ATM Community

Overview

A community needs focus - common interests, meeting space, diversity. Common interest can be discovered just by mentioning a plan to organize such a community around the subject of telescopes and telescope making. This I have done in the limited circles I frequent, but publicity can be helpful (word of mouth, websites, public events, etc.) and a sufficient number of participants has led to a loose "organization."

Virtual meeting spaces have become popular and can be quite useful for presentation of general ideas and concepts, answering questions , organizing face-to-face meetings, reporting progress, sharing experiences, etc. But ATMing is a hands-on exercise. Much of the work in building a telescope can be done at home but a central "workshop" can be invaluable. I found such a "workshop" in the Inventors Forge Makers Space in St. Peters, Missouri. Inventors Forge teems with creativity and enthusiasm to "make things." To that end they have put together tremendous resources for wood working (most Dobsonian telescopes are made of wood), metal working, 3D printing, electronics (many modern telescopes rely on electronic assistance). I have added a mirror grinding machine to help with making mirrors up to 10-inches in diameter.

Organization

The plan is to set up a series of virtual meetings using Google Meet (weekly, on Wednesdays). Google Meet is a free service that uses a web browser to participate (not sure which browsers work best but I have tested it on Chrome and an Android phone). Participants must have a Google account (which is free). We will post the link to join the meetings on the email group used by the ASEM ATM group. (Use link to get a free account.) The email group will be our primary mode of general discussion, questions and postings.

The virtual meetings will be where we will discuss telescope design, projects and answer questions. They will be free and open to the public. We will try to spread the news about them widely to grow our community

This is a hands-on activity. We anticipate many folks will want to work from home workshops with the occasional visit to use the facilities at Inventors Forge for their resources. Some will want to use the grinding machine at Inventors forge. Members of the Inventors Forge have 24/7 access to the facility and we will use the "champions" format to qualify folks to use the machine (safety is our number one objective but the machine needs to be protected from unknowing abuse as well). Non-members of the Forge will have to work under the supervision of a member. I (Jim Roe) will help as much as I can for as long as I can, but we need to develop some Forge members as mentors for long term continuity. I would hope for show and tell get togethers (maybe monthly or ad hoc?)

Projects

Currently (June, 2022) we have folks working to grind and polish 6 inch diameter mirrors. These are quite suitable for beginners telescopes, the finished instruments can be expected to show more celestial objects than anyone is likely to actually seek out. We can supply "kits" for $50 (4 left).

We have one individual who wants to finish a 4 1/4 inch mirror he started some years ago. We can certainly consider other projects that folks might want to try.

We have another project for a 4.25 inch Schiefspiegler telescope. See more at sites.google.com/asemonline.org/jroe/telescope-making/schiefspiegler-project

How to Join Our Community

Basic "membership" (nothing formal) is free and open to the public. Join the email group to keep up with what's going on, especially the virtual Google Meet links and participate! (with questions, answers, chat). Attend the Meet events when scheduled where we will discuss telescope theory, mount design, other topics of interest in an informal space. Join us for "build" activities at the Forge which will be announced on the email group.

You should definitely consider joining Inventors Forge for easy access to their resources (including the grinding machine which is located there) - at least for the duration of your telescope project.

How To Get Started

We are not reinventing the wheel here. Amateur Telescope Making has been going on for a long time and there are lots of resources on the Internet that we urge you to investigate. A slight warning: the fundamentals of telescopes are the same but the ways they are achieved are almost as varied as the people doing it. As long as the fundamentals are observed, there is no right way, nor wrong way, to build a telescope. Stolid old ways work quite well but innovation is encouraged. Below is a recommended site but we will add others that you think might be especially helpful.

Stellafane Telescope Making

Making Your Own Telescope, Allyn J. Thompson Inter Library Loan

How To Make A Telescope, Jean Texereau Inter Library Loan

Spherometer

(3 July 2022)

A spherometer is a very handy tool during grinding to measure the radius of curvature (ROC) of the mirror under work. It is based on the sagitta formula which relates the depth of a spherical curve at a particular chord to the ROC. It is given by s = r^2/(2*ROC) where r is the semi-chord length. Conversely, the ROC is given by ROC = r^2/(2*s).

The spherometer consists of a 3D printed disk with three "feet" located on a circle of radius r. A hole in the middle of the disk allows a dial indicator (available on Amazon for about $15) to be inserted to measure the distance between the plane defined by the three fee and the surface under study. The spherometer is calibrated by setting the zero mark on the indicator when the spherometer is placed on a level surface. It can measure both concave and convex spheres.

See image below for a spherometer in use. In this case r = 0.185 inches and the reading of 0.0122 inches indicates the ROC of the mirror is 114 inches.

The .STL file for the base is available in the Files Folder.