Dear Mike

Knowing that the tabletop legs are not practical for field use, I decided to find a tripod solution for my ETX-90. US made stuff are expensive here, like the Meade field tripod which costs more than 300$, and there are not many choices around anyway. I thought I could come up with something cheaper. I also have the do-it-yourself bug of course…

 

a) Tripod

First, I looked for a reasonably priced suitable tripod. I saw several camera tripods made of aluminum on the market, with prices starting from $80. Luckily, I also found a beautiful old wooden tripod in a friend’s junkyard. This friend is a surveyor, and this tripod was used with his old Wild T-series theodolite. This is a precision optical instrument, and quite heavier than the ETX-90. Therefore, I thought that it should be sturdy enough for the telescope use. The tripod is more than 20 years old, and it was in a pitiful state. However, the metal parts like the connecting top mechanism, and the stop-bolts of the sliding legs, looked OK. I dismantled the tripod; I sanded the metal parts and painted them five thin layers of paint and two hands of varnish. I sanded the wooden legs and painted them three hands of dark varnish. I assembled the tripod, and attached a small metal chain on each leg, connecting them in the middle. This is to prevent the legs from spreading apart when they are used on slippery surfaces. Then, I gave it a thorough test. Everything looked right. The tripod is very sturdy, and capable of safely carrying great weights without the legs sliding. I also realized that the original manufacturer (Wild of Switzerland) used first-grade materials (especially the wood) and great craftsmanship in their work.

 

Cost of tripod:	$0
Cost of paint and other necessary stuff:	Appr. $35
Working time:	10 hrs.
Weight:	5.2 kgr

 

b) Mounting

Next step was to find a mounting system, able to hold the telescope both in Alt-Az and Polar-aligned positions. I was lucky to have a Mechanical Engineer friend that helped me to design something efficient, simple and at a reasonable cost. We gave it a lot of thought and finally decided to build a simple mechanism with two holding parts and a pitch axis screw and bolt, plus a base to put on the tripod and a top unit to bolt the telescope onto. We also applied a simple leveling mechanism with three screws, similar to those used on surveying equipment, but much simpler. We chose aluminum for our material. I gave my friend George my final designs, and he went on to build the thing. It took around 4 working hours on the lathe and 6 more on other finishing equipment. Since he is a friend, he didn’t charge anything, but this should mean a small fortune if you have to pay the machine shop! We assembled the mechanism, attached and adjusted a leveling bubble, and screwed the whole set on the tripod. I also attached a small plastic protractor and made some markings to be used on the polar alignment procedure. With a little practice, I managed to be able to easily level and polar-align the scope. The first flaw we found was that the bolt of the pitch axis screw required a lot of strength to be safely fastened. This was because of the low friction between the two aluminum surfaces. I made it a little better by putting a small piece of strong tape with a rough surface between them. At last, it was ready! It has proved to work fine till now. The leveling works great, and is very precise, probably more than necessary. The telescope performed fine at a polar-aligned setup. The weight of the mounting system is over 2kg, quite heavy, but works in favor of the stability of the system. The system won’t budge easily, and is hard to tip over, even with the telescope at 38° (Athens, Greece). It is even better at an Altazimuth positioning. I’m quite happy with my work, and have no major complain after a total of about 20 hours of use. I have not tried any special equipment on it yet.

 

Cost of aluminum:	$20
Cost of screws, protractor and other necessary stuff:	Appr. $30
Working time:	10 hrs to build, but a lot more time to think of the design and produce the plans
Working cost:	$0
Weight:	2.3 kgr

 

c) Conclusions

I had great fun trying to design and build my custom field tripod. There is nothing that can replace the pleasure of making stuff and having good laughs with friends over the process. I also believe that the final result is simple, practical and aesthetically pleasing. Therefore I can say that I am very happy with my field tripod. The only drawback is its weight, and the not so efficient pitch screw and bolt. The cost seems very low, but you must bear in mind that I had for free what should be the most expensive part of the project, which is the working hours of the mechanic. A wooden tripod could be expensive, but a plain aluminum tripod costs a lot less. I would recommend my design as a cheap solution only to one that can find access to cheap heavy machinery tools. Otherwise, it could cost as much as something available on the market.

 

d) Photographs

Pict. 1: The tripod, the mounting and my ETX carrying bag.

Pict. 2: The ETX on the tripod at Altazimuth position. You can see the three leveling screws, the protractor, the pitch screw, and the top of the tripod.

Pict. 3: The ETX on the tripod at a polar-aligned position.

Pict. 4: The ETX on the tripod at a polar-aligned position. Note the screw of tripod connecting the mounting mechanism. You can also see the bolt of the pitch screw and one of the two ¼” screws attaching the telescope to the mechanism.

Pict. 5: The top of the tripod. Note the screw. Its threading is of a weird size, and carving the aluminum base of the mounting was a challenging task

Pict. 6: Here are the parts of the mounting system. You can see the base, with the three leveling screws and the bubble. You can also see the screws connecting the base part with the lower part of the pitching mechanism and the protractor. On the top part, note the 4 screws connecting the mounting base to the upper part of the pitch axis. Note the little carving on one end, to host the ETX’s rubber pad under its base. More details to be found in the drawing.

Pict. 7: This is a bitmap of the 3D model of the system in exploded view.

Right-click or option-click to download 564K file

Pict. 8: This is a bitmap of the plans

 

e) Digital drawings

Attached (Right-click or option-click to download 148K file) you will find the drawings of my work. The format is Autocad2000, and it is the vector version of picture 8. I have also included an animation of the exploded model. Click to begin movie. It will appear in a new window.

Note: One could notice minor differences between the final drafting and the final output (Lucky as I was to have great mechanics work for me, they took the initiative to make some last minute “enhancements”). The differences are:

q       The lower block has a different base and the upper block final shape is a little altered.

q       The way the lower block is attached to the base is different.

q       I haven’t cut yet the telescope holding ¼” screws. Instead I used two plain ¼” screws of 30mm height. The screws of the drawing are on their way.

These changes are not important and do not affect the efficiency of the system at all. After all, these drawings are mainly useful as an idea of the concept.

 

f) Credits

Many thanks to my friend George Vettas and his father Stelios, for their invaluable help. They provided their machinery workshop in their factory in Athens. They are worthy engineers and great artists! Thanks to my friend Costas Thanos for lending his digital camera.

 

You can put any of this on-line if you want to. Since English is not my mother language, you may find spelling or grammatical errors. Please correct them. I also hope that I am clear enough with my engineering terms!

Thank you for your time, I wish to you and your web-page visitors clear skies.

 

Spyros Michas

michas@tee.gr

Athens, Greece