Re: [ATM] New with starters questions

["Scott Ewart" <scott.e@quicksurfer.com>]

Joel,
    Let me give it a shot.  Here is some of my advice.  If you go with 10", 
I'd make it f/6, not f/5 unless you're short.  Makes for more comfortable 
viewing.  F/5 is fine for a 12".
1.  Don't size or make your mirror box first if you want the upper cage to 
nest inside the mirror box for transport.  Build the upper cage first.  Then 
build the mirror box big enough to fit.
3.  Half circles are fine.  Just make a full circle and cut it in half. 
However, keep in mind that half circles restrict the separation of the 
bearing pads to under 90 degrees apart.  If the radius isn't big enough, 
there may not be enough friction for a light-weight scope.
4.  Hopefully someone can find a link to plans, but if not, the Kriege book 
is good to work out of.  Most of what's in there can be scaled to your size. 
It might even help you to make a scale or even full-size drawing starting 
with the mirror and its light cone.  There's no one "right" way to do it. 
Just make it the way you want it.
5.  You can use simple math a lot to help you get the balance at least 
close.  Use the book.  This is another reason to make the mirror box after 
the upper cage.  You'll need to know how much the cage weighs.  The height 
of the mirror box is determined by the required position of the altitude 
bearings.  Math should get you close.  Build the whole tube assembly, find 
where it balances, and mount the altitude bearings at that point.  Then 
build the rocker box last to clear the mirror box.

Scott


----- Original Message ----- 
From: <frog3@freeler.nl>
To: <ATM@atmlist.net>
Sent: Thursday, April 14, 2005 5:33 PM
Subject: [ATM] New with starters questions


Hello all,
i'm Joel, from the Netherlands, i'm new to the group.

i would like to ask a few things to help me on the way to building a
first 20, 25 or 30 cm truss dobson telescope. (8", 10" or 12")

probably a 10" as this seems to be the best compromise for me at this
time, regarding cost and final size, i would like to make it about F/5,
so around 1250mm in the case of the 25cm.

first general question:
is it alright if i talk in centimeters and milimeters here? as it is
easyer for me to think about than to think in the feet and inch conversions.

first atm question:
if i want a 25 cm dobson tlescope, should i make the mirrorbox about 30
cm? or is this too small or too big? (roughly 2" more than the size of
the mirror)

2:
What is better costwise: making a mirror out of a blank and having it
aluminized and coated or buying the most inexpensive ready-made usable
10" f/5  mirror?
and what will  both of these options more or less exactly cost?
and where should i buy it? here in the netherlands? or in europe? or
doesn't it matter? what would be the best for the price including all
shipment(s) and where should i 'shop'? and do any of the people of this
list also sell atm supllies?

3:
I would like to make the , what i believe are called sidebearings, in
sort of a half circle, instead of a circle, is this a lot more difficult
to do than just a making a plain circle, or does it make no difference?

4:
does anyone have any drawings or plans (or how should i be calling this
in particular? please help the novice) with exact sizes for everything?
just to function as an example for me to 'draw on', because it's quite
difficult to be doing this from scratch, or even a boook, that is what i
find at least, i have the Kriege book of "The Dobsonian telescope".

5: (very important, so i'm not sure why it ended on place 5 ;)
what to make first? and when does the balancing of the telescope have to
be done? which part is it that neds to be re-adjusted for the balancing,
and therefore

6:
What am i forgetting?!..... :) ....very important to ask. :)

Thank you all,
Joel



_______________________________________________
ATM mailing list http://www.atmlist.net/