The 8 inch Telescope, Time and Money
Mirror Making Grinding
Job Description Personal Time
8 inch Pyrex blank roughed to F6, under size tool.
8 1 Making full size tile/epoxy tool.
4 3 30 6 Rough Grinding, full size tool and adjusting focal length. 100 grit
2 30 1 Fine Grinding, one grit per day to avoid contamination.
Grit Time, minutes 120 90 220 75 320 75 400 75 600 60 17 micron 60 12 micron 60 05 micron 45
27 16 Polishing
Making the Pitch Lap
Painting and Prep
Pouring the pitch lap
2 45 30 4 6 Polishing Out
6 30 2 Figuring, fixing the bad edge.
9 15 8 12 Figuring, actually figuring.
6 30 6 10 9 Coating, including shipping.
70 15 39 Telescope Making
Cut plywood and pressed board disks and sand.
Paint mirror cell parts.
Glue mirror cell and tube cover disks together.
3 2 Drill and test assembly of mirror cell.
2 1 Cut, glue, sand and paint tube box.
5 1 Cut and base boards
Assemble castors to base board.
Cut altitude bearing disks.
4 1 Assemble bando on one end of the tube.
Trim cell to fit over index nuts.
Install mounting screws.
3 1 Glue sheet metal bands to altitude bearing disks.
Install altitude bearings on tube box.
3 1 Cut cradle boards and sand.
Test assembly of cradle boards to tube box.
Lay out structure location on rotating base.
3 1 Compete base structure.
3 1 Install base bearings and altitude bearing pads.
3 Cut and glue spider parts.
Spray spider black.
Glue diagonal to spider.
5 2 Make silicone mirror pads for mirror testing.
1 1 Cut tube to length
2 Focuser and assembly of focuser to tube. Buy drain tubes and cut to length and de bur.
2 1 Sand seals to fit.
Glue one seal.
Glue the other seal.
3 1 Layout and cut hole in the tube for the focuser plate.
2 Cut focuser plate and focuser tilt plate.
Drill holes and sand and glue in focuser outer tube.
2 1 Peel the moisture barrier plastic from inside the tube.
Spray the focuser and the inside of the top of the tube black.
Prime the outside of the tube.
3 1 Assembly, tube balancing and first collimation.
2 Cut down the overly tall structure and re-sand and touch up paint.
Telescope making total. 53 17
Grand Total 150 hours 72 days
Telescope Maker Skill Level
Motivated but little experience with tools.
Working without help or instruction.
? ? Reasonably skilled with tools but never made a telescope before.
Has other things to do besides telescope making.
150 hours 72 days Made many telescope of similar design before.
Many materials and tools already assembled for ready use.
? ? Team of telescope makers working together.
Minimal 6 inch telescope, uncoated.
Some parts pre assembled.
? 1 day
It is presumed you have a few tools. Hand saw, hammer a few drill bits, wood chisel.
For power tools an electric drill, a 8 inch circular saw, a small reciprocating saber saw, a small belt sander and a small bench grinder. Plus eye protection glasses. If you have an accident this project can get expensive fast!
If you do not have a circular saw and don't know anything about it I suggest you find a small local cabinet shop to saw the parts for you to assemble.
If you live in an area where telescope making classes are available then take advantage of that opportunity. Even if you do not follow their program exactly they will have many of the materials you will need. Also see the Supplies page. Prices rounded to nearest dollar.
Part number Part Contact Price, as of 2003 8 inch Pyrex mirror blank from Chabot SaSS 65 Willmann-Bell
Mirror making kits listed only in paper catalogue.
http://www.willbell.com/ Tile nippers ( alternatives available )
Home depot. 40 10 inch diameter cardboard concrete form. Local building supply. 18 Various oak plywood and pressed board.
50 Wheels for ground board / dolly. Home Depot 40 Curved altitude and flat azimuth bearing sheet metal. Local sheet metal shop. 45 Focuser parts, polyurethane glue, extension tube, flanged tail. ( plumbing parts ) Orchard Hardware ( also Sears Hardware ) 15 Paint: polyurethane, flat black, tube primer. 25 Other parts, mostly hardware:
screws, washers, screw eyes, springs, etc.
Ronchi Ruling, 100 lines per inch.
Diagonal, 1.5? inch minor axis. See alt_21.htm.
Edmund Industrial Optics 37
22 mm eyepiece
Shorty 2X Barlow Lens
The total is somewhat approximant. You may have some of the materials already. The minimum of some materials is enough for two telescopes so if you are working with another telescope maker it can be a saving.
Note on eyepieces
I don't pretend to be an expert on eyepieces. My feeling is that you are better with one or two good eyepieces than a set of crummy eyepieces. Even with a set of good eyepieces you will find you almost always use just one or two of them. The Barlow is not a sacrifice way to get high power. The Barlow / low power eyepiece combination gives more eye relief than a typical high power eyepiece alone. If you want two eyepieces with the Barlow then chose focal lengths that are not two to one ratios. If you bought an 11 mm eyepiece that would be the same as the 22 mm with the Barlow. If you want two then get a 30 mm and a 20 mm for instance. Then you will have 30 mm, 20 mm, 15 mm equivalent and 10 mm equivalent. Shorter ( more powerful ) eyepieces will only be useful in unusually good seeing conditions. And remember the telescope we built won't track so with high power we will spend a lot of time at the finder scope. Did you want a good finder scope? Add another $60 or so.
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