CHAPTER 20 ■ COUPLER
Gluing the Coupler Together
Glue adheres best to parts that are free of dust and oil. Be sure to clean the individual tubes and the LEGO
cross axle before gluing. An ultrasonic cleaner works well, but hand cleaning in soap and water is perfectly
acceptable. Let the parts dry completely before gluing.
Coming Unglued
Until recently, I always skipped the step in directions that said, “Clean and dry parts completely.” Then, I ran
across a LEGO cross axle that would not glue.
LEGO axles are made of polypropylene thermoplastic (the same as Sandwich’s body container). Both
polypropylene and polyethylene are beloved for consumer containers due to their incredible resistance to
chemicals and leftover lasagna. That same property makes those plastics almost impossible to glue. After all,
what substance do they make glue containers out of?
Polypropylene has an inherently low surface energy. With oil, grime, and dirt coating the surface, there
are even fewer available binding locations for the glue. By thoroughly cleaning the axle of all contaminants,
the glue has additional opportunities to grab hold. For best results, immerse the axle in isopropyl alcohol
and wipe with a cotton ball.
Some special glue kits on the market contain a separate bottle of hexane, which acts as an accelerant.
Cyanoacrylate adhesive (super glue) dries extremely quickly on hexane-treated surfaces, thus locking the
glue in sharp shapes that grab at the surface, rather than allowing the glue time to pull away like water beads
on a freshly waxed car. Hexane is a last resort—a clean surface usually does the trick.
Notching the Cross Axle
Before cleaning the axle, consider using a file to cut notches into the end of the axle (see Figure 20-16). The
glue will fill these voids. When hardened, the glue in the notches will prevent the axle from being pulled out,
even if the glue didn’t adhere to the axle surface..
Figure 20-16. Notch the coupler-inserted end of the cross axle with a file. Don’t disturb the tapered end where
the wheel fits
Using Epoxy
Two-part epoxy resin works well for gluing together the entire coupler. Epoxies are thick, strong, and
appropriate for filling voids. There are a variety of epoxies available from hardware stores. Try to find one
that dries clear (see Figure 20-17).