This was my first pier designed for Takahashi EM-100 mount. As it was not a perfect design, I want to share here some lessons learned.

The pier was made of 90cm length of 4" steel water pipe, threaded on both end.

Two steel flanges (standard water equipment) were threaded on both ends, forming top and bottom. The bottom part was anchored in a concrete column (separated from the terrace as construction, but having common tiling) with 4 x M12 stainless steel bolts.

Another set of M12 stainless steel bolts 25cm long was carrying the mount base adapter. This adapter was made on lathe from stainless steel by a friend of mine, and it "mimicked" the top of the tripod hub. The 20cm space between top adapter and flange allowed me to reach under the mount head to attach the main screw.

You could also see a sort of cap for the pipe, preventing me from dropping into the pier some small accessories. Finally, a number of power and signal cables were run through the conduit visible on the first image, up the pier and were connected to a "control panel" - a piece of plastic board attached to the upper bolts, carrying a couple of 12V sockets, LAN, RS232 etc.

What should be done better:
1. I was in hurry to get the pier on my terrace and did not tighten well enough the flanges. They *looked* like tightened but there was a bit of play under load. I should screw a wooden plank to each flange, call in my friend and screw them really tight. Some epoxy on threads could also help with this.
2. The bolts in the concrete column were bit too thin and the spacing forced by the (factory made) flange was a bit too close apart. I should use M16 stainless steel rods and space them wider.
3. The top adapter could be made from aluminum - would be easier and cheaper to manufacture.

Finally, the 4" pipe was surprisingly solid and completely adequate for EM-100 and 4" APO, but lacked capacity for heavier mounts.

A good practice which I ma trying to follow since than was to use 6" pipe for 20kg mount load (Takahashi EM-200) and 8" for 35kg load (Takahashi NJP) - in line with recommendations of such experts like Astro-Physics.