Very cool.
And far more reality-minded in scale than the guys who tried to use undersized bolts, similarly epoxy-set but only maybe one foot long, to hold up the massive concrete suspended-ceiling panels in part of Boston’s Ted Williams Tunnel 20 years ago. ?Instead of anything ?Whereupon after a couple of years some of them spalled out of the roof and dropped a panel or two on a lone car passing through at 2 AM and squashed it. ? Husband survived and wife didn’t. ?Photos in the papers afterward showing big turnbuckles suspended from roof bolts half their gauge were pitiful.
Regarding the length of time to spin to get it mixed, I don’t know whether it would be 60 seconds or 120, but surely more than 1: ?in a college shop class I helped run, we had a young lady who would take a packet of 5-minute epoxy, squeeze out the two compartments’ contents onto her scrap of cardboard where she’d be mixing it, and take the popsicle stick supplied, and give the pile ONE SWIPE back and forth, as if she were stirring the cream in her coffee, and call it mixed. ?Then came to us complaining about the inferior epoxy. ?Uh, well, your coffee is thinner and keeps on swirling for a while. ?Keeping the epoxy swirling is up to you. ?These students were at MIT, too. ?I decided to write my PhD thesis about such misunderstandings in these highly-educated whippersnappers. ?(Google “So can you build one?”)
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On Wednesday, May 08, 2019 08:50:26 PM Crispin Miller?crispinmm@...?
[sunfish_sailor] wrote:
> Nice technique for a heavy-duty gluing dowel!
Just to give a different perspective, you can use a similar technique to hold?
up the roof in an underground coal mine (and probably other similar mines) --?
use a roof bolter machine to drill a 30 to 72" long hole (sometimes longer,?
iirc)(I forget the diameter maybe 1 1/2"?) and then pack the hole with?
specially prepared bags of thick epoxy (the bags have separate compartments?
for the epoxy and the hardener) then use the roof drill hydraulic pressure to?
push a "roof bolt" (which in this case is essentially a 30 to 72" long rebar?
(with the typical rebar "pebbled" surface) with a square head on the end.
Pushing the rebar into the hole breaks the bags, then use the drilling?
function to spin the rebar (again, I forget, either for 60 or 120 seconds)?
then continue to use the hydraulic pressure to hold the square head (and a?
steel plate (a 6x6" square "washer") against the roof for another 60 to 120?
seconds which allows the expoxy to at least partially cure.
(I probably should have noted that, after cutting a typical 20x20 foot section?
of coal and before installing roof bolts, you set temporary roof supports?
using timbers cut to the proper length, a wooden half header, and wooden?
wedges.)
Works a treat, holds up mountains! ;-) (Well, at least in drift mines -- in?
deep mines it holds up the earth's surface ;-)
