Foamy and the beam

We are starting to make some real progress on the beams now.  Weather is cooperating enough so I can mix epoxy.  Here you see several hours of work gluing the high-density inserts into the beam sides.  It was a lot of inserts (over 60) and each had to be neatly prepped, glued and adjusted to be flush.  In the foreground you see my 2-part MAS epoxy and hardener in 4-gallon containers.  This plus 4-gallons more epoxy I have in storage should be more than enough for the beams.  The 4-gallon jugs come with both valves, as shown, and hand pumps.  Although more $ per gallon, I do like them for convenience.

With the foam parts all ready for assembly, including sanding and vacuuming for good adhesion, I prepped the mold.  I had already drilled holes for screws to hold the foam parts in place from underneath, which allows me to apply the carbon fiber on top (actually on the inside).  Here you can see the mold covered in clear packaging tape to (hopefully) prevent the epoxy from sticking to the mold.  In the worst case, I have to disassemble the mold to pop the beam out, which is doable thanks to all screws being accessible.  But best case is I remove the screws holding the foam in place and the beam comes out with a little persuasion. In any case, I have the first two pieces of foam in place at either end.  Now it is a race to assemble the other pieces of foam before the epoxy kicks.

And here is the mold with all of the foam parts assembled for the forward port side beam.  I ran out of screws so I had to use every spring clamp I have to hold the aft side in place.  To assemble the foam, I wetted each edge to be bonded with straight epoxy mix, no fillers. Then I applied a bead of slightly thin putty along one edge.  The piece was pressed in place carefully to minimize epoxy squeezing out on the mold side.  Finally I installed screws from outside (underneath and on sides) to hold the piece securely while the epoxy sets.  I did have to install a couple screws on the top side to hold the curved piece in place, so I will fill those holes lightly before applying carbon fiber and epoxy.  I also lost the race with the epoxy and had to toss half of a small batch when it got too thick to use.  But I am mixing smaller batches, either 2, 4, or 6 oz at a time, so less is wasted.  I think I need to add fillets along all edges next, but I have to check the plans to make sure.  That will be the job for tomorrow.

Here is a close up view of the recessed pocket for one of the support struts.  We are looking at the inside of the beam so this recess is inside.  The bolt and nut are holding the solid GRP bolt plates in place with some precision so the folding structure all fits and aligns properly in final assembly.  Lots of little pieces are put together to construct this recess.  Hopefully the epoxy breaks lose of the tape as planned, otherwise I may have a bad day on the way.  Once I add fillets, and the epoxy cures, I will do some final sanding to round over the edges and corners.  This will help the fabric drape the form more easily, making for a stronger beam, and the beams need to be very strong.

Back in a sticky spot, finally

 All right, the icicles have finally melted, and I am done cutting expensive foam board into little pieces.  We are back to work and mixing epoxy.  The first items glued together were the solid glass reinforced plastic (grp) side plates that will support the struts that link the main hull to the beams.  As shown in the photo, the thickening rings were glued to the side plates.  Both parts were fabricated a long time ago when I was making the parts for the central mounting modules.  Each piece is approximately 3/16" think solid glass and epoxy.  To ensure the hole in the rings and plates were properly aligned, I ran a bolt through them while the epoxy cured.  The biggest risk in this step was the parts becoming permanently glued to the bolt.  To help avoid this, I wrapped the bolt with a layer of clear packing tape, which the epoxy doesn't stick to very well.  Then I simply cleaned up any excess epoxy before threading the parts on the bolt.  Since these are high stress components, the epoxy mix included some cabosil to thicken and toughen the glue.  I still need to round over one side of the long edge on each piece, as well as a little general clean up sanding, then these parts are ready to go into the beam mold.

I used the left over glue from the reinforced side plates to start bonding the high density inserts into the various pieces of foam that will make the beams.  There are a total of 16 inserts in the pieces shown here.  Although I still had glue left over at this point, it started to kick and got too thick to use.  I only made about 100 mL, combined with about an equal amount of cabosil.  So it doesn't take much epoxy to do this job.  I covered the table with a sheet of vacuum bagging material, which the epoxy doesn't stick to very well.  Then I just pressed the inserts into their openings, squeegeed off most of the excess epoxy, and evened it up on the table.  Once cured, the parts popped off the table with minimal persuasion.  Before assembling these parts into the beam mold, I will sand both sides clean.  Easier and quicker to do the sanding now than when assembled into a complex form with lots of inside corners.

These parts are the foam pieces for the beam sides, including all 72 high density inserts.  I spent the past couple weekends custom fitting each of the inserts so I could glue them in place efficiently.  Each piece is labelled so if I drop the stack I can figure out which insert goes where.  Next good weather day, i.e. reasonable temperature and moderate humidity, I will permanently bond the inserts in their respective cut outs.  Then a little sanding and ready for installation in the beam mold.  I could have installed all of the inserts when assembling the parts in the beam mold, but I figured it would be easier and less stressful to separate the tasks.

I still need to do a little prep on the mold before starting assembly of the foam.  Some of these tasks include drilling holes for screws to hold these parts in place until they are bonded together, and marking and taping the seam locations to prevent gluing the parts to the mold.  Hopefully old man winter has gone to bed, and the spring showers cooperate so we can get on with the fun.