Montana State University method for custom feedthroughs for equipment cabling in a glovebox

Overview

The gloveboxes require custom feedthroughs for many of the cables that will connect to instruments inside the glovebox. These are created by pouring resin or epoxy into a mold surrounding the cable/connector in a KF-40 adapter fitting. We are currently using Loctite STYCAST 2850FT BLK, mixed with the hardener Loctite CATALYST 9. The molds are 3D printed pieces that hold the adapter fitting and have custom holes that are the size of the cable/connector intended to pass into the glovebox.

This process was developed by Dr. Torrey McLoughlin at Montana State University with the help of Josh Gosh at the University of Arkansas

Figure 1 - 3D printed epoxy mold pieces. On the left is the cover for the top of the KF 40 fitting to keep it free from epoxy. On the right are the pieces that clamp around the cable and form the bottom of the epoxy mold.

Directions

1. Measure the diameter of the cable/connection you will be making a feedthrough for.
2. If using a cable, measure how far into the glovebox the cable needs to go and mark that spot on the cable; this will be set into the feedthrough so leave some wiggle room.
3. CAD the appropriate mold for the correct KF-40 fitting and cable/fitting diameter. CAD files for existing files are on Fusion, in the 3D printables folder ->GB feedthrough mold. The printable includes the split clamp section that goes around the cable and forms the bottom of the epoxy mold, as well as a top cover plate that blocks the epoxy from getting on the clamping area of the KF40 fitting. For a connector, also CAD a cover for the top of the connector to stop epoxy from getting in.
4. 3D print the mold. ABS or PLA are fine (Figure 1).
5. Use sandpaper to abrade the cable (if applicable) going into the feedthrough. This will help the epoxy adhere.
6. 

   Figure 2 - KF40 fitting with cable and epoxy mold pieces clamped together on clamp stand.
   Assemble the mold around the connection, or the marked part of the cable. Use clamps and the clamp stand to hold the mold/cable assembly together and level as well as the cable out of the way so that epoxy can be poured in (Figure 2).
7. Mix the epoxy:
   1. Place a disposable cup with a disposable stir stick on the scale and zero the scale.
   2. Stycast and CAT9 are mixed in a ratio of 100:3.5 in mass, and 100:8.5 in volume. To mix 30mL of resin (an appropriate amount for one feedthrough), requires 66.420g of Stycast, and 2.325g of CAT 9.
   3. Using the stir stick add globs of Stycast until there is ~66.42g.
   4. Add drops of CAT 9 until the total mass is 68.745g (66.42g+2.325g).
   5. Stir for at least 2 minutes.
8. Pour /glob the epoxy into the mold using the wooden stir stick.
9. Let sit for 16 to 24 hours @ 25°C (or 4 to 6 hours @ 45°C, 1 to 2 hours @ 65°C).