Major rethink ...

[Demonperformer]

But it depends on how much you are going to need.  According to my calcs, 10 bags of each (sand and aggregate) will be more than enough and will total £29.80.  The jumbo bag is £38.24.  Fine if you are going to need it, but spending an extra £10 to get even more left over doesn't strike me as being very cost-effective .

[yesyes]

True that.

If you don't need a whole bulk bag, there's no point buying one, even if you could.

I used 100 bags of ballast (pre-mixed sand and aggregate) for the obsy foundations and the path I build leading up to the obsy. So it would have been well worth it for me.

[Gina]

I used a little bit more than one bulk bag on my construction and oredered two but with other jobs about the place there isn't that much left over   I thought some weighty foundation blocks were a good idea in this windy location so the obsy stands on six blocks of about 18" cube to which it is screwed down.

[dmahon]

I'd just buy bags of all in ballast and use 1:4 Mastercrete/ballast - by volume, not by weight. I reckon you'll need 4-5 bags of Mastercrete and about 700kg of ballast for your 1/3rd cubic metre.

[Demonperformer]

OK, quick recalc:

volume = 0.36205 yd3

4/5 ballast = 0.28964 yd3 = 0.22145 m3
1/5 mastercrete = .07241 yd3 = 0.05536 m3

ballast:
http://www.wickes.co.uk/invt/220111

1 bag = 0.35m2 x 50mm = 0.0175 m3
13 bags = 0.2275 m3 > 0.22145
If 10+ bags = all at £1.41 each = £18.33
If it is £1.41 for each of 10 bags and so the extra 3 are at £1.84 = £19.62

mastercrete:
http://www.wickes.co.uk/invt/154100
http://www.wickes.co.uk/invt/220023

assuming this is the same 94lb/ft3 as listed above:

0.07241 yd3 = 1.95507 ft3 = 184lb (rounded up) = 82kg

=3* 25kg + 1* 10kg (85kg)
=3* £6.28 = £18.84
+1* £4.19 = £ 4.19 = £23.03    
total = £23.03 + £18.33 = £41.36
or £23.03 + £19.62 = £42.65

In this case, an additional 15kg mastercrete is only an additional £2.09 and as I will also have the posts to the decking to concrete in, it would probably be worth the extra at this point - depending on how "resealable" it actually is in practice.

Going to have to work out the figures for those posts now, I suppose!


 

[Paul M]

If I couldn't get ready mixed delivered because of access I'd buy in a few bags of this: http://www.diy.com/nav/build/building-materials/aggregates-cement/cement/Lafarge-Quick-Set-Concrete-Large-11867930?skuId=12378638

Probably not the cheapest source of materials but a low fuss route!

And just to put the tyrannosaurs amongst the pterodactyls, I'd pour it in dry     

My back just won't take mixing concrete by hand. Maybe a small amount with a mixer but not much.

I've done it this way a number of times. My caravan decking is on posts fixed in dry laid concrete. Our big heavy back gate hangs off a 4x4 post that I fixed with dry mix concrete.

You can gently water it from above or if you are real daring and have damp condition and time, leave it to absorb moisture from the ground. I'm told concrete is very strong when done like that.

You just need to make sure it's compacted in nice and tight.

[dmahon]

 

OK, quick recalc:

 

volume = 0.36205 yd3

4/5 ballast = 0.28964 yd3 = 0.22145 m3

1/5 mastercrete = .07241 yd3 = 0.05536 m3

 

Unfortunately it's not that easy. Be aware that X volume of ballast and Y volume of cement does not make X+Y volume of concrete (it actually makes less than X)!

 

http://www.concrete.org.uk/fingertips_nuggets.asp?cmd=display&id=440

 

(1m3 of ballast weights about 1,700Kg, because you'll buy it by weight not volume)

[Demonperformer]

Thanks for the input.

@Paul - yes, it looks simpler, but it says that 1 bag makes 17"x17"x2" = 578 in3, which is 0.01239 yd3.  This means I would need 30 bags to make up my 0.36205 yd3, which is just over £200 - quite a difference.  Would have to give that quite a lot of thought!

@dmahon - thanks for that link.  Presumably I would want to use the 'B' options for the pillar to make it as solid as possible.  Will do a few more calculations based on those figures.

Thanks

[Demonperformer]

Right, B2 calculations:

0.27681 m3

1 m3 =

14 bags of cement

1.3 m3 ballast

0.27681 m3 (rounded up) =

<4 bags of cement

0.36 m3 ballast

1 bag ballast = 0.0175 m3

0.36 m3 < 21 bags

4 bags cement @ £6.28 = £25.12

21 bags ballast @ £1.41 = £29.61

mixer from post #44 £28.46

Total cost: £83.19

[Paul M]

Thanks for the input.

@Paul - yes, it looks simpler, but it says that 1 bag makes 17"x17"x2" = 578 in3, which is 0.01239 yd3.  This means I would need 30 bags to make up my 0.36205 yd3, which is just over £200 - quite a difference.  Would have to give that quite a lot of thought!

Thanks

Gadzooks!

That's a dear do

If I ever get round to setting a permanent pier I'll have to tell the MD it's only 50p a bag..

[DrRobin]

Hi,

I mixed and poured about 200Kg of concrete for my pier and obs, mixed by hand in a bucket using 2 bags of cement and around 10 bags of ballast, all bought from B&Q as the cost difference between them and anyone else is only pence. It meant I could mix and pour when I was ready. I did contemplate buying from a ready mix or mix on site, but then you need to be ready for the full pour and that would have been difficult to schedule.

Total cost, 2 bags of cement, about £5 each and 10 bags of ballast, about £1.80 each, not very much in comparison to everything else I have spent.

Robin

[dmahon]

I mixed and poured (and wheelbarrowed 100 yards) 6 1/2 tons of concrete. I used a mixer. It's hard work.

[Tinker1947]

My Workshop footings were 25' by 16' either side and across i made them 18" deep and wide with a mixer sat over the hole, i spent 9 hours shovelling, and then being wet enough pushing it round either way until i reached my full level,,,,,,then there were the 18" X 9"x 9" Celcon bricks, roughly 500 again a cement mixer and all laid by me, the roof is 9" X 6" concrete tiles, i carried and laid them all....at the time i was a young 53 year old.....I think  it took my body a few months to get over the workload...i would certainly not attempt it again....

[adamsp123]

DP, looking at the area you have to place your obsy and some of the other constraints you have I would recommend a different approach.

Firstly consider ditching the concrete pier and consider what I did here with the pier ...   

http://stargazerslounge.com/topic/46537-what-lies-beneath/

I have twice used this method of base "construction", the reason I went this way initially was that I was renting the property but wanting to move to my own place... I found that the base was completely adequate for imaging and it was easy to remove, a few hefty push and pulls got the pier out.

It was such an easy and effective method of pier construction I decided to do the same at my new place after I moved.... and it is still solid the second time around.

Secondly your strip of land would probably be ideal for a roll off shed as I had the problem with space so my next move up was this

http://stargazerslounge.com/topic/67833-my-roll-off-obsy/

You could lay treated planks in shallow trenches on your lawn and roll off a 4x6 foot shed along the planks, this would work nicely for you IMO.

Hope that gives you an alternative worth considering

Pete

[Demonperformer]

That is certainly a novel idea, Pete, and it has got me thinking.

Admittedly, my first thought was - yeah, great if you've got the bits (pedestal, table, water butt), which I haven't.

Then I got to thinking a bit more:

By the time I have spent £84 doing the concrete bits and the same again to get the mounting plate fabricated, plus the rebar, threaded rods, nuts, etc, I am getting very close to the £187 required to purchase an EQ6 pillar (Sherwoods price - maybe cheaper elsewhere).

Now, using your idea of burying the feet of a pillar, this could save me an awful lot of work and (probable) frustration. OK, I would still have the price of a couple of bags of sand as a bedding material, but that would not break the bank.

My concerns (probably the wrong word, but you will get what I mean):

1. How deep was your hole?

2. How tall is the skywatcher pillar (none of the seller-sites seem to have these dimensions - which strikes me as a pretty basic info-requirement!)?

(These two together will give me the overall height of the mount above the ground. I would not really want to go to the extra £55 expense of a pillar extension to be able to see over the fence.)

3. None of the images of these pillars shows the top (they all have a 'greyed-out' mount on the top), but presumably the pillar has a 'peg' on the top (similar to the tripod) for AZ alignment, which would mean the mount would go on in the same position each time. I am not convinced that leaving the mount outside in my garden is a good idea - it is fairly secluded, but I suspect it is best not to underestimate the ingenuity of the local tea-leafs. So I would want to be able to put the mount back onto it and know it was going to keep good PA (for imaging).

Thanks.

This is getting less 'DIY' by the minute!

[wxsatuser]

This is what it cost me to do my pier, prices circa May/June.

The hole was approx a tad bigger than 600mm cubed with a slightly deeper bit in

the middle for the pipe.

20bags of Wickes Readymix concrete.......got each five for £5.49 each......Total £109.80

I already had two bags of Postcrete, think they were on offer......Around £4.50....£9.00

3metres of 8inch brown drain pipe from ebay........£51

Two 10inch 10mm plates from ebay.......£31.60

Four 1metre 16mm rods plus nuts and washers from ebay.........£42

So total for pier base, pier and mounting hardware........£243.40

and I bought an HEQ5 adapter think that was around £70ish

[Demonperformer]

Thanks for that.

Seems to bear out the economic argument for using an SW pillar - even with the extra £55 for the extension if needed.

[wxsatuser]

That is certainly a novel idea, Pete, and it has got me thinking.

2. How tall is the skywatcher pillar (none of the seller-sites seem to have these dimensions - which strikes me as a pretty basic info-requirement!)?

(These two together will give me the overall height of the mount above the ground. I would not really want to go to the extra £55 expense of a pillar extension to be able to see over the fence.)

3. None of the images of these pillars shows the top (they all have a 'greyed-out' mount on the top), but presumably the pillar has a 'peg' on the top (similar to the tripod) for AZ alignment, which would mean the mount would go on in the same position each time. I am not convinced that leaving the mount outside in my garden is a good idea - it is fairly secluded, but I suspect it is best not to underestimate the ingenuity of the local tea-leafs. So I would want to be able to put the mount back onto it and know it was going to keep good PA (for imaging).

Thanks.

This is getting less 'DIY' by the minute!

The SW pier is I believe about 800mm tall with a 120mm pipe

[wxsatuser]

Thanks for that.

Seems to bear out the economic argument for using an SW pillar - even with the extra £55 for the extension if needed.

I suppose some of this could be got cheaper but I did'nt have time to faff about so just went for it.

The pipe could be smaller and you could look around for an offcut.

The plates I drilled myself in the shop at work, that was about it.

[Gina]

Thank you folks - that's very interesting   I'm looking for ideas for my second pier which will be outside the obsy as there's no more room in there.  The SW pillar looks like it colud be a good idea   As you say, by the time everything else is costed up - not to mention the work involved - it could well be a good option.  I already have the EQ6 extension now doing nothing so that's an extra 8"

[Gina]

The pillar does include the az post as can be seen in this ebay auction listing (ended, unfortunately )  This time FLO aren't the cheapest - this one beats FLO by a fiver plus delivery cost.  Sorry FLO/Steve

[Demonperformer]

Thanks for that, Gina.  You've knocked another 51p off the Sherwoods figure.

That said, isn't Pulsar part of the S'n'S group? - I think I'd rather pay the extra 51p.

Or, indeed, try to get FLO to price-match (even better!)

I'm still a little concerned that if it is only 800mm high, I could end up burying half of it to make it stable enough - or maybe the same rules don't apply because it already has legs spread out over a reasonable area?  Not enough of an engineer to have any real idea.  That is why I would be interested to know how deep Pete buried his.

[Tinker1947]

In the picture i would think about 12", once its covered it should be very stable, i would use 20mm shingle, be very easy to get back out again....

[adamsp123]

Hi,

Just gone out and measured the pier and it is around 800mm above ground, my little "table" shown in the pic attached is about 320mm from the deck.

In regards how deep I buried the pier it is about 150mm thats all, first time it was deeper but it wasn't really necessay to be so deep,  whole pit is packed with sand as is the pier tube, unless you knock it pretty hard it remains in place nicely and so long as you don't stopmp around it whilst imaging it won't shake, sand is a very good dampening material.

Without the table it could go a lot lower,  so long as the telescope and/or camera miss the ground/table at zenith all should be well.

Also from the pic you can see the slot in the shed base and one of four the wheels it runs on.

[Gina]

Thanks for that, Gina.  You've knocked another 51p off the Sherwoods figure.

That said, isn't Pulsar part of the S'n'S group? - I think I'd rather pay the extra 51p.

Or, indeed, try to get FLO to price-match (even better!)

I'm still a little concerned that if it is only 800mm high, I could end up burying half of it to make it stable enough - or maybe the same rules don't apply because it already has legs spread out over a reasonable area?  Not enough of an engineer to have any real idea.  That is why I would be interested to know how deep Pete buried his.

Yes, it would be good if FLO could price match   I know they generally watch other retailers prices and try to be as cheap or cheaper than the competition

Yes, I would have like it to have been higher but at least I don't have a 6ft fence to get the imaging rig above.  Just a 3ft wire fence.  I think I'll have the feet at about ground level and extend them below ground - maybe encased in concrete.  I might even consider a slightly raised area to gain height but I haven't had a measure up yet.  I don't think this project will start until next year for a few reasons one of which is all the other stuff I have planned