Permanent Telescope Mounting Pier Construction 2024

  Implementing an easier and cheaper solution to the mounting and pointing problem.

Event Report 2020418-22

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The Experience

I have been interested in astrophotography for many years and over the years have accumulated a set of tools to assist me.  But, the one tool that I never had was a permanent telescope mount.  In the run-up to the 2024 solar eclipse, I stumbled upon a much simpler approach to building a pier than the typical poured concrete pier.  While I did not  bookmark the source of the plan, the crux was that the column was constructed of concrete block rather than having to form and pour a column.  During the multi-day drive from San Diego to Illinois for viewing the eclipse I further simplified the plan to remove the need for any concrete mixing.

Any mount has to be 1) rigid and stable; and 2) level (i.e. the upper surface has to be normal to the gravity vector).  Any concrete structure meets the first requirement, but meeting the second is more challenging than one would expect especially since "level" need to be within an arc-second or so of true level.  So, we devised a couple of tricks to make our life easier.

Most tracking mounts available today have some kind of metal adapter that allows connection of the tracking head to the pier.  These adapters should be assumed to be brand/model specific.  We obtained a tracking head and its associated pier adapter.

The photos below show the initial construction of the pier and the subsequent completion with provisions for electrical service at the pier for the drive motor.  Should anyone be interested in following this plan, the bill of materials is as follows:

  1. 2 standard cored concrete blocks (sometimes called cinder blocks).  About $3 each.
  2. 1 sack 3/4" crushed gravel.  About $4.
  3. 1 pre-fabricated concrete pier block (they come in sizes, we used the smaller size because it is was a scrap  block that we had on hand, but I would use the bigger size if this action were repeated).  About $20.
  4. 1 tube good quality multipurpose adhesive.
  5. 1 plastic shim pack.
  6. 1 package wooden grade stakes.
  7. 4 2x4s for framing.
  8. 1 2 gang junction box with weather cover.
  9. 1 90 degree conduit angle
  10. N pieces of 3/4" conduit to meet your wiring requirements.

We later decided to add a concrete skirt around the column to help reduce the dust when using the mount.  We framed and poured a 34" square skirt which used 6-60# sacks of Quickcrete concrete.  We also added some rebar "just because" to insure structural rigidity.

The first problem to solve is how to attach the pier adapter to the column.  The adapter we purchased has one 3/8" mounting hole in the center of the adapter.  So, we drilled on 3/8" hole in the center of the top block to allow passage for the 3" mounting bolt.  Diagonals were marked and the hole was drilled.  But, since we were using a hammer drill, the bit skipped early in the process resulting in an off-center hole.  Happily, the final performance of the mount was not impacted.  Final level of the adapter will be achieved using the 3-bolt leveler built into the adapter.

Next, a hole was dug at the selected location deep enough to allow burying the post pier and accommodate a thick layer of gravel.  Using the gravel as the base layer makes leveling easier and does not require the bottom of the hole to be flat or level.  Once the hole was big enough, gravel was added and a test fit of the post pier was performed.  The gravel was  adjusted and tamped to bring the pier into an acceptable position.  When level was established, soil was returned to the hole and compressed via tamping with a large hammer.  The returned soil was kept below the top of the pier block.  A cutoff tool and angle grinder were used to cut off the mounting straps and insure that the top of the pier was smooth and prepared for the gluing of the column blocks.

A test fit of the column blocks on the pier base was performed and shimming was estimated.  This step is easier as a two person process.  The level of the top (mounting) surface of the column was adjusted with shims until an acceptable result was achieved.  Once the shim requirements and locations were determined, a big goober of adhesive was applied to the clean, dust-free surface of the pier block and the bottom of the column block and the components were mated.  The the final shimming was installed.  Glue was applied to the top of the base column block and some clamps were added to prevent slippage.  Level was re-checked and shims were adjusted until acceptable.  Then, it is "Miller Time" until the adhesive cures (4 hours minimum, see the package label).  In the photo above, the pier adapter is visible (black metal cage).

  The next day, we attached the pier adapter and did some tests on the assembly.  The column was rock-solid as expected and had not shifted from level.  We cut off the exposed shims with metal shears to provide a cleaner look.  The adapter was attached to the column with the 3/8" bolt and the fine leveling was performed with the tripod screw adjustments.  Final adjustment of the orientation of the tracking mount would take some time and an accurate estimate of true north.  Typically, this is performed with a special-purpose tool or a process known as "drift alignment".  Both of these techniques require visibility of Polaris the pole star.  In San Diego, good visibility at night is a rare thing, so a more conventional approach was used based on a magnetic compass.  A usable alignment was finally achieved, but a more precise result will be needed for any star tracking.

After using the mount for a few days and noting our movement patterns around the mount, we concluded that a skirt was required for dust control.  So, we planned to pour a concrete slab at the base of the column and install provisions for electrical service at the pier.  Above, rough outlines of the form are marked in the soil.

Back to the Home Depot for electrical conduit and a 2-gang outlet box.  Trenches were dug and conduit was installed.  The outlet box was attached to the column using construction adhesive and clamped until the adhesive cured.

One the adhesive was cured, the trench was refilled and packed and the forms were placed using stakes to hold them in position.  Look carefully at the photo above: the post pier is visible.  This junction will be encased in the final slab.

We got some short rebar pieces and rod chairs to suspend them in the concrete.  The components were positioned and held together using small zip ties.  Form sides were checked for levelness.

Connecting form members were cut to fit and installed and levelness was re-checked.

Very few actions are as much fun as manually mixing and pouring concrete.  I say this tongue in cheek as it is hard, dirty work.  Fortunately for us, it was overcast and cool making the burden easier to bear.  I mixed and shoveled the mixture into the forms and Kathleen packed and floated the surface.

One bag of concrete left to mix and pour.

The finished product pending a final skimming of the surface for smoothness.

We will let this cure for a few days before busting off the forms.  We'll take the extra soil that came from the excavation and put it around the perimeter of the slab and clean up any excess concrete that was spilled on the "grass" area.

We are confident that this permanent mount will improve the quality of our astro-photos.  That said, no amount of construction will improve our coastal weather.  When the weather clears, we will use the drift alignment technique for precise alignment of the mount as described on ExploreScientific

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