**Technic pieces not matching**

2012-12-01, 15:40 (This post was last modified: 2012-12-14, 20:43 by Travis Cobbs.)

Consider the attached model, which belongs to http://www.peeron.com/scans/8841-1

I'm having trouble building the arch thing, which appears in step 12 of the instructions.

In the main model, I have the pieces set before final rotation and translation. The yellow and green pins should match each other. Given that the height (yellow-black or green-black) is 180 units and that the desired displacement (yellow-yellow or green-green) is 50 units, the rotation angle (around the black pins) should be asin(50/180)=16.13°. When I apply that, I get the assembled arch at the back of the model, and the problem is the teeth in the angle pieces (4273a) do not interlock properly.

Of course, since there are 16 teeth in each piece, the angle should be a multiple of 360/16=22.5°. But the result when I use this angle is in the back2.ldr submodel, and as you can see there's not enough space at the top of the arch.

So, am I doing something wrong? Is some dimension not correctly modeled in the LDraw parts? Or maybe the physical model relies on some flexibility of the plastic? Things would be easier if the horizontal offset were 70 instead of 50, since asin(70/180)=22.89°, much closer to 22.5°.

I'm having trouble building the arch thing, which appears in step 12 of the instructions.

In the main model, I have the pieces set before final rotation and translation. The yellow and green pins should match each other. Given that the height (yellow-black or green-black) is 180 units and that the desired displacement (yellow-yellow or green-green) is 50 units, the rotation angle (around the black pins) should be asin(50/180)=16.13°. When I apply that, I get the assembled arch at the back of the model, and the problem is the teeth in the angle pieces (4273a) do not interlock properly.

Of course, since there are 16 teeth in each piece, the angle should be a multiple of 360/16=22.5°. But the result when I use this angle is in the back2.ldr submodel, and as you can see there's not enough space at the top of the arch.

So, am I doing something wrong? Is some dimension not correctly modeled in the LDraw parts? Or maybe the physical model relies on some flexibility of the plastic? Things would be easier if the horizontal offset were 70 instead of 50, since asin(70/180)=22.89°, much closer to 22.5°.