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My wife is building the LEGO Typewriter set (21327). When she installs the gearbox mechanism at step 210, the whole thing jams when pressing the keys.

I am trying to help her and have "unbuilt" it back a few steps and checked everything in terms of being the right way round, etc.

The problem seems to go back to step 177 when a block assembly is placed. Up until then the large section installed at step 153 was free to move around an inch or so forward. After step 177 the new block installed severely restricts that movement. It is in the correct place from what I can see!

What might be causing this problem? How can I fix it?

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  • 2
    The only thing I can think of is if the grey pieces from step 155 were set too far forward and they restrict the little arm's movements. Did you figure this out? Some photos might help
    – GammaGames
    Oct 5 '21 at 3:38
  • 1
    I have actually rebuilt it for her again and have the same issue. Looking online it looks like many with the same issue - possibly gearbox too tight but I have put it together 4 or 5 times and still the same. Looks to me like there is simply not enough weight in the wee arm to re-engage with the rotor arm to move the carriage on (too much friction). She has decided not to bother but just to complete the build for its looks rather than practicality. Thanks anyway.
    – Mike P
    Oct 13 '21 at 12:10
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Core Issue

When she installs the gearbox mechanism at step 210, the whole thing jams when pressing the keys.

The gearbox in question is this one completed in step 208:

step 208 assembly

Here it is fully installed after step 210:

step 210

The function of this assembly is to store energy in the springs at the bottom and use it to move the carriage over a small amount on each key press. This is accomplished via the 8 bladed propeller and bush at the top that are used to form an escapement. Each key press allows the propeller to rotate 1/8 of a turn, and this rotation allows a small lateral movement of the carriage.

There are several issues that could cause this to not work properly.

Complete Failure

If everything is jammed, the following behavior may be seen:

  • Keys can't be pressed
  • Keys can be pressed, but nothing happens

There are many issues that could cause this. There are two specific issues called out in the instructions as common sources of errors.

Be sure the propeller is installed the right way around in step 197:

step 197 callout

Ensure that the escapement is built in the correct orientation in step 205:

step 205 callout

Either of those issue will prevent the mechanism from working properly.

A general issue that may cause this to fail is simply building the gearbox or keys with too much friction. It is important not to install gears or bushes too tightly to prevent friction. I will typically push parts together as tight as they will go then back them off by a very small amount. There used to guidance on this in the instructions for Technic sets:

too much friction

This doesn't always matter, but in an assembly like this where there are many connections and gravity is used to provide force to make everything work correctly, it is important not to add additional friction.

Typebar not Returning

If the typebar moves when a key is pressed, but never falls back down from hitting the page, then the core gearbox is likely working properly. This is especially true if the carriage moves as expected if the typebar is returned manually.

This could be due to excess friction in the gearbox as above. Another issue that I encountered was forgetting the half bush in step 152:

step 152 half bush

This prevents the keys from fully engaging with the escapement mechanism and limits its ability to return the typebar to its original position.

It's worth noting that the springs under the carriage are able to transfer some of their force back to the keys and typebar. The typebar is most likely to work properly when the carriage is in the rightmost position, and may have difficulty returning when the carriage is all the way to the left, as the escapement mechanism will no longer be transferring any energy back through the system.


Note on Restricted Movement After Step 177

The problem seems to go back to step 177 when a block assembly is placed. Up until then the large section installed at step 153 was free to move around an inch or so forward.

I want to clarify that this is the expected behavior. The following assembly is the one installed in step 153:

153 assembly

It has a lot of play until this assembly is installed in step 177:

176 assembly

Here it is after installation:

step 177

After that point, it has probably about a centimeter of play if installed correctly.

1
  • Thank you. Step 152 bushing helped
    – Flo Bolden
    Jan 5 at 22:21

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