How to pack an oversize screw hole

C

ColinR

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The hinges on my Lewmar forehatch are held by 4 chunky 40mm self tappers. The holes have become oversize so some of the screws can't be tightened properly. I am wondering about the best way to fix this. I thought of drilling them out to clean and make a bit bigger, then flooding with epoxy, then when cured drilling it to take the screws. Or other method? I am not certain what I am fixing into, I think the fibreglass is backed up with marine ply. The epoxy marine filler I sometimes use is like putty so I'm not sure I could be sure of packing it right down the holes, a less viscous alternative would better. Any thoughts? Thanks, C
 
My observation is that once self-tappers start letting go - its a path to machine screws and dome nuts.

You could use Plastic Metal ... basically epoxy based but formulated to provide more stable medium to drill / tap a thread. Epoxy fillers / glues are not really designed for threaded items ... the threads themselves shatter and break away.

You could look at carpenters plugs .... fibrous plugs forced or glued into oversize holes for screws to wind into.

But again ... all you are doing usually is delaying the inevitable bolt / dome nut solution.

If you decide to go bolt / nut ... then I suggest cutting lengths of plastic or CF tube to match the depth of hole .... then epoxy fill and set tube in place. This then reduces compression of the surrounding when you tighten bolt / nuts.
 
Another - is to use expander 'sleeved nuts' .... basically a knurled metal tube that presses into the holes, the inner part of the tube has a thread to match a bolt. As you wind the bolt in - the tube expands out similar to a Rawlplug.
Careful selection to ensure not too much expansion - it can crack surrounding Gel / GRP if too much.

I have used these to hold stanchions - properly set in ... they are secure and no need to drill through.
 
Refueler said:
Another - is to use expander 'sleeved nuts' .... basically a knurled metal tube that presses into the holes, the inner part of the tube has a thread to match a bolt. As you wind the bolt in - the tube expands out similar to a Rawlplug.
Careful selection to ensure not too much expansion - it can crack surrounding Gel / GRP if too much.

I have used these to hold stanchions - properly set in ... they are secure and no need to drill through.
Click to expand...

A Rivnut is possible but as you say the possibility of cracking the GRP is high and the original fixings of self tappers is a poor fixing. The only real solution is for the hatch to be through bolted with backing washers and either plain or decorative nuts. It's both amusing and interesting to see the various bodges proposed in this and other posts when sound solutions are very simple to effect.
 
I often use matches, if its an important job I have drilled it out and glued a dowl in , but usually a few matches will hold well.
 
Fr J Hackett said:
A Rivnut is possible but as you say the possibility of cracking the GRP is high and the original fixings of self tappers is a poor fixing. The only real solution is for the hatch to be through bolted with backing washers and either plain or decorative nuts. It's both amusing and interesting to see the various bodges proposed in this and other posts when sound solutions are very simple to effect.
Click to expand...

Thaink we've all used tissue ... matches ... all sorts to try to solve .... but none are really able to do the job well. The bolt / domed nut is a permanent long life fix. Especially is the infill between GRP top and bottom is filled with epoxy to resist the pressure of nut and bolt.
 
Refueler said:
Thaink we've all used tissue ... matches ... all sorts to try to solve .... but none are really able to do the job well. The bolt / domed nut is a permanent long life fix. Especially is the infill between GRP top and bottom is filled with epoxy to resist the pressure of nut and bolt.
Click to expand...

Maybe I am an obsessive or perfectionist but I like to do jobs properly the idea of a forehatch secured with self tappers let alone matchstick plugged holes fills me with horror. As I said it's amazing the bodges that people will come up with when the solution is so easy and obvious.
 
ColinR said:
The hinges on my Lewmar forehatch are held by 4 chunky 40mm self tappers. The holes have become oversize so some of the screws can't be tightened properly. I am wondering about the best way to fix this. I thought of drilling them out to clean and make a bit bigger, then flooding with epoxy, then when cured drilling it to take the screws. Or other method? I am not certain what I am fixing into, I think the fibreglass is backed up with marine ply. The epoxy marine filler I sometimes use is like putty so I'm not sure I could be sure of packing it right down the holes, a less viscous alternative would better. Any thoughts? Thanks, C
Click to expand...

I always set self tappers into grp with some epoxy resin ( eg Araldite) adhesive , If the screws are not cleaned . or even very very lightly greased, they can always be unscrewed if necessary.

If the holes are now oversize use a filled epoxy such as JB Weld or if you have any liquid epoxy resin mix it with a little filler, choosing one which will add strength and gap filling properties, mixing to a mayonnaise consistency.

I'm not so sure about using self tappers for anything like a fore hatch though, and certainly not screwed into match sticks. or any form of wall plugs
 
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VicS said:
I always set self tappers into grp with some epoxy resin ( eg Araldite) adhesive , If the screws are not cleaned . or even very very lightly greased, they can always be unscrewed if necessary.

If the holes are now oversize use a filled epoxy such as JB Weld or if you have any liquid epoxy resin mix it with a little filler, choosing one which will add strength and gap filling properties, mixing to a mayonnaise consistency.
Click to expand...

In the application mentioned ( a critical one) you have to ask the question as to why the fixings have become lose and the holes oversize and the answer points in the direction that the method of fixing ie self tapping screws was unsuitable and to repeat it is unsatisfactory.
Self tapping screws are suitable in some circumstances but not in others and I would suggest that securing a fore hatch is not one of them, do it properly.
 
ColinR said:
I thought of drilling them out to clean and make a bit bigger, then flooding with epoxy, then when cured drilling it to take the screws
Click to expand...
When I drill out holes larger to fill with epoxy then I use the "Advanced Fastener Epoxy Bonding" method on this page. I use 404 thickener and a little WD40 on the thread, to ensure the bolt can be easily removed once it is hardened. After 24 or 48 hours I tug as hard as I can and see if it comes out - I find that one or two times in ten I need to redo the hole, but usually I can put my full weight on it. Also use wax around the hole to ensure that epoxy does not adhere to it.
 
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