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Old 13-01-2021, 13:05   #1
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Backing Plates and doublers- Aluminum or Fiberglass?

I have to get a sheet of 1/4” something to cut out backing plates and doublers for outdoor use, painted, but fully exposed. Also a couple of the cut outs will be used as backers inside the boat.

What material would you choose and why?

Here are the sheets I’m looking at. Ordering today.

Aluminum:

https://www.mcmaster.com/9246k425

Fiberglass:

https://www.mcmaster.com/8537k45
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Old 13-01-2021, 13:08   #2
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

I'd probably use fiberglass or stainless. I'd skip aluminum for outside use, as it'll be harder to keep it from looking crappy.
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Old 13-01-2021, 13:09   #3
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Definitely fiberglass. However, GPO-3 is not the right kind. It is for electrical installations and does not have the strength required for this application. G10 is the gold standard.

Edit: attached a picture of my new electric installation. The red surface is GPO-3.
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Old 13-01-2021, 13:11   #4
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Quote:
Originally Posted by s/v Jedi View Post
Definitely fiberglass. However, GPO-3 is not the right kind. It is for electrical installations and does not have the strength required for this application. G10 is the gold standard.

G10 is epoxy based though, so Chotu can't DIY the cutting and drilling on it readily. It's pretty much my material of choice for backing plates at this point though. If GPO-3 isn't adequate, then I'd tend towards stainless. Aluminum will work if thick enough, but corrosion is a bigger issue.
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Old 13-01-2021, 13:13   #5
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Quote:
Originally Posted by rslifkin View Post
G10 is epoxy based though, so Chotu can't DIY the cutting and drilling on it readily. It's pretty much my material of choice for backing plates at this point though. If GPO-3 isn't adequate, then I'd tend towards stainless. Aluminum will work if thick enough, but corrosion is a bigger issue.
G10 is heat cured under pressure... I don’t think there’s any uncured hardener and he bought fancy PPE which should protect adequately
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Old 13-01-2021, 13:13   #6
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Quote:
Originally Posted by s/v Jedi View Post
Definitely fiberglass. However, GPO-3 is not the right kind. It is for electrical installations and does not have the strength required for this application. G10 is the gold standard.

Edit: attached a picture of my new electric installation. The red surface is GPO-3.
Yes, that was a bad link. I copied the wrong one.

I fixed it with and edit.

Proper fiberglass link is there now.

Sorry for the confusion
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Old 13-01-2021, 13:14   #7
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Quote:
Originally Posted by Chotu View Post
I have to get a sheet of 1/4” something to cut out backing plates and doublers for outdoor use, painted, but fully exposed. Also a couple of the cut outs will be used as backers inside the boat.

What material would you choose and why?

Here are the sheets I’m looking at. Ordering today.

Aluminum:

https://www.mcmaster.com/9246k425

Fiberglass:

https://www.mcmaster.com/8537k45
GPO3 is fine if you need the electrical insulation properties, if not then GPO1 is much less expensive.

https://www.lbifiberglass.com/produc...lass-products/
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Old 13-01-2021, 13:20   #8
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Quote:
Originally Posted by s/v Jedi View Post
G10 is heat cured under pressure... I don’t think there’s any uncured hardener and he bought fancy PPE which should protect adequately
There’s a thing about epoxy I’ve discovered through all of this. When you machine it, even if cured for 5 years, it breaks the bonds and releases part of the polymer. Enough amines are released to give me an anaphylactic reaction.

Think kids dying from sniffing peanuts on a plane or in a cafeteria.

That’s basically where I’m at.

The dust produces from cutting this is deadly.

Cutting the deck of my boat and stuff can be done very carefully with a hepa vacuum and help.

In this case, polyester is a no brainer.

Whenever I can find someone to do my chainplates and bow tube, I’ve found a good workaround. If they do polyester as a top coat to an epoxy project, it seals it off from the atmosphere and entombs it so I can come back on the boat. Otherwise, I have to leave for 6 months, minimum.

It’s serious stuff
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Old 13-01-2021, 13:24   #9
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Quote:
Originally Posted by s/v Jedi View Post
Definitely fiberglass. However, GPO-3 is not the right kind. It is for electrical installations and does not have the strength required for this application. G10 is the gold standard.

Edit: attached a picture of my new electric installation. The red surface is GPO-3.
This looks cool for an electrical installation. That’s coming up too, so I’ll keep it in mind for that.
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Old 13-01-2021, 13:28   #10
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Fiberglass is unanimous!! I’ll use it!

Thanks!

I was leaning toward it myself but wanted to double check
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Old 13-01-2021, 13:32   #11
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Quote:
Originally Posted by Chotu View Post
Yes, that was a bad link. I copied the wrong one.

I fixed it with and edit.

Proper fiberglass link is there now.

Sorry for the confusion
No worries. G10 is 5 times as strong as FRP. This may not be a dealbreaker in every case but for me when it concerns backing plates for chainplates, cleats etc. I would find a way to use G10 or, make two backing plates with the first one bigger.
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Old 13-01-2021, 13:36   #12
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Quote:
Originally Posted by rslifkin View Post
G10 is epoxy based though, so Chotu can't DIY the cutting and drilling on it readily. It's pretty much my material of choice for backing plates at this point though. If GPO-3 isn't adequate, then I'd tend towards stainless. Aluminum will work if thick enough, but corrosion is a bigger issue.
G10 is great stuff, not sure why you can't DIY cut it. I've made all my backing plates from G10 cut out of 1ft x 1ft sheets I've ordered online. It cuts fine, you just need good sharp blades (carbide) and need to go slow and keep the heat down.
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Old 13-01-2021, 13:40   #13
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Aluminum. When you drill it you have nice big chips that when your foot finds them in the middle of the night and you finally stop screaming ...the lasting pain and bleeding will remind you to vacuum up your work area with more care.
Fiberglass. Your bed sheets feel like bedbugs. The next person using your towel will make a doll in your image and stick pins it it. Your nickname will be straight from Rocky and Bullwinkle ...Itchy Brother. Women will call the police about your hands in your pants. Children will think you’re square pants sponge bob.
Aluminum dust shows up on X-Rays. Fiberglass does not but stays around longer.
You can recycle your scraps of aluminum for a few dimes. Leftover fiberglass on fire makes a inexpensive and dramatic distress signal when added to a pail of rags doused with acetone.
My manatee crew prefer titanium purchased from the reward money they received from dropping a dime, after the Feds lock up the loonies. Helps pay their pizza and beer tab at the local yacht club bar.
Happy trails to you.
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Old 13-01-2021, 13:51   #14
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

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Originally Posted by pcmm View Post
G10 is great stuff, not sure why you can't DIY cut it. I've made all my backing plates from G10 cut out of 1ft x 1ft sheets I've ordered online. It cuts fine, you just need good sharp blades (carbide) and need to go slow and keep the heat down.
BECAUSE I CAN DIE!!
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Old 13-01-2021, 14:27   #15
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Re: Backing Plates and doublers- Aluminum or Fiberglass?

Won’t a dust mask take care of protecting your lungs?
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