For anyone who migrates past the kit stage of hobby rocketry, inevitably the subject of cutting airframe tubing comes up.  There must be a million ways to go at cutting a tube, but do we ever find one that truly meets our criteria for what the ultimate rocketry airframe tubing cutter should be?

Kraft cardboard, phenolic, flexible phenolic, quantum tube, even fiberglass.  It all comes with its own set of individual considerations and seems to be approached differently for each material. I dare to venture a guess at the number of hours that has been spent by people daydreaming of the perfect tubing cutter.

This 6" PML air frame is supported by 4 in-line skate wheels and turned by a rubber band. The stop on the right keeps the tube from moving.

The Dremel is tie-wrapped to a stand so the base of the stand slides against the bracket that holds the wheels. Just push the Dremel forward as the tubing turns.

When all tubes are cut for a rocket just unclamp the pieces from the table and store on a shelf. The right angle head stays with the base while the Dremel goes back in it's case.

David Flynn seems to be someone who turns those type of daydreams into reality.  When cruising around his web site, I stumbled upon numerous innovative ideas and concepts that had been converted into cold, hard reality.  Dave's tubing cutter was indeed a very innovative device and one that would certainly capture the attention of readers.

The idea behind airframe tubing cutters is pretty simply: give the user a way to precisely position a given body tube so that it can be squarely cut around the circumference of the tube without the tube drifting in either direction, causing an unsquare cut where the beginning cut point did not meet up with the ending cut point.  Anyone that has used a plumber's copper tubing cutter knows that just because the tube is held squarely in the V-joint of the cutter does not always mean a square cut.

The tried and true method of cutting airframe tubes has always been to create a tube holder which consists of two flat surfaces attached to each other to form a 90-degree angle, but rolling an airframe tube by hand while trying to make a straight cut it not an easy task — it's one of those things that makes you feel like you have two left hands. Flynn's design takes a similar approach but with much better results. 

Instead of two flat surfaces, he decided to "roll with the changes," supporting the airframe tubing using four wheels he bought from K-mart that were designed for use on inline skates.  Inline skate wheels usually have excellent urethane or similar hard rubber "riding" surfaces that are perfectly round along with good ball bearing-type mounting points which let them rotate freely without noticable wobble.

Flynn started by mounting the wheels to two angled metal supports in which had drilled and tapped holes for mounting the inline skate wheels.  He calculated the proper mounting points to drill the holes so that for a given size of tubing, the tubing could rotate freely above the bracket without striking it. These dimensions were duplicated in both brackets.

To positively stop the tube and hold it in the same spot, Flynn places a simple stout metal upright at the end of the tube to stop it from moving any further. On tubes with square ends, that's all that he's needed.  On larger tubes or tubes with uneven ends, the stop upright is replaced by a larger version with a large flat face that allows the tube in question to rotate against it in its entirety, a process which usually requires three passes to make sure both ends end up with perfectly square ends — hardly a consideration to get the desired perfect results.

Making the tube rotate is a task resolved by slipping a large rubber band over the tube and then placing it over a small low-RPM motor with a v-pulley on it. The motor is a 300 RPM gear motor with a 1" diameter output pulley so that the tube surface moves into the cutting wheel at about 600 to 900 inches per minute, give or take some slippage. Small tubes turn more RPM than big tubes, but the surface moves at the same speed. Flynn said the trick is in aligning the brackets and the spinning motor so that the tube slowly walks toward and seats itself against the upright stop at the end. Once that has been done, it works as smooth a silk.

Handling the cutting duties are a Dremel tool with a 90-degree adapter that houses either a Dremel 1-1/4" fiber-reinforced abrasive wheel for kraft cardboard and phenolic tubing or for quantum-style or other plastics, a rotary saw blade. Dremel no longer makes rotary saw blades, but Micro-Mark has a good selection of small to large saw blades. Flynn says that the 1-1/4" or larger fiber-reinforced abrasive wheels have cut every kind of tube he's tried.

Flynn designed his setup so that the bracket that held the Dremel butted up against one of the brackets that held the inline skate wheels, so the tubing's cut length is set by moving the stop at the other end.  Once the tubing is mounted and spinning, Flynn just turns the Dremel on and moves it up to the tube for the cut, cutting extremely square and smooth ends.

Do you have a favorite technique that would make a great Tech Tips Series article?  Please send us an email and let us know.  For your contribution, you could receive free gifts from friends of Rocketry Planet.  Please read the program details page for complete information.

07-06-2007 03:30 PM  #1
JohnCoker Not-so-new Member   Joined: Jul 2007 Posts: 23	For cutting composite tubes, a wet saw works really well and has the advantage that it captures the dust in the water. http://www.jcrocket.com/tubesaw.shtml

09-06-2007 06:37 PM  #2
sberfield New Member   Joined: May 2007 Posts: 5	I use a table saw Two strips of wood, a stop block, some clamps and my table saw work great for me. Considering that I don't cut tubing all that often, most of the jigs I see online seem like WAY overkill.

09-10-2007 01:21 AM  #3
mc2rocket New Member   Joined: Sep 2007 Posts: 3	Table saw works great I've cut tubes from 1" to 10". Just make sure you use a fine cut blade. Irv

09-20-2007 11:38 PM  #4
LeeR New Member   Joined: Sep 2007 Posts: 9	Unless you need to cut a 34" tube in half, most bandsaws are excellent for cutting tubes. The thin blades also minimize the waste. I have a Powermatic 14" for woodworking, but my little Delta tabletop model is perfect for cutting rocketry items. I also use it to trim plastic nose cones, straight or at an angle, for making intakes and nozzles on fantasy/fighter style scratch-builds.