Steel and Concrete EQ pier.

[marcopolo]

Making good progress with the 1930's Newtonian scope rebuild on cast iron GEM EQ mount. About 180kg for the scope+GEM mount/head. This weekend is dopping the pier in. I've got a couple of questions though one regarding alignment and two regarding the concrete pouring. I'll start with the latter.

1.The steel i'm using is heavy duty 6in x 6in square section 1/4in+ thick steel. I've got good long sections so how deep I go and how much sticks up above ground is basically how far I choose to dig. The thing i'm wondering is. If I backfill the hole AND the inside of the tube at the same time is there the chance that when the concrete level rises in the tube ABOVE ground level, will it try to overflow round the outside or can I just make the concrete viscous enoguh not to do this? My gut instinct is it will be ok if I tap down on the tube top it will ebbed a bit in hte bottom of the hole and therefore not flow out into the hole from the tube. However this leads to my next question....

2. Is it better to float the base of the steel tube ABOVE the bottom of the ground a bit say by 4-6in so you have a continuous concrete piece running inside of the tube to the dug hole? (I could float it for example with a small strap of wood). Or am I overthinking this and just throw it in and pour? If the latter the internal concrete in the tube  is pointless other than to increase overall mass (vibration dampening I suppose) as it's not pysically tied to the concrete in the dug hole.

3. I was going to alight the square tube ROUGHLY N/S with polaris by clamping a long baton of wood to one side, put my phone compass on the end away from the steel and settign to about 1.5deg E on my phone compass. Magnetic declination at my loaction is -1.05deg (W), polaris is at 0.43 Az (E). I'm not too worried as i've built about 5deg adjustment into the wedge interface anyway. but it would be nice to be close. Does this sound reasonable?

 

Thanks,

MArco.

 

[marcopolo]

All good. I threw it in all the ground, dumped some concrete in. made the steel tube plumb, aligned the tube square edge approx N/S. No mis-haps. Apart for a bird foot pattern. that was inevitable.