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Old 24 June 2017, 03:19   #1
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What size pilot holes when using screws on consoles?

Hi

Just fitted a new plotter and managed to chip off some of the gelcoat when tightening the screw.

Now I think this was caused by being too near the edge and also the pilot hole was maybe too small as I needed quite a lot of force to turn the screw.

I went small on the pilot hole as I was paranoid that if it was too big, the screw would not grip and not cut into the GRP properly.

Can anyone suggest any guidance, e.g. 6mm screw - 4mm pilot hole?

The Lowrance installation manual didn't specify a size.
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Old 24 June 2017, 03:48   #2
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What size pilot holes when using screws on consoles?

Ooh a hole drilling thread, I've haven't done one of these yet GRP is very unforgiving, for a 6mm screw I'd go 4.5-5mm pilot. Also counter sink the pilot hole just to clear the gel coat, this will stop it from spalling off.
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Old 25 June 2017, 00:58   #3
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Originally Posted by Gobuchul View Post
I went small on the pilot hole as I was paranoid that if it was too big, the screw would not grip and not cut into the GRP properly.



Can anyone suggest any guidance, e.g. 6mm screw - 4mm pilot hole?
I don't trust screws in GRP. In fact just today I replaced 4 of them with #10 t-nuts that I epoxied in so I can use real fasteners.
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Old 25 June 2017, 16:01   #4
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Seems to be a very tricky compromise between to small a hole that snaps screw or rounds it off to a hole to big that doesn't bite

By eye I make sure drill bit is no bigger than the non threaded element of the screw. If that makes sense. I don't know if it's correct but seems to work for me
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Old 25 June 2017, 17:02   #5
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Stainless screws snap like carrots best to use a steel screw to cut the thread then replace with stainless the same size
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Old 26 June 2017, 02:16   #6
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use self drilling screws and tape over the screw hole before drilling i find works well
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Old 26 June 2017, 03:09   #7
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Simple...
Unless it's absolutely unavoidable (ie retro fitting or access issues)...Don't use Screws..whatever flavour!..AT ALL!

On My Rib Craft build I used 100% Domed "Allen Key" Stainless "Nylock" Nut and bolts with washers...which are available in ALL sizes..
IMO makes for a Far superior job,ALOT stronger,better torsion control ,much less chance of cracking Gel Coat,easier to remove,..looks so much better/neater too
Just pick a the size bit (a slightly worn one is better as it won't snag in the gel coat) to suit the Bolt!
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Old 26 June 2017, 09:23   #8
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Another option might be to mount a piece of teak, perhaps even using 5200, and screw to that. Through-bolting is preferred all around but sometimes the back is inaccessible, though a strategic deck plate can assist.
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Old 26 June 2017, 13:04   #9
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Quote:
Originally Posted by Pikey Dave View Post
Ooh a hole drilling thread, I've haven't done one of these yet GRP is very unforgiving, for a 6mm screw I'd go 4.5-5mm pilot. Also counter sink the pilot hole just to clear the gel coat, this will stop it from spalling off.

Just how many "Self Tappers " Did you use Black Pig Dave!??
...Not many I bet!
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Old 26 June 2017, 17:15   #10
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Quote:
Originally Posted by Maximus View Post

Just how many "Self Tappers " Did you use Black Pig Dave!??
...Not many I bet!


Aye not many, I would've had to buy em
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