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Old 08-01-2016, 10:52 AM   #1
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Fastener help

I have some blind holes in my flybridge that a rail stanchion was screwed into with ? wood screws. They were stripped, so I drilled the holes out to 1/2 inch and filled with thickened epoxy. At this point should I drill and tap for machine screws or go back to a wood type screw?
Thanks for any help.
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Old 08-01-2016, 11:00 AM   #2
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Drill and tap. Solid epoxy does not like a wood screw.
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Old 08-01-2016, 11:55 AM   #3
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Quote:
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Drill and tap. Solid epoxy does not like a wood screw.
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Old 08-01-2016, 12:58 PM   #4
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Let us (me) know how the tapping goes and what thread you use.
I have never had good luck tapping into epoxy.
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Old 08-01-2016, 02:05 PM   #5
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Has anyone tried a Helicoil insert in this type repair?
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Old 08-01-2016, 02:16 PM   #6
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Perfect . Thanks!
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Old 08-01-2016, 02:20 PM   #7
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Has anyone tried a Helicoil insert in this type repair?
That was an option I was thinking of, it's not too late if anyone has used them with success.
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Old 08-01-2016, 02:21 PM   #8
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Let us (me) know how the tapping goes and what thread you use.
I have never had good luck tapping into epoxy.
What happened?
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Old 08-01-2016, 03:15 PM   #9
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What happened?
Crumbling and crappy threads that I couldn't trust.
Yes maybe this and that was wrong with my epoxy, I don't know, but I've tapped plenty of steel, plastic, brass, etc., so it was not my drilling or tapping skills.

I just felt better using a sheet metal or wood screw.

But I am not poo pooing tapping, I just want to know how you do, if successful or not.
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Old 08-01-2016, 03:47 PM   #10
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Drilling and tapping polyester/'glass or epoxy/'glass works fine. It's hard to bet on the capacity of the connection because of the shattered resin at the interface; my Naval Architect buddy advises against it because of the betting (betting is not engineering). Gougeon's handbook touts bonding threaded fasteners into epoxy/'glass holes for structural applications; that is, they take care of the shatter with epoxy, and subsequent removal of the fastener is a matter of heating it to destroy the epoxy.

One way to improve the bet is to tap into 'glass which is much thicker than the nut would be.

Drilling and tapping thickened epoxy works fine...if the thickener is touted as structural. If the thickener is for making fairing compound, not so good.

Sheet metal screws into polyester/'glass is, of course, commonly done. Sheet metal screws into a hole in polyester/'glass, patched with epoxy/structural filler would be OK for stuff you're not betting your life on. The hole would have to be clean and you'd have to know you'd gotten a decent, complete fill. Care needs to be taken with the size of the pilot drill; screwing into shattered filler or incomplete engagement of threads is undesirable.

Wood screws, I think, would be pretty undesirable for the purpose since they're tapered and they'd tend simply to drill out the hole.

Just for fun, here's a pic of the treble end of the registers of the Italian harpsichord I built in 1972 (one jack was removed for the pic). You can see the tops of the jacks, the tops of the tongues, plectra, felt damper, and a band of polyester resin that was poured into a groove in the stock before the jacks were cut apart. The adjusting screws (#4-40) for the jack's tongues threaded into holes drilled and tapped through the Walnut jack and polyester resin.

I've drilled and tapped a fair amount of 'glass over the years, as small as the #4-40, through #8-32, #10-24, 1/4-20, 5/16-18, 3/8-16 - nothing larger, yet.
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Old 08-01-2016, 10:54 PM   #11
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Threaded ID Rivets:
These seem like something that would work, I don't know if they are available in SS or other non rusting material

Plusnuts | Rivets In Stock - Rivets & Rivet Tools
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Old 08-02-2016, 06:58 AM   #12
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When looking at the drill list to tap a hole the drill is usually selected small (for metal) so the tap will cut both the major and minor diameter of the screw hole..

For taping in epoxy a bit larger drill will eliminate the cracking and still hold just fine.

The sooner the hole is drilled in fresh cast epoxy the springier it will be , so less chance of cracking to hold the insert even better.

The larger the surface area the better the insert will hold , so if one can be screwed into a second with a larger OD , the stronger the result will be.

A cheap overkill, that may not ever need to be re visited.
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Old 08-02-2016, 07:49 AM   #13
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I would think what type epoxy (actually the thickeners/strengtheners) might be the bugger issue.

I find epoxy mixes like marine tex or JB weld good for threading or tapping but a tad bit less aggressive in bonding (usually good enough though).

If using bulk epoxy.... choosing the best filler may be critical. For tapping or threading....not sure what that is...
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Old 08-02-2016, 04:27 PM   #14
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So, just finished with mounting the stanchion. First I should point out that this is a low stress situation, where the main force is vertical, not where someone would lean or fall against it.
Stripped wood screw holes were enlarged to 1/2" with a countersink bit and about 3/4 inch deep. The core was cut away a little more with a Dremel under the skin. I filled the holes with Total Boat epoxy thickened to ketchup consistency with wood flour. (Because I had it on hand.) Set up 24 hrs, and drilled and tapped for 1/4" x20 3/4"machine screws. Bedded with butyl tape. The screws torqued down really tight ,getting a good squeeze from the tape.
So, this time tapping worked. Thanks for all the input. Might try helicoil next time.
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Old 08-09-2016, 06:11 PM   #15
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Here's a pic of some tapped polyester work. Toilet base made of fiberglass sheets reinforced underneath with a backup of more fiberglass from McMaster-Carr. Bottom is 3/8", reinforcement is 1/2". 1-1/4" - 1/4-20 stainless cap screws. Raritan Elegance toilet.
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Old 08-10-2016, 05:07 PM   #16
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I have a couple of locations where I couldn't do a proper rail stanchion rebedding. Wound up repairing the mangled glass with wood core with West system epoxy. The drilled and tapped the new holes to accept SS helicoil inserts, and used 1/4 20 bolts to fasten. At 6 months in, good. Time will tell.

Prior, did a non scientific garage test with scrap FG, installing a bolt as described above. Took a 3' wrecking bar to pull it out - brought bolt, helicoil, and some surrounding epoxy and FG with it.
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Old 08-10-2016, 05:19 PM   #17
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ID:	55121i have this upright support extending up from the transom to the underside of the swim platform. It appears that the PO merely screwed them in however found butyl tape that was around these sceew holes----but all the screws pulled out. Should I just follow the advice above, fill the holes etc and use same kind of screws or thru bold them from the top and nuts under the platform and butyl tape on both sides?
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Old 08-10-2016, 05:34 PM   #18
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Mine is homemade and I thru bolted.

Dill oversize, fill with epoxy and then drill for bolt size.

Keeps water out of the core, if not cored, then drill, baby drill!
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Old 08-10-2016, 06:02 PM   #19
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Another idea
stainless tee nuts are cheap at Ace Hardware.
Grease threads to keep them clear of epoxy.
Drill a hole, lay in the Tee nut, back fill with epoxy.

The Hillman Group 3/8 in.-16 tpi x 7/16 in. x 1 in. Stainless Steel Round Base Tee Nut (8-Pack)-4146 - The Home Depot

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Old 08-10-2016, 06:31 PM   #20
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Ok guys, I used epoxy plugs for center console mounts, drilled out so the plug slid in with wallow room filled with thickened epoxy then slid the pre fitted factory plug into the hole. Then drilled. The time then is to determine whether to tap or use sheet metal-wood screws. Seems like factory made, under controlled conditions (these are like wooden dowels) might be a way to go. Just a thought.
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