Monday, January 7, 2013

Snap Bushing Mania

Now that the shielded wire for the navigation/strobe wiring has arrived, wanted to see how well the snap bushings accommodated the shielded wire and the Tygon tubing for the AOA plumbing. The verdict … just fine if you never plan on replacing either the tubing or the wire.  There is just barely enough room in the snap bushings provided by Vans to accommodate everything without crushing or deforming the tubing. That said, because the tubing has a relatively “soft” outer surface it doesn’t slide across the insulation of the shielded wire easily once it is in place. I’m afraid should the tubing ever need to be replaced or another wire run, the friction would be so great, it would be very difficult.
                                   Shielded cable and Tygon tubing inside the SB 375-4 snap bushing from Heyco
                                   included in the kit. Everything fits … but it is very snug as can be seen here.

Decided to up the size of the snap bushing to a Heyco SB 437-4 which has an internal hole diameter only .020 larger. Now 20 thousands doesn’t sound like much, but it makes all the difference because now there is just enough extra room to allow the Tygon tubing to slide across the shielded wire with far less friction.
                                             Shielded cable and Tygon tubing inside a Heyco SB 437-4 snap bushing. 
                                             The small amount of extra room contributes to very little binding.

Fortunately, there is no need to change all the snap bushings only the inboard eight bushings on the left wing where there is Tygon tubing and the shielded navigation /strobe wiring running together. Unfortunately, the holes for the bushings will require being enlarged to the next size larger using the step drill bit.