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Scrapheap Challenge pier

Kaptain Klevtsov

By Kaptain Klevtsov
in DIY Astronomer

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Kaptain Klevtsov

Kaptain Klevtsov

Posted
Posted

I decided to try making a pier mount for two reasons:-

1) I am fed up with waiting for it not to get dark so I can't do a polar alignment.

2) It might help with imaging and I had some bits lying around.

With reason 1 in mind I wanted something that I can just stick the HEQ5 head on without any twiddling, we shall see if that plan is workable, so I made the socket such that the head fits on and is registered for rotation. There is adjustment between the two discs for slight alignment changes and the two rusty bits of channel can be loosened and turned for more coarse adjustment.

As the position is not fixed yet I'm leaving the coarse adjustment but it might well get welded up in the future. The three "spokes" will also get concreted over.

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The pier in all it's glory (frame made from 4" and 3" pipe offcuts)

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The adjustable top bit (M12 rod stops the top bit falling down too low and clamps two bits of 4X2" channel to the 4" pipe)

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The socket that the HEQ5 head sits in (2" pipe flange is a good fit, surprisingly enough).

You can just see the M8 bolt head that is welded in the bottom of the bolt hole in the top flange. This is a loose fit in the hole in the bottom flange allowing for fine adjustment. There are three pegs welded to the top flange to centre it. Also visible is the tapered bit that fits against the notch in the HEQ5 head spigot.

Captain Chaos

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Kaptain Klevtsov

Kaptain Klevtsov

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Gordon, the diameter is fine. The websites that you referenced refer to thinwall tubing, not pipe. Pipe is much thicker in the wall as it is designed to be pressurised. The deflections from a 5 lb side load that I read about also won't be happening and i can't think why he thought that they would. Probably he is using this test load for his sums only.

Once the pier position is finalised it will have concrete inside the pipe as well to stop it waving about in the breeze.

Captain Chaos

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GordonCopestake

GordonCopestake

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From the link i posted:

"The foregoing example illustrates why filling a wobbly pier pipe with concrete or sand doesn't fix the problem. The difference in deflection between a solid rod and a hollow rod is surprisingly small. The way to reduce the deflection is by increasing the diameter. "

I believe him heh

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Ambermile

Ambermile

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Oh true, but you also wondered about the 5lb weight used and said it's not likely to happen. Filling the pier has more to do with damping vibration rather than making it stiffer. Hence a fluid substance (sand) being a better bet.

Arthur

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GordonCopestake

GordonCopestake

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Hehehe, the best argument i've heard yet CC! Very true. I'm very interested to see how it performs. I had a wooden sleeper about 8ft long and 6"x4" that i was planning to use for a pier, again, because it was there. I have yet to get around to it though...... hence my interest in your rig.

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  • 2 weeks later...
Astroman

Astroman

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Posted

When I first installed the pier in my rolloff, I used a 6" diameter thick walled steel pipe. I covered it with another flat chunk of 1/8" plate steel with mounting bolts installed. Bolted to anchors in a concrete block 2'x2'x3'. The pier was very solid, but when bumped took over a minute to damp out very low frequency vibrations. I drilled a hole in the flat plate and filled it with ~120lbs of sand. Vibrations were reduced, but still took 30 seconds to damp. I fashioned some "flying gussets" of steel cable, tensioned with turnbuckles from the corners of the steel plate to the mounting bolts. This helped a lot, but was rather unwieldy and expensive. I ended up scrapping the dn thing in favor of the current reinforced concrete pier, attached to the same bolts in the concrete block.

My findings: The steel pier while seemingly rigid oscillates at such a low frequency to render it worthless.

My tuppence. Best of luck.

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