Building the pier out of solid hardwood

Hi all!

I was thinking about the possibility of building the pier out of solid wood, but I am worried about the vibrations. Has anyone any experience with this?

My idea would be to build, instead of the aluminium extrusions, a block of solid, hard wood. This wood would still be mounted onto an aluminium plate.

Thank you all in advance,

Wagner.

@nem do you have some thoughts on this?

No strong thoughts. Large chunks of hardwood can be pretty stiff. I dont know much about the relative stiffness of hardwood vs aluminum extrusions. Youd have to google that. Or build it and test it perhaps. I know hardwood does not absorb water like other types of wood but I dont know how much it warps. I know its much lower than soft wood, but if it does warp, and drift with time your polar alignment may change. Not sure how that will effect calibrations. Probably not a huge effect if it doesnt happen during a night of observing or if its small. But am not 100% certain.

What is the motivation to use hardwood? To make it look nice? you want to use material in house?

Hi Nem,

This unit will be built in Bhutan, where it is pretty tough to get some materials, but there is an abundance of wood and tools to fabricate it however we want.

Getting other materials, such as the extrusions and aluminium plates, can be quite a challenge for us, so we are looking for alternatives at the moment!

I will do some research, but if you have any other thoughts, please do let us know!

Cheers!

Understood. Well, Id do some basic research on the behavior of hard wood and probably build a pier based on it and see how it goes.
Let me know if you need more help

I was wondering about the calibration tolerance to variability in height. I was doing some basic research on which is the hardest wood in Bhutan is, and oak is the number one apparently (by density of the wood).

Its coefficient of linear expansion along the grain is 0.000054 m/(m K), a bit over twice that of aluminium.

Thinking about it, I would need a more specific list of calibration tolerances to see which mechanical properties of the wood I would need to look at.

Also, how often is the unit calibrated? Because recalibration would be able to correct for any misalignment (warping due to moisture, linear thermal expansion).

I am also looking at locally available ways to weatherproof the wood and keep it as thermally insulated as possible, so as to reduce thermal expansion and warping. Example: Thermally insulating the wood it with yoga mat type of material (some type of foam). This would also keep it protected from direct contact with snow.

These are just some initial ideas about the not so good looking pier made of wood.

Please, do let me know your thoughts.

I have started a google sheet to gather some data from the available literature on the mechanical properties of oak vs aluminium.

The question about tolerances on the pier is a little tricky to quantify. We’ve been using aluminum as extrusions can be very stiff, lightweight and pretty inexpensive. Its also used by vendors who make commercial mounts. It does expand as you point out and we never tried to intentionally minimize this as the expansion is most likely negligible and would be hard for us to observe. Note that there are many other parts that are also exposed to the out door temperature including the mount, the dove tail rail, the enclosure, and to some extent the cameras on the mounting plates. How all this moves with temperature is pretty hard to model especially as we track a field. While we track we see small motions of the star across a few pixels do to imperfect alignment and guiding errors and my guess is that thermal expansion for the current pier is absorbed in this observed motion and challenging to extract.

What I would say is that if you find wood with a thermal expansion coefficient within a factor of 2 of aluminum, its probably good enough. What I was more worried about was twist type deformations. Soft wood can deform by a lot more than thermal expansion allows so I was basically advising to make sure that the hard wood you choose does not deform significantly (based on what people say online). This would be worth testing in any regard.

Once the unit is mounted at a site, and polar aligned, if it is not moved there is no need for a re-alignment. Our other units dont drift. Again, we do see star motion from many effects so unless we see something changing with time in a particular direction, we dont re-align. If you did observe warping of the pier beyond normal limits, then yes you could polar align again if needed.

Interesting idea about water proofing. Our unit sits at MaunaLoa where the annual snow storm will dump plenty of snow and the heat from the electronics in the control box have been sufficient to keep things at a comfortable temperature. Im not sure how they would work in extreme cold for long periods. Insulation might be needed.

My suggestion is keep it simple. Id start by building the unit and getting it going. Then if needed upgrade things like adding insulation for example.

donn’t forget that some of the most expensive astro tripods are made from wood, example = https://www.berlebach.de/?bereich=produkte&kategorie=89&sprache=english
Ivo

on the picture here = https://dailybhutan.com/article/fulfilling-his-majesty-the-king-s-vision-to-develop-space-science-technology-in-bhutan it is difficult to see how you finally have built the pier.

By the way: what is the number of this Panoptes module ?

Ivo