Harley,
I owe you an apology. When I saw this post before I started building my T30s, I thought " naah,
I don't need to worry about that... those T-nuts that
I have will be fine, they got nasty big pointy teeth and won't slip, I know better than the bloke who has been building these things for ages!"... I think you all know what happened next!

Luckily I was only slap testing at the time, so was able to whack in a few screws and get the thing out. The 'teeth' had all bent underneath itself and it wasn't gripping on anything. I have now put in at least 2 screws per nut, and usually 3, and another layer of epoxy doesn't hurt either

Thanks for the tip Harley.
Unfortunately as this is my 2nd box, I haven't been able to add the screws on the 1st. If they do decide to let go

I am going to have to chop the box to get access.

Probably just leave the driver in there!
So to recap...
+1 on Harley's T-nut securing method, especially the screw bit and I cede to your greater building powers Mr. H!
