[jarcher]

I recently 3D printed some plastic fittings of PETG which I adhered to my carbon mast using 4200. The purpose was to use some self tapping screws to mount an instrument bracket. After a few weeks, the 4200 these fittings came loose, and it's clear the 4200 just let go of the carbon mast.

Is it that 4200 won't adhere to carbon or did I not prepare the surface correctly? I cleaned it with soap and water and made sure it was dry. If 4200 won't work, what can I use? I was hoping for something not permanent but if necessary I can go that route.

I realize the best way to handle this is with a backing plate inside the mast, but I don't want to pull the mast right now.

Thanks...

 

[boatpoker]

Did you sand the gloss off the carbon ?

 

[jarcher]

Did you sand the gloss off the carbon ?

Hm, no...

 

[cb32863]

4200 isn't very strong, its more sealant then adhesive. Did you mean to use 5200? But then, that's pretty permanent.

 

[deniseO30]

Virtually nothing will glue, stick, or Bond to polyethylene which petg seems to be

 

[RichF28]

I put a cleat on a 2" x 5" or so base onto a carbon fiber mast with 3M VHB double back tape. I use it for my lazy jacks, so the only pressure on it is straight down. I doubt anything will hold if the pull is at an angle to the mast...

 

[jarcher]

I didn't use 5200 because I didn't want something so permanent, but I'm not sure 5200 will stick either. It's looking like I'll have to pull the stick and add a proper backing plate.

 

[colemj]

Just to be clear, it stuck to the polyethylene, but not the mast? My experience with 4200 is that it is a decent adhesive, so I'd have to go with something on the surface/coating of the mast causing release or a bad tube of 4200. I doubt it has anything to do with the mast being carbon in general, since the carbon isn't exposed to the adhesive. Is the mast painted or gelcoat? Has it been waxed in the past?

I've been using a lot of Loctite PL construction adhesive over the past couple of years to mount stuff like you are doing. Cheap and available in the hardware store. While it is technically a permanent adhesive, I've found I can release parts by carefully inserting a chisel on the adhesive bond line and giving it a rap. Or if it is a mounting block, just hitting it hard from the side can release it. It does leave cured adhesive behind, but this can be chipped off carefully. Really - I've mounted a lot of stuff, some of it pretty heavy, on vertical surfaces and it has never failed.

Mark

 

[deniseO30]

Marine grade toggle bolts might be the answer if internal halyards don't get caught on them.

 

[jarcher]

Just to be clear, it stuck to the polyethylene, but not the mast?

Correct. The mast is not painted, I have no idea if it was waxed. I may just try helicoils. I had not used them in the past because I can't find them in stainless.

 

[colemj]

Correct. The mast is not painted, I have no idea if it was waxed. I may just try helicoils. I had not used them in the past because I can't find them in stainless.

The mast isn't painted? Just exposed carbon? No UV problem with that, but a black mast. Stainless helicoils are very common, so you shouldn't have any issue finding them. Stainless and carbon are not compatible, so you would want to ensure isolation between the two.

Mark

 

[boatpoker]

Hm, no...

I guarantee you there is some type of gloss UV protection (usually Clear Coat) on that mast otherwise the epoxy would be severly UV degraded.
Not much is going to stick unless you abrade that coating.

 

[jarcher]

I guarantee you there is some type of gloss UV protection (usually Clear Coat) on that mast otherwise the epoxy would be severly UV degraded.
Not much is going to stick unless you abrade that coating.

Yeah I'm learning that there is some kind of clear coat on it. I'm reluctant to sand it but I guess I have to.

 

[jarcher]

... Stainless helicoils are very common, so you shouldn't have any issue finding them. Stainless and carbon are not compatible, so you would want to ensure isolation between the two.

Mark, can you help me locate some stainless helicoils? I'm not having much luck finding any. I would use Loctight when inserting them into the carbon mast.

 

[colemj]

Mark, can you help me locate some stainless helicoils? I'm not having much luck finding any. I would use Loctight when inserting them into the carbon mast.

Just google stainless helicoil and they are everywhere - Mcmaster Carr, Amazon, ebay. My local Ace carries them.

I still would caution on the stainless/carbon thing. At a minimum I'd probably drill the hole as large as possible to have minimal thread cut then set the helicoil in epoxy. When you drill, you will be exposing raw carbon fibers that will contact the stainless - I'd be concerned that loctite won't be enough isolation.

Also, are you sure your wall thickness is enough for a coil insert? Installing a stainless rivnut bedded in epoxy might be a better solution.

Mark

 

[jarcher]

Just google stainless helicoil and they are everywhere - Mcmaster Carr, Amazon, ebay. My local Ace carries them.

I still would caution on the stainless/carbon thing. At a minimum I'd probably drill the hole as large as possible to have minimal thread cut then set the helicoil in epoxy. When you drill, you will be exposing raw carbon fibers that will contact the stainless - I'd be concerned that loctite won't be enough isolation.

Also, are you sure your wall thickness is enough for a coil insert? Installing a stainless rivnut bedded in epoxy might be a better solution.

Mark

Thanks Mark, I'll do some googling to find some. No, I'm not sure the mast is thick enough for a helicoil, which is why I have been reluctant to try it.

I have a rivnut set, but have not had good luck with those. They seem to turn once installed. I had not thought to bed it in epoxy. I'll think about that thanks. My current plan is to use some starboard with a threaded insert as a backing plate. I can lift the mast a few feet using the hoist at my yacht club. But, I'll think about the rivnuts; less weight is always a good thing.