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  • Writer's pictureWouter Horselenberg

Making your own rubber seals ( Glass scale repair )

The lathe in my workshop came with linear glass scales for digital readout of the X and Y axis. During a cleanup and maintenance round I discovered orange bits falling out of the glass scales. Uppon further inspection the whole seals of both scales where crumbling to bit leaving debris onto the glass scale itself.

After some searching online I could not easily find new seals, and if I found some it was rather unclear if they would fit as proper dimensions often missed.

So I though, how hard is it to make them myself? Might give me a good valuable experience, and I had silicon laying around that was pretending to be aged cheese.

I will explain the process below for who is interested, but the result was better then I expected:

I tried to measure the old seals, but specially the small scale was so far gone that I ended up measuring the aluminum slots where the seals should fit in and redesign it myself.

First test, seals for the small scale :

I tried the small scale first as it seemed more easy to make and I wanted to try out the silicone result before I commit to the more complicated bigger seal. The silicone I had laying around had a toughness of Shore 40A and turned out to be perfect for the seals. Maybe go a little bit more stiff, but I think you should not go softer. I also wanted to experiment a bit with coloring and ended up with good results using a tiny bit of hair dye mixed in with the silicone before pouring.

The mold was designed using Fusion 360 and then 3D printed. I thought I could get away with just an open topside because the small seal was flat on one side. But it turns out to be pretty hard to fill the mold precise enough to get the correct thickness let alone being uni-formal across the whole length. I cheated a bit by making a lid that I could press on it after I poured it. This turned out to work perfectly!

Fitting them into the glass scale (with some help of lubricant) was a pleasure as I did not expect it to work so well and gave me confidence in trying to make the big scale seals.

The big scale :

The big scale was a little more complex as it was much bigger and needed a 2 part mold as it had no flat side. Because of the length and my 3D printer bed size I needed to make it modular.

Again the mold was designed in fusion 360 and 3D printed.

The mating sides of the molds are sanded on a flat surface to remove the 3D printed top layer impurity's so the mold is closing as good as possible. I made clips to connect all the modules together until I end up with just a 2 part mold. This made it more easy to handle and to enabled me to fill up the seems with mold release wax without the parts shifting and breaking the seems again.

The molding wax I use is originally for epoxy molds, but it works well to seal seams and groves while also helping with sealing the edge when clamping the 2 sides together.

After pouring the silicon I used an electric toothbrush for vibrating out most bubbles. I had a lot of problems with bubbles everywhere in the silicone that I could not get out. I tried heating, thin stream pouring, vibrating on sanding disk, slamming on the ground. None helped really. Placing the silicon in a vacuum chamber might be the only real option in this case but I don't have one of those. I think my silicone was just to old (~2,5 years old).

Cutting the top part of while in the mold was easy to do following the 45 degree angles and using the grove I made in one side to guide the knife. This left me with a seal of perfect dimension for my application.

Cleaning every part. The inside is cleaned with some alcohol and swats and soft rags.

Reader head is also cleaned with alcohol an swats, bearings where oiled, and seals where fitted again with a bit of lube. I sanded the aluminum extrusion ends to remove dirt and old sealing. Before screwing on the end caps again I added some new silicone liquid seal.

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