Tips for making your own wing rod tube or ballast tube

I thought I would post a collection of ideas sent to me when I was asking for help building some Kevlar wing rod tubes for my Supra. I had read a few techniques before I started, but ran into some problems along the way. In my situation I was making a Kevlar tube that would be cut up into 4 individual wing rod tubes. I started by waxing the .375 dia. x 12” long carbon fiber rod several times. I then wrapped the rod one time with waxed paper with about 1/16” overlap. I then wrapped 5oz bias Kevlar 3 times around. I then wrapped several layers of waxed paper around that and then some stretched masking tape over that. (Just a note here. In the Supra, this tube will be glued into a solid basswood block to carry loads to the spar caps.) The biggest question I had at the time was what kind, and how many wraps of material was needed to create the right tolerance for a snug fit. I felt I wanted a snug fit so opted for just one layer of waxed paper. In the case of a ballast tube, you would want to increase that quite a bit.

All went well up to the point of getting the rod out from inside the cured tube. I tried many things but here is what finally worked. First I post cured the tube at 140 degrees for 24 hrs. The tube was much harder after it came out of the oven. Still stuck on the CF rod good though. I drilled a hole the size of the CF rod through an oak board. Mounted that in the vise. Aligned the rod & tube assembly over the hole so just the tube would catch, then drove the rod through from the top. The end of the tube took a little mashing but that got cut off anyway. All the pieces finished up fine, and the fit is just right. Maybe a bit on the tight side.

Kevlar Tube

Kevlar Tube

Here are a few suggestions that were sent to me for constructing a tube:

Next time use at least three wraps of waxed paper and DO NOT use anything to stick the cloth to the waxed paper.

A better thing to use instead of waxed paper might be 3" wide clear packaging tape.

One trick I use is to run a piece of kevlar tow lengthwise in the layed up kevlar. Leave a tag end dangling out. After the epoxy is set, the tag end allows you exert more force to pull the box off of the joiner.

I made my joiner tubes from ½" carbon sleeve stretched over the rod and wet out. I melted some white candle lights in the oven at 225F in a trough made from alu foil and placed in a pan to catch leaks and submerged the rod in the melted wax. When I took the rod out I held it vertical to let the excess wax run off until the wax was hardened. After the epoxy was dry I cut off ½" in one end of the tube with a knife so I could get a hold on the rod inside with pleiers. Then I set it in the oven at 225F for 10min to melt the wax and pulled the rod out with a pleier. I preheat the oven every time. After some light sanding with 320 the rod fits snug inside the tube.

I keep posting this whenever I see people having release problems with tube shaped mandrels. The following talks about an aerosol based mold release that builds a wax coating on the mandrel just like the candle wax in a previous post. The old version was #3270 Ready Release made by Crown. The newer stuff still carries the Crown name on the label but Crown was bought out by Aervoe and now the name is Reliable Mold Release for Epoxy, #3470. It will quickly leave a nice even coat of wax and then when its time to release the part, you simply put it in a warm oven, a tub of hot water, or just run hot tap water over it. The wax melts and the part comes right off.

I attached the mylar to the carbon rod with a thin layer of vaseline. The tub slid off with no problem. This was after I did a practice tube around a wood dowel where I used wax to attach the mylar. It was a problem to get that one off and ended making a mess out of the dowel.

I have read that olive oil works good as a release and using balloon mylar as a spacer.

Work in shorter lengths. Instead of working with the 12” piece, cut it in half and do two separate layups. There will be less friction when it comes to removing the rod.

Start with a rod that is very smooth and perfectly round. No scratches or dings. Make sure the rod is longer than your tube by a little bit. Bevel the ends of the rod before the layup if possible. Put a few extra wraps of fabric at one end of the tube so as to have something to grab onto or a strong lip to pound against for removal. The extra wraps would get cut off after.

Here are a few ideas to remove a stuck rod:

Let the rod cure for at least 48 hours before trying anything. Partially cured epoxy is fairly flexible and will not part cleanly from a form that has no draft. Then try placing the part in the freezer until it's pretty cold. Remove the tube from the freezer and whack the inner tube. This 'should' get the part to release. Now a little heat on the outer surface should allow you to slide the tube off the form. Also. a little high pressure air blown between the two tubes should help.

Have you heated the thing up? Put the thing in your oven on 250 degrees F. This makes the wax go liquid and then you can probably pull the tube off the mandrel. Of course, you have to use gloves for that (or be really quick about it).

Have you tried placing the part in warm water? Also, if you have an air compressor you can try shooting air from the end of the rod. Try to aim the stream of air between the rod and the layup.

Drill a hole in a piece of oak block the size of the wing joiner rod. Heat up the kevlar tube a little, and lightly tap the rod out through the hole in the oak block.