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Jul 05, 2014, 09:04 PM
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Discussion

paper blast tube test


A while back, I asserted that kraft paper rolled up with glue makes a convenient and durable blast tube. I encountered a lot of scepticism, although no one really said why it couldn't work except that it wasn't strong enough. Or something like that. Anyway, I thought it might be good to do a reality test. So I rolled up a tube around a 1 1/4 inch (32mm) dowel. I used enough layers so the wall thickness was around 0.040" (1mm) or maybe 0.050" (1.3mm). I used Titebond 3 for the glue. I meant to test it after only a few hours, but I ended up leaving it in the car for weeks. The workmanship is lousy and it's ugly, but it works fine. I made up a 32 strand motor from old 1/8" FAI Tan (or Tan II? box doesn't say). Batch was June 00 2001. I've tried to take care of it over the years. The whole thing was pretty short because I didn't want to waste rubber. No damage was apparent. After, I tried supporting a cinder block with the tube. The ends of the tube weren't square, so it did to some damage to the very end of the tube. Unfortunately, I seem to have deleted the picture.
The rest of the pictures should be attached to this post.
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Jul 05, 2014, 09:35 PM
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quick to make


If I'd known where everything was, I probably could have rolled this thing up in 10 minutes. I've rolled some small ones without a form, though that's a bit trickier and tends to come out oval. Anyway, it's less time than going to the store or looking tubes up on line, particularly if you need an unusual size.
Sep 04, 2014, 06:57 AM
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Cool.

Many years ago I ordered the "make your own rocket motors" book from that ad in the back of the various magazines ... one bit that came with the documentation was how to "roll your own" paper tubes. I promptly made one and it was bulletproof. I think I still have it, haha ... I rolled it in like 1988 or somesuch so it's pretty old.

I still have the instruction sheet, if you're interested let me know and I'll scan it.

Cheers-
Dave
Sep 06, 2014, 09:57 PM
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Thanks! That would be nice. Maybe they have a few tricks in that instruction sheet that I haven't thought or heard of. Seems to me I once made a rocket with a tube like that to fly with my nephew, who liked rockets at the time. Never did get to fly it with him. The nose cone was a cork turned on the hub of a pedestal fan after removing the guards and fan blades.
Sep 09, 2014, 01:41 PM
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I thought I had it on my machine ... no luck. I have some paper copies I made after I unearthed it. I'll bring it to work and PDF scan it for you.

Cheers-
Dave
Sep 10, 2014, 11:38 AM
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Paper tube instructions ... scanned in PDF (attached).

Regards-
Dave
Sep 11, 2014, 03:23 PM
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Thanks! I don't think I've run into some of the problems he writes about, but blast tubes don't have to be quite as precise as rocket motor tubes. It's now in my airplane files.
Dec 06, 2015, 08:59 AM
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I was curious if you had tried rolling paper tubes?

I rolled about 8 tubes over the year. I was attempting to fabricate a motor tube to accomodate an Estes "F" engine. Turns out an F has a 24mm OD (IIRC) ... and so does 1" CPVC (again IIRC ... I cleaned up my shop and the CPVC form tube is not lying around).

I also found the tube I rolled back in the late 1980s. The tubes I rolled recently weren't as good as the one I made waaay back when. The newer ones didn't roll smoothly and have little bubbles and delams here and there. I don't think they'd harm the structural integrity at all, but they certainly don't look nice.

Idea here was to build a scale (flying) model of an Estes "Alpha" using oatmeal "boxes" as body tubes. Project, like many others, is lying around about 1/3 complete.

Also interesting is that 24mm OD is the same as some of the smaller reloadable rocket motor cases. So, rolling tubes like this would be handy for other projects as well.

Anyhoo, rolling the tubes per the instructions I scanned/posted for you results in a product that (not surprisingly) shrinks as it dries. So I had to figure out how to compensate, which I did by wrapping the CPVC form with a couple of turns of 6mil polyethylene (from Home Depot ... "drop cloth" in the painting aisle). There is some technique in there that I can share with you if you're interested - removing the plastic after the tube comes off the form required some noodling.

Also, wallpaper paste (the "glue of choice" per the scanned instructions). That can be had at Lowes and Home Depot as premixed adhesive. Comes in a resealable tub, and cleans up with water. Very handy, although the water base is a bit problematic with the paper since it causes shrinkage, etc. ... although not terribly different than what we see with Japanese tissue (or balsa) and water ...

Cheers-
Dave
Dec 07, 2015, 11:15 AM
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I don't remember rolling any precise tubes. Or any tubes at all,lately. Hmm...I might have rolled a tube for a rocket glider I built, but that flew away, so I can't check it.

Most of the blast tubes I rolled were many years ago.

Epoxy and kraft paper is very tough stuff and probably doesn't shrink as much. But you'd have to compress it over the form, I think. Plus it has to have some time to soak in, and the epoxy probably needs to be relatively low viscosity.

Your Alpha project sounds spectacular. What are you doing about a nose cone?

I seem to recall having trouble removing plastic from some of my projects as well. At one time I tried to make large tailbooms for RC gliders. I foolishly post cured them before loosening from the mandrel. Very tough to remove after that!

I wonder if baking parchment would come out easier?
Dec 07, 2015, 11:29 AM
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Quote:
Originally Posted by lincoln View Post
Your Alpha project sounds spectacular. What are you doing about a nose cone?
I'm thinking pink foam. Circular sections (perpendicular to the cone axis) glued to a dowel. Attach to drill, sand to shape.

Quote:
I seem to recall having trouble removing plastic from some of my projects as well. At one time I tried to make large tailbooms for RC gliders. I foolishly post cured them before loosening from the mandrel. Very tough to remove after that!

I wonder if baking parchment would come out easier?
The plastic film comes out easily, the problem is rolling a long tube (say 20" in length) and then removing the sheet plastic without disturbing the shape of the finished tube (but wet - the kraft paper has been pretreated with wallpaper paste (and left to dry), to roll the tube one has to first wet the kraft paper and then roll on a form).

I settled on making some "loops" with the plastic sheet that sit on the inside of the tube after removal from the forma. I capture the loops with 2 arrowshafts, clamp, and then "roll up" the plastic by rotating the arrowshafts. Writing doesn't explain it well ... maybe I need to make a video.

Anyways, the plastic needs to come out so that both sides of the wet tube can dry evenly ... otherwise I think the tube would warp.

-Dave


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