creating threads for instrument panel cover

[anon]

My instrument panel cover was broken so I have cut a new piece of acrylic. The threads for the retaining screws are shot. I was thinking of putting some filler in the holes, installing the screws and waiting for the filler to harden, creating new threads. There is very little stress on the cover and it does not need removing very often. Has anybody else tried this trick and which type of filler have you used?

[Roc]

Sophie,
Can you post a picture of the situation.

[Noah]

Are. You talking about the plexi splash guard?

[KWKloeber]

 Sophie,

You need more to cut threads than just the thickness of the flange through which CTY screwed the panel face.  If there's not much stress and it doesn't need removing often, why are the threads stripped out?

You want a positive,  fix it once and forget it, forever repair here.

If the holes are intact, get proper size/head machine screws and Nylok nuts.
Roughen up the face of the nuts (well!! to create grab) and the back of the flange.

Wax up the threads on the machine screws.

Get oversize nut spacers or other spaces so that. -- well  let me finish with the fix, and then come back to this and you'll understand...

Dab thickened epoxy onto the back of the flange and face of the nuts.

Hold the nuts in place to cure using the machine screws, with oversize nuts that fit the head of the machine screws and allow you to pull the nuts tight against the back of the flange.   The reason I say oversize nut, is you don't want any epoxy coming up through the holes and grabbing the not spacers.    There's probably other ways you could do it -- like cutting vinyl tubing spacers that the epoxy won't stick to.

The wax on the machine screw threads will allow you to back them out without the epoxy sticking it once it kicks.

If you set your excess epoxy mix aside after you tighten the nuts you can tell when it kicks. Then afterward back the machine screws out so that there's no chance of the epoxy grabbing them and holding them in place.

The reason for using nylock nuts is that you can snuggle the panel down just enough yet the machine screws will not loosen with vibration   

  Get a roll of closed cell foam or EDPM rubber (better) weatherstripping tape at your hardware or a big box store and apply that around the outside edge of your panel back or to the flange before putting it  back together. That will seal moisture out of the gauges . Don't use butyl or caulking to seal the panel.

[KWKloeber]

ahhh

Good point, Noah.  I took it that it was the panel itself (I have that precise issue so know it first hand.)

Re-reading, I see it's the acrylic.

Sophie,

That can also be fixed with thickened epoxy.  But again, it's best that you get some backing behind the screw holes.  I realize that it's tight space to get behind unless you pull the panel but trying to just fill holes from the front won't do a lot. 

I would remove the panel.

Soak foam ear plugs in epoxy resin (cut to size and dry fit to the space beforehand.)  Stuff them in behind the holes until some epoxy oozes out the holes (clean off immediately with Acetone.).  Since it's not a fine-tuned machine you're doing there,  if the foam plugs tend to work their way out you could simply hold them in place until the epoxy kicks (use fast hardener).

There's a lot of trick you can use with epoxy, ear plugs, foam in a can, etc., to create a solid backing where you need a food grip and all you have might be a thin gel coat and a void between it and the liner behind.

ken

[Stu Jackson]

KISS.  They don't need threads.  Only HOLES.  That's the way mine are/is.

[Noah]

I agree with Stu. If the holes are stripped, just fill and re-drill new pilot holes, either in the same spot or nearby. The rubber gasket idea (instead of caulking) does have merit to seat the instrument panel. It makes it less messy to remove and replace.

[KWKloeber]

I agree with Stu. If the holes are stripped, just fill and re-drill new pilot holes, either in the same spot or nearby. The rubber gasket idea (instead of caulking) does have merit to seat the instrument panel. It makes it less messy to remove and replace.

Here's the deal - I knew you'd make me write a primer on thread forming and strength of materials. 

1) of course there's threads, not "just holes."  The self-tapping screws cut threads into the edge of the fiberglass (which is what, maybe 1/16" thick?)  #8 Type A self tappers have 15 threads per inch (Type A/B are 18/inch), so you have ABOUT ONE turn of a complete thread form on each each screw.  That's not much, but enough to hold plexi when there's no stress on it. 

But it stripped out -- so......   

When the hole strips out, it has increased from the minor diameter of thread form (i..e., the thread valleys) to its major diameter (the thread peaks.)  For a #8 tapper, that difference is 0.045 inch.   That's what you need to theoretically replace to put a female "thread" back into the panel so that the male screw has bite. 

2) Slapping filler in a hole -
SO, if you slap filler in the hole, then drill it out to just smaller than the minor diameter, what you have replaced is a ring of filler that is essentially a ring (washer) that is 0.06" thick and 0.022" around the circumference inside the stripped hole.  The ONLY holding power is the 0.06" of material, grabbing the virgin material along the outside edge of the new ring. 

Will it hold?  Nah.  At least not at all like drilling into/tapping virgin fiberglass.  And just like occurs when self-tapping into the virgin fiberglass, the tension that holds the screw from loosening is created by crushing the fibers of the glass into the fiberglass around the hole.  When you do that with a thin 0.022" ring of filler, it will crack, not compress into the virgin material next to it.  A portion of the 0.022" thickness of the ring will break and then you have, what, maybe half of what you had when you first redrilled the "repaired" hole???  That's not a repair -- that's a cobb job.

The way to add back the missing strength that was removed when the hole stripped out, is to get NEW tappable material behind the original hole.  In essence, creating a "fender washer" behind the hole, and tapping into the new material.   In other words, increase the thickness of the material from the original 1/6" to 1/6"plus "X."   The "+X", isn't critical - even another 1/16" is enough.  Can you do that  precisely?  Nah.  You don't  have to be precise.  Simply overdo it -- give the male threads enough to grab/cut into.

Think about a corollary.  We wouldn't rely on the friction of the barrel of a pop rivet pressing against the wall of the material -- we want a "washer head" behind the material.  In this case it's much much less critical in terms of holding power on the panel, but the same principle applies nonetheless.

Sophie, bottom line - if you want a quick, temporary, cob job fix that may last a while, gob filler in there and redrill it to the minor diameter -- i.e., don't undersize the hole so the crushing of the fiberglass fibers keep the screws from loosening (because the repair will crack.)  Instead use a dab of silicone adhesive on the threads to hold them.  But if you want a permanent repair that won't strip out again, do it "right."  First time .... every time. 
Catalina makes the panel tray thick enough to get the boat out the door, not to last if there;s any abuse as to stripping the threads.  Use that as a guide whether more/thicker material is needed there.  If it was adequate -- it wouldn't strip out in the first place, 'eh?

PS - you can even use foxy poxy to add material.  Just minimally clean the backside -- and stuff a small gob of foxy behind each hole, redrill when cured.   

Cheers,
kk

[kh3412]

Took my panel off and expoxied small pieces of wood like a popsicle stick to the back.

[Stu Jackson]

Here's the deal - I knew you'd make me write a primer on thread forming and strength of materials. 

That's very helpful.n  IIRC, Sophie asked about the acrylic, not the fiberglass.  Good info to have though.

[anon]

Wow. I love this forum. Yes, it is the splash guard.
I was looking for a quick fix but I am now firmly persuaded to do the job properly.
I am beginning to understand that quick fixes are not good for boats and not in the lexicon of C34 owners.
Thanks everyone.

[KWKloeber]

IIRC, Sophie asked about the acrylic, not the fiberglass.

My instrument panel cover was broken so I have cut a new piece of acrylic. The threads  for the retaining screws [into the panel tray - ed] are shot. [/i]

I first mistakenly thought it was screws for the panel, not the acrylic.

[Ron Hill]

Sophie : Look in WiKi and the Mainsheet tech notes as there are a number of articles on fixing your problem.

I screwed around with a number of fixes, but the best was to fill the holes with epoxy paste and just re-drill!!

You also might look at my article Mainsheet tech note article where I made a full poly carbonate cover for the panel.  I cut round holes for "blower" , "Starter button" and the "ignition key switch".  I cut a slot for the Fuel cutoff. 
That way the entire panel is covered.  I installed rubber boot covers on the key, starter and blower switches

To further protect the panel/switches from the elements and made a sunbrella cover for when the Boat just sits!!

A few thoughts

[britinusa]

Don't laugh too much.

But how about http://www.wickes.co.uk/Wickes-Plasterboard-Plugs-7mm-Pack-25/p/510055


Paul

[Stu Jackson]

IIRC, Sophie asked about the acrylic, not the fiberglass.

My instrument panel cover was broken so I have cut a new piece of acrylic. The threads  for the retaining screws [into the panel tray - ed] are shot. [/i]

I first mistakenly thought it was screws for the panel, not the acrylic.

I went back and re-re-re-read the OP, and, dagnabbit, I believe you're right again!    Good point:  [into the panel tray - ed]

ITWMB, I'd simply fill the holes with Marine-Tex and re-drill slightly smaller than the screws and re-screw them in without the acrylic, back out the screws and and then reassemble.