Designing The Pier Head

[Gina]

How about using an intermediate plate with three holes to bolt to the block and five for the puck?

[tooth_dr]

On 27/06/2018 at 11:32, Dr_Ju_ju said:

As you say you are using a concrete pier, this is my arrangement.... 

All studding is A4 Stainless and the red box highlights the studding that lock the mount in-place.

Similar to mine, although yours is nearer being all circular ??

Bolted up through the middle from between the black plates. 

 

[Peter Drew]

Just bolt through the complete assembly using the puck as a spacer.   ?

[nightvision]

Not sure I understand the problem; with the Todmorden type pier wouldn't you just use the disc without the 5 bolts and just use the single centre bolt?  I intend to use the centre bolt and the old tripod-top with the legs removed.

[russellhq]

16 hours ago, nightvision said:

Not sure I understand the problem; with the Todmorden type pier wouldn't you just use the disc without the 5 bolts and just use the single centre bolt?  I intend to use the centre bolt and the old tripod-top with the legs removed.

Think I'll give this a shot. I'm just not sure what will happen when I start making azi adjustments. Is the puck just going to rotate in the opposite direction?

[JamesF]

On 30/06/2018 at 09:37, russellhq said:

Thanks Peter, this is something I had seen before and am considering as an option for the pier.

The only issue i can think of with this is the pier top I have for connecting the mount to the pier, it's got 5 screws to hold it down which I don't fancy drilling the holes for in the concrete block. I don't think I will be able to get them aligned correctly.

I made a jig for drilling the holes to bolt mine to the concrete foundations which made it much easier to get them in the correct places.  I clamped the jig in place and started with a smaller size bit than I needed, going up a few mm in size a couple of times to get the size I wanted.  I think doing that (and not using the hammer action on the drill) helped with accuracy.  You could also make the holes a little oversize to give you a bit of room to play with.

James

[nightvision]

2 hours ago, russellhq said:

Think I'll give this a shot. I'm just not sure what will happen when I start making azi adjustments. Is the puck just going to rotate in the opposite direction?

Hmmm I see what you mean, not sure.  If the centre bolt was not tightened right up and the tripod head was restrained via one of the 3 leg connectors then the assembly wouldn't move and azi could be set and then the centre bolt tightened.  Hope that's the way it'll work as it will be less work and less expense.

[russellhq]

On 30/06/2018 at 09:02, Peter Drew said:

The "Todmorden" piers come with "owl's nests" ready cast in.   ?       

I meant to ask, how have you secured to the pier to the ground? I can see a threaded rod that looks like it's going through the slab at the bottom, but how is the slab secured?

I was considering digging a small hole and filling with concrete and submerging one of the blocks half way. This would help me get the height I need and would also allow the concrete to fill the first hole and anchor the block. I'm thinking of doing it in 2 pours. This first pour would be to establish the level for the block to sit on. Once set, I'd then place the block on top of the first pour and fill in the rest of the hole with the second pour. Think this would work?

[russellhq]

7 hours ago, JamesF said:

I made a jig for drilling the holes to bolt mine to the concrete foundations which made it much easier to get them in the correct places.  I clamped the jig in place and started with a smaller size bit than I needed, going up a few mm in size a couple of times to get the size I wanted.  I think doing that (and not using the hammer action on the drill) helped with accuracy.  You could also make the holes a little oversize to give you a bit of room to play with.

James

Thanks James. I don't have the drill bits for the size of the holes I need. I'd need to make holes for the M6 screws and M10 screws. What sizes would you suggest I buy?

[JamesF]

If I've understood Peter correctly I don't think the slab is secured to anything.  It just relies on the weight of the materials to stay put.  Each of the blocks probably weighs around 25kg and I imagine the slab is similar (probably nearer 40kg if it's one of the old 2" thick ones).

I don't see why your plan wouldn't work.  You might need to add some weight to the top of the block just to keep it in place whilst you do the second pour.  Perhaps some lengths of bent rebar to help tie the two blocks together might be good too.

For my observatory build I've used shuttering to build the concrete block higher than the ground level and used threaded rods to secure the block.  I need a two-and-a-half block high pier, so I'll be chopping the top block in half with a disc cutter.

James

[JamesF]

3 minutes ago, russellhq said:

Thanks James. I don't have the drill bits for the size of the holes I need. I'd need to make holes for the M6 screws and M10 screws. What sizes would you suggest I buy?

I'd have thought M6 should be fine to do directly.  If you had a set of, say. M6, M8, M10 and M12 then you could start all the holes using the M6 bit and enlarge whichever holes needed a bit more play to M8 after trying the puck for size, then take the centre hole out to M10 (and then to M12 if you need a bit more wiggle room).

I have a huge collection of SDS drill bits for some reason (not really sure where they all came from) and started mine off with a 5.5mm bit and then worked my way up to M12 via M8 or M10, but I did the first block with a standard corded drill and masonry bits.  My father-in-law was desperate to join in the fun and went straight for the SDS drill in hammer mode with the final size bit, resulting in a 50mm disc of concrete being blown off the inside of the block as the bit went through, rendering it largely useless, so I'd recommend avoiding that (especially the bit where my father-in-law "helps" :)  He was lucky that the next job for that drill wasn't a trepanning...

James

[JamesF]

Whilst I remember, I'd recommend drilling all the holes before you fix the block in place.  That way if there's an "accident" you won't have a broken concrete block fixed in the ground :D

James

[Peter Drew]

52 minutes ago, russellhq said:

I meant to ask, how have you secured to the pier to the ground? I can see a threaded rod that looks like it's going through the slab at the bottom, but how is the slab secured?

I was considering digging a small hole and filling with concrete and submerging one of the blocks half way. This would help me get the height I need and would also allow the concrete to fill the first hole and anchor the block. I'm thinking of doing it in 2 pours. This first pour would be to establish the level for the block to sit on. Once set, I'd then place the block on top of the first pour and fill in the rest of the hole with the second pour. Think this would work?

The paving slab is secured by gravity. It's 600x600x50 so combined with the two blocks necessary for a 8" SCT it's pretty heavy and stable. The only safe way to move it would be to dismantle it. Your modification would work but means extra effort which starts to detract from the basic simplicity.

[russellhq]

Thanks Peter, that sounds even simpler, think I'll give up on the concrete pour idea. Looking at the photo, it looks like a threaded rod with large washers? holding it together. What did you use for the fixings?

[JamesF]

You may find that it's easier to get hold of 38mm or 22mm slabs these days.  The 2" ones Peter has used don't seem quite so common.  Perhaps because they are really quite heavy.  No reason you couldn't use a couple of the lighter ones on top of each other though.

I suspect having a gravel base to lay the slabs on is also important.  Peter might be able to advise on that.  I put our chicken drinkers on top of 6" solid concrete blocks laid side down on the ground and they tend to settle into the soil quite noticeably over a few years despite being significantly lighter than a pier.  I imagine the gravel helps to avoid that occurring by improving the drainage around the slab.

James

[russellhq]

I think you can get them from B&Q

https://www.diy.com/departments/grey-british-standard-b50-paving-slab-l-600mm-w-600mm/35830_BQ.prd

Would be good to know what to put on the ground under it.