Very Amateur Astronomy

The intention when I built the roll off roof shed was always to install, at some point, a proper pier. I had with the help of my Dad, knocked up a temporary solution which was composed of three different parts bolted together, and  as a result was extremely unstable. Even more so with the much heavier CGEM head on it. You might hope for vibrations to vanish within five seconds, but I was having to wait for quite a while longer than that.

All of this stirred up the requirement to build something more substantial, so I started hunting around for the hardest part to find, a short length of large diameter steel tube. I found various sites offering offcuts but the price was always way more than I was willing to pay and would have pushed the total cost up to that of buying a purpose built pier.

Eventually though I located a seller on ebay with a length of 6″ outside diameter stainless steel tube, however the wall thickness was only 2mm which was a bit of a concern.  I did some research however and came across this article from which I took the basic understanding that it is the diameter of the tube rather than the thickness of the tube that influences it’s stability. Provided the tube is strong enough to take the weight the thickness of the tube is not so relevant.

I also learnt a bit more about the dynamics of a telescope pier, understanding that it works like an upside down pendulum, so the base should be strengthened as much as possible to reduce movement.

With this knowledge in hand I bought a 1m length of the stainless tube for a very reasonable price, a half meter square piece of 10mm thick mild steel plate and a length of 20mm threaded rod which in hind site made things much harder and is a bit over kill. Though saying that now  every thing is in place they do provide a rock soild hold for the mounting plate.

To work then, and I wish I had remembered to take pictures of all this but it seems to be a habit that I forget :

• Cut the plate into four 250mm square sections for the top, bottom and mounting plates. The last piece can then be further cut up for gussets for the top and bottom plates. I used an angle grinder with a 1mm thick cutting disk, easy work.
• Drill the holes for the threaded rod to mount the mounting plate to the top plate. If the holes are big you will need a drill press or a good speed controlled clutched drill. The clutch is important as it keeps the drill from breaking your wrists when the bit catches. My hobby drill press was not up to the job, but Dad’s SDS drill had no problems.
• Weld the top and bottom plates on with the gusset pieces, again thanks to Dad for the welding skills.

And basically that’s it, I had a few issues with mounting the pier to the concrete, the old threaded rods that were sunk into the base were at weird angles and I couldn’t get the pier to drop down to the floor without drilling bigger holes in the base. Unfortunately by this point I was far away from the tools I needed to do that and all my blacksmith bits were blunt.

Instead I chopped off the old rods and drilled new holes for anchor bolts, they seem to do the job nicely though they can be a bit of a pain to get working.

The pier was painted with a coat of primer I had in the garage and a mix of blue car paints which ended up giving it a nice dark shade, all back together the finished article looks like this :

I’ll be testing it this evening with any luck, and I’ll try and take some video of the vibration after go-to and knocking the tube.

This entry was posted on Thursday, March 4th, 2010 at 10:22 am and is filed under The Shed. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.