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Sven
05-26-2010, 07:10 AM
Hi. I saw on one of Stewmac's newsletters or what it was how a guy put a shellac finish on a miniature guitar (no uke). He was working rapidly, finishing the guitar in a couple of days. Lots of pics and advice but I would like to know something that I couldn't gather from his description. It was just that he glued the bridge on after the third coat or something and no mention was made of scraping down the shellac to bare wood before glueing. Is it totally obvious he did that, and my question is of course; anyone ever seen titebond on shellac? Would it set, or would it, as I presume, be a rubbish joint?

I'll see if I can find the description on their site, got the link on another forum but forgot which.

Sven

Vic D
05-26-2010, 07:24 AM
Hehehe, this thread made me laugh. I'm just guessing there's gonna be a major mishap on the cellular level.. *POP!* *TWANG!*... I could be wrong... but I don't think so..

Matt Clara
05-26-2010, 09:36 AM
Aren't they always telling us shellac adheres to anything?
;)

Vic D
05-26-2010, 09:53 AM
My guess is that since I haven't heard of bridges glued with shellac, coupled with the fact that the glue is formulated to bond the cells of wood yet it can't now because of the shellac barrier... my hypothesis is that the shellac and titebond will bond to each other until there is a load put on the bridge and then there will be a pop twang result certainly, it's just a matter of how long.

Sven
05-26-2010, 10:51 AM
You are probably right. I'll go look for the article now anyway.

Matt Clara
05-26-2010, 11:01 AM
Here's one from 1919.
http://www.treesearch.fs.fed.us/pubs/32258

Sven
05-26-2010, 11:08 AM
Matt, that's a great find. I found the article I was referring to:

http://www.stewmac.com/tradesecrets/ts0110_frenchpolish.hzml?utm_source=newsletter&utm_medium=email&utm_campaign=ts0110

Sven

thistle3585
05-26-2010, 11:49 AM
Although they don't show the bridge area, I am betting that he masked off that area with painters tape.

Sven
05-26-2010, 12:35 PM
It does show on the fifth pic with no tape. But I'm sure he scraped the area.

erich@muttcrew.net
05-26-2010, 12:46 PM
Sven, we have always masked the bridge area. I am quite sure that the bridge bond would not hold otherwise and I would not want to leave the joint unmasked and have to scrape it down to bear wood. Alternatively you can glue and then mask the bridge before finishing (or maybe scrape it afterwards, but we've never tried that).

Vic D
05-26-2010, 01:07 PM
I've tried it two ways, glued before finish and scraping after finish. I definitely don't like the result of gluing the bridge before finishing but scraping after finish is tedious, not unenjoyable but tedious and I really wished at the time that I had a magnifying visor, which I have now. I think I'll try the masking of the bridge area before spraying this time. My only concern is the buildup and how it will look when the bridge is in place, but a plus would be that there's no doubt that any finish has left the bond of the joint compromised in any way.... hmmmm decisions decisions...

Side note, totally unrelated. Solid spanish cedar linings bend like butter, even in the waist of the tiny soprano...

Michael N.
05-26-2010, 01:40 PM
Some bridges on production Guitars are glued directly on to the finish. No idea which type of glue they use but personally I'm an advocate of wood to wood contact. I have masked the area but French Polishing can leach out the adhesive from under the tape resulting in an unsightly ridge. I now prefer to scalpel around the bridge and scrape.

Matt Clara
05-26-2010, 02:05 PM
Some bridges on production Guitars are glued directly on to the finish. No idea which type of glue they use but personally I'm an advocate of wood to wood contact. I have masked the area but French Polishing can leach out the adhesive from under the tape resulting in an unsightly ridge. I now prefer to scalpel around the bridge and scrape.

Welcome to the the Ukulele Underground/Luthier's Lounge, Michael.

Vic D
05-26-2010, 02:35 PM
Some bridges on production Guitars are glued directly on to the finish. No idea which type of glue they use but personally I'm an advocate of wood to wood contact. I have masked the area but French Polishing can leach out the adhesive from under the tape resulting in an unsightly ridge. I now prefer to scalpel around the bridge and scrape.

Yep, I know of at least one of the companies that do that. It's foolish IMO and the results are seen by busy luthiers. I guess the luthiers can use the work. To me, it's not a question of if but when the joint will fail. I think I do prefer the score and scrape after the finish method.

ecosteel
05-26-2010, 02:51 PM
A freshly sharpened chisel with the burr still on works really well for this job but you guys knew that already.

Philstix
05-26-2010, 04:50 PM
I have reglued about 100 guitar bridges. Almost without exception they have been glued onto finish. The exceptions have been wood to wood glue joints where the bridge split, that is the bridge failed before the glue joint did, or very old hide glue joints where the guitar has been stored in a huimid environment. Whatever time you dave is not worth the poor joint.

Vic D
05-26-2010, 05:03 PM
A freshly sharpened chisel with the burr still on works really well for this job but you guys knew that already.

I didn't know about the burr part, makes perfect sense though. Thanks ecosteel.

erich@muttcrew.net
05-26-2010, 08:53 PM
You can polish the burr with the spike of your burnishing iron - if it has one. But only use one sweep, otherwise you'll dull it - the burr that is.

Vic D
05-26-2010, 09:07 PM
:cool: Cool beans Erich. I'm just now getting my sharpening rig together.

Michael N.
05-26-2010, 10:51 PM
I find a chisel a little 'top heavy' for scraping the bridge footprint. I use a blade from a small bull nose plane that is around 3/4" in width. I sharpen it as one would a normal plane blade ie. without a burr. That helps me to locate it in the scored line left by the scalpel.
I guess there are many methods. I do know that some makers rout a very small 'rebate' all around the edges of the underside of the bridge, effectively the very edges of the bridge 'overhang' the finish. You could probably achieve the same effect by simply filing a very tiny chamfer.
My finish of preference for a soundboard (Spruce) is a simple oil finish. Bridge glued before any finish is applied. End of problem.

Sven
05-27-2010, 04:51 AM
Thanks for all your input. First, just in order to set the record straight, I don't and wouldn't glue on finish. Masking before finish is an option, but so far I have glued my bridges before finishing. Works well with oil, works less well with shellac applied with cloth. And I would be hesitant to put shellac on masking tape, thanks for the warning.

And another thing - I use string through bridges, they're not subject to the same kind of stress as an ordinary tie bridge.

All the best / Sven

Matt Clara
05-27-2010, 05:43 AM
Just one more thought. I'll bet a dozen q-tip swabs and an ounce of denatured alcohol would remove 90% of the shellac from the bridge area and a razor blade used as a cabinet scraper would get the rest.

Vic D
05-27-2010, 06:17 AM
Sven: I'd like to try the string through bridge, on top of the less stress thang, they're prettier and easier to make. You know what, I'm gonna go for it.
Matt: Dunno about the alcohol thang, that might work but in my mind I see the alcohol maybe allowing the shellac to soak deeper into the wood. I'm scraping through shellac and waterbase clear though. The razor blade is a good idea, I used a combination of exacto blade, exacto chisel and a 3/8ths stanley. The Stanley worked best for the initial removal of most of the finish, then the exacto chisel was good for fine tuning it all. I can see tossing all that out the window and using a small plane iron though...

Dominator
05-27-2010, 09:03 AM
My finish of preference for a soundboard (Spruce) is a simple oil finish. Bridge glued before any finish is applied. End of problem.

Michael, just curious whether you experience any issues with uneven or blotchyness in the finish when using oil on a softwood top? I used oil on a spruce top and experienced this problem and then consulted with an experienced luthier who strongly discourages oil finish on softwood such as cedar and spruce. He recommended spraying a laquer or other finish of choice for the top and then oil the rest. This is what I did on my spruce top tenor and the top was much better and consistent with the laquer. Less yellowing also. Just curious as to your findings.

erich@muttcrew.net
05-27-2010, 10:32 AM
...I would be hesitant to put shellac on masking tape, thanks for the warning.

This hasn't been a problem for us.

Michael N.
05-27-2010, 11:52 AM
Michael, just curious whether you experience any issues with uneven or blotchyness in the finish when using oil on a softwood top? I used oil on a spruce top and experienced this problem and then consulted with an experienced luthier who strongly discourages oil finish on softwood such as cedar and spruce. He recommended spraying a laquer or other finish of choice for the top and then oil the rest. This is what I did on my spruce top tenor and the top was much better and consistent with the laquer. Less yellowing also. Just curious as to your findings.

Is Yellowing an undesirable? I quite often put instruments in a UV cabinet to achieve a more 'antique' effect.
The oil finish I am referring to is just Danish oil. It's a seriously thin finish and adds very little colour to the wood. As far as I'm aware it is a mixture of drying oils and (probably) a modern synthetic resin. Oil straight onto bare Spruce is often considered a big no no in Luthier circles. I don't think it has been detrimental to the sound of my instruments. Many Lute makers are using it as well as a few big name (and serious money) modern Classical guitar makers. It does not offer much protection against dings or nail marks. . but then again neither does shellac. Having said that it is extremely easy to put on another coat after a couple of years playing the instrument.
There are basically two approaches to it's application. The method described on the back of the tin is simply wipe on, wipe off. With something the size of a Baritone Uke I would divide the top into roughly 4 equal segments - top bout up until the bridge and the centre line, side of the bridge and behind and across to the cenreline. The other two segments being the other half of the soundboard. Wipe the oil on covering the first segment and with a fresh dry cloth wipe it all off and I mean wipe it all off. In reality it is impossible to wipe off all the oil but the objective is to stop any build up and blotchy finish. 3 or 4 applications and that's it.
The other method of application is to apply it as though you would do French Polishing. With this method you put very,very little oil onto the cloth. It just about feels damp and after the first few coats it seems as though you have achieved nothing. It takes perhaps as many as 20 coats or rather applications to obtain the desired finish. If high gloss finishes are your thing then forget simple oil finishes. It's more of a dull sheen but retains the real feel of wood.
Just one word of warning. The sanding of the Spruce has to be impeccable. Nothing quite beats oil directly onto wood IMO but it also has the habit of magnifying the tiniest of scratches. I sand right up to 600G in the manner of a plane landing and taking off ie. single strokes. After the sanding I burnish the wood with a non scratch pan scourer.
I have also tried (recently) diluting Tru oil (adding 40% turps) and applying that in a similar manner. I first sealed the Spruce with two coats of egg white and applied 4 coats of the dilute Tru Oil. No blotchiness but it certainly adds a little more colour than the Danish oil.

Dominator
05-27-2010, 12:01 PM
Thanks for the info Michael.
Though I didn't necessarily care for the yellowing that wasn't the biggest issue I had. The issue was mainly in the blotchy and uneven look to the finish. Surface prep could have also contributed to that as well.

Timbuck
05-30-2010, 12:47 PM
When I first started making uke's...I once masked off the bridge area before spraying with laquer...But!!! I had already applied stain to the wood..the stain was still on when I glued the bridge... About two months later the bridge failed...... This was the first and only time (as far as I know?) that I had a bridge pop off..since then I've always scraped down to the fresh wood before gluing.

Moore Bettah Ukuleles
05-30-2010, 12:53 PM
..since then I've always scraped down to the fresh wood before gluing.

And that's the thing, scraping down to bare wood. This means getting beyond any grain filler or sealer you might have on there as well.

Vic D
05-30-2010, 06:31 PM
Right on, you need wood to wood bonding... I've heard of people using solvent to take away the finish in that area... don't do that. I'm pretty certain that it's a nono. Using a solvent I'm pretty sure creates a slurry of stuff that sinks into the wood, that's how I see it. Scrape to bare wood and plant it.

erich@muttcrew.net
05-31-2010, 07:49 AM
Right on, you need wood to wood bonding...


This means getting beyond any grain filler or sealer you might have on there as well.

This is why I prefer to mask before finishing - or staining or sealing or grain filling or anything else, just masking the bare wood. Another alternative to consider is to put the bridge on before finishing - we've done this a couple of times; once with an oil finish and once with a shellac/alcohol based varnish. Worked fine both times.

ecosteel
05-31-2010, 03:52 PM
Chiselled a bridge off one of my ukes today. I'd glued it with Titebond original and some proper clamps and it was a bugger to get off. At least 90% adhesion, pretty reassuring.

Moore Bettah Ukuleles
05-31-2010, 07:28 PM
This is why I prefer to mask before finishing - or staining or sealing or grain filling or anything else, just masking the bare wood. Another alternative to consider is to put the bridge on before finishing - we've done this a couple of times; once with an oil finish and once with a shellac/alcohol based varnish. Worked fine both times.

The only problem with masking off first is having to work around that lump when you are sanding and buffing. The difference is noticeable in the glassy smooth surface I shoot for.

Allen
06-02-2010, 11:26 AM
I much prefer to spray without masking, then scrape back afterwards as Chuck does. I've done it both ways over the years, and feel the best results are not masking, but scraping.

With some sharp tools it's really not that difficult. And if the finish is very thin as it should be, really not a bid deal.