Here’s the design for my hard-point for harness mounting bolts. It’s 3mm thick steel, and the channels are 2x1mm cuts. What you’re looking at is the underside. The channels and holes are to allow resin to flow through and past the hard-point. The big hole in the middle is where the 7/16 insert will go and get welded. Each channel has been tapered down at the entry point so the resin can easily flow into the part.
I’m hunting around now for prices to get them CNC’d. I need 6 per side (six point harnesses) and I’m getting a couple of spare for welding practice.
So, in feeling around the part, I’ve found a few small undercuts where I’d repaired the gel-coat with more gel-coat. I went around it with my fingers to look for issues, and found a few where the repair I’d done accidentally still went in a little, like a dimple. I’ve started using Dolphin Glaze as filler – it’s really thin and spreads well. It also comes in a squeezy tube so application is easy. I also bought a pack of onion paper for mixing on – wish I’d done it much sooner.
It’s styrene based though, but because I’m spraying in a barrier gel-coat first, I’m not concerned.
So, next is to make a 2×2 frame and apply plastic sheet to keep the dust down, and then I’m making cloth templates.