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Author Topic: Making fiberglass tubes  (Read 1137 times)
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jakepF1D
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« on: April 19, 2017, 01:06:47 PM »

I'm making fiberglass tubes for the VP hubs I'm planning to sell and I took a few pictures of the process.  In this case the tubes are going to be 1.8mm ID, and they're made from 2 layers of 0.6oz fiberglass with EZ-Lam 60 resin. 

The mandrels are spiral wrapped with plastic from a grocery bag to create a thin barrier between the resin soaked fiberglass and the mandrel.  The fiberglass is prepped by spraying it with hairspray to keep it from falling apart when it's cut into narrow strips.  All of the cutting is done with a rotary cutter from a craft store..

After spiral wrapping each mandrel with 2 layers of fiberglass in opposite directions, they're thoroughly soaked in resin to make sure the fiberglass is saturated.  I then place the mandrels between paper towels and use a Foodsaver vacuum bag to remove as much excess resin as possible. 

The final step is wrapping them very tightly with another layer of spiral wound plastic strip.  For this outer layer I use plastic from a window insulation kit.  It's much tougher than the plastic bag material.  This compresses the fiberglass against the mandrel and produces a nice finish on the outside of the completed tube.

I'll post more photos tonight when I pull these tubes off the mandrels.  Right now the resin is curing.
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Making fiberglass tubes
Making fiberglass tubes
Making fiberglass tubes
Making fiberglass tubes
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OZPAF
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« Reply #1 on: April 19, 2017, 07:40:12 PM »

Interesting approach. Do you have any trouble releasing the tubes from the mandrel and have you tried the technique on larger say 1/4 to 3/8" tubes?

John
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jakepF1D
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« Reply #2 on: April 19, 2017, 08:27:12 PM »

I've attached a few more photos.  The first shows the mandrel with the outer layer of clear plastic.  The second shows a tube that's cut to 15mm long and slid back over the mandrel after removing the liner.  The third just shows the finished tube.  These tubes are weighing about 6-7mg for a 15mm length.  That works out to about 11mg per inch.
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Re: Making fiberglass tubes
Re: Making fiberglass tubes
Re: Making fiberglass tubes
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jakepF1D
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« Reply #3 on: April 19, 2017, 08:29:52 PM »

Interesting approach. Do you have any trouble releasing the tubes from the mandrel and have you tried the technique on larger say 1/4 to 3/8" tubes?

John

I haven't had any success removing a full length of tube, but if I cut the tubes to length on the mandrel with a razor blade they slide off without much trouble.  I'm not sure this method would work well for larger tubes as the increased surface area might make it very difficult to get the mandrel out.
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OZPAF
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« Reply #4 on: April 20, 2017, 04:21:50 AM »

Thanks for that.

John
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« Reply #5 on: April 20, 2017, 10:01:24 AM »

Your trouble is that the inner plastic sheet sticks to the metal mandrel. And perhaps because the spiral wrap does wrinkle in the process to slide it out of the mandrel.

Try to smear a thin film of grease, butter or vaseline on the mandrel and then 2 turns of household plastic (over here trade name is Domopac) lengthwise, not spiral wrap. In this way the plastic slips on the grease and you can remove the mandrel. For me, with a bit larger tubes, it works every time, hope the same for you  Grin

If not try the same but on one end you put supplementary wraps of glass cloth around to build up a thicker wall, take a piece of hard material with a 1,8mm hole and hold the mandrel in a vice and use the hard piece as extractor. In this way you push the tube rather than pull it out.

Urs
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jakepF1D
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« Reply #6 on: April 20, 2017, 10:39:49 AM »

I've experimented with Vaseline, 3-in-1 oil, and PTFE dry lube. None of them allowed me to pull the mandrel out of a full length of tube, and all of them created at least some mess. Ultimately I like the method I'm using specifically because it doesn't use a lubricant. I don't want any contaminants to end up on, or inside the tubes. For me this method works as long as I don't need a tube longer than perhaps an inch.

For these particular tubes I was using 3 mandrels that were 12 inches long each. In the end I got about 35 good tubes that are 1/2" long.
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leop
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« Reply #7 on: April 20, 2017, 11:00:02 AM »

One technique used in commercial production of composite tubes over a mandrel is to make the final wrap with a heat shrinkable material.  For hobby uses, one can buy heat shrink plastic sheet, like that used for packaging, at many craft stores.  This heat shrinkable final wrap makes for a very tight compression of the uncured composite.  I regularly use this for composite tubes that are about 2-3cm in diameter. One can cut the plastic sheet in thin strips for the wrapping.  Heat shrink tape in various widths is also available commercially.  I have also used this in my attempts to make small diameter fiberglass/epoxy tubes.  It works for small tubes, too, although the rest of my technique for small tubes was not as good as Jake's.  I thank Jake for sharing his techniques.

LP
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jakepF1D
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« Reply #8 on: April 20, 2017, 11:35:39 AM »

Leo,

The window insulation film I'm using is actually heat shrinkable.  During my early experiments I was shrinking the film, but I've found it made no discernible difference in the finished tubes.  I can get enough tension on the plastic while I'm spiral wrapping it that heat shrinking doesn't seem to be necessary.  YMMV.

For reference I'm using film from this kit.  I picked it up at a local hardware store for around $5.  It also includes a roll of double sided tape which can be useful for other things.

http://a.co/6KQA0ra

Jake
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jakepF1D
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« Reply #9 on: April 24, 2017, 11:32:18 AM »

Here are the tubes installed on a prototype VP hub.  This is the same hub I'm using on my own props, but with tubes to allow the use of balsa spars instead of my normal carbon spars. 
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Heikki K
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« Reply #10 on: September 26, 2017, 03:46:45 PM »

Just a basic feature on epoxy resins, do you heat treat the cured laminates? Most of the serious stuff needs to be heat treated (I was told by the big guys) for an hour or so after curing in 60-80 degrees. I assume this may make the separate sticky stains of epoxy hard and "brittle" to crack off from plastic films, and moreover, any force applied to the tube itself would not deform it so easy, but make the tube to come off clean from a cooled mandrel.

For me, your tiny tubes look like they will lack the "critical mass" of resin, I wonder how uniform and correct is the chemistry of the mixed microscopic batch, will it cure and give the strength as intended originally, or shall one wait for an extra day?
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jakepF1D
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« Reply #11 on: September 26, 2017, 04:20:42 PM »

It really depends on the type of resin you're using.  I'm using a resin that cures at room temperature, but heat helps it along so I typically cure it at around 110F (43C).  I am planning to buy a different resin with better physical properties, and it requires higher cure temperatures, but I don't know how much difference it will ultimately make considering how little resin is left in the finished parts.  The plastic I use to wrap the mandrel and the outer plastic wrap don't adhere at all to the resin, and come off 100% clean with no effort.

As for the accuracy of the batches I mix, I use a milligram scale and typically get the mix to better than 99% accuracy by weight.  I then mix for a couple minutes to make sure the resin and hardener are thoroughly integrated.  So far I've made more than a dozen batches this way, and I've never had one fail.
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mkirda
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« Reply #12 on: September 26, 2017, 04:57:35 PM »

Just a basic feature on epoxy resins, do you heat treat the cured laminates? Most of the serious stuff needs to be heat treated (I was told by the big guys) for an hour or so after curing in 60-80 degrees. I assume this may make the separate sticky stains of epoxy hard and "brittle" to crack off from plastic films, and moreover, any force applied to the tube itself would not deform it so easy, but make the tube to come off clean from a cooled mandrel.

For me, your tiny tubes look like they will lack the "critical mass" of resin, I wonder how uniform and correct is the chemistry of the mixed microscopic batch, will it cure and give the strength as intended originally, or shall one wait for an extra day?

My experience mirrors Jake's. I typically make up more than I need simply because it is easier to measure and mix uniformly.
Occasionally a layup will be a bit 'gummy' during a room temperature cure.
I think humidity has more to do this this than anything else.
A quick post cure in the hot box helps immensely.
Read the instructions for your epoxy to know how high and how long for best results.
FWIW, I really like the MGS resins, just difficult to get here.

Regards.
Mike Kirda


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jakepF1D
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« Reply #13 on: September 26, 2017, 05:37:14 PM »

FWIW, I really like the MGS resins, just difficult to get here.

Regards.
Mike Kirda




I keep hearing good things about MGS, and it's not difficult to get here, but man is that stuff expensive!  I haven't seen it sold in anything smaller than gallon bottles for the resin.  Once you add a couple quarts of hardener plus shipping and fees it soars to well over $200 .  I typically only mix a few grams at a time for prop blades, tubes, or rudders so a gallon would last me a lifetime, except it typically goes bad in a few years.  Maybe a group buy would be in order if enough people were interested.  I could easily get by with 8 oz of resin and 4 oz of hardener to match.  If I ever decide to make molds, I would just buy an inexpensive resin with a high enough Tg to withstand the 140F cure temperature of the MGS resin.
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mkirda
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« Reply #14 on: September 26, 2017, 11:32:44 PM »

Going bad is relative. Going out of date is probably bad from a safety perspective if you are building your own full sized plane.

For F1D prop blades, not so much. As long as the physical properties are fine, use away.

Wicks has had issues getting MGS in stock from the supplier in Canada. I've been waiting several months for some 285 resin to get in stock.
They had out of date stuff they were giving away. Gallon of 385, had to purchase the hardener, works fine for layups.
It is what I use for the fiberglass prop forms.

If I can get some 285 in hand, I'll separate out and sell to folks down in West Baden.
It really is better than anything else I have found.

Regards.
Mike Kirda
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jakepF1D
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« Reply #15 on: September 26, 2017, 11:43:41 PM »

It's listed on the CST website for $150 a gallon, but I haven't tried ordering it.  It's also available at Aircraft Spruce for $142.
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