Introduction: Easy Carbon/kevlar Tubing
There are a number of ways to achieve consistent, high quality results with carbon fiber or other braided sleeve materials. This is just one fairly simple method. The finish is not going to be a smooth as that achieved through some other techniques, but I prefer a bit of texture for paddles and other boat parts.
Step 1: Semi-rigid Forms
In this case, I need a piece of strong tubing, with very specific dimensions, particularly the angle and radius of each bend.
I start with a PVC form, and use a heat gun to bend it according to a pattern I drew on a piece of cardboard.
That is covered with self adhesive foam pipe insulation, the diameters of which fit the pvc snugly, and give me the desired outer diameter.
After I cover the pipe, I check the measurements against the pattern again.
Step 2: Cover the Form
The braided sleeve material I use can cover forms from around 30 to 50mm. For this project, I am using a form of about 40mm. The braided sleeve is available from the usual online retail sources, and is not inexpensive. The length of braid you will need is pretty hard to estimate before you put it on the form, so I put it on right from the roll, and cut it slightly long.Carbon can be cut with stout scissors. Kevlar or Kevlar/carbon, which I am using is best cut with Kevlar shears. I am keen on a product called Vampliers!. The exclamation point seems to be part of the name.
I don't have pictures of the process, but I usually mix my epoxy at this point, and start saturating the braid in the following manner:
I bunch it all to one side, and spread epoxy on the exposed side of the form. Then I bunch the braid on the glued side, and cover the rest of the form.
Next step is to spread the braid evenly over the form, avoiding twists or lumps.
I then apply epoxy to the outside, to completely saturate the braid. I generally use gloved hands for the process, of spreading and smoothing out the epoxy, using techniques that will probably be familiar to anyone who has been an adolescent boy.
It is super important to completely saturate the braid with resin. I use a very slow cure epoxy, to give me plenty of time to work it in.
I usually ties off the ends with a zip tie, sausage style.
Step 3: Curing
The form is a best semi-rigid, so I let it cure on a base that keeps any stress off the form, keeping the desired bends, and leaving the straight parts straight.
A wise move might be to rest the assembly on peel ply or teflon coated sheets while it is drying. I just use random plastic sheet material, which I had earlier coated with parting wax. I have no doubt that parting wax is subtly different than regular auto or furniture paste wax. But parting wax is pretty inexpensive, and available online.
It bears mentioning that epoxy resin is not the same as polyester fiberglass resin, especially for this process. Polyester resin tends to dissolve the foam form, so that would not be optimal.
Besides ensuring complete saturation of the braid, it is also fairly critical to carefully follow the manufacturers instructions on mixing ratios and working temperatures. I pretty much use West System exclusively, because their range of products have worked well for me for decades, and their mixing pump system is pretty much foolproof.
I also come back to it periodically as it cures, and very gently wipe any drops of epoxy that form on the bottom. I do try to make sure that the areas that rest on the base are places that will not be seen on the finished piece.Light sanding after complete cure can deal with that issue as well.
There are lots of techniques that will result in a smooth, flawless finish on the piece. But the idea here is to describe a super easy way to do this, not the best way for perfect results.
Step 4: Finishing
After the part is completely dry, it is a simple matter to remove the inner pvc form. The foam insulation can be carefully fished out, or melted out with acetone. If you melt it out, be very sure that the epoxy you use will not be affected by any solvents you use.
More layers of braid increase the strength and diameter of the final product. I used two.
You can have a lot of fun covering shaped foam with carbon or fiberglass, and later melting out the foam. When I use that technique, I usually use extruded polystyrene, which is the big pink or blue sheets at the big box hardware stores. It can be worked with the same machinery you would use for milling metal or wood, and sands reasonably well.
But for this case, I am not bothered by the foam, so I left it in and just pulled the pvc pipe out after it cured.
It can be lightly sanded for smoothness, just don't try to sand all the way through the epoxy to the Kevlar. Carbon sands acceptably, but Kevlar does not.
The epoxy and the Kevlar are sensitive to deterioration from uv light exposure. I finish up by spraying the piece with a two-part epoxy automotive clear coat with a strong uv rating.