Classical guitar repairs?

[AJB Temple]

Great. Well done. As a player, I would not obsess too much about string height on this guitar. If the neck is not in great alignment, your trade off for a lower action may well be some fret buzz. Therefore, when filing out the nut and lowering the saddle, do it a bit at a time. Buzz is almost always worst on the wound strings. As you are learning to play (Father and Son is a nice tune if it the one I am thinking of by Cat Stevens - has around 5 chords in it) then most of your initial learning will be in first position, where your are forming the chords between the nut and the fifth fret. A high action on a nylon strung should not hamper you much and may well improve your chord technique as a side benefit!

When you file the nut, a bit of graphite rubbed in the slots can help the strings slide smoothly and aid tuning stability.

Welcome to the world of guitarists ;-)

Adrian

 

[profchris]

I *think* the bridge will hold, purely because one of the strings I took off was STEEL. This implies that the guitar (and bridge) once held the tension of steel strings, so I don't think (optimist!!) that nylon strings will pull the bridge off.

I'll keep my fingers crossed for you. But I build ukes, only four nylon strings and lower tension, and they pull bridges off. In fact I'm picking up a sopranino scale uke (even lower tension) this evening for a bridge re-glue. I'll have to build or improvise a clamping system for that, so will post pictures here in case yours lets go and you need to reattach it.

 

[Kalimna]

If I may hijack the thread slightly, I built a couple of ukes a year or so ago, and I was never happy with the action (combo of nut and bridge too high, I think). They were made as practice pieces before moving onto guitars, and anyway my two young boys love them.
So, to the point of this ramble - a string snapped at the saddle last night giving me a good excuse to fiddle around and improve things. What would advise as to the height of the bottom of the nut slot over the first fret, and saddle height over fret tops, using a straight edge as earlier mentioned? They are both concert scale.

Cheers,
Adam

A very interesting thread, by the way.

 

[MIGNAL]

You can always do it by trial and error. Just make a dummy top nut out of any hardwood, cut the grooves so that the string only just starts to buzz on a forte note. Measure this nut, it's grooves and make the new one + 0.2 mm's.
That's how I did mine. I now have a series of wooden gauges that I just place against the Nut but under each string. Each groove is filed until the string reaches a mark on that gauge. This works with a definite fret height. For other fret heights I have to use a different gauge. I never had much luck filing down to a feeler gauge. No idea why but my method seems to work much better for myself. Measuring from right next to the nut takes a lot of the saddle height out of the equation, although you may as well get that close to final height first.

 

[John Brown]

I was thinking about this a while ago, while replacing the nut on one of my guitars. My plan was to stick a couple of pieces of masking tape or similar over the first fret, then file the slot until the string buzzed. In the end I got by with bravery, and I'm fairly happy with the result, but I'd be interested to know if anyone thinks some similar method would work.

 

[Kalimna]

Thanks Mignal, that approach certainly makes sense. I also need to 'thicken up' the saddle as I cut the slot a smidge too wide, but I reckon some thin veneer, cyano and judicious use of a file/sanding block should do the trick there.
Out of interest, do you have a ballpark height you start off with prior to fine tuning with your gauges?

Cheers,
Adam

 

[MIGNAL]

It's very near 1.1 mm's for a fret height of 0.90 (maybe 0.95). That's for a nylon strung guitar, high 'E'. The G is a little higher at 1.2 mm's, the low wound E and A at 1.3 mm's. On a uke it will be nearer to the high E, apart from perhaps the thickest plain string.
Of course a lot depends on what string tension you play at and just how much energy you put into the string. As someone once remarked, you can make any guitar buzz if you really want to.

 

[profchris]

What would advise as to the height of the bottom of the nut slot over the first fret, and saddle height over fret tops, using a straight edge as earlier mentioned? They are both concert scale.

I wouldn't aim for either of these as a measurement.

At the nut, I find the best way of setting each slot's height is to hold down that string between the second and third frets and then look at the height of the string over the first fret. I aim for a tiny fraction of clearance, which you can gauge by gently pressing the string on to the top of the first fret - if it doesn't move, you've gone too far (though you might still be OK, but you're definitely at the bottom of the range). Take it as low as you dare, which probably won't be low enough, and you can always lower it a little more later. This will transform the instrument's playability more than you could imagine!

To get the saddle height I measure the distance from the top of the 12th fret to the bottom of the strings. For a uke somewhere between 2 and 3 mm is correct - 3mm for heavy-handed strummers, 2mm for delicate fingerpickers, 2.5mm for the rest of us. To reduce that measurement by 1mm you need to reduce the saddle height by 2mm. The actual height of the saddle over the top of the instrument has no relationship with playability, what you want to adjust is the string height over the plane of the frets. Though, of course, a really low or really high height above the top gives other problems - somewhere around 12mm seems standard for ukes, but a bit more or less is not significant.

 

[Kalimna]

Many thanks for your detailed reply - much appreciated. You don't frequent MIMF by any chance do you?

Cheers,
Adam S

 

[John Brown]

What would advise as to the height of the bottom of the nut slot over the first fret, and saddle height over fret tops, using a straight edge as earlier mentioned? They are both concert scale.

I wouldn't aim for either of these as a measurement.

At the nut, I find the best way of setting each slot's height is to hold down that string between the second and third frets and then look at the height of the string over the first fret. I aim for a tiny fraction of clearance, which you can gauge by gently pressing the string on to the top of the first fret - if it doesn't move, you've gone too far (though you might still be OK, but you're definitely at the bottom of the range). Take it as low as you dare, which probably won't be low enough, and you can always lower it a little more later. This will transform the instrument's playability more than you could imagine!

To get the saddle height I measure the distance from the top of the 12th fret to the bottom of the strings. For a uke somewhere between 2 and 3 mm is correct - 3mm for heavy-handed strummers, 2mm for delicate fingerpickers, 2.5mm for the rest of us. To reduce that measurement by 1mm you need to reduce the saddle height by 2mm. The actual height of the saddle over the top of the instrument has no relationship with playability, what you want to adjust is the string height over the plane of the frets. Though, of course, a really low or really high height above the top gives other problems - somewhere around 12mm seems standard for ukes, but a bit more or less is not significant.

By that metric I may have gone a bit too far. Although I don't have any buzzes to speak of. Anyway, I'll remember that next time I get my expensive nut files out!

 

[profchris]

Many thanks for your detailed reply - much appreciated. You don't frequent MIMF by any chance do you?

Cheers,
Adam S

Yes, if that was for me. But I'm a humble self-taught uke builder, no more, far from expert!

Of course, that means I can ignore the rules and have fun.

 

[profchris]

I had to make a repair this weekend on a tiny ukulele whose bridge had come off, and therefore had to make a clamp for the re-glueing.

Here is the patient:

The centre of the bridge is about 75mm from the centre of the sound hole, and the body is only about 30mm deep. The top wood is less than 1.5mm thick, so my clamp mustn't put any pressure on it around the sound hole.

And this is why the bridge came unglued:

Those screws were in place of clamping, to save money in production. There wasn't enough glue in the joint, so it only adhered where wood fibres have been pulled away (this is Western Red Cedar, which is notorious for fracturing like this).

My first step is to make the leg inside the body and the upright. The plywood triangles are glued to the leg/upright. Then it needs shaping to make sure it will actually fit inside the instrument. It needs a transverse caul at the far end of the leg (visible later), to press upwards under the bridge and also to clear the bracing on the underside of the soundboard.

My clamping force comes from the upper arm which has an M6 bolt in the end. 10mm hole up from underside, 6mm hole down from the top, bang the nut in with a hammer, job done.

Here's the completed clamp. I fixed the upper arm once I knew I could still insert the clamp inside the uke. If the arm would interfere, just drill a couple of holes and pin with loose nails.

Finally I need a caul to go between bolt and bridge, and to apply pressure at the ends as well as in the middle. This has two M5 bolts and nuts, as before, with a 6mm hole (not all the way through!) to locate the clamping bolt.
Underneath is 1.5mm plywood pinned at the centre, so the M5 bolts can flex it down onto the bridge. Bolt sizes aren't critical - these were what I had lying around.

Here it is, clamping the bridge to the top.

I left the wood fibres on the underside of the bridge, scraped the visible glue off (none on the soundboard, of course, so that just got a light sanding), put a dam of masking tape all around and then applied hot hide glue. Hot hide glue is favourite for bridges because it doesn't cold creep, and you don't want the bridge gradually to migrate towards the neck! Left it overnight, strung it up this morning, and the bridge is still on. But I'm keeping my fingers crossed - the broken top wood fibres mean the joint can't be as strong as I'd like.

If Bugbear wants to re-glue his bridge, first he needs to remove it (heat and spatula, or maybe meths might soften the glue), then shape its base to the top (sandpaper taped to top is slow but effective). Then he must make a clamp along these lines (or Google for alternative styles of bridge clamp). Potential differences:

1. His bridge is wider, so I'd make the top arm about the width of the meaty part of the bridge and use two bolts to apply downward pressure.

2. Underneath my bridge the soundboard is flat. Bugbear might find some braces there, and if so will need to work out how to shape the internal caul.

3. His upper caul will need to be shaped to put downward pressure on the "wings" of the bridge, so a bolt at either end bearing on a smaller caul might do it. A bit fiddly to tighten up, but because hot hide glue remains liquid while hot, just keep warming the whole lot with a hair dryer and clamp until squeeze out is visible.

You don't need much clamping pressure for this operation provided the bridge is a good fit to the top.

 

[custard]

How can a repair like that be commercially viable? Surely there's two or three hour's work in that repair (including making the cramp), so at say £25 an hour that's a £50-75 job...on an instrument that only cost £40 or £50 to begin with!

It's a genuine question by the way, I'm not having a go at anyone, I'm just trying to understand the economics of luthery work.

 

[profchris]

Ah - I'm only an amateur, doing this for fun (and maybe a beer) as a favour for a friend.

A professional luthier would probably have suitable clamps already, in which case preparation and glueing is less than 30 minutes.

But you're right - luthiery is essentially an uneconomic activity unless you're good and well-known enough to be able to charge £5k plus for a guitar, and even then it's not a generous living.

This kind of production line instrument (the iUke retails for under £100) is in essence a disposable item unless you know a hobbyist.

Edited to add:

I believe that repairs to electric guitars can be a reasonable living, and also repairing/setting up high end acoustic instruments. Building them - not so much.

 

[custard]

Ah - I'm only an amateur, doing this for fun (and maybe a beer) as a favour for a friend.

A professional luthier would probably have suitable clamps already, in which case preparation and glueing is less than 30 minutes.

Got it, thanks!

Incidentally, I don't buy that it's only 30 minutes work for a professional. There's probably 30 minutes work just in liaising with the client at both ends of the transaction, add in inspecting the instrument, cleaning off old glue, fiddling about with the strings, warming up the glue pot, and I bet it's still a two hour job. Which i guess just underlines your point that it's essentially uneconomic.

When I was training as a cabinet maker there were a few luthiers that were switching from instruments to furniture because they couldn't make a living ...like furniture makers all drive Bentleys, but hey ho, I suppose the grass is always greener!

 

[bugbear]

I had to make a repair this weekend on a tiny ukulele whose bridge had come off, and therefore had to make a clamp for the re-glueing.

Here is the patient:

And this is why the bridge came unglued:

Those screws were in place of clamping, to save money in production. There wasn't enough glue in the joint, so it only adhered where wood fibres have been pulled away (this is Western Red Cedar, which is notorious for fracturing like this).

Thanks for all the helpful info - noted.

I do have a topic-drift question about your uke. Surely screwing into long grain 1.5mm timber is pointless?

So I'm guessing (and asking) - was there a block underneath the bridge, for the screw to engage with?

BugBear

 

[profchris]

I do have a topic-drift question about your uke. Surely screwing into long grain 1.5mm timber is pointless?

So I'm guessing (and asking) - was there a block underneath the bridge, for the screw to engage with?

BugBear

No block, but another 1.5mm plate with the grain at 90 degrees. Like I said, these screws were only a cheap substitute for clamping.

Even with a hefty block (which would make the instrument much quieter) screws eventually pull through. Even nuts/bolts/washers pull through over time. Plus the holes weaken the top wood and reduce gluing surface.

Hide glue is remarkable stuff. It can hold a bridge against string tension for centuries if the instrument is not abused (inside a car on a hot day has disassembled quite a few, though even there the hide glue joints tend to hold). Titebond etc start to soften around 50-60C I believe, and string tension does the rest.

 

[MIGNAL]

That bridge reglue would be more than 30 minutes work. A professional would charge for 1 hour, at the very least.
Last year I sent a Guitar to Colorado. 3 months later the bridge had come off. Colorado (with it's very low humidity) is known as guitar graveyard. It cost me £120 to have it reglued and I sent the repairer a ready made caul. The bridge had been originally glued with Hide glue. I had no option but to pay it otherwise my client was going to have to make a 160 mile round trip to somewhere else.
Colorado is where you are going to make big money repairing guitars!