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Old 04-04-2016, 07:34   #1
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Novel idea for fabricating backing plates

Hi:

At least I think it is novel, as I did not see it on Maine Sail's site.

I needed exactly three backing plates for two 1 inch seacocks and a depth sounder transducer on a Tanzer 22. I routinely have peanut butter jars and similar about the shop, most of same eventually being screwed into the ceiling for hardware storage. A light went on, the lids sure look like a mold to make backing plates!

Using IIRC large peanut butter jar lids, maybe 4.5 inches in diameter. I pre-cut from my junk pile about 15 layers of matte and cloth disks just under the required diameter, and then glassed it all in the lid. When set, I scored the edges of the lid in 3 or 4 places with a hacksaw and destructively removed the lids from the molding with no adhesion noted. It came out about 1/4 to 5/16 inch thick IIRC. I installed rough side down in the boat with a layer of thickened epoxy in the usual manner.

This is probably a good idea for up to 3 or 4 units. Past that and likely making a big plate and using a big drill and (expensive!) hole saw as described by Maine Sail is probably quicker. Also bigger "molds" might be hard to find if your seacocks are larger - maybe restaurant jars?

Boulter
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Old 04-04-2016, 08:13   #2
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Re: Novel idea for fabricating backing plates

Excellent!
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Old 04-04-2016, 10:03   #3
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Re: Novel idea for fabricating backing plates

Not a bad idea, but I usually just use a hole saw and some G10 board. Doing a good quality hand layup in a small space can be hard.
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Old 04-04-2016, 10:31   #4
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Re: Novel idea for fabricating backing plates

hand layup on bench. apply finished disk to hull.easy-peasey
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Old 05-04-2016, 10:27   #5
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Re: Novel idea for fabricating backing plates

Not a new idea as I have been using it and other plastic tops for years but as you said a very good idea. Fair winds and small seas.
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Old 05-04-2016, 10:56   #6
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Re: Novel idea for fabricating backing plates

Plastic chopping boards work very well.
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Old 05-04-2016, 15:38   #7
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Re: Novel idea for fabricating backing plates

Actually the plastic chopping boards do not work well over a long time.
The polymer is not suited to continual loading and it will creep - i.e. the fitting will come loose over time.
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Old 05-04-2016, 15:57   #8
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Re: Novel idea for fabricating backing plates

G10 board and a $10 coping saw would do it quicker and arguably cheaper. Or a band saw, or other means. UHDPE or cutting board stock would also work nicely.


But you didn't vacuum bag the frp layers while you were laying them up? What kind of cheap backing board it that?


And no attempt to actually mold the backing plate to the exact curve of the hull?


We have standards to uphold in this forum, you know.(G)
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Old 05-04-2016, 16:18   #9
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Re: Novel idea for fabricating backing plates

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Originally Posted by Djarraluda View Post
Actually the plastic chopping boards do not work well over a long time.
The polymer is not suited to continual loading and it will creep - i.e. the fitting will come loose over time.
+1

If using PE you want UHMWPE which has excellent dimensional and creep resistance. Cutting boards are mostly LDPE. Not structural at all.

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Old 05-04-2016, 22:53   #10
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Re: Novel idea for fabricating backing plates

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Originally Posted by hellosailor View Post
G10 board and a $10 coping saw would do it quicker and arguably cheaper. Or a band saw, or other means.
I agree. If you already have the G10 and a means to cut it round, the material is about $2 for a 5 inch diameter 1/4 inch thick disk.

However, I found G10 so miserable to cut on a table saw with a 7 inch carbide blade, that it never occurred to me to try a hand tool to cut it round. I think a 5 inch hole saw was some dozens of dollars and required a trip to the store to acquire, so in the end I rolled my own.

Next time maybe I'll try a metal blade in the jig saw and see if the blade survives long enough to get a few pieces made. I have vague memories of once cutting something nasty and wearing down the teeth very quickly, like after a few of feet, but don't recall if it was G10 or something else.

Boulter
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Old 05-04-2016, 23:03   #11
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Re: Novel idea for fabricating backing plates

Boulter,

Try a jig saw with a fine metal carbide blade. If you have a bandsaw any fine tooth blade works great, but non-carbide ones will dull quickly.
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Old 09-04-2016, 08:31   #12
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Re: Novel idea for fabricating backing plates

Quote:
Originally Posted by Boulter View Post
I agree. If you already have the G10 and a means to cut it round, the material is about $2 for a 5 inch diameter 1/4 inch thick disk.

However, I found G10 so miserable to cut on a table saw with a 7 inch carbide blade, that it never occurred to me to try a hand tool to cut it round. I think a 5 inch hole saw was some dozens of dollars and required a trip to the store to acquire, so in the end I rolled my own.

Next time maybe I'll try a metal blade in the jig saw and see if the blade survives long enough to get a few pieces made. I have vague memories of once cutting something nasty and wearing down the teeth very quickly, like after a few of feet, but don't recall if it was G10 or something else.

Boulter


Use carbide abrasive saw blades for cutting glass.
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Old 09-04-2016, 09:15   #13
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Re: Novel idea for fabricating backing plates

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Originally Posted by minaret View Post
Use carbide abrasive saw blades for cutting glass.
Can anyone shed light on how a diamond bladed holesaw and circular saw will fare when used to cut G10 ?

And to cut normal fibreglass?
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Old 09-04-2016, 10:44   #14
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Re: Novel idea for fabricating backing plates

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Originally Posted by Marqus View Post
Can anyone shed light on how a diamond bladed holesaw and circular saw will fare when used to cut G10 ?

And to cut normal fibreglass?
I would think it would cut far better, but unless you are running a production shop the cost probably isn't worth it over standard carbide. G10 is very abrasive which is exactly where diamond blades shine, but their cost is obviously far higher.
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Old 09-04-2016, 11:22   #15
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Re: Novel idea for fabricating backing plates

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Originally Posted by Marqus View Post
Can anyone shed light on how a diamond bladed holesaw and circular saw will fare when used to cut G10 ?

And to cut normal fibreglass?


Diamond blades are much cheaper and easier to find than carbide abrasives, but don't cut near as well. A diamond blade in a circ saw or table saw will leave burn marks and potential delam on your G10, if it's thick enough. A carbide abrasive will not. In both cases feed rate is important. I wouldn't use a non abrasive blade in G10 over about 1/4", personally. They do make a buttload of dust though, suit up!
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