Of all the skills it takes to be a good amp builder, upholstery is the hardest, at least for me. I am getting better and can do a great job for corner covers, which isn’t too difficult. But it’s a trick otherwise.
Good glue is essential. I’m now using the Wilsonart H2O and it is the best I’ve used. The Tolex glue from Antique Electronics is good too and easier to get in many locations. The second imperative is good glue coverage. I’ve found that if I painted the inside of the amp with a gloss black, the glue bond is not as strong. Third, make sure there is plenty of dry time, don’t rush it.
The rest is practice… Some tips I’ve heard about corners that don’t really help outside of context but may be of some guidance. When cutting the corners, like in the video, you have to cut through both the top and bottom layers of Tolex in 1 cut. If you rock the blade from top to bottom it helps to do it in one shot.
And there is no harm in using some superglue to touch up the tricky parts.
More after this next round, I’ve got 4 boxes to cover