Moving to a fairly dark site helped me enormously for astrophotography, but for long exposures I decided to install a concrete pier into my garden. This would help to keep the scope stabilised during these times.
The project comprised of:
Although the garden is approximately 100' x 60', the site had to be carefully chosen to give me the best open sky coverage, but without impeding on the rest of the garden too much.
Surprisingly, my better half also suggested I find somewhere that gave me enough room to add an observatory, if I later decided that I required one. Not one to pass up an opportunity like that, I agreed with her at once, praising her for her forward thinking, and anything else I could think of to say, to put her off from changing her mind immediately!!!
So now the site has a position for the pier and an area of approximately 12' x 12' for such a future project.
The chosen site was as far down the garden as I could go, to keep away from any light emanating from the house. No point in moving to a fairly dark site then observing ten feet away from the nearest light source!!!
The pictures below show the chosen site for the pier, between two small trees.
The distance between the trees is approximately 13 feet.
It may be noticed that the largest tree in our garden is not too far away from the chosen site. However my better half has never liked this tree so, again, I had to agree most whole heartedly with her, that it needed to be removed, and as a lucky bonus it will give me an even larger exposure to the southern skies.
Below are some pictures of the sky from the pier vantage point.
...and West from the pier.
All in all not a bad outlook.
The direction for true North is extremely important in terms of getting a telescope setup properly, and therefore I needed to know where this was, in relation to my pier position, so I could align the top plate correctly.
I found a very useful website that allows you to find out the exact longitude and latitude of any position by simply clicking on a map. The map also allowed for a satellite view, which meant that I could select the exact point in my garden as well.
I first selected the pier position and noted down the co-ordinates.
Next, using the option to enter your own co-ordinates, I added a second point with the same longitude but a slightly higher latitude value. This point was just to the right of some trees and nearly 250m away (another part of the website tells you the distance between two or more points).
I can easily see the trees from my garden, so I now had a very good idea of the direction for true North from the pier position.
Here is a closer view of the trees from the satellite view...
...and the ground view.
Unfortunately the buildings in the picture were not built at the time that the satellite images were taken, and the further away your target is the more accurate your true North position would be, however since the telescope mount also has some adjustment for true North anyway, it did not need to be exact.
Since the satellite image suggests the distance between the second and third tree, is the same distance as the third tree to the true North position, I will aim for the left side of the last building on the right of the picture as my true North starting position.
A few days later.................
Not being one to be outdone, I utilised the website that told you the distance between two points and drew a line from the pier to some trees as far in the distance as I could see.
This new position was 670m away from the pier position, over 400m more than previously. I then placed the available stick man on a road in between the two points, allowing me to look North from that point.
I saved a picture of the view, and drew a line in the centre, to show true North. Using three trees as guides, I could now tell more precisely where North was, in the photograph taken from the pier position.
Photo from the pier position with the three trees outlined and the true North position marked.
Google worked overtime, looking for others who had already built their own piers, and although there were several different designs they all seemed to be along similar lines:
Dig a hole, fill it with some concrete and strengthening bars, add a tube for the pillar, fill tube with concrete and strengthening bars, place bolts into wet concrete, allow to dry, bolt on telescope, (with or without a steel pier extension), and use.
The only difference between the designs seemed to be how much time and effort, (and concrete), was expended. Some seemed to be quick and dirty, whilst others were pure works of art.
The design also took into account that although at present I only own an 8" Newtonian scope, if I ever upgraded it, I would want the pier to be able to cope with any extra weight that may be added.
I decided on a pier 1200mm high and a base of 1m3 of cement and strengthening bars.
Click HERE to download a .PDF file of the pier base design.
Click HERE to download a .PDF file of the pier top design.
The steel top plate is the connection between the concrete pier and the telescope mount, in my case an EQ5 type. I first decided that three or four lengths of M16 threaded bar would be used to hold the plate to the pier, no matter what the design ended up like.
To make sure that the threaded bars would be set in the concrete in the correct place, I would construct an MDF template and the bar would be bolted to it. After filling the pier with concrete this would then be fitted on top of the wet cement and aligned to true North. When dry, the template would be removed and the threaded bar would be located exactly where it needed to be.
At first I purchased a useful looking piece of steel from a boot sale, for just £2.
Apparently it is a spare wheel holder for a Land Rover.
The wheel holder was stripped down to see what I had bought...
...three of the nuts placed on the studs...
...another plate added with more nuts, and a centre hole drilled...
...and the telescope mount base added, The plan is to add brackets to hold the three arms of the mount base.
In theory the three nuts will allow me to level the mount
The complete mount fitted.
Since I started the project, I have now read that this approach may not be the best one, in terms of the ability of the pier to stop vibration. The theory is that if you have a very strong concrete pier, then at some point rely on three substantially smaller structures to support the mount and telescope, and the majority of that area is just air, it will not be as stable!!!
Hard to visualise at first, but imagine a concrete pier only a few inches high compared to one four feet high. You would rightly imagine them both to be very strong. Now imagine three bars as above only a few inches top to bottom, and then again four feet top to bottom. Would you trust the longer one to hold your telescope?
The point is, that the use of bars this way, of any length, substantially weakens the piers ability to recover from vibration - which is the main reason for building it in the first place!!!
The only reason for the original design, was that I needed to attach the mount from underneath, with a single bolt, (see below), otherwise I would have simply attached the plate to the top of the concrete pier.
I have since decided to try another approach, whereby the concrete pier will have a gap on one side, just big enough to put a hand in and tighten the locking nut, but allowing the pier to keep most of its original strength.
My second attempt at designing a top plate now focused on not utilising the original mount base, but somehow just using the upper part of the mount.
After making some measurements, I found this meant finding a steel plate that had some sort of step up in the middle, at least 40mm in overall height, with a hole in the middle of approximately 60mm to fit the top mount, and an overall diameter of over 200mm. A smaller piece of steel would then be attached underneath with a central hole drilled to allow the fixing screw to be fitted. This would need to be wider than the step up of the top piece.
After drawing the design out it became apparent that it looked very much like - a brake disc for a car!!!
These can be obtained relatively cheaply nowadays and are extremely strong. I trawled through dozens of eBay listings and eventually came across one for a Skoda Favorit front brake disc.
The dimensions were:
Overall height - 46.6mm
Centre hole diameter - 62mm
Disc thickness - 12.9mm
Pretty much near to perfect for my needs. The lower steel part could be used from the £2.00 spare wheel carrier I had already purchased, so not wasted after all.
A day later, and the brake discs arrived, (they came in pairs so I have a spare for my next pier project!!!!)
All of the measurements were as described.
Base of the mount showing why I needed 40mm height and 60mm diameter clearances.
The base of the mount shown from below.
And with the brake disc fitted. Such a good fit!!!
And finally with the lower base plate fitted using the original mounting screw.
The final assembly from side on. I think it should look pretty good when installed.
Due to the fact that the disc is not vented in any way, there is a lot of space to add fixings, so I decided that I will now use seven M16 threaded bars to hold it to the pier. Maybe overkill, but I figured that too many is better than too few.
Click HERE to download a .PDF file of the top plate design.
The parts required for the pier project are listed below.
|Reinforcing Bar 12 x 2m||
Stainless Steel M16 threaded bars x 2m
M16 Nuts and Washers x 14
|Concrete Pier Tube||Essex Tube Windings||£36|
|Digging the hole, removing the earth, and supplying and pouring the Concrete x 1.25 cubic metres||Local Builder||£100|
|Wooden Support Frame||B&Q 100mm x 50mm x 2.4m||£15|
The pier tube was company were excellent, and even called me the day before delivery, to let me know the tube was on its way. My tube dimensions were:
Wall thickness 6mm
The brake disc was first cleaned of its protective film, using methylated spirits. It was then given its first coat of paint. I know I still have holes to drill, but I wanted to get a feel of what it will look like with the mount, (and I was being impatient).
I next drilled a hole on the north side of the plate to allow me to add a metal pillar for the mountís azimuth adjustment. A star washer was used to try and help the pillar to stay in place at all times.
I do hope the designer of this brake disc doesn't mind me destroying it with paint and drilling holes!!!
The pencil marks will disappear after the second coat of paint is applied.
Here is a close up of the mount attached to the base, showing the adjustment screws. They lined up perfectly with the pillar.
The paint match is not too far off, but no-one will notice in the dark anyway!!!
I printed off a copy of the top plate drawing and taped it to the brake disc, ensuring that it was orientated correctly.
The disc rim lined up perfectly with the drawing.
I then marked the seven holes to be drilled using a centre punch, and removed the drawing.
First pilot holes were drilled...
...then then the 16mm holes. This was very hard work!!!
Upper Pier Construction
I constructed a very rough MDF box, with the sizes of the aperture I was going to leave in the concrete for tightening the mount screw, just to make sure the dimensions I had chosen were adequate.
As it turned out I could get my hand in and tighten the nut fairly easily so I was happy the dimensions were correct.
The 'real' MDF box I make will have a curved outer edge and be fitted to the tube somehow before pouring the pillar cement.
The next day the piling tube arrived.
In all its 1200mm x 282mm x 6mm glory.
I drew the outline of the tube for the top plate template...
...and then taped my drawing over it - perfect!!! I knew my technical drawing skills learnt at school would come in useful at some point in my life. But 35 years later!!! At least it's easier drawing on the computer nowadays. Now I can drill the holes for the M16 threaded bar (still to arrive).
All seven holes drilled.
And paper template removed. The gap in the middle at the bottom is where the aperture will be for fixing the mount from underneath - hence no fixing bolt there.
The M16 threaded bar...
...together with nuts and washers, arrived.
The bar was marked at 250mm intervals with tape...
Top view of the threaded bar in the brake disc and top template...
...and a side view
Not too bad.
A new box was constructed for the screw fixing aperture.
A little neater than the first one.
This time the outer dimensions are the same as the inner dimensions of the first box, since the sides will form part of the aperture size created. I also constructed a new top template at the same time.
Next I taped the drawing to it, and curved the edge to match the piling tube inner radius.
I then cut it down to size as I had forgotten to reduce the height - DOH!!!
I made a simple carrier that fits on top of the brake disc...
...to hold the telescopes spotting scope.
This can then be used to assist in aligning the top to true North, when seating it into the wet cement. (Sounds like a plan but we shall see how successful it is!!!
Lower Pier Construction
I picked up the rebar from the eBay seller. He even cut it into 2m lengths for me. Eight of the lengths are for the pier strengthening. I drilled holes into the old top template, and the new top template, so the rebar could be held in position.
It may look long, but nearly half of the length of the rebar will be below the ground.
Close up of the pier top plate in position, showing the spacing between the anchor bolts and the rebar. In reality the rebar will not come to the top of the pier, but overlap the bottom of the bolts by about 80mm. This means there will be some sort of strengthening over the entire height of the pier.
May 2013 Project Continues
After nearly two years from doing anything with this project, due to work commitments etc.., I have more updates to add.
Test fitting of the mount to the template and tube.
I also decided to simply screw down the carrier for the spotting scope to the top of the template for ease of use.
Kitting Out The Tube
I cut a hole in the tube to allow me to place a piece of wood which would make a flat surface on the concrete pier, onto which I could mount a weatherproof 13A socket for powering my laptop, camera and DSC.
The 13A socket with the tube which will be encased in the cement for housing the cable.
Building The Support Frame
I then built a frame to hold the pier in position whilst the concrete was drying out.
I bought three lengths of 100mm x 50mm x 2.4m, and cut them each into two parts.
I then assembled the base of the frame, out of three parts, such that they formed a triangle into which the tube would fit snugly.
I placed these 'legs' onto a concrete blocks and a small piece of wood which gave me roughly 240mm of tube below ground level. Originally I had designed the pier to be the full 1200mm in height, but after assembling my telescope on its original tripod it became clear that I only needed around 1m in height to the mount.
The remaining three pieces were then fitted in such a way as to secure the tube with coach bolts. The bolt heads are on the inside of the tube, and will therefore leave a small dimple in the concrete. This design was VERY sturdy.
I then test fitted the box for the aperture, the top template and the spotting scope.
Two of the screws could not be done up until I 'modified' one of the supports.
The same was true for the top template, seen here with two cut-outs to clear the supports.
Spotting scope attachment fitted OK!!!
Digging The Hole
One of the reasons for finishing off the project now was that we were having a kitchen extension built, and the builder offered to dig the hole, and supply the concrete when the base was due to be laid.
Good old Ernie and his trusty digger.
The hole was finished in around 40 minutes, including the two labourers shifting the earth from the back of the garden to the front of the house for disposal.
Tube and mounting in place and covered for the night.
Preparing The Tube For The Concrete
The next day, I ensured that the frame was in the correct position, checking for North with the spotting scope, and then fitted the electric pipe work.
Looking down the pier at the electric supply tube.
I then added just three lengths of rebar, (the builder thought eight would be fine if it were holding a house up).
Looking down the tube. The rebar was pushed into the earth until they were 120mm from the top of the tube. The mounting bolts will add strength to the top of the pier without rebar.
I used a hot glue gun to seal around the pipe and the piece of wood to hopefully stop any concrete seepage.
Finally Adding The Concrete
The first of the concrete is poured and two pieces or rebar added.
More concrete and rebar added.
The last of the base concrete now added. Still smiling even after barrowing most of the concrete from the front of the house to the end of the rear garden.
Finishing Off The Template
Whilst the base of the concrete was left for an hour or so, I set about putting the threaded bar in the top template. Instead of trying to bend the bar, I had a local mechanic weld some bolts to the bottom of the bars. The plan is that these will stop the bar from spinning in the concrete when the nuts are tightened.
All of the bars fitted and tightened down.
Final Concrete Pour
How many builders does it take to pour a concrete pier?
Checking for a level pier.
Just have to let it set now!!!
Finishing The Top Plate
A second coat of paint applied to the top part of the pier.
All Is Revealed
After three days it was time to take off the tubing. First the template was removed.....
....then the tubing was slowly peeled off....
....to finally reveal the pier!!!
The top box slowly gave way to being removed.
I can get my hand in!!!
I even managed to remove the temporary electric tube. The proper sized one will be fitted when the electrics are installed.
After a little fettling I managed to fit the top part of the pier.
The telescope mount was then added.
And finally the scope!!!
All that remains now is to install the electrics. The armoured cable has already arrived and simply needs to be buried between the house and the pier.
This is as far as I have got with the project. I will update the page as I progress further.
Copyright © 2004 - 2013 Phil Davis
Last updated 30th May 2013