Original bridge height of early gibson A4 required.

[Mike Keen]

Repair of the the 1906 Gibson A4 continues. It's now back in one piece - fretboard. The fretboard was off when I got it and it had been attached by something resembling floor adhesive.

The bridge that came with it was a flat piece of ebony about 1/8th wide with a height of only 5/16th inch. This is much lower than my 1921 A3 and 1925 A1. I need to set the correct angle for the fretboard. Does anyone know what bridge height and style would have originally been fitted. All the Gibson of that period in the archive seem to have different style of bridges so I'm a bit confused.

Thanks again everyone.

Mike

[Ned Knepp]

Take a look at this thread:
http://fretsnet.ning.com/forum/topics/need-help-trying-to-make-a?x=...

On the first page I put up so pics of one I have and gave measurements of the same.

Ned

[Mike Keen]

Thanks Ned

The A4 have is earlier serial 5655 and has an earlier body design. The the wood under the fretboard was quite damaged, so I'll have to build it up slightly and plane flat to get the correct angle, before attaching the fretboard. I think your bridge design is much higher.

5/16th seems very low to me. Does anyone know what it should be for a 1906 A4

[Ned Knepp]

Mike,
I forgot that the earliest mandolins were fit with shorter bridges.

Are you sure that you are not approaching this backwards? Usually the bridge height is a result of the design of the instrument and not the other way around. The neck angle is the prime factor in the height of the bridge so any measurement we might give you may or may not work for your instrument. If you have the mandolin assembled again, perhaps you can make a dummy bridge and shim it up until you get the action you want them fabricate your bridge.

Ned

[Mike Keen]

Ned

The problem is the neck on this mando was broken (just repaired it) and has also previously had a repair near the peghead. It looks as if the neck was "modified" as on top of the mahogany neck there's also a strip of "spruce" looking wood, about 3/32 thick that was badly damaged. I've had to patch it and sand it flat (removing almost all of it). I'll need to glue a strip of wood about 1/8th on top then sand it to give the correct angle for the fretboard to be attached. The neck on the earlier Gibson A's are quite thin and i suspect the neck has raised over time. I think I need to slightly slope it upwards toward the body to compensate. I therefore need to know what the bridge hight should be so I can get this angle right. I could guess it, but it seems sensible to get an actual measurement to work to.

Thanks so much for your help.

Mike

[Jeff Highland]

I know NOTHING about mandolins, but with any floating bridge instrument, the break angle over the bridge is the important factor, rather than just the height of the bridge.
I don't know what this should be but I guess you could measure from another A type.
Too much and you are going to collapse the top, too little and you wont drive the top properly.
Tailpiece design, neck angle and height above the soundboard and fingerboard and fret height all affect this.

[Tim Mace]

I agree w/ Ned in that bridge ht will be determined by the construction of the instrument and what kind of action suits the player. I like low...010 +/- under the 2nd fret capo on 1st fret.Gotta clear the body joint and extended frets so trial and trial is the way I go about it.There is no set stat 'cause every one is different... handmade or assembly line.Ballpark and beyond.

[Ned Knepp]

I see what you are trying to do but it seem to me that the issue might really be neck angle and not bridge height. I've seen some mandolins of the same year and model that have as much as 3/8 inch difference in the bridge height so neck angle is what you need to know.

I'm not sure I understand what you are wanting to do with the neck when you say " I think I need to slightly slope it upwards toward the body to compensate." The neck on archtop instruments are always angled back from the plane of the top. I'm not sure how angling it "upwards" will help you. Maybe I'm just visualizing it incorrectly. If you have some pictures it might help.

If the concern is that you don't know IF or how much of the original neck surface has be removed it may be possible to get a fairly close estimate by looking at how much width would be needed to fit the original nut width then figuring how much height is needed to fit the width of the neck to the nut and keep the curvature of the shape.

If nothing has actually been removed yet it shouldn't be too hard to get figure out the angle because it isn't or at least shouldn't be set by sloping the finberboard, it should be set by the angle of the dove tail. If the dove tail and the head block are right a straight shot down the finger board should at least get you into the ball park.

Ned

[Mike Keen]

Thanks everyone.

I'm sorry if I've confused anyone.

Ned, you've seen what my problem is. The neck has been badly messed around with, so I need to determine the correct neck angle. The height of the fretboard needs to be raised near the soundhole to get a suitable neck angle.


The previous repairer, probably 40 or 50 years, bodged it and used a thick adhesive to position the fingerboard. I've cleaned and leveled the top of the neck and will build it up with a strip of wood, then plane sand to get the correct neck angle.

I wanted to get a "feel" for the correct bridge height. The one fitted was only 5/16th. The bridge height on my 1921 A3 is set at 3/4 inch (much higher) which requires a neck set to give about 5/8 ths.

I think I'm just going to have to use my gut feeling over this one and set the fretboard angle to aboutso that the bridge height will be around 3/8th to 7/16th inch.

Cheers Mike

[Jeff Highland]

It's because everything is messed up that I recommended that you make sure that you have an appropriate break angle over the saddle rather than leaving this to chance.
Just chosing a bridge height and matching the neck angle to it may not achieve this

[Frank Ford]

The bridge on that early mandolin would be much lower than the ones on your 1920s instruments. Look carefully at these photos, and notice that the operative issue is that the strings run from the tailpiece to the bridge, and barely clear the arch in the top:

http://www.frets.com/FRETSPages/Museum/Mandolin/Gibson/1904GibsonF/...

http://www.frets.com/FRETSPages/Museum/Mandolin/Gibson/1905A3/1905A...

IF the bridge is too tall, there's a clear and serious risk of the top collapsing under the load - it was not designed to handle the downward force typical of the later mandolins.

[Greg Mirken]

Pay particular attention to the side view Frank posted- the plane of the fingerboard lines up with the edge of the top. A 1906 Gibson mandolin is a very different animal from even a teens Gibson.

[Mike Keen]

Frank and Greg

Thanks so much that's exactly the information I needed, especially the side view. I looked at a lot of photos on the archive but none were side on, so it would have been guess work.

I suspected that top collapse was a risk and that neck angle/bridge height were critical. The top of mine is in good shape and I've reglued the top brace. With the info you've supplied I'll be able to set the fretboard angle correctly.

Frank, I must complement you on you site. I'm an avid reader of your tips.

The repair is going very well - fretboard goes on today.

Cheers Mike