I'm thinking of sinking a cheap 4x4 wooden post into my yard to install a lightweight mount, maybe even an Alt/Az, for purely visual observation. I would only be putting a 5" mak or 4" refractor on it so no real weight. I also looked at 6x6 posts but the price shoots up.
Apart from the usual "why are you not sinking a 12" concrete pier? No such thing as over engineering" comments can anyone make an educated guess as to what the maximum loading would be? I dont really mind a good few seconds dampening but I dont want the thing moving in the ground. I'm not really planning on using concrete just backfilling and good tamping down with a sledge hammer. The post is 2.4m and i'm going to sink about half in the ground so i'm hopeful it wont be too unstable.
4x4 wooden pier
Started by
GordonCopestake
, Apr 09 2014 01:23 PM
45 replies to this topic
#1
GordonCopestake
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Posted 09 April 2014 - 01:23 PM
#2
TCW
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Posted 09 April 2014 - 01:34 PM
You really need to answer your own question. What scope/mount will you use? Any post will move around unless you use concrete. A 4x4 will flex under load but for visual might be just fine.
#3
GordonCopestake
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Posted 09 April 2014 - 01:39 PM
The largest mount for this would be an EQ5 class, I'm certainly not going to use an atlas or something. Maybe a cheap cg5. Scope wise a low moment 5" mak or fast 4" refractor. I'm thinking total weight including counterweights might be 10-15 kg.
#4
FOUNTAIN1
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Posted 09 April 2014 - 01:43 PM
Maybe Chris (Reginar) will chime in soon. He has a wooden pier, and I think is in the process of removing it. However, I believe he has a favorable opinion of one with some exceptions.
#5
GordonCopestake
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Posted 09 April 2014 - 01:56 PM
I would be interested in how difficult it is to remove as that's the reason for lack of concrete - the need for easy removal
#6
mich_al
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Posted 09 April 2014 - 02:20 PM
I've got 4 six by six pressure treated timbers bolted together. They are 10 ft above ground and 2 ft into a large block of cement. CGEM with a 30lb OTA on top. Over the past 3 years it has been twisting and I expect it will continue to. Probably 1 inch of twist so far, still fits thru the deck. That was unexpected but also unexpected was that sometimes I need to re-align the mount. Turns out the whole thing moves around a bit. Last Spring I pointed it at a marker about 200ft away and every morning I looked at where it was pointing. some days a few inches left and some a few right, some as much as 10 inches or so. Sometime a little up and down too. It wasn't really a scientific study I was just looking to see what it would do. Some days, especially after observing I'd re-center it. Point is that wood moves. If I had it to do over again I'd find a nice piece of old barn timber. It would likely move too but I'd bet less movement and zero twist/warp.
#7
roscoe
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curmudgeon
Posted 09 April 2014 - 02:22 PM
Gordon,
I'm assuming it'll be perhaps 5' tall - like an 8' piece buried 3' or so..... sounds a lot like a lot of fenceposts here on my farm.... if you rap it, it'll vibrate for a few seconds, but if not, it'll be plenty stable enough for visual work. Some lumberyards also sell 4x6 timbers, you could check the price of them. Depending on your soil composition, you could also backfill it with packed sand, which would absorb vibration better than very heavy soils.
Russ
I'm assuming it'll be perhaps 5' tall - like an 8' piece buried 3' or so..... sounds a lot like a lot of fenceposts here on my farm.... if you rap it, it'll vibrate for a few seconds, but if not, it'll be plenty stable enough for visual work. Some lumberyards also sell 4x6 timbers, you could check the price of them. Depending on your soil composition, you could also backfill it with packed sand, which would absorb vibration better than very heavy soils.
Russ
#8
TCW
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Posted 09 April 2014 - 02:22 PM
If removal is the issue could you pour the concrete a few inches below grade and then saw it off and fill over with dirt? A wood post sunk several feet below grade cannot be pulled out by hand and you would have to dig it out.
#9
GordonCopestake
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Posted 09 April 2014 - 02:49 PM
Russ,
I have seen "sleepers" that are 6x4 but they are only 1.2m locally. If I can find a 2.4m sleeper for cheap I will go for that as it sounds like it will be fine.
I have seen "sleepers" that are 6x4 but they are only 1.2m locally. If I can find a 2.4m sleeper for cheap I will go for that as it sounds like it will be fine.
#10
GordonCopestake
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Posted 09 April 2014 - 02:51 PM
TCW,
I had expected to have to dig it out when the time comes but I don't fancy breaking up concrete! I hadn't considered just sawing it off and leaving the footing, that might be an option.
I had expected to have to dig it out when the time comes but I don't fancy breaking up concrete! I hadn't considered just sawing it off and leaving the footing, that might be an option.
#11
Raginar
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Posted 10 April 2014 - 08:39 AM
I've got a 6x6 post in my shed. It's better than a tripod, but it still is pretty touchy if you're doing visual. Someone built a 4 x of 6x6 posts and bolted them together and I think that would give you the mass you need to keep it stable. Not nearly as cheap, but what's 150 bucks in lumber?
I'd say a 4x4 isn't nearly big enough and is going to flex.
Chris
I'd say a 4x4 isn't nearly big enough and is going to flex.
Chris
#12
GordonCopestake
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Posted 10 April 2014 - 09:09 AM
Chris,
Thanks for your input, it's always good to get opinions of people with hands on experience of these things.
Gordon
Thanks for your input, it's always good to get opinions of people with hands on experience of these things.
Gordon
#13
mich_al
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Posted 10 April 2014 - 09:20 AM
I've got a 6x6 post in my shed. It's better than a tripod, but it still is pretty touchy if you're doing visual. Someone built a 4 x of 6x6 posts and bolted them together and I think that would give you the mass you need to keep it stable. Not nearly as cheap, but what's 150 bucks in lumber?
Don't forget the price of the bolts. Those big ones aren't cheap.
#14
GordonCopestake
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Posted 10 April 2014 - 09:47 AM
I've found a local source for 8x4's for £25+tax so I think i'll pop around and have a chat with them
http://www.gardiners...Sleepers/New...
Should be just the ticket
http://www.gardiners...Sleepers/New...
Should be just the ticket
#15
Raginar
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Posted 10 April 2014 - 06:49 PM
I agree. I'd still get like 4 of them and bolt them together... mass is what matters 
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#16
RGM
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Posted 11 April 2014 - 07:14 AM
I built a hollow wooden pier for my G11 and Istar. I used 4 2*6 screwed together making a hollow 7*7 pier. I then cut 4 strips of 1/2" plywood 7 1/2" wide and screwed those on the outside of the pier. This completely eliminated all flex. This set up resulted in a very sturdy visual arrangement.
#17
roscoe
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Posted 11 April 2014 - 09:45 AM
I agree....a hollow box is normally stiffer than a single timber.....a timber is certainly easier to install, though.
#18
GordonCopestake
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Posted 11 April 2014 - 12:44 PM
I'm sure I read somewhere here that a piers strength is directly proportional to its diameter and not it's wall thickness or mass. I seem to remember the discussion was a steel pipe had no benefit to being filled with concrete or sand; although I could be wrong. It would support your 7" pier being solid though
#19
TCW
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Posted 11 April 2014 - 12:50 PM
Your problem is mostly that of anchoring the pier solidly to the ground. Just tamping dirt around a post will not make it solid enough for a telescope. Concrete is probably the only way but you could try buying road base (a mix of various size aggregates that compacts well) and tamping that in with a heavy tool. You will need to make the hole big enough that there are several inches free all the way around the post. I would set as deep in the ground as the above ground height.
#20
GordonCopestake
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Posted 11 April 2014 - 01:04 PM
TCW i was thinking a 50/50 split above ground /below ground with a 2.4m length post.
I was also thinking of screwing bits of 2x4 horizontally across it to give it better anchorage in the backfill.
I was also thinking of screwing bits of 2x4 horizontally across it to give it better anchorage in the backfill.
#21
TCW
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Posted 11 April 2014 - 01:33 PM
Since it is a small investment and not that much work I would go ahead and see how it works out. Good Luck!
#22
Raginar
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Posted 11 April 2014 - 01:44 PM
It's a real pain to rip out of the ground though... as I'm trying to do as we speak
#23
GordonCopestake
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Posted 11 April 2014 - 02:25 PM
Thats my worry Chris! SWMBO says it has to be removable without a trace!
#24
John Fitzgerald
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Posted 11 April 2014 - 03:42 PM
My pier is 12 inch inside heavy pvc sewer pipe sunk in the ground and filled with concrete. It's like a heavy sonotube form that does not have to be removed. Looks nice and its smooth on the outside. There is concrete below it also, but if I broke off the pvc part, the base concrete would be well below ground level.
#25
Raginar
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Posted 12 April 2014 - 07:54 AM
Gordon, I changed my mind It was pretty easy! I used this:
http://sawyerventure...-offer-expired/
At first when I posted I thought there was no way it was going to work.. but I kept at it, and after about 45 of poking that thing around it I pulled it out of the ground.
I'm pouring concrete today.
It was pretty easy! I used this:http://sawyerventure...-offer-expired/
At first when I posted I thought there was no way it was going to work.. but I kept at it, and after about 45 of poking that thing around it I pulled it out of the ground.
I'm pouring concrete today
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