Are there any shallow anchor sort of things I can use for attaching interior additions to the inner liner? I'm thinking of the way drywall anchors work but I know those are too long/deep. I'd be doing things like adding strips which I could then screw into or use as supports - either temporary or permanent.
Screw anchors? For interior modifications.
- Thread starter Macboy
- Start date
I'm no expert here, but I'll chime in with my limited experience anyway. I'm assuming your interior liner is fiberglass, of ~1/16-1/8" thickness.
For low-load attachments, you can tap threads into fiberglass. @thinwater says at https://sail-delmarva.blogspot.com/2017/02/stainless-steel-bolt-specifications.html that you need 1-2 bolt diameters to get full strength of the screw. So there's no way you'll get full strength (and I'm not sure if that scales down linearly to #6 or #8 screws anyway). But for some applications, you don't need anywhere close to full strength. So in that case, you might be able to skip support strips and just screw in directly to the liner. Previously, I've mostly used sheet-metal screws, but always find it hard to select a hole size that will let the threads engage properly without undersizing and splitting out the fiberglass. So I'm switching to tapping and machine screws instead. We'll see how it goes.
For higher-load applications (e.g. battery tie-downs), I've bonded a G10 block to the hull, with threads tapped into the G10. The table linked above says G10 should be full strength at 1 bolt diameter, so 1/4" G10 ought to be pretty strong, and 1/2" nearly bombproof even if my threads aren't perfect. I found it easier to drill and tap before bonding, covering the bottom of the tapped hole with a tiny bit of masking tape to keep the epoxy out of the threads. The tape just stays in place, and (so far as I can imagine) doesn't hurt anything. Others might chime in to tell me what I'm doing wrong. And as always, your mileage may vary...
For low-load attachments, you can tap threads into fiberglass. @thinwater says at https://sail-delmarva.blogspot.com/2017/02/stainless-steel-bolt-specifications.html that you need 1-2 bolt diameters to get full strength of the screw. So there's no way you'll get full strength (and I'm not sure if that scales down linearly to #6 or #8 screws anyway). But for some applications, you don't need anywhere close to full strength. So in that case, you might be able to skip support strips and just screw in directly to the liner. Previously, I've mostly used sheet-metal screws, but always find it hard to select a hole size that will let the threads engage properly without undersizing and splitting out the fiberglass. So I'm switching to tapping and machine screws instead. We'll see how it goes.
For higher-load applications (e.g. battery tie-downs), I've bonded a G10 block to the hull, with threads tapped into the G10. The table linked above says G10 should be full strength at 1 bolt diameter, so 1/4" G10 ought to be pretty strong, and 1/2" nearly bombproof even if my threads aren't perfect. I found it easier to drill and tap before bonding, covering the bottom of the tapped hole with a tiny bit of masking tape to keep the epoxy out of the threads. The tape just stays in place, and (so far as I can imagine) doesn't hurt anything. Others might chime in to tell me what I'm doing wrong. And as always, your mileage may vary...
Depending on your specific application and material thickness, these inserts work great. I especially like them for fasteners that are frequently unscrewed because the screw hole in the material never becomes enlarged after multiple uses. They are perfect for thin materials like interior fiberglass liners.
https://www.mcmaster.com/#catalog/124/3394/=1bvbhxb
https://www.mcmaster.com/#catalog/124/3394/=1bvbhxb
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Another suggestion are well nuts:
https://www.mcmaster.com/#well-nuts/=1bvfsyz
They grip pretty good and can be removed easily. Well nuts are used for attaching items in aircraft.
https://www.mcmaster.com/#well-nuts/=1bvfsyz
They grip pretty good and can be removed easily. Well nuts are used for attaching items in aircraft.
@Macboy
EZ-Lok inserts come in stainless, available in common sizes, 1/4-20 or 10-32 and would easily fit in the liner of the Mac. Fastenal has them locally and there’re a buck something. The part # for a 1/4-20 is 400-4-cr for stainless.
When I tried to access the McMaster website from Italy, to look up a part number, access to the website was blocked. When a client in Texas tried to order from them, they would not sell the part because the company's name had the word "International" in it. McMaster is very fussy about who they support.
Back to the original question - there are some really good adhesives out there these days. There are some really good double adhesive tapes too. 3M makes one that is used in the automotive industry to hold body panels in place. It's about 1/8" thick with a foam core between the two adhesive layers. I used a 1" square of that stuff to mount the brake controller in my pickup truck back in 2001. I have yet to kick that thing loose & I have kicked it plenty of times. 3M also makes removable adhesive fastener systems. They make all kinds of really useful stuff.
I went with the rubber type well nuts. Hopefully they work. I’m sure as long as I plan the setup right it’ll be great. I think the only snag I may run into is not having enough space between the hull and the liner in my installation points. I hope not. It appears as though the well nuts require a longer fastener than a rivnut would need so a rivnut might be better suited where clearance is very marginal. They just seemed too permanent for me.
Rivnuts come in a wide variety of sizes & lengths. Getting the right length is important if you do end up using them. I have had good luck with them in the past.