Another stuck tube

[Scrapmaster87]

So the back story:. I got myself a 40 some inch long 4" alumnium pipe to use as a mandrel for my next (now two) projects. I polished it up, gave it a wrap of parchment paper, sealed the seam with grease, and proceeded to make a 20" trial tube.

Rolling the 3 layers of 7781 eglass was trouble free, as was the follow-up coat of epoxy to smooth it out. At first the tube rotated freely a few degrees and moved lengthwise a few inches. Unfortunately my 2x4 and rachet strap technique only yielded a few inches.

To salvage the operation I picked up some dry ice and reversed the straps. The game plan was to get the tube un-stuck so I could polish the mandrel to allow the tube to pass. Sadly I could only reverse the tube a 1/2"

My next thought is to use my pressure washer to "float" the tube off via a hole I've drilled in it. I'm starting to think this is more trouble than it's worth and that the tube should be split to be used for couplers. Does anyone have a better idea to salvage the situation?

Once this little saga is over, what should I do next? I need a 4.5" ID tube for my projects (and I'm painfully cheap). Should I resort to a PVC or ABS pipe as a replacement mandrel, or is there someone here willing to turn this pipe true for me?

 

[watheyak]

I've used a long piece of all-thread, washers and other hardware to force another tube up against the stuck tube. Then tightened with a ratchet. Slow going, but it worked.

You may have a mandrel that isn't straight or varies in diameter. If that's the case, nothing will help.

It also could be that some of the parchment paper has bunched up underneath the layup. Especially since it won't move in the other direction. I believe that's what happened in my situation with the all-thread.

Parchment paper works or other release films work for lots of folks. I've had mixed luck. Now I just wipe on a product call Frekote 700NC. You can find spray cans of it for relatively cheap.

It works like magic. I just chill the mandrel a bit and it slides right off.

 

[tfish]

Is this just a random tube, or is it 'fairly' true end to end?
Is there any tape holding the parchment paper under the fiberglass? If so, you're screwed. If not there is some hope.
Cut the parchment paper flush with the FG tube.
remove the ratchet strap stuff.
Place masking tape rings about 1/2 inch away from the ends of the FG tube. These will be markers to see if the tube moves any.
Spray some WD-40 around the ends of the FG tube.
Stack 2 or 3 door mats together to form a good base on the floor.
Take the tube and drop one end from about 12 inches high onto the rubber mats.
did it move any?
can you twist the FG tube any?
No If the tube does move some..then hangs up..try getting it to move the other way. Does it move further one-way?
drop the tube on the other end?
did it move?
Can you twist it?
Repeat above steps
dropping form higher
no
start slamming the tube
still no?
Freeze both the tube and mandrel
repeat the above steps.
still no?
Tube is stuck to mandrel.
Rethink project

Ben there done that more then once!

Tony

 

[jqavins]

Warning: I've never done any of this stuff and am talking out of my backside.

How did you apply the dry ice? If it was from the outside, that would mean that the tube was cooled more than the mandrel. Both shrink and, yes, the aluminum shrinks by more per degree of cooling. Still, you'd be better off if the mandrel is cooled by more degrees than the tube rather than fewer.

So if that's what you did, you might try putting the dry ice inside the aluminum pipe instead, so that's what cools off the most.

Or I could be all wet.

 

[kalsow]

I cut a tube off a mandrel just a couple days ago. I believe it happens to everyone!

I have better luck if I remember to pull the layup when it's still green. Epoxy tends to shrink (~1%?) when it cures. It's much easier to get the tube off the mandrel before the final shrinking.

 

[tfish]

I do that sometimes too. Don't do it to early...the tube may not hold it's shape. Once the epoxy starts to set up..you can untape the parchment paper and spin and slide the tube every few minutes. This seems to help with mandrels not perfectly round.

Tony

 

[SDramstad]

Until I know the mandrel is straight and true i use 2 mil mylar to wrap around the mandrel instead of parchment paper. I found it slides easier then the parchment paper. If you insist on parchment paper put 2 or more layers on the mandrel. That helps also. With a 4 inch mandrel and standard parchment there isnt much overlap. Epoxy can migrate to the mandrel and if it does you are pretty much screwed.....

 

[n27sb]

I think your parchment paper has bunched up. As mentioned in one of the responses you may be able to press if off by rigging something to push it off.
As an alternative, this is how I set up my tubes.
I use 2 mil mylar and no wax or grease. Dry, dry dry and clean is the key.
My mandrels are usually .010 to .020 undersized and I use enough mylar wraps to get to the desired ID.
This particular mandrel has a layer of CF permanently applied in order to attain the desired OD.
Using this method you can make body tubes and couplers from the same mandrel.
I set up some clear packing tape by securing it sticky side up on the work table.
I cover about 1/3 of the width with masking tape.
Carefully place the top edge of your mylar on the tape, covering about 1/2 of the sticky surface.
Start rolling up the mandrel on the bottom edge of the mylar.
After a wrap or so you can apply a little pressure to tighten the wrap by pulling down away from the top taped edge.
Now roll all the way to the top over the sticky side of the tape.
Using a razor carefully cut the masking tape where it meets the mandrel.

You now have a multi layer of mylar that is not taped to the mandrel but is taped on the outer overlapped end.
This prevents epoxy from seeping underneath the edge.

After your layup is cured it will slide easily off the mandrel. DO NOT TWIST as you remove it as it will cause the mylar to tighten or bunch. In the past I tried waxing the mandrel or mylar and it alway caused things to stick.

Hopefully the photos show this method. It is hard to see the clear tape but look for the glare. Hope this helps.
Feel free to PM me if you have more detailed questions.