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I'm trying to create the 42052 (Heavy Lift Helicopter), and other Technic sets. Aligning gears' teeth is relatively difficult, and the 'Hinge Align' tool rarely works. Please help!

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Use math.

Here is a simple example... Suppose we want to line up two 8 tooth gears. Start by placing two axles and one of the gears...

unaligned

Since there are 8 teeth on the gear, we can figure out that the teeth are 360° / 8 = 45° apart. So, to put the next gear on, the space between the teeth of the second gear needs to line up with the tooth of the first gear. This space is half way between the teeth, so we need to rotate the axle 45° / 2 = 22.5° to make them line up. Select the hinge tool, then select the axle that does not have a gear yet. Notice that the hinge tool allows you to enter numeric values directly....

hinge tool

The axle is already at -180°, so we need to rotate it +/- 22.5° from there. Let's say, we want to rotate it clockwise. In mathematics, counterclockwise is positive, but apparently in LDD, clockwise is positive, so we need to add. We simply type in -180° + 22.5° = -157.5°...

hinge tool again

Now, the axle is exactly where it needs to be to add another 8 tooth gear...

gear and axle aligned

There are no collisions preventing the gear from being placed...

two gears aligned

Now, the second gear is precisely aligned, making it easy to place additional gears.

Tip: All (modern) LEGO gears come with multiples of 4 teeth, so adding a gears at right angles will line up the same as gears in a straight line.

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