Pier Design

[Mckechg]

Hi all,

i am designing a pier for my darker site in NE Victoria and the father in law who is a retired boiler maker will build it.

I will get an adapter plated machined by another mate.

i have looked at many designs and this is my hy-bred of them.

i intend to fill it with sand to reduce any possible oscillation

thoughts?

Grant

[troypiggo]

Off the top of my head, and without knowing what you're putting on it, I'd go with thicker top and bottom plates. Something like 10-12mm min. For the baseplate stiffeners, I'd go with 6-8mm. For the wall thickness of the post, 6mm (nominally) is probably fine. You can buy circular hollow sections (CHS) off-the-shelf, but the sizes are empirical. Close to what you've called up would be a 165x5.4 CHS (165mm diameter, 5,.4mm wall thickness).

If you're after more feedback, you'd be better off listing key equipment such as mount, largest telescope, maybe camera that you're putting on it.

What about footing? What's the ground like (clay, sand, rock, gravel, subject to frost, fill or natural?), and what type of footing are you thinking about (bored pier, pad footing)?

[glend]

Plenty of guys on the Cloudy Nights forum just pour a concrete pier - less vibration transfer and usually cheaper. You would still need an adjustable top plate/mount adaptor. A square footing with a cardboard form tube and a bit of reo is all you need to DIY. You can mix the concrete yourself in a wheelbarrow but don't use quickset post concrete, you want structural stuff. I plan on doing one of these in a few months.

[clive milne]

Grant, in the design you posted 99% of the flexure will be in the bottom flange plate. There are two easy ways to avoid this; make the flange plate as thick as you can (20mm is not too thick) and put the bolt holes in the flange as close to the webbing as you can, leaving just enough clearance for a ring spanner. The top plate should be at least 10mm.
Incidentally, there is a popular misconception with respect to the primary function of the webbing plates in a permanent pier. They are not just there to add strength but also to disrupt standing waves. If the strength of the pipe varies along its length, it will not resonate.
If it were me, I would make them no less than 400mm high.

Regards
c

[jenchris]

As noted, your top and bottom plates are very skinny. Post diameter is a little under cooked also.
I used 15mm for the plates and it feels nice and solid.
instead of going with a steel post, I went with 250mm water pipe(mains water wall thickness is about 12mm)
Filled with concrete and rebar. j bolts hold the top on, m10 adjusting bolts
base is a cube about 18 inches on to bedrock.
making a steel post is cool, but imho they ring like a bell.

[Mckechg]

all great feed back. Thank you.

I will post the incorporated points.

The earth is clay-ish and i will dig a 800mm wide by 600 deep. Concrete with the bolts in place.
I will keep the hieght (and suffer the pain) as I will be building an ob around it in the future.

G./

[Mckechg]

Updated Doc

Thanks for the feed back. I have to remember I am not imaging with the Hubble and keep it simple :-)

g./

[jenchris]

Here's a simple one I've drawn up
Base plate thickness was 20mm sorry forgot to pop that in
If anyone would like to add something I can alter and repost then we can get a decent pier design by committee.... it'll probably look like Simpson's Car.

[clive milne]

Yep, that is much better.
I would avoid the rat box all together if possible though,
if not, I would make the bolts as short as possible (there should be no more than a couple of mm of thread visible between the nuts) and use something like 5/8" or 16mm bolts if you can.

fwiw) 1 degree of Az adjustment requires 3mm of clearance in a rat box with a pcd of 200mm

[clive milne]

One more thing to keep in mind... if you employ the services of a laser cutter, don't specify hole diameters smaller than the thickness of the plate they are being cut in to.

[jenchris]

Drilled mine with a Hitachi battery drill.
Including the 3 inch one in the middle. ...
li-ion batteries and hole saws are ace.
15 mm steel plate ain't so hard

[Dealy]

I agree with Clive re plate size etc.

Just go as beefy as you can and use bigger bolts than 10mm.

Mine has 16mm steel top plates and bolts, and 20mm bottom plate and bolts.

[troypiggo]

Oh noes, the rat cage. Please no rat cages.

[jenchris]

Ok Mr Bennett no lace

[Mckechg]

Its funny how intent and time are two things that never seem to meet.

I have just started to get quotes for this pier.

I now have an ob to put it in and infact are putting two piers in.

Even though its been a couple of years I still appreciate the support guys

thx
g./