Posts Made By: Sam Greenlaw

You can get standardized dovetail mounts at any gun shop.

The sizes are smaller, individually, than big custom telescope mounts. But they're cheap. Strong. Hardened steel.

I use two four-inchers mounted side-by-side 2" apart. It looks like they could take 100#. The base is 1/4" aluminum cut 4" wide by 6" long.

There's a Yahoo Group for Obsidian Optics customers.

http://groups.yahoo.com/group/obsidian_optics_mirrors/

It's free. Main issues are delivery dates and doing mirror cells to support OO's very thin mirrors.

Start mirror work with a 6". If you don't like it, you won't be out much time and money. Then a pair of 10" mirrors for a bino... sounds doable.

Hand making a 16" is a huge job. The figuring is tough and just getting a great blank has become difficult. Not for a first-timer.

I minimized cost for a 16" by grabbing an eBay auction from Mark Cowan (Obsidian Optics.) Couldn't resist and added the Pyrex option.

Mark's been s-l-o-w to get his grinding system t-u-n-e-d, but his latest 14"ers have come out 1/22.1 and 1/11.7 MWF. Prices will go up soon. Maybe way up....

Coating by Bob Fies (Aluminum Coating in San Carlos) is a whopping $60. I told Bob that he doesn't charge enough; he just chuckled. Great guy, 100% up to his reputation.

Total's about $900 plus some shipping. Talk about winning the lottery, particularly if Mark's compulsiveness about figuring perfection gets something in the 1/11.7 -> 1/22.1 MWF range.

One odd choice is to hit the marine supply shops. A nylon drain plug can be had in the 2" to 4" Interior Diameter size range. My first one was a 1 3/4" for 1.25" EP's but a 2 1/2" would have been jsut as easy.

These screw closely enough to be useful, if you add some plumbers tape. Very smooth feel. A 4" finger wheel up top makes the action silky.

Make appropriate adapters to cut the size down to fit 1.25" or 2" EP barrels. You'll want a wood lathe. But....

I cheat: a drill press, 1" work head up top (or a V-shape screw in a pre-drilled hole will do), and a pivot head at the bottom. With soft pine wood the chisel cuts right through with the rotation set in the mid range. When the work's down to 1/8"-big, go to a 40 grit block then smooth it out from 1/32" to perfect. You get the idea...

The inside hole can be cut a little big. Then lined with felt. Lots of ways to skin the cat. EP's don't need screws to be happy.

You have a little work with a Dremel to make necessary modifications to the original nylon drain plug. Cutting off unnecessary formed parts. Maybe a quarter-hour's work.

5 minutes for the second one.

These drain plugs are a bit difficult to aim properly. Amateurs, wrong tools, etc. Errors happen. If your hole is drilled perfectly, that's a help; it's not absolutely required.

One "cure" is to insert the adapter in the drain plug body -- made to home drill press accuracy, remember. Then insert a pipe of the right diameter and a foot long into the adapter. Then you can measure to points equidistant from the edges of the main hole.

Straight enough.

When the screws at the base get it to look really good, make the installation permanent with plumbers epoxy.

Cost's about $5 - $10 total. Gets very low profile, great longevity, nice feel. Nylon's wonderful stuff.

And if there are any problems at all, ever, it's my fault. Not yours......;^)

From a copier lens ???

Your own coatings ?

Cool project.

The least expensive is probably Bob Fies. Aluminum Coatings in California. He's on the Sidewalk Astronomers site. Excellent work and fast.

Bob does a zillion mirrors.

Bob Fies
897 Rutherdale
San Carlos, CA 94070

Bandsaw: the recommendation for the little 3-wheel bench model is interesting. These sell for $100 - $160. $140 gets a 3/4 HP motor, variable speed control (220-2300 fpm) and access to wood and metal blades.

Everybody likes band saws. The professional models are the preferred basic tool for home work.

Table saw. Recommended strongly, but not universally. A first-rate fence is the #1 requirement. Grizzly.com has a belt-driven super saw for $ 825 (G1023) and a competent worm-gear positioned direct drive for $325 (G1022SM). Somewhere in there....

Router. Big votes for the router. Shapes wood end-surfaces quickly and precisely. Cuts circles, odd shapes to patterns.

Ed recommends building your own router table -- large and convenient. James, the same. Sounds good.

Fein Cutter oscillating machine. Fein's a German company. Fein originated oscillating power tools. This is not the Fein MultiMaster. Cost is high: near $500. Zillions of attachments.

Most ATMers have a Dremel. Add a flex shaft... get similar functionality to the Fein Cutter.

Pocket joiner. Got zip for this on google. A small cabinet joiner, but I'm not sure what James has in mind. The biscuit joiner is a professional tool, but the biscuit attachment for a router is an ace.

Most amateurs use dowels to get strength. A hand drill makes clean doweling holes with crisp Forstner drill bits. Forstner set, $25 ecomm. A drill jig is useful.

Scopes make light demands.

Planer... portable, high-speed knives. The portable planers cost $200 - $350 for a 12" capacity throat. The hand power tool type of planer is not as useful, unless you're building houses.

An alternative is the hand finishing plane, $30 new. The hand plane does small surface corrections and bevels. Test of finger skills.

Ed Taychert has a wonderful comment about building a scope with just a jig saw and a drill. Ed poo-poo's the mighty table saw. He gets those cuts done at the lumber yard.

Sanders. Porter-Cable's electric finishing sander get the nod for 110V units. If you have air, a small jitterbug and any 6" orbital rotary are useful. The air 6" orbital is tops for removing lots of material.

Drill press is universally recommended. Bench top, $ 100-175. Get one that has a crank to set the table height.

Joiner. Heavy equipment. Bevels and rabbiting. Not necessary, as a router with a big table does the trick.

Clamps. Buy 'em, make your own. All are good.

Thanks to everyone !!

Mark Cowan does custom f/ mirrors.

For an 18" here's a Dobson range of f/'s and heights:

Height = FL - diagonal distance(~11") + thickness (~1.5")+ base-and-cell(~3.5") clearance:

f/4 72" FL >> 66" Height
f/4.2 75.6 >> 69.6"
f/4.4 79.2 >> 73.2"
f/4.6 82.8 >> 76.8"
f/4.8 86.4 >> 80.4"
f/5 90 >> 84"
f/6 108 >> 102"

One item: NEWT OK's a 2.6" diagonal for the f/5 18" for natural EP's up to 50mm. That's using a 2" EP focuser with a 1" height and typical construction numbers.

I was doing numbers on a 16" this morning. Your 18" came to mind. The prototype for my 10" f/5 went well, so a prototype for the 16" is in the works. Sidewalk Astronomers plywood ideas with a truss-and-strings OTA and various design follies. Easy enough to do one for your 18".

A PLOP 18" cell is surprisingly easy. Couple of evenings. Hardest problem is getting the holes drilled dead-on to mm accuracy.

Your low-enough 18" looks doable.

There's a program called NEWT that includes semiechnical explanations. It runs in a browser and shows light rays

home.att.net/~dale.keller/atm/newtonians/newtsoft/newtsoft.htm

NEWT is useful.

I've been doing prototypes based on NEWT calculations. Works every time.

Very old turret vertical mill. Note that there is no columnar axis in the stand body. Just the quill/drill mechanism.