Channel Master/Laminas 1.8m project

[archive10]

Hey CJ,

My two cents:

if you want to continue with your plans as outlined above, I would go for a "mushroom" type dig, with a central and deep (80-100 cm) hole of, say one spade-width, and then stick vertical re-bars in there (before you pour the concrete) for structural strength. You should also put a couple of horizontal ones in the plinth.
This would give you a nice platform to drill into / work on.

Something like this (pardon my bad mousing skills):



You do not need to stick any plastic liner in the whole before pouring concrete as far as I am concerned.
Not even if you are using instant concrete mix - I did my summer cottage installation in soft soil as well, and it worked out well (of course there is the pipe to give it structural strength, but still).

Channel Master 120 for 28.2E in rural southern Sweden

Depending on how thick the concrete mix is (ie. the viscosity), I might consider planing the top with a rake, measuring regularly with a plank + spirit level.

This approach would make for best re-use of the materials you have.


HOWEVER, from my own experience with 180cm dishes, and lots of deliberation, I would opt for an embedded "deep" concrete block (1m deep, 40x40 cm), with rebars and all, and then threaded bards sticking out for mounting using a king post.
This makes adjusting for plumbness much easier, as adjusting the nuts on the threaded bars can tip the kingpost in any direction.
(Mind you this is not how I ended up doing it, but I managed to not pour lots and lots of concrete).

If there was no soil-limit to the depth (base rock), I would make the hole as deep as possible (I went down to 110 cm which was the practical limit for digging by hand), and then leave the top of the concrete 20 cm lower than the general soil level. (This requires a slightly longer kingpost, so you need one custom made.)
In case of moving house, this would allow you to simply unscrew the retaining bolts, remove the kingpost, and cover the top with 20 soil. Job done.
I would also make the bottom wider than the hole (just 10-15 cm), to make the concrete stick in there like a cork...

 

[purplemarina]

if you want to keep the base to minimal thickness, i would drive some thick rebar/1m studding or metal fence spikes into the ground under the slab to prevent tilt. use wire mesh in the slab to prevent cracking you can wire this to the rebar for extra strength,do this before you pour the concrete.
i have my 1.2m play dish fixed to a 3ft concrete paving slab i drilled 4 holes and drove 4 16mm 1m studs into the ground for stability i also fixed some guide wires this was ment to be temporary that was 5 years ago hasnt budged an inch!!

 

[Captain Jack]

All very good advice chaps - much appreciated.

The 'mushroom' shape sounds like a very good idea, especially with rebar spikes in there holding it all together. The base will be peeking above ground about 20cms as well, just to give the dish a little bit of extra height. But maybe I shouldn't bother for what might be very little gain?

 

[Archive4]

I´ve done a few concrete bases her for Famaval and other dishes using standard 80mm poles to mount them on. OK they are prime focus, not offset, so have a little less wind resistance. We have had several very windy days in my patch over the last few months, in excess of 160 kph / 100 mph ( sometimes up to 200 kph ) and none of the ones I have fitted have moved.
I usually make my bases 0.8 - 1m square and 150mm deep, then bolt the foot plate down using decent raw plugs ( 12 or 14 ) and suitable bolts. Due to the base your using I can see the need for the larger width and length, but I,m sure 0.5 m deep is plenty. Also, I never bother with reed bars or deep rooted centre steels. That said, the ground here is normally much drier and " stronger " than UK soil.

 

[battenfan]

The need for Scandinavians to dig deep is that the top soil expands when it freezes and move what ever is on top of it. Half a meter is usually enough in the South where over a meter is needed in the north. If it was me I would go for 5 deep concrete legs (shaped like upside-down mushrooms, small bases at the bottom). If it is to be a large block and concrete is expensive one could just dilute it with large rocks. It's not structurally important, it just needs to be heavy.

 

[Captain Jack]

Progress... made a bed yesterday and spent most of today filling the thing. Went through loads of bags of ballast and cement, mixing it all and pouring it in. Hard work... but it's done. In end went with @st1's suggesting of digging a smaller but deeper hole in the middle with rebars.

Now have to wait a few days before I try it out.

 

[Archive4]

I thought you were putting up a dish, not an earth station!
Looks as though it will do the job though, at a push!

 

[Captain Jack]

Well, it ain't going anywhere, that's for sure!

 

[Archive-8]

Well, it ain't going anywhere, that's for sure!

Looking good :-) that's really the sort of thing I should have gone for.

It just goes to show how a little forward thinking can go a long way.

 

[Archive4]

Well, it ain't going anywhere, that's for sure!

Hope you remembered to clean the hosepipe and trigger spray head, otherwise you are in big trouble when SWMBO next tends to the garden!

 

[Lazarus]

Great work, CJ.

Looking forward to the next instalment.

 

[RimaNTSS]

This summer I am also going to make base for 1,8m dish., but my goal will be to hide this base in the ground as much as possible. Concrete block will be wider in the ground and relatively not so big on the surface. Took a picture of pedestrian bridge, that has supports I like.

 

[moonbase]

CJ,

Can I ask why you went for the NPRM option rather than something like a tripod mount?

 

[Captain Jack]

It's the only thing I had with the 4.5" pole. Came 'free' with the CM 1.8m... I do have a tripod but that only has a 3" pole.

 

[moonbase]

It's the only thing I had with the 4.5" pole. Came 'free' with the CM 1.8m... I do have a tripod but that only has a 3" pole.

A 4.5" pole NPRM is a very nice freebie.

The reason I asked is that I recently swapped out a NPRM and installed a tripod mount. With the NPRM I found it was not a simple task to get it plumb vertical and there was not much adjustment. With the tripod mount I found it a lot easier to get it plumb vertical.

 

[Captain Jack]

Yes and I am expecting the same sort of troubles with the plumbness. That said, all four corners will be on a threaded rod which I should be able to adjust without too many issues. We'll see...

 

[Archive4]

One could of course bother to level the concrete and level flash with sand and cement screed before it dries , then you have no problem. Unless your bubble's bent!

 

[Captain Jack]

I did that! Though I haven't had time to go out and check it's condition. Probably all crumbled away now...

 

[Archive4]

I did that! Probably all crumbled away now...

In that case you got your mix wrong!
But you may be lucky, none of us want to see the progress held up.

 

[Archive4]

Jokes aside, did you use any washing up liquid in the last concrete or screed mix?