Acoustic saddles... how low can you go?

Strat_a_tat_tat

Looking to shave a bit off my saddle... but not sure how far one can go before it's buzz-city. Any advice?

I don't beat the strings very hard... so I guess that means I can have a fairly low action - but I'm not sure if there's some way of measuring how low I can take the saddle.

Thanks.

Sassafras

You want a decent break angle over the bridge. Take it too low and the strings will sound dull and lifeless. I never measure, I just take it slow and steady, checking every few swipes of the diamond plate I use to sand down the saddle.

Strat_a_tat_tat

Thanks @Sassafras.

Excuse my extreme ignorance... but what's a diamond plate... and where do I get one?

I guess if the break angle becomes too shallow, I'd also have to make some alterations to the bridge?

Sassafras

Strat_a_tat_tat said:

Thanks @Sassafras.

Excuse my extreme ignorance... but what's a diamond plate... and where do I get one?

I guess if the break angle becomes too shallow, I'd also have to make some alterations to the bridge?

I use DMT diamond plates, they're just sharpening stones with crystalline diamond coating. I like them because they're perfectly flat, cut quickly and don't wear out. There are other makes, I just happen to have a few of these. Great for sharpening tools in general.
If the break angle gets too shallow you would have to sand down the bridge behind the saddle but I'd try to avoid that.

Strat_a_tat_tat

Sassafras said:

Strat_a_tat_tat said:

Thanks @Sassafras.

Excuse my extreme ignorance... but what's a diamond plate... and where do I get one?

I guess if the break angle becomes too shallow, I'd also have to make some alterations to the bridge?

I use DMT diamond plates, they're just sharpening stones with crystalline diamond coating. I like them because they're perfectly flat, cut quickly and don't wear out. There are other makes, I just happen to have a few of these. Great for sharpening tools in general.
If the break angle gets too shallow you would have to sand down the bridge behind the saddle but I'd try to avoid that.

Thanks... I'll Google them.

... and yes... I see your point about trying to avoid sanding the bridge

FelineGuitars

Ok - the secret to making light work is measuring.
Put a capo on at the first fret
Take a set of feeler gauges and measure the gap between the 12th fret and underside the string on both treble and bass strings.
I use imperial gauges that measure in thousandths of an inch.For most purposes unless you are a heavy strummer you want an action of about 78-88 thou on the bass and 60-70 thou on the treble side (with a fairly straight truss rod)
Now anything over those desired heights is the amount you want to lower the strings by
To do this you need to lower the bridge by TWICE that amount 
If the resulting saddle gets too low for a decent break angle towards the pins you may need to consider creating a ramp for the strings down into the hole to maintain a decent break angle

Strat_a_tat_tat

@FelineGuitars... that's great. Much appreciate your advice. Should the neck be perfectly straight when I'm doing my measurements and my adjustments... or should the neck have the normal amount of relief that I use on that specific guitar?

Also... I'm trying to work out why I'd need to remove twice the measured 'excess'... and not just 1x the measured excess. I'm a bit mathematically challenged on that one!!

BahHumbug

You can shave the saddle down using abrasive paper and a sanding block, or even a delta sander.  Just go slow and remember that you are trying to get the bottom face f the saddle flat, straight and square.
its possible to do this by just running the saddle over abrasive paper on a flat surface, although to reliably acheive  the flat, straight and square result it's better to put the saddle in a vice and run the abrasive over it.

Lewy

There's another element to this that often doesn't get mentioned which is the string height off the soundboard. 

There is a school of thought especially among American luthiers and repairers that this is of significant importance because it governs the torque applied to the top. Measuring from the underside of the A string to the surface of the top right in front of the bridge, they aim for half an inch.

It's interesting, because I don't think I've ever seen a British luthier ever mention it...but a browse of threads over at UMGF reveals that it's generally seen as being more important than break angle as a thing.

FelineGuitars

Strat_a_tat_tat said:

@FelineGuitars... that's great. Much appreciate your advice. Should the neck be perfectly straight when I'm doing my measurements and my adjustments... or should the neck have the normal amount of relief that I use on that specific guitar?

Also... I'm trying to work out why I'd need to remove twice the measured 'excess'... and not just 1x the measured excess. I'm a bit mathematically challenged on that one!!

Set the relief to almost zero - just a tiny bit of relief
The reason for the TWICE the excess is down to a geometrical  thing called "Similar triangles"
Picture that the line of the string , the level along the top of the frets and the height from fret to string make the three sides of a right angle triangle. 
The 12th fret is half the distance of the bridge saddle from the nut so if you imagine another such triangle with the bridge as the far end and the line from the nut to the bridge as another side and the string once again as the third, all the distances DOUBLE compared to the above mentioned triangle.

So to reduce the height of the top of fret to underside of string at the 12th fret by a certain amount , you will remove DOUBLE that height at the bridge.

Strat_a_tat_tat

@FelineGuitars. Really clear explanation... many thanks for that.

(Now... I feel like a complete dolt! A degree in engineering... and I forgot about similar triangles!!! It must be my advancing years.) 

Thanks again.

Strat_a_tat_tat

@Lewy. Never come across that factor. Will do a bit of reading up (and a bit of measuring - to see what I've currently got).

ICBM

From experience I've found that the 'twice the height' rule needs some care, especially when taking off a lot - I think it's because, due to that torque factor on the top, when you reduce the bridge height you also reduce the torque and so the top will move back down slightly… which can then make the height reduction now too large and you get rattle.

So I now prefer to use 'one and a half times' as the rule, and test the result before more finely taking some more off if necessary. It does make it a two-stage process, but it avoids having to shim or replace a bridge saddle when you've made it just slightly too low.

Strat_a_tat_tat

@ICBM. Thanks... that all makes perfect sense.

The more I look into this stuff... the more I realise that simple stuff is never simple.

FelineGuitars

OK - my take was broad brush strokes - ICBM is correct that the top deflection will decrease

Strat_a_tat_tat

FelineGuitars said:

OK - my take was broad brush strokes - ICBM is correct that the top deflection will decrease

Thanks. I guess it depends on stiffness of the top / bracing etc.

Lewy

@ICBM & @FelineGuitars - do you guys measure the string height over the top...have you found it to be a critical factor or is it just something the Martin-istas get het up about but may not be that important?

ICBM

Lewy said:

@ICBM & @FelineGuitars - do you guys measure the string height over the top...have you found it to be a critical factor or is it just something the Martin-istas get het up about but may not be that important?

I think it's a factor, but I'm not sure it's more important than break angle. It's hard to be sure because obviously the two are usually related. I don't think I've ever measured it other than out of curiosity when I first read about it - because there's not a lot you can do about it normally. It isn't a factor you have any control over, unless you want to reset the neck or are doing it anyway - so it's a bit of a moot point really. There's a small amount of leeway between a higher bridge and a very straight neck vs a lower bridge and a bit more relief, but not much - and not enough to really change the height significantly.

FelineGuitars

The leverage factor is important , but usually I get presented with a guitar where the player wants a playable action  and often the neck angle isn't ideal but the guitar's price doesn't warrant a neck reset.
If the strings are sky high off the top then lowering will reduce that force for the better.

If the string height is too low then it's not ideal but then it's often too low to play with your right hand.