How to not crack gelcoat
 

I need to put some stainless steel snaps into my gelcoat area. I thought I remembered a thread where someone gave advice on how to do so without causing any cracks in the gelcoat. Any help would be appreciated.

Make you hole as normal, then counter sink the hole, you can use the phillips screw bit on your screw gun.

I have a counter sink bit I use, but as NEM said, just cram the screw bit in the hole, spin it for a few, them put the screw in the hole. Ive run the screw backwards for a few and had it work as well

Thanks Spare and NEM. Another question. What I am doing is putting curtains made of sunbrella over the cutouts where my rodboxes were--basically making that area a storage area for skis, life vests, etc. I have lined the area with indoor outdoor carpet to protect the hull and reduce noise from vibration. About how far apart should I have the snaps?

Snaps on my top are about 8-9" apart...

and on the screw thing, they're right on the money on use of the counter-sink or phillips-head bit!!...and another thing is bit selection when drilling the hole...doesn't take much glass to get a strong bite, so size the hole you drill accordingly...I hold up a bit shank to a screw when determining hole size...showing about 1/2 the thread looking past the bit is about right...

Thanks guys. I have rod boxes from a 1991 V 20 cuddy that need some slight repairs that I might just let go after I complete this. They are not the nicest rod boxes (i.e. no teak or anything), but for someone in need who has a hull in that year range, they would work.

Nipper, sounds like a good idea to get some extra storace space. Just curious - will a kneeboard fit in there?

I've found (through a lot of trial and pain) that when drilling holes I just use whatever size drill it would be if I was going to tap the hole instead of put a screw in it.. So (for instance) a 1/4" screw gets a #7 drillbit which gives you (roughly) 75% thread in plastic, copper, brass etc. A 1/8" screw (snap thread size?) would use a #38 drillbit for that same 75% thread in plastic, brass or copper. Just use a 1" micrometer or a good set of verneer calipers to determine what the size is of the screw you are installing, then size your drillbit accordingly. You can find several charts on the internet for determining what drill to use for what size. This is a good source:

http://www.shender4.com/thread_chart.htm

Thanks, Destroyer, but I really do not have good tools, I am sorry to say, and I certainly do not have a set of calipers. When you say 75% thread, does that mean that the hole I drill should be 25% of the size of the size of the screw or does that mean the hole should be 75% of the diameter of the screw. Sorry to be an idiot on this, but, admittedly, I am.

I guess that leads me to another question. Should I have the curtain made first and then position the screws with snaps according to where they are on the curtain or vice versa. I am thinking curtain first then place the screws/snaps to fit the curtain, but I am not sure. And if I am right, I guess that leads to yet another question. How tightly should I stretch the curtain when determining where to place the screws/snaps into the sides of the liner. And now that I think of it, yet another question. Assuming the curtain is a rectangle approximately 5' long by 2 1/2', is there a particular sequence I should follow in placing the screws and snaps into the liner? For example, should I go corner to corner, then corner to corner again and fill in the snaps between the corners or some other sequence? I want to avoid "puckers" if I can!

Nipper, the only enclosure I've ever had was on a different boat and I paid someone to make and install it. They put in the snaps etc. I really cannot help you in that department.. I'd probably make it so the two corners were 2 inches apart and then sit there wondering what I did wrong. :head:

As to tools and your other questions... You can buy a nice cheap set of 4" digital calipers for $9.99 on sale at Harbor Freight.

http://www.harborfreightusa.com/usa/tabviewer/startBrowseBook.do?bookid=275&preview=&type=RET&si mple=

Just take whatever screw you're going to screw into the fiberglass and measure across the TOP of the threads to find the dia. of the screw. Then, using that measurement as a guide find what the proper tap drill size is for it. You can usually find a fractional drill that is close to a number drill. For instance, using the examples I gave previously, a 1/4-20 screw hole would use a #7 tap drill which is .201 thousands of an inch. But a 7/32 fractional drill is .218 thousands of an inch and could be used in it's place. You're only talking about .017 thousands of an inch difference and when dealing with fiberglass it's unimportant. A 1/8" hole would use a #38 tap drill which is .101 thousands of an inch, but a 7/64 fractional drill is .109 thousands of an inch. That's only .008 thousands of an inch difference. To put that into perspective, a typical human hair is only .003 thousands of an inch thick. So you can see we're not talking about a lot of slop. Use the chart I gave a link to... read across and you'll find the right size tap drill for any hole you need to put threads into. If you run into any trouble just ask me, I'll be happy to help.

75% thread just means that when you run a tap into a tap hole you drilled you will widen the hole to the point that a bolt threaded into the hole will encounter 75% threads and 25% empty air. That's a normal fit for threaded holes in metals, plastics, etc. The empty air is needed so that the bolt can screw into the metal. If there were no gap then it would bind and score and probably be destroyed. (When you use an anaerobic liquid thread locker (like Loctite 242) on a thread it fills that 25% empty air space and locks the bolt in place)

BTW, Be very careful if you're thinking about using that stuff on fiberglass. It's intended for metal to metal and can either weaken or harden plastics.