I was hoping to have Tool Cowl Serial Number 2 done by today. But as these project go, multiply time estimates by 2 and add a couple weeks, cost estimates by 3 and add one aviation unit. You’ll be close. The last few days I have been distracted with errands, maintenance on the Legacy (it needed a new battery), and learning about next steps. I have also been awaiting my glass and carbon delivery. It was supposed to be here yesterday, but arrived late this afternoon.
For the most part today was more of what you’ve already seen. Mold release preparation. Seems like this should go faster but alas it takes time to buff that much area. Same story as the last few times. Five coats of mold release wax. Wax on, wax off Joey-son.
While I was waxing, I heard a crunch along the filleted edge between the tooling flange and the cowl surface. There was a large air bubble that I figured I needed to take care of. Since the surface of the mold is a single layer of deck cloth, it isn’t very strong. If I pull vacuum on this part, that area is liable to crush or crack. So I did the syringe trick to fill it and preempt later repair.
Basically you drill a hole in each side of the bubble. Then using a syringe I injected a mixture of fumed silica and epoxy. I mixed it to a wet, but shape holding consistency a little runnier than toothpaste to get it to flow easily. One hole is your injection site, the other allows the air out. Fill the void and you are done. To prevent gravity from pulling the fill out, I clamped the mold to the table on edge.
With that repair done, I spot waxed, five coats, the area that I repaired plus a few inches around. I wanted to make sure that there was no possibility that future parts would bond to my repaired area.
A quick trip home to pick up my cloth delivery and vacuum bagging materials and it was back to the airport. It was getting late in the day, but I figured I wold make an attempt to be able to lay up the tool cowl. Since it was after working hours, Kevin was available to help which would be a great advantage.
We started by cutting cloth and all the vacuum bagging materials. Since the goal of this part is to be a translucent tool cowl, we only cut 2 plies bid, and a few 3″ wide strips of mat to use as reinforcement. Then it was peel ply, bleeder bag (perf ply), bleeder ply, and vacuum bag film.
From there we covered the stack of materials in plastic and shot PVA on the mold. I did a misted on tack coat as recommended and then did 3 more coats on top of that.
In between coats of PVA I was rigging up my vacuum setup, changing a few fittings, and testing the equipment. With just the pressure pot that I use as a resin trap and reservoir, my lines, and the pump it was pulling 22-23.” There is a leak somewhere but a relatively small one. It will certainly be ok for the 4-5 hour cure time we have in these temperatures. It is just the el cheapo vacuum pump from Harbor Freight. But it has worked on other parts for me before.
Unfortunately, time was running thin and we decided it wouldn’t be prudent to try to do a vacuum bagged layup yet tonight. So that will have to wait for another day. But we are all ready to go.
Since this is only a tooling cowl, we certainly could have skipped the vacuum bagging and made it easy. But we wanted to use this layup to learn and practice. We intend to vacuum bag the carbon cowl we will use as our actual part, so it makes sense to make this layup a two-for-one. We get a tooling part, and we also gain experience.