How to cut sonotube?

I bought a Discovery 12.5" PDHQ skeleton for my Meade 12.5" F4.8 optics. The
sonotube is 6" longer than I need, and removing the excess up at the focuser
end might help with a balance problem. (The tube is already as far back as
it can go without hitting the base, and it is still nose-diving.)

How do I cut it cleanly, and true, so that the end ring can be re-installed?
Would just a regular old fashioned wood saw do the trick? What kind of wood
saw? I don't know much about this stuff, but IIRC, there's a cross cut and a
rip cut? With the correct saw in hand, how do I make sure it goes in a
straight line to keep the end "square".

Any help would be appreciated.

Stephen Paul
Shirley, MA

I'd leave that 6" alone its affect on balance may not be insignificant, But
many ATM'ers recommend that the tube extend 1.5 times the tubes diameter beyond
the focuser to act as a light baffle. As any off axis light entering this end
of the tube could strike the field lens of the eyepiece and effect image
contrast, even produce ghosting. Also a longer tube helps slow dewing of the
secondary.

Besides if The tube is already as far back as it can go and it's still
nose-diving then you really need to add a bean bag or two to the primary end of
the tube. . .

I know adding weight to the tube isn't very appealing, but it can be extremely
effective.

I think you should at least try out the bean bag approach before chopping down
the tube.
Hey there is no need to get fancy for the bean bag test. Next time your at the
grocery store get a couple of 2 lb bags of dried pinto beans NOT The 1 lb
bags!

I took a pair of white tube socks and stuffed them with beans. I also added a
patch or two of Velcro to hold them in place. Seems to work fine and nobody
even notices they’re there.

As for cutting the Sonotube I use a Jig Saw. . .

Clear Skies, Roger ?:^)

Hi Stephen-

I'd suggest using a cross-cut saw (one with more teeth per inch). The
problem of keeping the cut square is tough if you don't have a jig of
some kind, and it would be tough to make one that would handle such a
wide tube. If you're confident that the forward end that is on it is
square enough, then take a framing square and lay it on the end of the
tube, then carefully mark of a bunch of dots six inches from the end.
Draw a line joining the dots with a pencil. Make the cut freehand making
sure that you follow the line.

If you happen to have a decent table saw, you could make a cradle to
hold the tube perpendicular to the blade and clamp it to the table,
place the fence 6 inches from the blade, butt the end of the tube in the
cradle up against the fence, and then rotate the tube into the blade to
cut it. I'd advise making a couple of cuts at an inch or two first to
make sure you have the technique right. It would give the cleanest cut,
and if you jig everything right so that the tube can only rotate and not
move in any other direction, this will give the perfect result. Be
careful though - table saws are dangerous. Figure out before hand
exactly how this will work so it's clear in your mind. Raise the blade
only high enough to cut a quarter inch or so into the tube. Make sure
that you dont pinch the cut and trap the tube against the fence because
it can kick back. Safety first! (The voice of experience talking).

Best of luck - Chris


Stephen Paul wrote:
I bought a Discovery 12.5" PDHQ skeleton for my Meade 12.5" F4.8 optics. The
sonotube is 6" longer than I need, and removing the excess up at the focuser
end might help with a balance problem. (The tube is already as far back as
it can go without hitting the base, and it is still nose-diving.)

How do I cut it cleanly, and true, so that the end ring can be re-installed?
Would just a regular old fashioned wood saw do the trick? What kind of wood
saw? I don't know much about this stuff, but IIRC, there's a cross cut and a
rip cut? With the correct saw in hand, how do I make sure it goes in a
straight line to keep the end "square".

Any help would be appreciated.

Stephen Paul
Shirley, MA

Instead of cutting it ( no the wood saw would not cut right, been there,
done that ), I'd put a velcos strip on the bottem of the rear of the tube
and use some bean bags with velcos on them.


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"Stephen Paul" wrote in message
...
I bought a Discovery 12.5" PDHQ skeleton for my Meade 12.5" F4.8 optics.
The
sonotube is 6" longer than I need, and removing the excess up at the
focuser
end might help with a balance problem. (The tube is already as far back as
it can go without hitting the base, and it is still nose-diving.)

How do I cut it cleanly, and true, so that the end ring can be
re-installed?
Would just a regular old fashioned wood saw do the trick? What kind of
wood
saw? I don't know much about this stuff, but IIRC, there's a cross cut and
a
rip cut? With the correct saw in hand, how do I make sure it goes in a
straight line to keep the end "square".

Any help would be appreciated.

Stephen Paul
Shirley, MA





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Stephen Paul asked:

I bought a Discovery 12.5" PDHQ skeleton for my Meade 12.5" F4.8 optics. The
sonotube is 6" longer than I need, and removing the excess up at the focuser
end might help with a balance problem. (The tube is already as far back as
it can go without hitting the base, and it is still nose-diving.)

How do I cut it cleanly, and true, so that the end ring can be re-installed?
Would just a regular old fashioned wood saw do the trick? What kind of wood
saw? I don't know much about this stuff, but IIRC, there's a cross cut and a
rip cut? With the correct saw in hand, how do I make sure it goes in a
straight line to keep the end "square".

Any help would be appreciated.

Stephen Paul
Shirley, MA


Hi There

If you take two double pages from a Newspaper and tape them together so
the total length is more than say 50" and inline, you can wrap the tube with
them. Being the least bit careful they will square up. Once that is done
tape them in place. You now have your edge guide.
To cut the tube, I've found a Common Hack Saw works fine. Just do your
"clean up" with a "Utility Knife".
But as was mentioned - a counter weight is easier!

Crazy Ed

"Stephen Paul" wrote in message ...
I bought a Discovery 12.5" PDHQ skeleton for my Meade 12.5" F4.8 optics. The
sonotube is 6" longer than I need, and removing the excess up at the focuser
end might help with a balance problem. (The tube is already as far back as
it can go without hitting the base, and it is still nose-diving.)

How do I cut it cleanly, and true, so that the end ring can be re-installed?
Would just a regular old fashioned wood saw do the trick? What kind of wood
saw? I don't know much about this stuff, but IIRC, there's a cross cut and a
rip cut? With the correct saw in hand, how do I make sure it goes in a
straight line to keep the end "square".

Any help would be appreciated.

Stephen Paul
Shirley, MA

Wrap a very large newspaper or length of lining/wallpaper round the
tube as a marking edge. Align the edge you want to use as a marker
dead straight at the overlap. Then snug up the paper tightly round the
tube. Tape tightly at the overlap. Tape to the tube when satisfied
with your alignment and final cutting position.
Now either saw to the edge of the paper. Or draw carefully along the
edge with a fine magic marker and then remove the paper. A carpenters
hand saw is quick. But a tenon saw (US=backsaw?) will make a neater
job. With fewer fluffy bits floating in the air afterwards. Power saws
are for wimps and complete overkill. Never miss a chance for a little
exercise. Even if you don't need it the rest of the population
probably does. ;-)

Chris.B

How do I cut it cleanly, and true, so that the end ring can be
re-installed?
Would just a regular old fashioned wood saw do the trick? What kind of
wood
saw? I don't know much about this stuff, but IIRC, there's a cross cut and
a
rip cut? With the correct saw in hand, how do I make sure it goes in a
straight line to keep the end "square".

The advice about wrapping the tube with paper is good - this is what we do.
As far as a saw goes, we use a Japanese razorsaw with 14 teeth per inch. It
cuts sonotube beautifully, and wants to cut straight. If you get one, I
think you will find yourself using it for other cutting as well.

However, I too wonder if this is going to solve your balance problem.
Adding weight to the rear is not the best solution, but maybe necessary?

Dennis

I've had success using a jigsaw with a metal-cutting blade. I found
the wood blades to give a rough cut. A band saw or table saw with a
fine-toothed blade might also be an option to help you keep things
square, but I've never used one for such a purpose.

How do I cut it cleanly, and true, so that the end ring can be re-installed?
Would just a regular old fashioned wood saw do the trick? What kind of wood
saw? I don't know much about this stuff, but IIRC, there's a cross cut and a
rip cut? With the correct saw in hand, how do I make sure it goes in a
straight line to keep the end "square".

Any help would be appreciated.

Stephen Paul
Shirley, MA

Thanks for all the ideas.

-Steve

Just make sure you have at least 13" of tube beyond the focuser. This helps
ensure good shielding from stray light outside the tube. Anything beyond 13"
is "safe" to cut off.






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