Cutting Sonotube--conflicting views
Christopher Gunn
I may have to cut about an inch off the bottom of the tube of an older
Coulter 13.1" Dob, and I'm finding quite a few recommended ways to
do it on the AstroNet ATM archives. Suggestions include:
--A mat/package/"hardware" knife
--A razor blade (after scoring surface with knife above)
--A hack saw
--A saber saw
--A Ginsu knife (this from Phillip Harrington; unclear if he's kidding...)
What's the story here? Saber saw's obviously easiest, but I worry about
it leaving a messy edge. This is the 16" tube, probably 3/8 of an inch
thick. Suggestions from experienced Sonotube cutters?
Christopher Gunn Molecular Graphics and Modeling Laboratory
1k1...@kuhub.cc.ukans.edu University of Kansas
Phone: 913-864-4428 or -4495 Malott Hall
Lawrence, KS 66045
Raymond Cash-Le Pennec
In <1k1mgm-1908...@kumgm3.pharm.ukans.edu>
Hi Christopher,
The saw I use is one made by the Swedish firm Sandvik; I am sure it is
their most popular saw: about 3" wide, 14" long, recognizable by a
curved veneer saw on the upper front of the blade (which you don't use
for your application). A good saber saw will work too, but I feel I
have more control with the Sandvik hand saw. Yes, you will have a
little "fuzz," but nothing a little sandpaper can't clean up. The real
trick is how to cut it square. If you are only cutting 3" off an
already square tube, no problem--just use a combination square set at
3"; if however the end you want to cut is not square, you will have to
wrap something flat, flexible, and wide around the tube to score a
line; a 4" piece of formica would be ideal, but in a pinch, I remember
using a strip of brown wrapping paper--worked fine.
--Ray--Sidewalk Astronomers, SF:
http://members.aol.com/raycash/sidewalk.htm
Michael Heinz
1k1...@kuhub.cc.ukans.edu (Christopher Gunn) wrote:
>What's the story here? Saber saw's obviously easiest, but I worry about
>it leaving a messy edge. This is the 16" tube, probably 3/8 of an inch
>thick. Suggestions from experienced Sonotube cutters?
I have a related question - how do I (a) cut a decent hole for a
focuser and (b) accurately place the holes for the spider and the
cell? I practiced on a test tube, trashed that with a hole cutter
bit. After practicing and getting reasonable results with a razor
knife, I trashed what was supposed to be my main tube by cutting the
hole to large on one side - it partly overlaps one of the focuser's
mount holes and generally looks awful. The final straw is the slight
errors in the mount holes for the !@#$%@## spider.
I've just bought my third tube - anyone have any hints???
-----------------------------
Michae...@worldnet.att.net
Greetings New User! A clever or insightful quote or saying should
be placed in this file before you use this program.
bryan leenheer
Christopher Gunn wrote:
>
> I may have to cut about an inch off the bottom of the tube of an older
> Coulter 13.1" Dob, and I'm finding quite a few recommended ways to
> do it on the AstroNet ATM archives. Suggestions include:
>
> --A mat/package/"hardware" knife
> --A razor blade (after scoring surface with knife above)
> --A hack saw
> --A saber saw
> --A Ginsu knife (this from Phillip Harrington; unclear if he's kidding...)
>
> it leaving a messy edge. This is the 16" tube, probably 3/8 of an inch
> thick. Suggestions from experienced Sonotube cutters?
>
> 1k1...@kuhub.cc.ukans.edu University of Kansas
> Phone: 913-864-4428 or -4495 Malott Hall
> Lawrence, KS 66045
Hello Christopher,
I wouldn't use a saber saw unless you have some way to keep the sonotube
from jumping with the blade. A good quality, high tooth-per-inch handsaw
will cut that sonotube just fine, with a minimum of fuzz. As for the
fuzz, just use a sanding block with some 100 to 200 grit sandpaper and
it'll come right off.
--
All opinions are my own and do not
necessarily agree with the op-
inions of my employer.
Tim Gillespie
Christopher:
Just a few observations:
Christopher Gunn wrote:
>
> I may have to cut about an inch off the bottom of the tube of an older
> Coulter 13.1" Dob, and I'm finding quite a few recommended ways to
> do it on the AstroNet ATM archives. Suggestions include:
>
> --A mat/package/"hardware" knife
Sonotube is fairly thick and impregnated with wax. It would be quite
difficult to get a good clean edge with any kind of knife. You would
not. I suspect, be able to get it in one pass, and that would cause
problems.
> --A razor blade (after scoring surface with knife above)
See above.
> --A hack saw
A hacksaw might work, but is somewhat difficult to handle. It is
designed for rough cuts in metal. It has a very thin blade, with fairly
small amount of tooth offset, cutting a narrow kerf and creating good
potential for tearout. This is further aggravated since the saw must be
cutting at two points on the tube at once.
> --A saber saw
This tool would be my suggestion. I have used one before to cut Sonotube
with good results. First, get a GOOD quality fine woodworking blade.
Don't skimp here. The cheapo blades are not as sharp, and sharpness is
key. Next, put masking tape over the path of the cut, on both sides of
the tube (inside and out). Make sure that the tape makes good contact.
This will minimize tearout. The tape on the outside of the tube is the
most important, since the sabre saw cuts on the upstroke, so make SURE
the tape is tight. Put two layers on if you need to. Mark the cut line
clearly on the tape. Make your cut. Take your time. The faster you go,
the more you risk tearout. You may want to cover the shoe of the sabre
saw with masking tape to keep it from marring the tube. Immediately
remove the masking tape (carefully). This is best done by pulling it at
a right angle towards the end of the tube, with the tape pulled back
over itself. If you do get a rough edge, or some tearout, some light
sanding will take care of it. Finally, most hardware stores carry
aluminum edging that bends and cuts easily. You could trim the ends of
the tube with it.
> --A Ginsu knife (this from Phillip Harrington; unclear if he's kidding...)
Hmmmm. I think he's kidding. If not, I would advise against this tool.
>
> What's the story here? Saber saw's obviously easiest, but I worry about
> it leaving a messy edge. This is the 16" tube, probably 3/8 of an inch
> thick. Suggestions from experienced Sonotube cutters?
>
> Christopher Gunn Molecular Graphics and Modeling Laboratory
> 1k1...@kuhub.cc.ukans.edu University of Kansas
> Phone: 913-864-4428 or -4495 Malott Hall
> Lawrence, KS 66045
Good luck...
Tim Gillespie
Michael Edelman
Christopher Gunn (1k1...@kuhub.cc.ukans.edu) wrote:
: I may have to cut about an inch off the bottom of the tube of an older
: Coulter 13.1" Dob, and I'm finding quite a few recommended ways to
: do it on the AstroNet ATM archives. Suggestions include:
: --A mat/package/"hardware" knife
: --A razor blade (after scoring surface with knife above)
: --A hack saw
: --A saber saw
: --A Ginsu knife (this from Phillip Harrington; unclear if he's kidding...)
: What's the story here? Saber saw's obviously easiest, but I worry about
: it leaving a messy edge.
After cutting, sand the edge with medium sandpaper to remove most of the
fuzzies. Then get some plastic weatherstripping from the hardware store-
the kind that just slips over the edge of a sheet- trim it to length,
and affix it to the cut end with Polyseamseal. (You want the kind that's
a square channel)
To seal cutouts made for focusers, sand and dribble a little superglue
around the edge. Works great.
--mike
Bob Scholtz
I have cut a number of focuser holes in sonotube with a hole saw with
no problems. You may be pressing too hard which will cause the saw to
tear through on the inside. Press just hard enough so the saw will
cut, and let it do the work. If you must press excessively hard you
may have a dull saw. Also, I am assuming that you are using a single
cutter on an arbor, not one of the cheap hole saws with multiple
diameters all stacked together.
As far as positioning the optical elements in the scope; the distance
between the primary mirror (front face), and the diagonal (center) is
as follows:
Distance = Focal length of the primary - (OD of the tube/2) - racked
in focuser height - about 1inch of focuser travel
Leave about 6-8 inches at the front of the tube, in front of the
focuser as a dew shield. Cut the focuser hole, and then position the
spider such that the diagonal is centered under the focuser. Usually
the diagonal holder is on a stud that can be adjusted in and out, so
the location of the spider is not real critical.
Then measure back down the tube and mount the mirror per the above
formula. Do a little pre-measurement to make sure the mirror won't
end up out the back of the tube.
This is all described in Richard Berry's book, "Build Your Own
Telescope". It's available from Willman-Bell, and might be in your
local library.
Good luck,
Bob
Michae...@worldnet.att.net (Michael Heinz) wrote:
>1k1...@kuhub.cc.ukans.edu (Christopher Gunn) wrote:
>>What's the story here? Saber saw's obviously easiest, but I worry about
>>it leaving a messy edge. This is the 16" tube, probably 3/8 of an inch
>>thick. Suggestions from experienced Sonotube cutters?
>I have a related question - how do I (a) cut a decent hole for a
R. Klappal
1k1...@kuhub.cc.ukans.edu (Christopher Gunn) wrote:
>I may have to cut about an inch off the bottom of the tube of an older
>Coulter 13.1" Dob, and I'm finding quite a few recommended ways to
>do it on the AstroNet ATM archives. Suggestions include:
>--A mat/package/"hardware" knife
>--A razor blade (after scoring surface with knife above)
>--A hack saw
>--A saber saw
>--A Ginsu knife (this from Phillip Harrington; unclear if he's kidding...)
>What's the story here? Saber saw's obviously easiest, but I worry about
>it leaving a messy edge. This is the 16" tube, probably 3/8 of an inch
>thick. Suggestions from experienced Sonotube cutters?
>Christopher Gunn Molecular Graphics and Modeling Laboratory
>1k1...@kuhub.cc.ukans.edu University of Kansas
>Phone: 913-864-4428 or -4495 Malott Hall
> Lawrence, KS 66045
Assuming you can get some clear surface to 'roll' the tube on, why not
build a jig to hold the tube and cut it on a table saw? A V-shaped
jig would let you rotate the tube over the blade, and I'd expect a
very clean cut.
Rich
kla...@xnet.com
41N48' 88W15'
================
A new civilization is emerging in our lives, and
blind men everywhere are trying to suppress it.
A. Toffler
================
lskr...@wizard.com
Tim Gillespie wrote:
> > --A saber saw
>
> This tool would be my suggestion. I have used one before to cut Sonotube
> with good results. First, get a GOOD quality fine woodworking blade.
> Don't skimp here.
Yes! Exactly!! Listen to Tim, this is the best way. Use a very fine (many
teeth per inch) blade.
For tight cuts, focuser holes, etc, I used a Dremel tool with a very good
cutter wheel, but you got to have a steady hand and patience.
Regards,
Tom
Russell Durkee
Tim Gillespie <tgil...@conc.tdsnet.com> wrote:
Whenever I cut Sonotube...or more often rocket tubes...
I always use a razor blade. This takes some time but if
you do it carefully the edge will be smooth and square.
Measure the amount of tube you want to cut off.
(Critical part)...draw a line around the tube where you
want to cut the tube. (Better idea here?)
Stick 3 or 4 layers of masking tape on the portion to cut
off so that the tapes edge follows the line you drew around
the tube. This gives you a relatively straight edge to work from.
Make several light passes over the line with a very sharp blade...
only scratch the surface on the first few passes. On the second or
third pass apply a little more pressure..the key here is to follow
your original line and not let the blade stray. Do not try to cut the
tube in 1 pass, you cannot get a clean line this way. It usually
takes 10 or so passes to get through.
Sand the edge square with a sanding block or a belt sander.
I have used this method to cut cardboard tubes for years and
it is much better than using a saw.
Good Luck
Russ
Russell Durkee
oops ignore the first line in my last post....
Russ
Brian Nestel
Christopher Gunn wrote:
>
> I may have to cut about an inch off the bottom of the tube of an older
> Coulter 13.1" Dob, and I'm finding quite a few recommended ways to
> do it on the AstroNet ATM archives. Suggestions include:
>
> --A mat/package/"hardware" knife
> --A razor blade (after scoring surface with knife above)
> --A hack saw
> --A saber saw
> --A Ginsu knife (this from Phillip Harrington; unclear if he's kidding...)
>
> What's the story here? Saber saw's obviously easiest, but I worry about
> it leaving a messy edge.
A sabre saw works ok just make sure you get a good guide line and also
use a very fine toothed blade or a piece of broken hacksaw blade to
minimize the rough edge when you cut. Finish the edge with sanding.
Aloha
Brian
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