Reluctant to toss a fair amount of epoxy, I mixed up a larger batch of about 8 CC, just to make sure I got a good mix ratio. The first batch I had mixed to test the suspect glue was very small, and I figured I may have just muffed it. No such luck.
I mixed 8cc, then glued two pieces of capstrip together with a totally unscientific scarf joint. I then glued in two short pieces of geodetic brace stock, ends cut at roughly the angle of the braces in the ribs. After 24 hours of cure time, all three joints came apart at the glue line, not the wood. Into the bin it went, all of it. I’m glad I didn’t use any of it for construction. Fortunately I have another quart of epoxy here, unopened, and some new syringes. I’m now set up with fresh glue in new dispensers.
Nothing new, but last night I gathered up all 47 full ribs and stacked them up, carefully aligning the cross pieces for the main spar, aft spar, and nose spar. I was a little concerned about the amount of variation I might find, considering the ribs came out of two jigs over a period of 20 months. I was very happy to see that there’s no more variation than could be attributed to wood thickness. Less than 1/64″, probably under .025″ anywhere along any of the ribs. Then I stacked up the dozen false ribs I have done so far, same story.
Wait – 47 full ribs? Yes, it seems somewhere along the line I must have lost count and built one extra aileron rib. I’ll either keep it around as a wall hanger/test piece, or maybe stick it under the wing walk for a little extra support. I’m not sweating it.
This exercise has also reinforced my idea to build a sled for the table saw to lop off the ends of the ribs for the leading and trailing edge pieces. They are very highly consistent, as they should be, so I think that will save time and make subsequent assembly steps easier.
The bad news is — my T88 epoxy is junk. I refilled the dispensing syringes and the resin looked a little “off”, not perfectly smooth and clear as it usually is. Maybe a little cloudy and with a different texture. I mixed up a small amount and glued up some test pieces. Where I glued the flat sides two sticks of capstrip together, the joint held well and pulled apart well into the wood. However, where I had glued a couple pieces of geodetic brace into the slots, the glue joints failed allowing the braces to pop out without breaking. The glue also was not clear and hard, as it should be, but had an almost grainy or mealy texture to it. I don’t have any trust in the remaining glue in those bottles. I’m certainly not going to risk using substandard adhesive to save about $20 worth of epoxy! Into the trash it goes. I have two new bottles here, and half a dozen new 60cc syringes on the way from Amazon.
I was filling the 60cc syringes I use for dispensing T-88 epoxy in an exact 1:1 ratio. Typically I overfill them a little, then stand them on end tips up to let the bubbles rise to the top, then squeeze a little back into the bottles to get the amounts in each syringe evened out. Yeah, it’s a little picky, but it lets me easily keep the ratios exactly the same. Anyway, I got a little distracted, and accidentally squirted about 4cc of hardener right into the half-full bottle of resin. Oops. All I could do without making things worse was let it sit. I thought about trying to scoop it out with a long handled spoon, but decided all I’d really do was mix it in. I figured either I’d end up with a hardened mass on top that I could scoop out later, or it would ruin the entire remaining half bottle of resin. That would be about $22 worth of epoxy… not the end of the world, but it would kinda suck. I was hoping the hardener would not slowly sink to the bottom, ruining resin as it went.
Well, I got lucky (or science worked in my favor). Today there was a gooey layer of semi-cured epoxy sitting on top of the resin. I was able to scoop it out using a chunk of scrap spruce. Assuming things don’t go south in the next few weeks until I need to refill the syringes again, it looks like things will be OK.