Charlottesville Astronomical Society

October meeting

11/1/2006

McCormick Observatory

Attendance: ~25

Guest Speaker: John Turchi, Dob Conversion

Club Business

Dues are collected in December and are due in January.

Nominations for Officers 2006-2007

The current officers have agreed to serve a second term

Steve Layman – President

Richard Drumm – Vice President

Wes Epperly – Secretary

Larry Saunders – Treasurer

Are there nominations from the floor?

No Nominees…and the list of officers was elected.

Observing

Will try to have a club observing at McCormick over the observing holiday.

Club Outreach

NRAO Open House – Sunday, November 5 10:30 – 4:00

Visual solar observation and Radio Jove demo

November 8 -Mercury Transit / Moon viewing

November 10 – McCormick – Contact Larry Saunders

January – Northside Library – Jewels of the Night Display. Contact Ken Harker to submit photos or digital images

March 23 - Ivy Creek – Moon and Planets

Upcoming Speakers

December – Dr. Adrienne Juett

X-Ray Observations of Neutron Stars and Black Holes

January – TBA

February – Al Wootten, NRAO – Director of the ALMA project

Motions form the floor:

Susan brought up an issue of a subdivision going South of Town. Motion was raised to draft a letter to send to the county and or developers to limit the light pollution. Gary and Rich seconded the motion.

Door prize

Larry won the door prize, a $25 certificate donated by Mike Rodemeyer.

Main Presentation: By John Turchi

Task…to convert a 12-1/2” sonotube Dobsonian Telescope to a Truss tube Dobsonian for lighter weight and increased portability.

Note…John showed hundreds of photos…and these meeting minutes do not do his presentation justice.

Tools Used:

Router

Jig Saw

Circular Saw

Palm Sander

Framers Square

Hammer

Tape Measure

Tube Cutter

C-Clamp

Drill

Used ½” flute bit

Made circular Cutting jig from Plywood and Mahogany blocks of wood

Materials

Plywood

Formica

Aluminum tubes

Virgin Teflon from Virginia Industrial Plastics in Elkton

Started with a 12 ½” Discovery Dob with sonotube

Important to mention the distance to the spider

First modification was to make the telescope a split tube Dob.

But this was still too heavy and cumbersome to move.

Measured the Centerline from the spider to the mirror, so no calculations were required

He re-used the original mirror cell. If he had made jis own…he would have

The Dobsonion Telescope by Kriege and Berry

Used high quality circular saw blade.

Rule of thumb. Mirror box needs to be at least as deep as is wide.

Always mark your centers before you cut…that way it is easier to mark true center then after you cut

Made home-made stick compass.

When making the secondary. Mark the secondary rings by dividing it itnot eight equal sections.

When cutting inside arc. Leave a little bit when you cutting on the inside. Then

Glued two disks together to form the altitude bearings.

Make the Rocker box about ¼ inch bigger so that they do no rub (rocker and mirror).

Rule-of-thumb. Make bearing 6” bigger then primary bearing.

Alternate grain on the altitude bearings.

Use contact cement to glue Formica to altitude bearings. The water clean up and no-odor version of the cement does not work.

Cut groove in dowel so that glue has someplace to go when it expands - -secondary tube ends for mounting.

Use laminate cutter bit to trim Formica flush

Made pole clamps from two pieces of scrap to make clamp blocks.

Must use drill press vise to hold the block steady…otherwise your likely to break your thumb.

Screwed clamps together to make sure that they don’t split.

Made focuser board from ¼” Baltic birch plywood.

Water based polyurethane works fine. Foam brushes work great. Polyurethane the rocker and mirror boxes.

Early he painted mirror box inside black.

Use cardboard to test place the altitude bearings. Then mark the bearings.

Made custom jig for drilling 10 deg angle to hold the clasps of the poles for the secondaries.

Laid telescope out horizontally so that tubes could be measured, cut and fitted. Cut long the first time and then fit latter by trimming a little off at the time.

Install self adhesive pads to the inside of the rocker box to keep it from banging the mirror box.

About 50 hours to build.

10 Minute Topic:

John Avellone with 10 minute topic on spectroscope.

Showed solar spectroscope that was made by a kid in the 60’s for a science project. This was a large device that required a large mount. He wanted to measure the rotation of the sun by using the Doppler shift. Johns Calculation show that he would not have been able to measure the rotation due to being off by an order of magnitude. But not a bad project for a high school student.

Then John showed a spectroscope that he built.

John suggested that the club by a spectroscope.

Then John showed his 10 x 63 binoculars that he made.