Gluing acoustic bridge, level sanding shellac

[Tweaker]

Hi guys,

I am finishing up an acoustic ukulele that I used the super old figured redwood for. I've taped off where I'm going to glue the bridge down, but since this isn't a solid body instrument, I'm not sure how I'm going to clamp the bridge without cracking the top or back. I guess ultimately, the question is how much clamping pressure do you need with Titebond (I, II, or III)? Can I get a solid glue joint just by placing say, a dictionary on top of the bridge while it dries?

Here are a few pics with just a few coats of shellac on:

Second, I've wiped on about 17-18 coats of dewaxed shellac over the last couple of days. I wiped it on because it's been extremely humid here lately...sort of a modified French Polish. I wet the pad enough to apply a decent coat before it started to stick to the previous coat. I didn't do any kind of oil on the pad to prevent stickage, so my final coat isn't perfectly smooth. (Didn't want to mess around with the oil without testing the process elsewhere) So today I plan on doing some level sanding and polishing the shellac. I know I can't use a buffing wheel because the heat will destroy the finish. My question is, can you level sand with a random orbital sander and a 600 or 800 grit pad? Will that be a high enough grit that I won't cut through the finish too fast? Perhaps its safe to just use a piece of 320 and do it by hand?

I read somewhere that you can also take a small amount of shellac and slightly more denature alcohol and rub the final coat smooth...does anyone have any experience with this?

Thanks!

 

[Greg's Guitars]

I believe there are special clamps for acoustic bridges that apply pressure from the top and from inside also acting as support to circumvent the problem of damaging the top.

 

[Bill Hicklin temp]

I'm not sure how I'm going to clamp the bridge without cracking the top or back.

You need to make a clamping caul: a block of wood or mdf slightly larger than the bridge footprint. Ideally you would have done this before closing up the body, but then IIRC a uke is ladder-braced and flat-topped, so you don't have to worry about slots for the bracing or contouring for the radius like you would have to on a guitar.

You then need two (not one) fairly deep-throat clamps - cam clamps are good - although I guess on a uke the throat doesn't have to be very deep. The caul goes inside, under the bridge (your life is way easier if you stick it in place with masking tape), and you put the clamps' lower jaws through the soundhole.

Sanding: don't use a power sander on shellac. The heat will soften it and it will gum up your paper in jig time (followed shortly by furrows). Use Wet-or-Dry paper lubricated with naphtha. (It's a uke, fer crissake- how long will it take?)

 

[Tweaker]

Looks like I'll have to go get some bigger clamps...the biggest I have only have a throat of 3". Looks like I'm just short, I need 4". What I'm gathering here though is that I can't set a heavy book on top of the bridge for sufficient clamping pressure

Regarding the shellac, I'll wet sand it...I unfortunately don't have any naptha. I've read that soapy water works, but I've also read that a glass of water leaves cloudy marks on shellac so I'm not sure I want to wet sand with soapy water..

 

[the great waldo]

Hi
You can use lemon oil as a lubricant. The stuff from Kyser works ok. You can also use lemon oil on 3m gold paper. Your'e going to have to hunt around for a clamp as it has to be long enough to reach the bridge but short enough to go into the soundhole. If you can get some wood to go between the top and back you could clamp the bridge from outside, the block inside would stop the top caving in with the clamp pressure. You will have to be careful of marking the finish, as if you have put 17 to 18 coats on in 2 days the finish is going to be hard as butter it'll probably take weeks to harden. Good luck.

Cheers

Andrew

 

[Bill Hicklin temp]

You can get naphtha at any hardware store or Home Depot. You can also get it at any convenience store under the name "lighter fluid."

The problem with using mineral oil (lemon, baby, etc) is that then you have to get it off or you're left with a greasy instrument. And the best cleanup solvent is... naphtha.

 

[Tweaker]

The finish was very hard. These were VERY thin coats. Not soft at all, I couldn't dent it with my fingernail..

That said...I goofed, bad. I sanded through (because that's what I do best ) so I tried to fix it with more shellac and got frustrated and made a bigger mess. So I sanded everything back quite a bit and tried spraying the shellac with a Preval sprayer. Worst sprayer ever. Even with thin shellac and light coats, the shellac dripped all over the uke and fogged up a ton. SO, I had spent 20 minutes rubbing alcohol all over the uke to strip the finish. I'll be starting over this evening.

It hasn't been a very good day.

 

[jkes01]

Hi guys,

I am finishing up an acoustic ukulele that I used the super old figured redwood for. I've taped off where I'm going to glue the bridge down, but since this isn't a solid body instrument, I'm not sure how I'm going to clamp the bridge without cracking the top or back. I guess ultimately, the question is how much clamping pressure do you need with Titebond (I, II, or III)? Can I get a solid glue joint just by placing say, a dictionary on top of the bridge while it dries?

Here are a few pics with just a few coats of shellac on:



Second, I've wiped on about 17-18 coats of dewaxed shellac over the last couple of days. I wiped it on because it's been extremely humid here lately...sort of a modified French Polish. I wet the pad enough to apply a decent coat before it started to stick to the previous coat. I didn't do any kind of oil on the pad to prevent stickage, so my final coat isn't perfectly smooth. (Didn't want to mess around with the oil without testing the process elsewhere) So today I plan on doing some level sanding and polishing the shellac. I know I can't use a buffing wheel because the heat will destroy the finish. My question is, can you level sand with a random orbital sander and a 600 or 800 grit pad? Will that be a high enough grit that I won't cut through the finish too fast? Perhaps its safe to just use a piece of 320 and do it by hand?

I read somewhere that you can also take a small amount of shellac and slightly more denature alcohol and rub the final coat smooth...does anyone have any experience with this?

Thanks!

I must be the only one that can't see the pics

Anyway, you got me searchin and I came across these clamps from Grizzly for $11.50.

http://www.grizzly.com/products/Ext...MIwpixwY681QIVB6ZpCh1CZQngEAQYASABEgJ7M_D_BwE

Basically the same style clamp StewMac sells for $38.

http://www.stewmac.com/Luthier_Tools/Types_of_Tools/Clamps/Ibex_Bridge_Clamp.html

I will definately get a couple of those for myself at that price, especially since building an acoustic is on my bucket list.

 

[Tweaker]

I'm using google photos, I wonder if no one can see the pics...

I also found clamps with a 3 7/8" throat at Harbor Freight for $3...they have bigger ones too, if there's a Harbor Freight in your area you might check them out. Possibly cheaper than the Grizzly clamp, not sure. Regardless, I won't be picking up any clamps until I can get my stupid finish issues worked out!

EDIT: Here's a clamp with an 8" throat: https://www.harborfreight.com/8-inch-deep-throat-c-clamp-45917.html

And here's the rest of the deeper throat style clamps: https://www.harborfreight.com/catal...ured+Weight,f,Sale+Rank,f&q=deep+throat+clamp

 

[JMT Guitars]

I went about it a slightly different way... I covered my madnes... ahem* Method in this thread:

http://www.mylespaul.com/threads/the-bodgers-attempt-at-bridge-repair.393402/#post-8259163

cheers

 

[Tweaker]

So how did the bridge hold after the second gluing? I'd assume you could only apply so much pressure with your...unique...clamping methods

 

[JMT Guitars]

Heheheh yes unique is one way of putting it. The bridge had been fine since, no intonation problems and no flinging across the room in search of audience member eyes... yet.

Even so remember things don't glue stronger the tighter you clamp it XD as long as you have spread the glue properly and it is all in contact then your clamp is there to hold it in place and prevent slippage. You don't actually need a great deal of strength when clamping. As my old mentor said, "if you tighten a clamp so much it is hurting your hand, you have over tightened it." The pressure on the back and front of the uke was substantial enough to hold the bridge in the same place for two days to allow full curing. If we had deep jawed clamps then sure but it worked and is an easy way of doing it. everyone has access to string and a vice...