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| Some finishing challenges http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=19210 |
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| Author: | vandenboom [ Thu Oct 16, 2008 4:29 am ] |
| Post subject: | Some finishing challenges |
I am trying to finish my 4th guitar which I started last January! I started spraying 12 weeks ago and still haven't got it all together - a succession of problems and events. I am left with a feeling that this has been so much harder than the first three and I don't know why. But in looking around for some answers on this forum, I found a great post that many of you responded to which showed that this is a common experience in the early development of many luthiers. So here is a run down of some of the things that have happened, with some questions along the way. Dreadnought - nitro finish. 1.] I left the guitar to cure in the lounge room for 2 weeks - temp range 10 to 22C. I never checked the humidity until I saw the 4" thin crack in the back - yes humidity was very low. The main centre rosette also lifted at 2 points (outer edge closest to sides if you can visualise that). I repaired the back easily thanks to Dad Erlewine guitar repair book - good section on dealing with cracks. But the rosette has become a botch up. After pushing it back in and sanding back, it has ended up slightly below the surrounding top and after 10 coats, I haven't got it level yet. I know why the back split but can't see why the rosette lifted in response to low humidity. Can anyone explain that? I figure that when gluing the rosette in, that it did not make good contact with the wood. I can't remember if I used a caul for this. So at this stage, the back is good, but the rosette isn't. Any other ideas? 2.] The back (Gippsland Blackwood). After final polishing I noticed there were still lots of little pin holes and even slits in the lacquer. I could have sworn I sanded them all out and I am puzzled that I did not see they were still there earlier. As usual, they are not always apparent. They are not just low points that look shiny from different angles, they are more serious cavities. Does this indicate I just did a lousy job of pore filling? So the back will need to be cut back pretty heavily to remove these, and then more coats applied. Potentially dumb question - can you refill pores after lacquer has been applied and then apply more coats going over that? 3.] Pickguard. I made a wood pickguard out of figured tasmanian blackwood. Initially I lacquered it (not stuck down yet) but could not keep it flat so the lacquer developed cracks. I asked the forum for advice on this a couple of weeks ago. As a result, I made a new one, and applied tung oil to both surfaces. I used double sided adhesive sheet to stick it down, but found it did not adhere well to the pickguard. It sort of blistered/bubbled in a couple of small spots. Nevertheless, I thought there was enough good contact made to proceed and stuck it on- silly idea #1. Frustration and impatience took over and I squeezed some CA under the edges were contact was poor - silly idea #2. CA has left a mess on the lacquer around the edges. I tried to sand the dry CA back but can see evidence of it at certain angles. So the pickguard has been removed - different approach needed. Questions... Is the oil interfering with the adhesive sheet? If so, what if I apply some shellac over the underside of the pickguard? How else could I stick it down? If I use Titebond, do I need to scrape lacquer off first, similar to the bridge? How does CA affect lacquer? Does it move into the lacquer or do I need to just sand back with something heavier. eg. P400/P600? I also have a question about drop filling. I have read that you can drop fill with water borne lacquer, but haven't found if you can do this with nitro. I tried it on guitar #3 to fill some pin prick holes in the spruce top, but after polishing, could see little circles from some angles. In conclusion, it hasn't been all bad. I have done lots of things differently on this guitar and, despite the above hassles, I think it is much better than the first three. It plays and sounds great. So while I let some problems remain on guitars 1-3 in order to progress, I am not satisfied to call this one finished. Funny thing is when family and friends look at it, they think it is fantastic and can't understand why I consider it unfinished. From a distance of 2 metres, it even looks good to me. But I know it isn't!!!!! Again, I appreciate the time some of you give to reading and responding to these requests for help. Frank |
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