Glueing on the Bridge

[Max Taylor]

Hello to all,

This is my first post on this Forum although I have been following it for some time after I purchased The Gore/Gilet Books some time back. Can’t say enough about the time and effort these two put into them for the benefit of Luthiers around the world. World Class all the way.

The Classical guitar I currently have is the second one I built in 1972 and still pick on regularly although the action is a bit high (strengthens the fingers, right?) and being retired it is time to start building again.

My first new Guitar will be another Classical with Falcate bracing and “BOBO” neck based upon the “Books”. It will have some interesting design considerations but all in the Classical style. This time around I have the extra funds to back up the build.

My first question regarding “Glueing on the Bridge” is as follows:

Other than applying a final finish (French Polish) is there any fully valid reason why the Bridge can not be glued onto the top after the Falcate Braces have been installed and prior to the top even being installed onto the body. Of coarse this assumes that the correct bridge position relative to the 12th/14th fret at the body has already been precisely determined in advance. Even if using a dish for curvature a simple cutout relief can be made to accommodate the bridge when glueing on the top so the bridge would not interfere with that process if one wanted to use the dish.

As I see it, the exact placement of the fingerboard on the neck once the neck is bolted on can easily be determined and adjusted fore or aft to make the Nut to Saddle length exactly what it needs to be. If this is feasible it will also make glueing on the Bridge much simpler.

I will be using a compensated Nut and Saddle as per the “Books” and all the details have been well thought out.

I have never seen this particular question on this Forum so it will be interesting to hear some of your thoughts.

Thanks in advance.

—Max

[kiwigeo]

Other than applying a final finish (French Polish) is there any fully valid reason why the Bridge can not be glued onto the top after the Falcate Braces have been installed and prior to the top even being installed onto the body. Of coarse this assumes that the correct bridge position relative to the 12th/14th fret at the body has already been precisely determined in advance. Even if using a dish for curvature a simple cutout relief can be made to accommodate the bridge when glueing on the top so the bridge would not interfere with that process if one wanted to use the dish.

—Max

Hi Max,

My first question is what advantage is there to fixing the bridge to the top prior to fixing the top to the sides?

I can see some advantage to fixing the bridge to the top _after_ the box has been closed up.....eg you'll have a better idea of final top resonant frequencies and can do a bit of trimming by thinning lower bout periphery. If you plan on using same finish on the bridge as the top then finishing isn't a big issue but if you plan on leaving the bridge bare then finishing can become a bit finicky.

[Max Taylor]

My first thoughts lie along the lines of making the glueing on of the Bridge easier from a clamping perspective as you can clamp it from any direction around the soundboard without having to fumble around through the sound hole where you can easily see where your clamps might interfere with the top bracings.

That said, my first and biggest concern had to do with finishing, where the bridge is typically glued on after the entire body has had the finish applied whereupon one must then remove the finish from under the area where the bridge is to be glued to.

—Max

[kiwigeo]

My first thoughts lie along the lines of making the glueing on of the Bridge easier from a clamping perspective as you can clamp it from any direction around the soundboard without having to fumble around through the sound hole where you can easily see where your clamps might interfere with the top bracings.

That said, my first and biggest concern had to do with finishing, where the bridge is typically glued on after the entire body has had the finish applied whereupon one must then remove the finish from under the area where the bridge is to be glued to.

—Max

1. If you use a clamping caul you don't have to worry about fiddling around to get your clamps clear of the bracing. IMO its a bad idea to have a clamp applying very localised pressure directly to the underside of the top or bridge plate. I make up a caul before the top gets glued onto the sides. I use MDF faced with 6mm cork. Cut channels into the caul to accommodate the braces and the sand the face of the caul in the same radius dish as you used for the top.
2. There are two camps when it comes to bridge glue up before or after top finishing....each school of thought has its pros and cons. I generally finish first and then scrape away the finish from the bridge area.....it's not a big job. Fix the bridge temporarily with two wooden pins through the saddle slot. Scour around the bridge with a scalpel blade, remove bridge and then scrape off finish with same blade(s).

[Max Taylor]

Thank you for your feedback and your time.

Using a padded clamping caul goes without saying so the final options are to glue on the bridge first or wait until the body is finished as you do but it appears you say that either option is doable, each a little different.

Here is the caveat I am up against. I have worked for months carefully refining and tweaking the final design for this Classical model with full sized very accurate drawings with all the details well thought out in advance. Two things (immediately visible) are different from the norm in my design.

1. Even thought it will be a Classical in every right it will have a 14 fret neck with a full 24 frets. This brings up the same problem Gore/Gilet bring up in the books. That of necessitating the movement of the bridge ~35mm closer to the sound hole location and away from the center of the sound board which is not IMHO a good idea by itself, but;

2. To eliminate that problem I have moved the location of the sound hole from its traditional location thereby leaving the new bridge location almost centered in the sound board. The Falcate bracing location has also been moved upwards accordingly and slightly extended on its ends to within ~25mm from the side edges.

Now, no longer having the traditional sound hole location then clamping the bridge after the top is glued on presents a different set of challenges to solve due to distance from the sound hole. Hence the original question regarding whether or not glueing on the bridge prior to glueing on the top. The sound hole design is sort of a cross between that used on “McPherson” guitars and those typically produced by “DeVine” of Hawaii but not exactly as either.

I guess when you step off the beaten path you might expect to run into some new obstacles but none that are insurmountable but I lean more towards glueing on the bridge first and working backwards towards the exact Nut position at this point.

—Max

[Steve.Toscano]

is there any fully valid reason why the Bridge can not be glued onto the top after the Falcate Braces have been installed and prior to the top even being installed onto the body.

I did exactly this on a build last year. Figured it would be a better option as my bridge clamps would not have reached through the soundhole (longer scale)....

The problem I encounted was that it wasn't as easy as you'd think to align the fretboard useing this method. I'm not talking about for scale length, - more so to get it in line with the bridge string holes useing strings as alignment. I find it easier to align the fretboard to the centre line of the body, and then align the bridge to the fretboard (to take into account any miniscule movement of the fretboard when clamping) - talking spanish construction here.

EDIT: just read the whole thread and noticed you are talking about a bolt on/off neck join, therfore ^ might not be relevant for you.

The ONLY advantage to doing it this way is the ease of clamping of the bridge, but really it's not that difficult to clamp the bridge on once the box is closed.
Any advantages to finishing the top with the bridge on can be achieved by putting the bridge on pre finishing (this is what I do) - mostly because im anxious to get strings on and hear the instrument.

I would also have doubts about finishing the top side of the top prior to it going on the box as i believe it would be more likely to warp as it cannot breath (moisture with humidity changes) through the top but still can on the underside and is not locked in to the sides therefore able to move much more afterwards but before being locked in by glued onto the linings/sides. This is my speculation, certainly not backed by any science that i've seen or from experience.
Obviously if also applying a finish to the inside of the top at the same time would avoid this. But some would rather not coat the inside of their instruments for ease of later repairs.

[kiwigeo]

Steve makes a good point regarding fretboard/bridge alignment......to me this alone would be a good enough reason not to fix the bridge to the top before fitting the top to the box.

As an aside on lutes the bridge is fitted to the top before fitting the top to the belly...but this is done as lutes don't have a soundhole through which clamps can be placed.

[Trevor Gore]

Check out vacuum clamping for bridges.

[lamanoditrento]

As someone who recently french polished after gluing on the bridge, my strong recommendation is to glue the bridge on after the finish. Granted it was my first time french polishing, but I reckon I spent 3 or 4 times the amount of time due to the bridge and around the bridge is the only part of the finish that I am not happy with.

You don't have to scrape the finish off. You can tape the bridge area and polish over it... which is what I am intending on the current build.

I am not sure about the sound hole size you are referring to, but could you get a scissor jack in and under the bridge area? Then you go could just go bar the bridge on.

[Max Taylor]

Thanks for the replies.

Granted it was my first time french polishing, but I reckon I spent 3 or 4 times the amount of time due to the bridge and around the bridge is the only part of the finish that I am not happy with.

Actual experience coming through here and that I don’t take lightly.

I like the views I’ve seen of the vacuum clamp for attaching the bridge as Trevor stated. That just might do the trick for me. I do have a dust collector but not sure if that would generate enough vacuum to work a vacuum clamp. Will have to check that out.

As for alignment I am a meticulous individual in that regard so I don’t think that would actually be a problem. I will be using a replaceable compensated saddle also.

Note: From the treble side of the bridge to the closest point on the sound hole is about 9" (220mm) so some distance is involved.

—Max

[johnparchem]

I use a vacuum clamp to clamp on bridges. I do not think a dust collector has enough vacuum, you either need a vacuum pump, not a large one for a bridge or if you have an air compressor you can use a small venturi based air powered vacuum pump/

[jeffhigh]

Where are you located Max?
There may be someone near you with a vacuum setup.
It's what I use, a Dust collector would not generate enough Vacuum, it's high flow but low negative pressure

[Max Taylor]

For some reason I remember entering my location in my user options but now can’t find it and would like it to show on my posts. Any hints out there?

I live in Las Vegas, NV, USA but would rather be in AU or ZN for the next 6 moths as winter is coming on here. Starting to cool off fast.

Had a busy day taking care of things that needed to get done. I didn’t figure a dust collector would create enough vacuum but mentioned it anyway. It will be a while till I am ready for the bridge but I brought up the topic well enough in advance to be prepared for when I get there.

Speaking of Bridges, has anyone out there ever used the wood “Purple Heart” for a bridge or fretboard? I have some and it is a really beautiful hard heavy wood and just a purple as can be. Beautiful actually.

—Max

[garryalb]

Hi Max,

A fridge compressor makes a good vacuum pump, easy to find and more than enough vacuum.

Garry.

[simonm]

Look up Michael Thames you tube videos about gluing classical bridges with hot hide glue. If you haven't used hug, look up Frank Ford's hid e glue pages on frets.com. None of this is about clamping but useful. Make a caul from whatever solera or radius dish you are using when you glue the bar aces, then cut out channel in it to fit you braces (approximately). Then glue it on after the top is and the neck aligned. Shape the bottom of the bridge to the curve of the caul.

[blackalex1952]

There are some hand vacuum pumps available in the automotive trade which may or may not work for a small application like a vacuum bridge clamp.http://www.ebay.com/itm/Hand-Held-Vacuu ... 1950085253
It might be worthwhile checking with a local automotive repairer to see if one of these was suitable when combined with:http://www.lmii.com/vacuum-bridge-clamp
I'm not recommending this system because I have never used it, but the hand pump may work-easy enough to try one at an auto repairers.
I made myself a bridge vacuum gluing clamp using perspex and the yellow vacuum bagging seal tape along with vacuum bagging film. That might be a solution for you, and the cost is rather low for experimenting with a hand pump.-Ross

[Max Taylor]

Thanks to all for the multiple suggestions. At this point using a vacuum method sound like the most reasonable so I will lean in that direction first.

Might even be able to hook up the vacuum unit to my wallet as the suction created by the money leaving it might also do the trick. ;-}

Will update with anything that changes along the way.

—Max