Timber pier?

raymo · #1 23-02-2016, 01:37 AM

Is there any reason why one couldn't [or shouldn't] make a pier out of
appropriately treated timber?
raymo

bojan · #2 23-02-2016, 06:58 AM

It is not mechanically stable enough (it changes the size with temperature and humidity). So, precise and permanent alignment is not possible (which is the primary reason for having a pier).
However, it is better than nothing, and with autoguiding.. it could be quite OK.

raymo · #3 23-02-2016, 01:05 PM

Thanks Bojan; I didn't realise that a solid 4x4 chunk of hardwood
would be affected to that extent.
raymo

ZeroID (Brent) · #4 23-02-2016, 02:08 PM

I seen\heard of wooden piers made by crossbolting 4 4 x 4's. The movement elements tend to cancel out and if you seal all the timber before bolting up you can minimise movement considerably. I know of one pier that is an old tree stump ! Hasn't moved in years.
Wooden tripod legs seem to be better dampeners than metal.

raymo · #5 23-02-2016, 02:41 PM

Thanks Brent; the fact that wood dampens vibration better than metal is the reason I asked in the first place.
raymo

speach (Simon) · #6 23-02-2016, 05:18 PM

Quote:

Originally Posted by raymo

Thanks Brent; the fact that wood dampens vibration better than metal is the reason I asked in the first place.
raymo

I had a 8"x8" timber pier, wouldn't recommend it. Not really stable enough and it suffered from vibration which I couldn't dampen. BTW it was down 1m into the ground.

raymo · #7 23-02-2016, 06:36 PM

Thanks for the input Simon.
raymo

doppler (Rick) · #8 23-02-2016, 07:41 PM

Quote:

Originally Posted by speach

I had a 8"x8" timber pier, wouldn't recommend it. Not really stable enough and it suffered from vibration which I couldn't dampen. BTW it was down 1m into the ground.

I am confused, that's a big lump of wood to be vibrating. Not stable enough?, did you concrete it in or just ram the dirt?

speach (Simon) · #9 24-02-2016, 09:10 AM

Quote:

Originally Posted by doppler

I am confused, that's a big lump of wood to be vibrating. Not stable enough?, did you concrete it in or just ram the dirt?

concreted it in. any vibrations that were set up in it took along time to diminish. I think if you went for a 12"x12" and braced it then it maybe OK, but the bracing would negate the point of a pier.

doppler (Rick) · #10 24-02-2016, 10:04 AM

Cheers Simon,
I guess there would be a lot of variables to consider here as well, such as the source of the vibrations. Some areas have soil types that seem to transfer vibrations readily. I was thinking of putting in a post with a rats cage on top, in the middle of the backyard as a quick set up and alignment option. My ground is hard sandy loam, very inert so I might give this a go anyway, it won't cost me anything just a bit of my time.

GeoffW1 (Geoff) · #11 24-02-2016, 10:49 AM

Quote:

Originally Posted by speach

I had a 8"x8" timber pier, wouldn't recommend it. Not really stable enough and it suffered from vibration which I couldn't dampen. BTW it was down 1m into the ground.

Hi,

Agree. I don't have a pier, or a peer, but wood is mechanically more elastic than concrete, and can transmit and hold vibrations to a greater extent than the much stiffer masonry. I've imagined a pyramidal brick pier as easy to build.

Cheers

MattT · #12 24-02-2016, 07:00 PM

Hi Raymo,
I looked into this not so long ago and decided that a wood pier was too springy, even for visual. Now I'm thinking concrete block or brick pier...something that is easy to demolish at a later date, and bolt the EQ head to that.
Matt

raymo · #13 24-02-2016, 07:17 PM

Thanks everyone, that's given me something to chew on[not literally].
raymo

DavidH · #14 25-02-2016, 08:09 AM

Hi,

I have a wooden pier in my obs. Originally made it as a temporary structure to sort out the variables of height and stability, but it has worked well, so has been temporary for about 4 years. May still replace it with a steel pier in the future, but I see PE and camera issues as more obvious causes of instability than the pier. I realign the mount after each wet season, and it remains OK for the rest of the year.

It is made of 3 pieces of 4x4 treated pine (only had 3 pieces when I built it) with 17mm ply to join them together. The top of the pier is 2 thicknesses of 17mm ply, and the base is 50mm hardwood, which is bolted to a concrete pier at the deck level of the obs. The upright timbers are braced to the base by 6mm steel brackets. The deck is isolated from the pier to avoid vibration issues.

Haven't painted or treated the timber in any way, but it is in the obs, so doesn't get wet. Humidity has been more of an issue for scopes than the mount or pier. It is probably less stable than steel or concrete, but you can easily screw into it to mount eyepiece holders, powerboards etc.

Can supply photos if you are interested.

David.

raymo · #15 25-02-2016, 11:49 AM

Thank you for your reply David. I get the idea from your detailed
description. Glad to hear of someone who has had success.
raymo

niko · #16 25-02-2016, 12:29 PM

wouldn't a piece of sonotube filled with concrete be better than timber and just as easy to install?

bojan · #17 25-02-2016, 12:30 PM

Quote:

Originally Posted by niko

wouldn't a piece of sonotube filled with concrete be better than timber and just as easy to install?

It would, IMO.

raymo · #18 25-02-2016, 01:17 PM

The sonotube sounds like the simplest way. Thank you everyone.
raymo