Sizing guide and linear rail aligner for box section x-axis gantry beam tube

Designed for 20mm x 20mm box section tube often used for the x-axis gantry beam on corexy printers. Some tubes have relatively wide dimensional tolerances due, for example titanium tube might be 20mm +/- 0.3 mm - so anywhere from 19.7 to 20.3. Printed parts that attach to the tube (eg, at each end) might need to be designed to be a close fit. Using a printed sizing guide allows the inaccuracies of the printing process to be taken into account, and the correct size variation of the part to be selected.

The guide has nubs that will hold a 9mm or 12mm linear rail centred:

And there are centreline marking notches:

You will need to print two copies of the guide to hold a rail centred at both ends.

See this model for documentation about using as a sizing guide.

Printing

For use only as a centering tool, any precise profile will do. I suggest PLA, 0.2 layers, 0.4 nozzle, 2 or more perimeters. Larger nozzles or layers may affect the accuracy of the linear rail centering nubs, making the fit a bit tight.

If you are using this as a sizing guide for another printed part, you must use the same print settings as the other part. Print the guide, measure, then select the correctly sized part variant and print using the same material and settings on the same printer. While one sizing guide could be used to measure a small batch of tubes, the accuracy of the guide will diminish due to the printed surface being smoothed off by sliding on and off tubes. And the sized parts must be printed under the same conditions as the guide - ideally not weeks later. See this model for documentation about using as a sizing guide.