Curing Finishes With UV

saltytri

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Over on the Luthier's Forum, Michael N. posted some good information on his use of UV to cure Tru-Oil and other varnish finishes. This advice got me going on putting together a UV cabinet. It turns out that a 30 gallon garbage can is an easy way to make a suitable enclosure. It's the right size for ukes up to the baritone and has the additional advantage of good internal reflectivity without having to add reflective material. The tubes are 24" BL350 fluorescents that are readily available on line but probably won't be found at your local hardware store. Ready-made fixtures that incorporate ballasts are available but it's less expensive to buy the end sockets (called "tombstones") and ballasts separately and just screw them to the walls of the can. This also lets the ballasts be mounted on the exterior to keep heat on the outside. I found ballasts that drive two bulbs and that also saved some money. Without ventilation, the internal temperature stabilized at 88F, which seemed a little warm so a quiet, low-volume muffin fan was added along with holes at the bottom of the can to allow air to be drawn. A filter was added to keep dust out. It plugs into an inexpensive mechanical timer so that I can leave it unattended.

So far, I've found that it cures both Tru-Oil and poly. As Michael says, it really does speed up the finishing process. Here is the link to his comments:

http://luthiersforum.com/forum/viewtopic.php?f=10101&t=49036&hilit=michael+uv


And, please hold your fire about "garbage can ukuleles." :)


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Yes, indeed, it is. I'd be shocked if it weren't. It's always good to have reminders of such things, though.
 
Very informative post. Actually slickest idea as I've seen in awhile.... Dumb question: Does UV work on non-synthetic finishes like shellac? I'm thinking not since that is more an evaportive thing than a curing thing.
 
I haven't tried it on shellac. I vaguely recall reading that UV has little or no effect on it, probably for the reason that you identified. The alcohol is gone pretty quickly.
 
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True, Ken, then I wouldn't get much done in the shop and whatever I did manage to get done would be crooked, upside down and inside out. ;)
 
I gave up on wipe on/wipe off finishing long ago. It doesn't make sense to wipe off most of the finish just to keep it level. After trying wipe-and-leave to get a faster build I tried spraying. A cheap airbrush worked great, and it was almost magical how well it layed out. Then I got a tip to try Formby's Tung Oil Varnish, and I think I'm done with Tru Oil. After the second spray coat of Formby's it can be dry sanded to cut it back a bit to start eliminating pore dimples. When left over night it powders off without clogging the 320 grit. Tru Oil almost needs to be wet sanded to keep it from clogging the paper. Way back in gunsmithing school an instructor insisted that tung oil dried harder than any linseed oil varnish, and it seems to me that it dries harder and faster. Plus, you can find the Formby's in any hardware store.

How much money do you have invested in your trash can UV unit? It looks to me like a hot setup.
 
A quick tally of expenses shows about $140.

Thanks for passing on the tip about Formby's. The world of wiping varnishes is more than a little confusing, in large part because the manufacturers aren't interested in telling us what their formulations are. But the proof is in the pudding so I'll give it a try.
 
I gave up on wipe on/wipe off finishing long ago. It doesn't make sense to wipe off most of the finish just to keep it level. After trying wipe-and-leave to get a faster build I tried spraying. A cheap airbrush worked great, and it was almost magical how well it layed out. Then I got a tip to try Formby's Tung Oil Varnish, and I think I'm done with Tru Oil. After the second spray coat of Formby's it can be dry sanded to cut it back a bit to start eliminating pore dimples. When left over night it powders off without clogging the 320 grit. Tru Oil almost needs to be wet sanded to keep it from clogging the paper. Way back in gunsmithing school an instructor insisted that tung oil dried harder than any linseed oil varnish, and it seems to me that it dries harder and faster. Plus, you can find the Formby's in any hardware store.
How much money do you have invested in your trash can UV unit? It looks to me like a hot setup.

I doubt it's got anything to do with the type of oil. Tung oil finish isn't necessarily the same as tung oil varnish. There's a huge difference between pure tung oil and a tung oil mixed with resin i.e. made into a varnish. Linseed is no different. Use a high resin content and that type of varnish can get very hard and brittle. It's the proportions of these things that makes the difference, that and the type of resin. Tung oil has a better reputation than linseed in wet conditions, which is why you tend to find it in marine varnishes.
 
It occurred to me that I shouldn't toss this UV idea out there without a warning that looking at the light is a poor move. So, I made an effort to keep the light in the garbage can by covering all places where it could be seen. Also, I keep a pair of UV-protective glasses close at hand for the times when I take the lid off to inspect the workpiece while the timer is running:

https://www.amazon.com/gp/product/B003OBZ64M/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
 
Also, I keep a pair of UV-protective glasses close at hand for the times when I take the lid off to inspect the workpiece while the timer is running:

I love the vision of the luthier opening the UV can with sunglasses on. So science fiction. Wild hair and wearing a white lab coat. Love it.... But seriously, UV works because the big guys use it. It is a chemical physics thang that I don't completely understand. Something about cross linking polymers.... As for Formby's tung oil: I have used the stuff for years (the low gloss) on all sorts of wood and it works great. I have no idea what it is and Formby's ain't sayin. Very expensive of course for what you get. I still use it on my bridges which I don't want to be too shiny but look nice. That is the only place I use it anymore. The glossy stuff isn't as nice looking in my opinion. Really a good simple alternative that gives a nice looking and good sounding finish to an uke project. Impossible to screw up a tung oil finish and it is quick. Just don't overdo it.
 
I love the vision of the luthier opening the UV can with sunglasses on. So science fiction. Wild hair and wearing a white lab coat. Love it.... But seriously, UV works because the big guys use it. It is a chemical physics thang that I don't completely understand. Something about cross linking polymers.... As for Formby's tung oil: I have used the stuff for years (the low gloss) on all sorts of wood and it works great. I have no idea what it is and Formby's ain't sayin. Very expensive of course for what you get. I still use it on my bridges which I don't want to be too shiny but look nice. That is the only place I use it anymore. The glossy stuff isn't as nice looking in my opinion. Really a good simple alternative that gives a nice looking and good sounding finish to an uke project. Impossible to screw up a tung oil finish and it is quick. Just don't overdo it.

Formby's is a bit cheaper than Tru Oil, sprays better and sands cleaner. Its as easy to screw up as any sprayed finish, but way more forgiving than nitro lacquer. I don't know what "just don't overdo it" means in this case. I don't wipe the stuff back off unless I get a runny coating, in which case I wipe it quickly with paper towels and shoot another coat. No harm done. The high gloss is beautiful, as pretty as lacquer. If I'm after a satin finish I spray Satin Min-Wax Wipe-On Poly, which gives a nice protective build after 2-3 coats and (with luck) requires no work after the last coat. If you can't spray for some reason you are stuck with applying with fingers, rags, or a brush, all of which are obsolete wastes of time.
 
I find "Formby's Tung Oil Finish" but not "Formby's Tung Oil Varnish". Are there two different products, or is "Formby's Tung Oil Finish" what is being discussed?
 
I find "Formby's Tung Oil Finish" but not "Formby's Tung Oil Varnish". Are there two different products, or is "Formby's Tung Oil Finish" what is being discussed?

It is called "Formby's Tung Oil Finish"... Now the knock against Formbys by finish carpenters that I've known is not that the stuff is not any good, and it is good, but how much the stuff is over priced. There are other similar tung oil finishes that do the same job at a fraction of the price but they aren't "Formby's".

Now John, what I meant by "don't over do it" is that after 4 or 5 coats you are pretty much done. It is an oil based finish and one gets to diminishing returns pretty quick. I also do not agree that applying the stuff with cloths (rags) is an absolute waste of time. I think it works just fine and will give the inexperienced finisher a perfectly acceptable finish without resorting to elaborate spraying equipment.

My problem with this finish is not so much as how it looks as how it effects the sound of the ukulele.
 
What's the problem?

Who knows? Oil supposedly has greater dampening. I used to apply a wipe on oil finish to lute type instruments, direct on to the spruce soundboards. I can't say I ever noticed that it was detrimental to the sound, neither did the customers who bought them. Now the interesting thing is that these are extremely low tension strings, they have very limited energy. It's like playing on elastic bands. If you can't notice it on those, when can you? If you are worried then apply a sealer coat (or two) of shellac.

As for 'tung oil finishes', it can be confusing. I think in the Formby's case it's very likely tung oil with a modern resin, perhaps a urethane. I don't know because I've never used the stuff. I'm guessing that it's not unlike the Liberon finishing oil or some types of Danish oils. The liberon obviously contains tung (I can smell it) and a type of resin - it builds too quickly to just be oil by itself. Most Danish oils are practically the same type of thing. I have a Danish oil that again obviously contains tung. In fact on the tin it states that it's a mixture of oils and resins. I can't smell linseed but there certainly is a strong smell of tung. If you've ever used pure tung oil (just the oil) the smell is obvious.
As for spraying, wiping, brushing. Whatever. They all work. Wiping and brushing has the big advantage in that they are very simple. Even a good brush at £20 will last a lifetime or even two. There's not a lot to dislike. I can brush on 12 coats of Tru oil and it takes very little time at all - a few minutes per coat. There are brush marks but they are pretty shallow, it doesn't take much to rub them out. Having said all that I tend to use shellac, which in tests I found resists scratches better - apart from the very hard oil finishes such as rockhard.
 
Who knows? Oil supposedly has greater dampening. I used to apply a wipe on oil finish to lute type instruments, direct on to the spruce soundboards. I can't say I ever noticed that it was detrimental to the sound, neither did the customers who bought them. Now the interesting thing is that these are extremely low tension strings, they have very limited energy. It's like playing on elastic bands. If you can't notice it on those, when can you? If you are worried then apply a sealer coat (or two) of shellac.

As for 'tung oil finishes', it can be confusing. I think in the Formby's case it's very likely tung oil with a modern resin, perhaps a urethane. I don't know because I've never used the stuff. I'm guessing that it's not unlike the Liberon finishing oil or some types of Danish oils. The liberon obviously contains tung (I can smell it) and a type of resin - it builds too quickly to just be oil by itself. Most Danish oils are practically the same type of thing. I have a Danish oil that again obviously contains tung. In fact on the tin it states that it's a mixture of oils and resins. I can't smell linseed but there certainly is a strong smell of tung. If you've ever used pure tung oil (just the oil) the smell is obvious.
As for spraying, wiping, brushing. Whatever. They all work. Wiping and brushing has the big advantage in that they are very simple. Even a good brush at £20 will last a lifetime or even two. There's not a lot to dislike. I can brush on 12 coats of Tru oil and it takes very little time at all - a few minutes per coat. There are brush marks but they are pretty shallow, it doesn't take much to rub them out. Having said all that I tend to use shellac, which in tests I found resists scratches better - apart from the very hard oil finishes such as rockhard.

The Formby's is called a finish. Right under that it says varnish. Its nothing like a Danish oil, which never builds much above the wood, and which I haven't used on instruments for decades. I've included photos of a uke after two spray session with Formby's, trying to catch the reflection. After five sessions it should be done. A friend of mine worked for awhile in the finish room at Collings. For a significant upcharge Collings will finish their instruments in varnish. Rather than some arcane violin makers varnish, they spray on a bar top variety. I used that back in my dulcimer days, spraying it on with a blow pipe. Its very hard after curing.

Its hard for me to understand why anyone with room to spray would use any other method. The airbrush in the photo cost me less than $15 at Big Lots several years ago. Stew-Mac sells the exact same airbrush in a much nicer kit for about $25 (I just bought one). For technical sorts of work, like photo retouching, its a piece of junk. For spraying small instruments its fine. A small air compressor with a holding tank for the air can be had in the $65-$80 range. So anyone inclined to spray can get into the game for approx. $100. Spraying a neck takes less than 30 seconds, a uke body less than two minutes. I should time them to get real figures, but its a small detail.

The collection of finishing materials is stuff I'm trying for a story on uke making. There's no lacquer or quality shellac included because I have nothing new to say about them.
 

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Danish oil will build. . . if it contains a resin. The mistake you are making is assuming that all Danish oils are the same. They are not. Some contain a resin, others are just a mix of drying oils. Anything that contains oil and a reasonable proportion of a resin will build. There's no one single definition of 'Danish oil'. In the broader sense it simply means a wipe on finish, as opposed to a brushed on finish, which tends to contain less solvent. The actual ingredients of a wipe on finish and a 'varnish' can be exactly the same.
 
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