Craig & Ian, I got a NutSert set (RivNuts in the US) a while back & was so impressed with the results in the steel frame & aly brackets that I went back & re-did every tapped hole - it took a while, but I reckon it was worth it. You get some 8mm of good clean thread in the 4mm NutSerts (as opposed to about 3mm of dodgy thread when you tap into the frame directly), so you can really tighten things down a lot. The more you tighten these, the more they clamp down, there is virtually no risk of stripping the thread, & you can R&R the bolt repeatedly. Each one took maybe 30sec to do - just whip the drill through & clamp the NutSert in.
It took me a few days to finally figure 2 big differences between direct tapping & the NutSerts
- The little flange that the NutSerts leave sitting proud of the surface. When you attached a bracket/plate/etc with a NutSert, it sits a little above the surface of the frame. Sometimes when one direct tap would have been ok, I ended up putting 2 or 3 NutSerts in, just to ensure stability of the bracket.
- Earthing : Direct taps into the frame normally provide quite good earth contacts for wiring as the bolt threads bite right into the frame. My first few NutSert earth points were a bit suspect as I had just drilled a nice neat hole through the painted surface of the frame - paint seemed to be quite a good insulator ! Once I twigged to this, I just ran the Dremell around the hole so that the NutSert flange had some bare steel to mate with & all was well. A quick touch-up with engine paint then disguised my shaky handi-work with the Dremmel !!
I tried them on the f/glass, but without much success - one problem is that they need quite a high clamping force to deform & grip, & that usually resulted in some crushing of the f/glass &/or cracking of the gel-coat. I even tried a slight countersink in the gel-coat, but found it hard to get the clamping tool to seat right (& still got some cracking).
I gave up when I discovered the HeliCoils (ReCoils) - they do the trick in the glass. They take a bit more time than self tappers, but again, I think its worth the effort. The kit has the correct size drill & tap, & it probably takes a minute to do each one (not much in the scheme of things) !
The little inserts come in depths that relate to their diameter - a "1D x 4mm" insert provides a 4mm deep 4mm thread, etc. Most of the ones I used were "0.5D" or "1D", depending on the glass thickness. The real trick (learned the hard way) is to be very sparing in the application of any epoxy into the raw threaded hole before screwing in the ReCoil - too much & it oozes through the threads & you either can't run the bolt in if its already cured, or you can never get it out later if it hasn't cured !! I ended up using a pin dipped in epoxy to only just wet the surface of the raw tapped hole in the glass & this seemed to work 99% of the time. Sealing the raw glass is the really big issue - if water gets into it, you will get rot over time & then you will be screwed (or should that be "unscrewed") !!
I am still only half way through restoring my old '71 Vette & the long-term damage done by the factory in not sealing raw glass when they screwed & rivetted things is a huge PITA - where the water has got in, I have had to grind out about an inch in diameter around the hole, re-glass it, sand back & re-drill the hole - not happy !
Hope this helps guys - I know it takes more time, but doing it once is better than doing it 2 or 3 times !!
Kind Regards,
Peter D.