LVAAS - THE LEHIGH VALLEY AMATEUR ASTRONOMICAL SOCIETY: Promoting, Facilitating and Teaching Astronomy Since 1957

Welcome to LVAAS, Anonymous
Monday, December 17 2018 @ 10:03 AM EST


Work carried out on 2/28/18 (Rich, Ron):

Temporary arrangement installed to secure south side of mount to pier (until ready to drill new hole and install new hardware).
- Old t-rod and split nuts removed - these were 5/8”, not 1/2”!
- Replaced with a piece of 1/2” t-rod and some nuts and washers, from top plate to uppermost piece of perforated angle
- Spacing set at 2.75” which is approximately correct, also just enough room for this hardware
- This perforated angle is really thin; hopefully strong enough to allow repositioning, but need to be careful)
- Additionally, for now a stack of wooden blocks and the large C clamp are also in place to secure it.

- Used a pry bar (and Ron) to list up each corner of mount on North side a bit
- Removed rollers and replaced with stack of 1/2” washers near one corner
- Cleaned out interstitial space (superficially, scraping and wiping w/ hack saw blade and rag)
- Glued up a template in there to capture the angle

Example template:
When done, some additional washers were lightly tapped in near opposite corner, and C-clamp replaced.

Idea for next steps:

Fabricate wedges to carry load while matching angle as closely as possible.
(Molded from steel-reinforced epoxy? See below)
Then build a stack using wedge, 2 sheets of 1/16” UHMW, and a film of grease between them:

Hopefully this will allow us to move the mount laterally and rotate as we need to get it aligned and positioned properly. We may want to leave it there or we may want to replace this material with something more permanent when we are where we want to be.

Testing steel-reinforced epoxy:

I molded a little brick 1/2” x 1/2” x ~1.25” out of JB Weld. The mold was just shirt cardboard lined with a plastic bag, so it came out a bit rounded.

After it cured I squeezed it in a vice, tightened as hard as I could. I believe the compression stress here was on the order of 4000 PSI or more (i.e. 1000 lbs. between vise jaws.)

The material cracked and deformed a bit, yielding maybe 1/32”.

Conclusion: even though it cracked, it did not fail catastrophically, and this is with a stress much higher than it should see in the proposed setup. Even assuming a ton on each side, and if only 1 square inch of the wedge takes all of the weight, I feel it would still be lower stress than the test by at least a factor of four.

The UHMW is probably more likely to fail, though even if it smooshes or splits a bit it might still let us do what we want. But, is there another option that we could look at? If we have to use something a little thicker (say, 1/8” fiber-reinforced UHMW such as the “High-Strength UHMW” on we might need to raise it up a fraction of an inche, which should not be a problem.

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20180304.txt · Last modified: 2018/03/04 16:38 by rhogg
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