Anybody know what the edging that is often used to finish the ends of Sonotube
DOBs is and if it commonly available at some place like Home Depot or my local
autoparts??  

Thanks

jon isaacs

Hi:

Look for trim in an autoparts store or similar (stuff that goes along car door
edges). One thing we've done down here for small dobs is use the lip cut away
from an appropriately sized plastic flower pot.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
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Goto <http://members.aol.com/RMOLLISE/index.html>

Jon:
Ask for something like door edge guard material at a car parts place like
Pep Boys. It's sort of a "U" shaped  plastic channel. Comes in different
colors and has an adhesive in it. You just cut the right length and press it
onto the edge of the tube. Works well and looks good.
  Bill

I've had good success using wood embroidery hoops as "end rings". They often
fit 8", 10", and 12" sonotubes almost perfectly. If they don't you can cut
them down or split them to expand. I put the inner hoop inside the tube and
the outer hoop ring on the outside of the tube. I glue both on and then
{*filter*}them from the inside. They really add rigidity to the tube ends just
where it most needs it because of the primary cell and the secondary spider.
They only cost a $1 or so.

BPM

Hi there.  You posted:

You might want to try aluminum bar stock, as, iwht a little care, it can
be bent fairly easily to form end-rings which protect the ends of the
Sonotube.  You then just attach them with small bolts, and you have nice
rings which can be removed if you ever want to repaint the tube.  I have
done this with all my scopes, and it really saves on dents and dings
when the ends of the tube accidentally hits things.  Clear skies to
you.  
--

Prairie Astronomy Club, Inc.  http://www.prairieastronomyclub.org
Hyde Memorial Observatory:  http://www.hydeobservatory.info/

******************************************************
*     Attend the 9th Annual NEBRASKA STAR PARTY      *
* August 4-9, 2002  http://www.nebraskastarparty.org *
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I'm curious, David. How do you get the stock to bend smoothly to follow the
curve without denting it or leaving noticeably sharp bends?

TIA,
Chris

Hi Chris,

Good point - - There may be better ways, but I try to find a sturdy cylindrical object to bend
it over.  The cylindrical object has to be quite a bit more curved than the final shape because
of spring-back.  If you find a bending form the right size and bend the strip to contact the
form over perhaps 90 degrees at a time, I'm sure you'll find the curve fairly smooth.  But
finding that form is the hard part.  If the form is slightly too small, you can usually
"un-bend" it a bit here and there to bring the final size to what you need.

If you have to bend up more than one ring, it might be worthwhile to make a bending jig by
sawing out a disk bending-form from the end of a pine 2x8, or whatever width produces the
correct diameter,  and{*filter*}it down to the rest of the 2x8 with a number of heavy screws.  Then
add a heavy lag bolt spaced from the disk edge about the thickness of the material you're
bending so that you can catch the end of the material between the form and that bolt while you
force the material into a curve that contacts the disk around as far as possible.  With the
right size disk, this bending jig can turn out high quality and uniform bends.

Chuck

Hi there.  You posted:

Its kind of an "aquired" skill, although many experienced machinists or
metal workers can do it fairly easily for you if you don't want to try
yourself.  First, a "jig" can be constructed with the same diameter as
the tube (a reinforced cut-off section of tube material, ect.).  Then I
clamp the full-length piece of barstock (6 feet long) to the jig with a
Vice Grip (tm) locking pliers or a "C" clamp, using a thick piece of
cloth or thin carpet to protect the outer surface of the barstock.  I
then just grab the unattached far end and start pulling on the end to
*slowly* and gradually bend it around the jig, clamping it to the jig
every few inches with another "covered" vice grip as I go around the
tube (you need to have about 4 Vice Grips or C-clamps available, and
another person present is also helpful).  The 1/8th inch thickness
barstock is surprisingly flexable, so it bends a bit easier than one
might think.  Still, the whole bending operation does require just a bit
of hand strength to do properly.  
     This works until you get almost all the way around the tube, when
you have to remove the partially-completed ring and do some gentle hand
bending and fitting to get the ends to meet.  Sometimes, I put just a
tiny bit of initial bending into the end of the barstock with the stock
in a vice, but again, the actual technique is a combination of
cut-and-try strategies.  With my new aluminum tube (12 inch diameter
0.94" thickwall Aluminum irrigation pipe), I just use the tube itself as
the jig, since it is strong enough to widthstand the stress.  With
Sonotube, great care must be taken, as the clamping and bending can
distort or mar the tube (which is why I recommend using a small separate
cut-off section of the tube material with a couple of internal wooden
crossbeams to add strength, creating the "bending jig").  Clear skies to
you.        
--

Prairie Astronomy Club, Inc.  http://www.prairieastronomyclub.org
Hyde Memorial Observatory:  http://www.hydeobservatory.info/

******************************************************
*     Attend the 9th Annual NEBRASKA STAR PARTY      *
* August 4-9, 2002  http://www.nebraskastarparty.org *
******************************************************

of heavy screws.

You know, I was thinking the same thing after I read David's reply. Even for
making only a pair of ends, a jig would make them look really sharp. You
could rough cut a circle out of 3/4 inch plywood and then finish it smoothly
using a router and a simple circle-cutting jig. If you pre-cut and pre
drilled the bar stock, you could{*filter*}it down into the plywood using 1 inch
sheet metal (self-tapping) screws as you went around, eliminating the need
for any clamping pads (or clamps!). Then simply unscrew the finished
tube-end from the jig and install it on the sonotube.

Clear ones-
Chris

        Another tip to strengthen the ends is to take some superglue and run it
around the cut end of the tube. This will harden the tube end
significantly. Use a whole small squeeze tube per end. When you do this
use a lot of ventilation and of course don't touch the tube ends for a
while afterwards.

        - Mike -

To those who had suggestions:

I want to thank you for taking the time to help me out with this problem.

Some issues:

1. The tube has been sealed at the end with some sort of glue or sealer.

2.  The tube is 14+ in OD and about a 0.400 inch wall thickness.  I did
purchase some door edging at an autoparts but it did not fit.

3.  The aluminum is nice but requires significant work on my part.  I am hoping
for a cut and glue solution.

4.  The hoops sound interesting but there is little room between the sides of
the base and the OTA and a hoop would likely interfere.

5.  Mcmaster-Carr has some edging that looks just about right so I may go that
route or I might get my buddies at the machine shop to make me something
similar to what David K.. suggested except that they have roller.  

Thanks again....

jon isaacs

This is a good idea BPM. When making a sonotube ota I have
a standard technique if my mirror mounts and vanes dimensions
will permit. I double all ends of the sonotube by splitting at least
a foot of the tube, setting it inside the final tube and marking the
cut line needed, then recutting and gluing the inner doubler ...
sometimes Ill even expoxy it in. It improves stability where its
need most at the mirror mount bolts or screws and at that vital
vane-tube union. I like tubes that keep the optics in collimation
and if I cant have a fibreglass tube and if sonotube is my choice
then I double it at both ends. It makes a heavier tube, but the
optics stay in place especially over 8 inches.

The next thing I do is prime the heck outof my tubes.Prime and sand. Prime and
sand. Youc an even make a thin mixture of
water glass rosin and wipe that in and sand when set. That
makes a very rigid surface, surprisingly rigid. I then spray paint
eg. deRusto or something fairly good. If have made any number of ota that really
look like that have some rigid plastic surface
not to mention the hard shine which takes quite a beating and
holds up for years.

But I always double my tubes at front and rear even if Im going
to lay on the{*filter*}and forget a fine finish (just paint the leather,
as it were). Thereis nothing worse than a sono-tube that sinks
from the "strong forces' of mirror and vane bolts and screws.

Incidently, you can use a sonotube as a form,w hich is what these tubes actually
are. You can split them or cut a section
out of them, grease them up or use several brushed on layers
of dish soap (green soap works very well as a mold release)
and lay fibreglass right to the inside or over the outside of the
tube. Laying fibreglass matt works best - {*filter*} this with
rosin. It beats the high price of a Parks tube if you have no
other option.
Jerry