has been fully wound, the yellow gear is manually disengaged. See the first video at 1m 22s to 1m 32s, and see the device being activated at 1m 46s to 2m 10s.

Step 12: Regulating the Clock

A pendulum clock is regulated by raising or lowering the bob. This changes its effective centre of gravity.

The grandfather clock in the first video is regulated by placing a tyred wheel at an appropriate point (see the annotated picture).

In practice, the clock is a reasonably good timekeeper (given that it's made from plastic components!), varying by less than a minute each day when it has been regulated.

Step 13: Maintaining the Clock

The gears and axles must be liberally oiled, as must the escape wheel teeth. This should be done every few months. On no account must the K'Nex ratchet be lubricated in any way - it must be completely dry. Oiling it is a sure-fire way to gum it up and make it stop working.

The ratchets will need checking every six months or so because tightness can cause the clock to stop (see the Problems Encountered).

In the first video, the escape wheel was not strengthened like the one shown in this Instructable and had to be replaced with the new version; it caused undesirable pallet-bounce (See Problems Encountered).

It is possible that over the years other parts will show fatigue - K'Nex pieces are made from quite soft plastic.

It is also possible that there will be other occurrences of tightness, but over time (so to speak) these will be ironed out with a bit of redesign here and there. This project is by no means complete!

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