how-to make a straightedge

The biggest issue, to me, is how to adhere the silicone layer (that provides the non-slip surface) to the steel layer.

• 3M Super Weatherstrip and Gasket Adhesive — Purpose-designed for adhering weird polymers to metals. Look at ▶the reviews, they're glowing.
• Five methods of gluing silicone | Tribotec
• reddit.com/r/DIY/comments/37joje/adhesives_for_bonding_silicone_rubber/
• I see silicone primer coming up a lot in discussions about how to make a really good adhesive bond to silicone.
  • 3M Scotch-Weld Instant Adhesive Primer AC79 [details]
    • It's designed to work with a cyanoacrylate adhesive. They say it's designed to only work with their cyanoacrylate, but I bet it would work with other brands too.
    • Consider using the 3M brand cyanoacrylate though (3M PR40); the reviews say things like:
      • "This works as describe on a youtube video. I am impressed with its adhesive power on tires and inner tubes. Fixed several tractor tires."
      • "This is the stuff you need for tire repair. I did some tests first and the glue was stronger than the rubber when I pulled two pieces apart with pliers. ... I had a sidewall rip that is still together to this day thanks to this stuff."
      • "I recommend masking areas you don't want glued--it will FOREVER remain WHEREVER you put it. This is high quality glue and will work especially where contact cement/rubber cement will not work."
      • "I have been surprised at how well it works on rubber and hard plastics. ... I have butted "not lapped" together inter tube material to make large rubber band"   !
      • "Do not let it touch your skin ... Some of this spilled onto my hand and it felt like my glove was burning onto my skin. Painful but no serious burn."
    • 3M has several variants [2] — SF20 is fast-curing, CA40 is low-viscosity, PR100 is fast-curing and low-viscosity, (TODO: SF100, etc)
    • technical data sheets — PR40, CA40, PR100, SF20
    • This contains a curing-accelerator, so if you want an overall average cure time, you'll actually need to pair it with a slow-cure variant of superglue.