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| awemawson:
Very nice work on that burl Simon. You certainly set yourself some challenges :bow: |
| vtsteam:
Liking the woodwork, Simon! A few words on polyester and epoxy resins as finishes on wood: Polyester (what most people call "fiberglass") resin has poor adhesion on wood, it also eventually yellows and becomes opaque if not protected from sunlight with a UV resistant varnish. There are "water clear" casting resins, but they aren't designed as thin finishes -- they are for casting. I'm sure it can be used where sunlight isn't strong for some interior purposes, but i wouldn't put it on a banjo. Polyester laminating resins do not cure on the surface in the presence of air -- they are designed that way so the next layer of glass fiber roving or mat or cloth, whatever the schedule is, will adhere to the last one in the mold. The next layer of resin and catalyst will kick it hard, though will also have a sticky surface to accept the next layer. The final layer of resin is called "finishing resin" and it does have wax added, as Andrew said, to block air, and allow a hard surface cure on the inside of the molded item. Finishing resin can be bought that way -- you don't have to add wax -- it's pre-waxed. It's no good for laminating of course, because the wax prevents further adhesion. Epoxies also yellow and go milky opaque very quickly on exposure to sunlight-- even more quickly than polyesters. They are a poor choice for something that is finished bright where you want to see the wood. Talc added to lacquer makes a fine sanding sealer under paint, however it isn't very clear or even and isn't good under a bright finish. Here's what I would try for filling the meranti grain -- spread a very small amount of carpenter glue on a small patch of the surface, and then immediately, before it dries, sand with fine sandpaper. This mixes fine sawdust with the glue and wipes it into the grain divots, while removing it from the surface. The color will fit well, just slightly darker in the grain than the meranti, as it should be, but a good tonal match. This also works well with small cracks in glue joints. There a trick to sanding enough, but not too much to fill what you want, and to sanding in the right direction to fill, and not pull out your filler material. But a little practice on scrap will show you what to do. Hope that helps! |
| S. Heslop:
--- Quote from: vtsteam on July 19, 2015, 06:06:18 PM ---Polyester laminating resins do not cure on the surface in the presence of air -- they are designed that way so the next layer of glass fiber roving or mat or cloth, whatever the schedule is, will adhere to the last one in the mold. The next layer of resin and catalyst will kick it hard, though will also have a sticky surface to accept the next layer. --- End quote --- That's cool. I never knew that. I just always assumed I didn't add enough hardener to the fiberglass resin. As for the glue and sanding thing, it seems similar to the (what people claim to be) old method of getting pumice embedded in the cloth wad you're applying shellac with and rubbing it a whole bunch over the surface and keeping it wet with shellac. It confused me at first since I thought people were filling the grain with pumice, but that stuff would show up as white. But I figure it's just sanding the surface and clogging the pores with the sawdust/ shellac mess. It seems like a long winded way to go about it. But the thing i'd worry about glue is how well the shellac will stick to it. I'm thinking about testing it at some point, but I ran out of the mixed shellac (from the accordion) I had about. |
| vtsteam:
Simon, I use shellac a lot and also occasionally sanding to fill a problem glue line crack. There is basically no glue on the surface of the wood, it's only in the crack or grain. you use very little glue and the sandpaper removes it immediately. But, I've also never had a problem with shellac over glued joints, anyway. For that kind of work I usually use titebond 2 -- the yellow aliphatic type of glue -- seems fine with shellac. I don't think this is similar to the rottenstone thing, which is part of getting a fine rubbed shellac finish. Not filling grain. Do try it on some scrap. I think you'll find it's no big deal. Try it on a bad joint with scrap and see the results. They do need to be level with eachother, at least, so sand them flush first. Use very little glue, and start sanding with a piece of paper in hand -- I dunno maybe 320 grit or so. Coarser if it goes too slow. If I remember correctly I first sand crosswise to the joint. When it fills I stop, let dry, then sand with the grain to clean up. Sanding with the joint at first tends to pull the homemade sawdust putty back out. A little practice and you'll get the hang of it. |
| S. Heslop:
Routed the fingerboard out, following an mdf template. Decided it probably doesn't need edgebanding. There's one spot that's not too great but it's alot of effort by the end of the day, and I don't have the materials on hand. Finished off the truss rod too. Kinda bungled up the first attempt to stick nuts pairs on tightened against each other. So for the second I pinned them. It works. I maybe could've gotten a bit more done, but i've been having alot of cramps lately and standing up for more than an hour wasn't doing me any favours. So I took a break and never got back to it. I think the cramps might be from stopping codeine since I think I remember the same thing happening in the past. |
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