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Simple and Inexpensive Techniques for Making Carbon Fiber and Composites Shafts

Jon Soller

Owner

Soller Composites

original Copyright 2004
updated & Copyrighted 2007

All Rights Reserved

Customer comments: "...I must say the method you've outlined on your web site for creating tubes is down right excellent.  I had high expectations of this material, and it still has managed to impress me."

I.                     Introduction

We are constantly asked how to cheaply make shafts from our carbon fiber and other sleeve material.  This brief paper explains simple ways to effectively make Carbon Fiber and Carbon Kevlar shafts of virtually any size.

There are many ways to make shafts from composite sleeve materials.   This paper focuses on the simplest and most inexpensive techniques we are aware of that produce professional results.  Although more advanced techniques are available, the ones discussed here are adequate for professional results.  The more advanced techniques are beyond the scope of this paper.

II.                   Safety

This paper's intent is not to discuss the safety precautions that need to be understood and applied when working with epoxy, Carbon Fiber, fiberglass, and other composites.  Please read, research and understand the materials, safe use, and application of such techniques and materials.  If you would like more information regarding this, please contact us. We’ll be glad to help you, or point you to appropriate resources regarding these topics.

III.                 Choosing Your Mold or Shaft

The simplest molds you can use to make a shaft are copper or PVC tubing available at any hardware store. 

You will find that PVC piping provides the best and cheapest mold for easily removing your shaft after it cures.  Unfortunately, PVC pipes bend very easily.  Because of this, their use is limited to very short shafts.

Copper water pipes work quite well for applications up to about 5 feet (possibly 6 feet if you are very strong). 

For very small shafts of less than ¾ inch, try using steel rods as a mold.

No matter what you use as a mold, be prepared to hang your shaft vertically while the resin dries so that the shaft remains perfectly straight.

IV.                Adjusting Your Mold Diameter to Virtually Any Size

After you selected your mold “base”, you may find that it is not quite the right size for your application.  There are several ways to address this issue:

1)       Not very cheap, but you can always add more layers of sleeving material until you reach the appropriate shaft size

2)       You can sand down carbon fiber for micro adjustment.

3)       You can wrap your mold with any number of substances to thicken it up:

a.        Plastic (home vapor barrier or painters sheets).  Just please don’t use plastic wrap (it is too thin and will stick to epoxy).  Tip – if you use plastic, the fewer layers the better -since many layer may warp your final shaft slightly.  After wrapping with plastic, pull it tight and tape it off with standard household tape.

b.       You can carefully apply any number of tapes over top of each other.  Be careful to perfectly line-up the edges of each piece of tape as you apply it horizontally down the shaft 

V.                  Preparing Your Mold

You now need to apply a barrier between your mold and the sleeve.  We recommend using a thick plastic:  yes again (home vapor barrier or painters sheets).  It is important that the sheet be perfectly flat, no creases please!

But before you apply your plastic barrier to your mold, you need to apply a lubricant between your mold and the barrier.  Silicone spray or baby oil works well for ex., but virtually any lubricant should work.  Just please make sure it is non-flammable, and won’t interact with epoxy. 

Apply the lubricant to both the mold and the “inside” part of the barrier.  Wrap the barrier around the mold and secure with one small piece of household tape (in the middle of the mold).  If your shaft is large, let's say 3ft or more, you can use two small pieces of tape (more about this later).

Now simply pull your sleeve over top of your shaft, carefully...  You will notice that your barrier seems to be a bit care-free at the ends (not tied down since you only used 1 small piece of tape in the middle…).  As you work the sleeve over the mold you can start to pull tight the sleeve, by pulling on the ends and twisting slightly in the middle.  This will flatten out your “care-free” barrier ends and will provide you with a nice round shaft.  If you decided to tape the barrier edges down with more than 1 small piece of tape, you will probably find that you can’t make your shaft look nice and smooth at this point. 

Note that you can push epoxy through two layers of light sleeves or 1 layer of heavy sleeves. If you tried to push epoxy through more than this amount, you will likely find that not all of the carbon fibers wet-out.

To wet-out more layers during the same cure process, turn the edge of the next layer of sleeve inward and roll this next layer into the mandrel inside out (similar to a rolling a stocking). Now wet out this sleeve as needed. You can use this method to add as many layers as you want to 1 shaft in the same curing process

VI.                Preparing Your Exterior Shaft Surface

If your shaft is 100% carbon fiber, you can sand it down and apply a final coat of all-weather epoxy over it to give the shaft that nice finish.  You can also apply a coat of urethane as well.

If your shaft is all or part Kevlar, sanding it down will make it quite hairy.  That is, it will basically destroy the aesthetics of the shaft.

Another option, is to use our special heat-shrink tubing.  Don't use generic off-the-shelf heat shrink tubing, you will likely find that it will stick to your shaft....

    1) Slip our special flexible composite-grade non-flammable heat shrink tubing over top of your
        epoxied sleeve. Note: this heat shrink tubing works great around bends too!
    2) Use a low temp heat gun (starting in the middle of the shaft/sleeve and working
        your way to the ends of the shaft). The heat shrink tubing will squeeze out excess epoxy and
        provide you with that smooth professional finish!
    3) After the epoxy dries, use a sharp seam-cutter (from your local fabric store) to remove the shrink   
        tubing or score the heat-shrink tubing with a knife and pull it off the shaft.
    4) Sand (if desired) the shaft lightly with 1500 or 2000 grit sand paper for a few seconds, then
        add your final clear coat (spray all-weather urethane or wipe-on a tiny amount of epoxy -
        just enough to barely wet the shaft and give it that gorgeous shine [as thin as possible -
        no weight added here]). Let dry, your done!

 To purchase this heat shrink tubing go to:

      /composites/carbon fiber sleeves.html#shrink

 

This makes for a surprisingly easy and nice finish. 

 

You can vacuum bag the shaft to achieve a slightly lighter shaft at a great expense.  If you have bends in your shaft you will find vacuum bagging extremely difficult. 

If your shaft is over 6.8" in diameter, our shrink tubing will not be large enough. In this case you generally have a few choices:
1) you can sand the outside surface or leave it rough. You can minimize the epoxy by wrapping a stretchable rubber tube around the shaft, pulling it tight (like when you are tying a shoe lace), then pulling the stretchable rubber tube down the shaft.
2) you can add a light fiberglass sleeve over the outside. Fiberglass turns clear when resin is added to it. The tighter & smoother finish of the fiberglass sleeve can more easily be sanded down than a heavy weave of the carbon sleeve.
3) You can wrap it with plastic (such as mylar or other plastic sheeting). This approach does not minimize the epoxy and can leave an uneven surface.

Please note that you can typically apply two layers of light sleeves at once and still be able to push epoxy through them.  If you are using Medium or Heavy sleeves, please only do one layer at a time…

Note that it is possible to do many layers of carbon sleeves at once.  To do this, for ex., add two layers of light sleeves (dry) onto your mandrel, or one layer of heavy sleeves & wet out the sleeve(s). Now turn you next layers of sleeve(s)  inside out and roll them on like a sock on your foot, wet out the layers, and repeat as needed.  We have done 15 layers at once using this method.  This is the best method we found to minimize epoxy and maximize strength for many layers of sleeving.

VII.              Curing Your Epoxy

If you are not using shrink tubing...  many people complain about bubbles when epoxy is drying.  Know that drying epoxy is a heat sensitive chemical reaction. Bubbles are produced when too much heat is used and when epoxy dries too quickly. Bubbles are sometime impossible to avoid, but try drying the epoxy in slightly lower temperatures, or sand them off and apply a final thin layer of Urethane (or epoxy). 

VIII.            Removing Your Shaft From the Mold

Gently twist the shaft back and forth as you pull it off the mold.  It should come off fairly easily. 

Once the shaft is off the mold, the barrier will stay stuck to the shaft.  Twist the barrier with pliers in the same direction until it is removed from the inside of the shaft.  If you have a 5ft shaft you may be doing quite a bit of twisting.  Don’t try to pull it out without twisting, since you are very likely to break it about 1ft in, making the remaining part of the barrier very difficult to remove.

IX.              Advanced Topics: Making Bends in Shafts

Composite fabrics are soft and ideal for bent and complex shape moldings.  The trick with these types of structures is creating and removing the mold.

The best solution is usually using a high density foam mold. Such mold can be custom made for you, but are usually reserved for large manufacturing runs (10,000+ pieces).  Assuming this is not an option for you, there are several other options:
             a) you can buy high density foam and create you own mold.  If you need to remove the
                 foam afterwards , it usually can be eaten out with acetone.
             b) you can make you own mold casing and spray liquid foam into you mold casing.
             c) you can use a flexible vinyl or latex tubing as a mold
             d) you can use a miter saw to cut 10 degree angle out of a straight shaft, reposition
                   the cut pieces to make a bend, then sand the outside smooth and round
             e) you can use a pre-exiting flexible or ridged foam mold such as one found in a craft store
                 or sporting good store (such as a wacky noodle)
            

The best foam to use to make such objects is water soluble foam. Wwater soluable foam mold making material is generally available in container of 5 gallons, but not smaller as of this writing.

X.              Advanced Topics: Very Long and/or Very Large Diameter Shafts

If your shaft is over 5 to 6 ft and/or you are working with large daimeter shafts (ex 6"+ diameter that is 4ft+ long) the plastic liner technique above becomes impractical. In this case, a much more involved technique can be used (as described here). Using an aluminum shaft (not steel). the shaft can be heated (ex to 150F). after the epoxy cures, cool the part/shaft and the part will slide off. Be make sure your epoxy can handle the higher heat!

Note that when using this technique a high grade (high temp) release wax or release spray can be used instead of the plastic liner method, but for best results we generally recommend staying away from the waxes.

 XI.       A Note on Sleeve Fiber Angles

At the nominal size, the size the sleeve is specified for (ex. at 3" diameter for a 3" sleeve), the fiber orientation of the sleeve is at a 45 degree angle. This is ideal for twisting applications, cosmetic applications, and for holding the shaft uniformly together while under stress. if the shaft is to be used as a push pole, then a fiber orientation along the length of the shaft is ideal. For stresses that would "effectively" try to break a long shaft in 1/2 (such as breaking a stick over you knee), you also want a fiber orientation along the length of the shaft.

All this being said, keep in mind that rarely does one have stresses just in one direction. For ex., even with a push pole using a 45 degree weave over a UNI sleeve will help keep the UNI sleeve fiber contained and will typically create a stronger shaft.

Also, one might consider using a larger sleeve and pulling it down so the fiber angles are more along the length of the shaft. For ex. in a kayak paddle shft that is 1.2" in diameter, using a 2" sleeve typically provides for a stronger shaft than a 1.25" sleeve, because of the fiber angle being more along the length of the shaft.

Expanding the sleeve beyond it nominal size (ex. using a 2" sleeve on a 2.2" shaft, will create better "hoop" strength (such as if you would stand on the shaft laying on the floor) . Rarely is this type of strength beneficial.

Determine where your stresses will be in your application, then choose wisely the sleeve size & thivkness you need for your application.

XII.       Final words

You will find these techniques to be simple, very cheap and effective.  If you have questions, please don’t hesitate to contact us. 

We often times find our customers find creative and unique ways to resolve problems.  If you find or develop techniques that you think we or others can use, please let us know -we’d love to hear form you!

 

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