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Saddle compenstion, Gibson LG-1

PostPosted: Tue Apr 16, 2019 11:08 am
by Matt Atkinson
Hi all, It's been a very long time since I posted anything here! Hope to hang around more for a while...

I have finished re-bracing a little LG-1 that my brother in-law was kind enough to give me. I was just going to fix a loose back brace but decided to x-brace the top as well. Pulled the back, braced and did a little cheater neck reset when gluing the back on again. Anyway, someone previously replaced the plastic bolt on bridge with rosewood and did a spectacularly lousy job so I have removed the bridge and will make a new one slightly larger to cover the gouged-in pencil marks left by the last guy :( Looking for numbers for saddle compensation to cut a new slot. I'm planning on using my saddlematic to locate, just wanting the correct adjustment info if anyone knows what's best. Thanks in advance!

Re: Saddle compenstion, Gibson LG-1

PostPosted: Tue Apr 16, 2019 11:11 am
by Barry Daniels
Cumpiano's book states that you should add 0.15" to the scale length at the middle of the saddle.

Re: Saddle compenstion, Gibson LG-1

PostPosted: Tue Apr 16, 2019 11:35 am
by Bryan Bear
I Stew Mac's fret position calculator (which is what I use to estimate how much compensation to build in) gives 24.836" for the treble e and 24.958" for the bass e using 24.75" as the nominal scale length. That would be an extra 0.086" on the treble side and and extra 0.208" on the bass side. That would average and extra 0.147" so right in line with the Cumpiano number Barry provided above. The Stew Mac calculator lists +or- 0.03" for compensation; 0.15 to 0.147 is a tenth of that margin. . .

Depending on what your scale length is (I was guessing at 24.75") the compensation will change a little bit. But, these are estimates to get you in the ballpark for final adjustment. If you plug in the values for martin short scale and long scale the difference is 0.002" treble side and 0.004" bass side. I can't reliably measure that closely on my shop made saddle-maticesque tool so I never really change the compensation unless I am using it for a drastically different scale.

Re: Saddle compenstion, Gibson LG-1

PostPosted: Tue Apr 16, 2019 12:07 pm
by Brian Evans
This is the calculator that I use, I find it extremely accurate and takes a lot of different factors into account: https://www.liutaiomottola.com/formulae ... sation.htm

I actually use more than a few of the calculators and webpages that he has there, it's a great site.

Edit: I just read this scholarly article, linked from the above site: https://osf.io/bqzf4/ I not only understand nut compensation for the first time, he made it make intuitive sense, plus it shows that fussing obsessively with compensation is a losing game because in blind testing even expert players and luthiers can't tell the difference to a degree that matters. Neat experiment.

Re: Saddle compenstion, Gibson LG-1

PostPosted: Fri Apr 19, 2019 12:03 pm
by Matt Atkinson
Thanks all. Scale is actually 24.625. I guess these little Gibsons were all over the place. Pretty sure the previous bridge replacement was a stock, pre-slotted version. Seems the repairer just placed it with the existing bridge pin holes. Slot is way off. The back of the slot is where the front should be. Freaked me out a little until I thought about it and triple checked my math. It's funny the only other guitar I've done work like this on was a mid 70s D35 and that saddle was 3/16 too far forward. Is it just my luck? :shock:

Re: Saddle compenstion, Gibson LG-1

PostPosted: Fri Apr 19, 2019 12:22 pm
by Barry Daniels
That is fairly common.

Re: Saddle compenstion, Gibson LG-1

PostPosted: Sat Apr 20, 2019 12:11 pm
by Freeman Keller
I replaced the plastic saddle on an LG-1 with a rosewood one and cut the slot at the scale length plus 1/16 on the high E and scale length plus 3/16 on the low E. I gave the saddle the usual B string notch and the intonation seems pretty good on this funky old guitar. Also had to reinforce the bridge plate and top which were pretty badly damaged, plug some holes, remove finish under the bridge footprint - the usual stuff

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And yes, there are a whole generation of Martins from the 70's with the saddles in the wrong place. And of course the dilemma of what to do about them

Re: Saddle compenstion, Gibson LG-1

PostPosted: Mon Apr 22, 2019 10:09 am
by Chuck Tweedy
Hey Matt! Good to see you.

Re: Saddle compenstion, Gibson LG-1

PostPosted: Thu Apr 25, 2019 11:18 am
by Matt Atkinson
Hi Chuck!

Re: Saddle compenstion, Gibson LG-1

PostPosted: Thu Apr 25, 2019 8:24 pm
by Darren King
Re: 1970s Martins - I guess you either hang them on a wall and look at them or get them fixed and play them. What other options are there? Too good to burn surely!!!
Seriously though, the https://www.liutaiomottola.com/formulae ... sation.htm calculator is awsome and takes into account string gauge and loads of other factors. Yes, there is always a degree of +/- with saddle position but you still need a pretty good idea of where the ideal position zero is. In the situation where you are repositioning the bridge on an old guitar I’d think it worth taking all the fret position measurements from the nut to establish the exact scale length as there is no absolute guarantee that the 12th fret is perfectly spaced in relation the the others. Excel is a dream for checking this kind thing as a simple spreadsheet can show a percentage deviation from the true position for any fret for any specified scale length. If they all come out spot on then great, if not then you can decide on how to average the errors and establish to optimum saddle position.
Hope it all went well, it certainly looks a great job.
Darren

Re: Saddle compenstion, Gibson LG-1

PostPosted: Thu Apr 25, 2019 9:19 pm
by Barry Daniels
The best way I have found is to use a Stew-Macs "The Intonator" which lets you move the saddle break point back and forth while measuring the intonation with an accurate tuner. Sort of the empirical approach as opposed to the theoretical. It might require the saddle slot be moved, but that is no biggie if you have a saddle mill.

Re: Saddle compenstion, Gibson LG-1

PostPosted: Fri Apr 26, 2019 9:00 pm
by Darren King
Hey Freeman,
I have just looked at you photos more closely. OMG! Is that injection moulded monstrosity really what Gibson were fitting to their acoustics in the 70’s? How on earth did they maintain their reputation?

Re: Saddle compenstion, Gibson LG-1

PostPosted: Fri Apr 26, 2019 11:40 pm
by Bill Raymond
How on earth did they maintain their reputation?

Did they??

Re: Saddle compenstion, Gibson LG-1

PostPosted: Mon Apr 29, 2019 4:01 pm
by Matt Atkinson
Did you cut that saddle slot twice? The last pic looks like it's cut right behind a filled slot? I was going to make a new one but if I use the bridge I took off it will look very much like that! That pic helps a lot because I was worried the low E string pin would end up crowded towards the saddle but I think I will end up right about there. Thanks!