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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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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:
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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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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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Old 27 June 2017, 03:30   #11
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Quote:
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Aye not many, I would've had to buy em

Atta Boy!
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Old 27 June 2017, 13:38   #12
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Aye not many, I would've had to buy em
Get away!

Don't tell me there aren't several boxes of s/s screws in that shed...
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Old 27 June 2017, 13:56   #13
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Get away!

Don't tell me there aren't several boxes of s/s screws in that shed...


Might be
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Old 27 June 2017, 14:12   #14
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ach...just rattle them right in
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Old 27 June 2017, 15:53   #15
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Is that how they fitted your new seats
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Old 28 June 2017, 03:43   #16
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ach...just rattle them right in
At least HE missed the Trailer Bunks!
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Old 28 June 2017, 04:03   #17
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ach...just rattle them right in


Ok Paul spill the beans what was the event that resulted in that horrendous botched job?
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Old 28 June 2017, 04:15   #18
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I seen it ages ago on another forum. Btw the owner done that to both sides of the boat so it would at least sink squarely.
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Old 28 June 2017, 04:31   #19
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ach...just rattle them right in
i looked at this a few times thought it was a pi55 take the screws look massive more like coach bolts they stick in telegraph poles
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Old 29 June 2017, 13:38   #20
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At least it should keep the barnacles at bay....
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