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RogerTheDodger

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Posts posted by RogerTheDodger

  1. I tried the Polar Alignment a couple of nights ago and all I can say is WOW! I was starting from no alignment at all so I had to run through a few iterations and also go back to my old QHY5 as my Starlight Express Loadstar isn't supported... but once done I did a 6 min unguided shot just fine... I've never had my PA that good before :)

  2. Considering I actually lift the mount and it's plate off after every session (it sits in the edge of a shrubbery, so I have to bring it in for weather protection)  I thought my problems were due to my pier compromise, but most of it was poor PA, even though I thought it was good, general backlash in the mount and PE.

    Having said that, I don't always get 30 min subs, but I'd take any bet that says it's my peir to blame.

  3. As I don't leave the mount out the top nuts are just finger tight. If you are building it inside an obsy then I'd use concrete instead of mortar for the top as you say... I tend to use two spanners in opposite directions if I am tightening nuts anyway.

  4. Zakalwe, is that an inch of concrete at the top of your pier into which the plat mounting bolts are set?  How far vertically down into the brickwork do your plate bolts go please or are they just set into the concrete at the top?

    There is no rebar at all on this then and it's just built directly on the concrete block below the ground?  A few more piccies of it please?

    No rebar needed. You only put rebar into concrete because concrete is flexible, and the rebar is to stop it flexing tto far and cracking, and if it does crack to limit the catastrophic failure... really not needed in something of this size.

    The top is actually standard mortar, I just built some wooden shuttering, sealed it around the top with bathroom sealant, poured in some mortar and then pressed the bolts in (the bolts were in the top disc so they were aligned).

    The disc is laser cut/drilled aluminium, I got a guy in Scotland to cut them for me.

    It's also not on a concrete block at the bottom, it's just a (very stable) paving slab... just keep it simple :)

    If you live in a heavy frost area then you would need better footing than a slab so frost doesn't move it, but this has worked down to -10 c so far without moving.

    • Like 3
  5. It seems that, in practice, brick piers are working. However, they don't 'feel' right to me without some rebar running full height down the middle. Bricks and mortar are strong in compression. If, for some reason, the mount is given a push from, say, the north then the north side of the pier will be put into tension and the south into compression. Mortar, my builder friends have always insisted, is not a glue but a bedding medium so it does not resist tension very well. The pier's resitance to tension is only as strong as its weakest brick to mortar surface.

    So, while there are successful brick piers out there, this nagging doubt remains in my mind. The whole point of rebar is that it brings strength in tension to concrete which is strong mainly in compression.

    Olly

    IMO people over complicate things, if your system is balanced then the only forces are compression, downwards through the pier, and none of our systems are heavy enough to even be noticed by the mortar. There are no torsion forces to worry about, and with any pier, you don't walk near it when an imaging run is on.

    Just remember that people happily carry a HEQ into a field and set it up on a tripod to do imaging without worrying that the legs are flexible (way more than concrete or brick/mortar) and resonate beautifully when vibrated :)

    I'm on my second brick pier, and it won't be my last :)

    • Like 4
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