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Altering Scale Length?
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=45459		 Page 1 of 1
Author:  Jimmyjames [ Mon Mar 30, 2015 8:49 pm ]
Post subject:  Altering Scale Length?
The Cumpiano Guitar has a 25.34 scale length. My sense of reason tells me that if I alter the scale length to 25.5 then the sound hole and braces wil have to be moved backward which sounds like a whole mess of problems that are over my head at this point. Anywho, I'd prefer my guitar to be 25.5. Is the solution to find another plan? Just wing it?

What effect/building complications will changing the scale length to 25.5 have?

Thanks,

-j
Author:  johnparchem [ Mon Mar 30, 2015 9:07 pm ]
Post subject:  Re: Altering Scale Length?
I bet if you just make sure the bridge is correctly placed you will be fine. I also would bet that if I gave you a 25.34 scale length guitar and told you it was a 25.5, you would not know the difference. Maybe you would but I read it takes more than 5 mm to really change how a scale length feels.
Author:  Nils [ Mon Mar 30, 2015 9:13 pm ]
Post subject:  Re: Altering Scale Length?
I haven't seen the plans...but my guess is that you probably don't have to change much really. I would probably go ahead and move the sound-hole down a tad, as with the bridge plate. Assuming the bridge is still going to be in a place where the wings would be over the legs of the x, I wouldn't worry.
Author:  James Ringelspaugh [ Mon Mar 30, 2015 9:48 pm ]
Post subject:  Re: Altering Scale Length?
A scale length increase of .16" is a very small change all things considered. To add .16" you'll actually lengthen the neck a hair more than .08" (this will put the 14th fret right at where the body meets the neck), and you'll move the bridge back towards the butt a hair less than .08".

Especially for an early build, .08" is miniscule. Just make sure that after it all comes together the X-brace will still cross the bridge wings and you'll likely be just fine following the plan you have.
Author:  DennisK [ Mon Mar 30, 2015 10:00 pm ]
Post subject:  Re: Altering Scale Length?
Don't sweat it. You're building a classical, right? That's only a 4mm difference in scale, which means 2mm longer neck, and 2mm lower bridge. The bracing shouldn't need changed at all, aside from maybe moving the bridge patch down the 2mm if you want (if you're even using a bridge patch). The soundhole may need to move a touch to keep the split frets exactly the right size, but getting everything perfectly aligned there is a tough challenge in any case, so you'll have to do lots of thinking and measuring to get it right anyway.
Author:  meddlingfool [ Mon Mar 30, 2015 10:58 pm ]
Post subject:  Re: Altering Scale Length?
Where's the 4mm come from?

It's what James said. I would just stick with the plan.
Author:  Jimmyjames [ Mon Mar 30, 2015 11:09 pm ]
Post subject:  Re: Altering Scale Length?
So if understand everyone correctly: I'm effectively lengthening the guitar from the center axis of the twelfth fret, half the distance each direction. I will also have to move my heel block .08 as well.

The book calls for 14.08 from the nut so I should add .08 to that and place the heel block at 14.16, correct?
While I was thinking about all this it occurred to me that I'm not used to 14.08, 14.16 measurements, I think in fractions and .0X makes my mind go tingly. I converted 14.08 to fractional and got 14 2/25ths )what am I gonna do with that? Hmmm bring it up to 14 10/128ths? Maybe I could get out a magnifying glass and count those up. Seems very, very exacting to the point where I might have to make a jig to measure it with precision. I use a scalpel to layout lines and it seems pretty precise but this .0X seems daunting. How do you layout such lines with precision?

Thanks,

-j
Author:  meddlingfool [ Tue Mar 31, 2015 12:00 am ]
Post subject:  Re: Altering Scale Length?
You don't need to make any changes to the guitar's body or bracing.
Author:  DennisK [ Tue Mar 31, 2015 1:59 am ]
Post subject:  Re: Altering Scale Length?
It doesn't need to be that accurate. 1/16" = .0625", so .08" is just a little bit more than that. And that's how I'd measure it... 14 and 1/16" and a little bit.

meddlingfool wrote:
Where's the 4mm come from?

25.5" - 25.34" = .16" = 4mm

I tend to switch between decimal inches, fractional inches and mm depending on what makes nicer looking numbers :P For small distances, up to 1/8", fractional inches and millimeters conveniently fall close to half way between eachother, so you can count like 1/64", .5mm, 1/32", 1mm, 1/16", 2mm, 3/32", 3mm. 1/8" is just a bit larger than 3mm.
Author:  bluescreek [ Tue Mar 31, 2015 6:39 am ]
Post subject:  Re: Altering Scale Length?
you are way over thinking this. The only think you need to really move is the bridge.
Author:  kencierp [ Tue Mar 31, 2015 7:56 am ]
Post subject:  Re: Altering Scale Length?
Nothing at all complicated --- bridge/saddle moves about .08" Spend some time to understand why this is just a simple alteration, this involves the math which is so important to get a guitar to play in tune. That said I doubt many would pass a blind test 25.5 vs 25.34
Author:  DannyV [ Tue Mar 31, 2015 8:23 am ]
Post subject:  Re: Altering Scale Length?
bluescreek wrote:
you are way over thinking this. The only think you need to really move is the bridge.

yup
Author:  Quine [ Tue Mar 31, 2015 9:54 am ]
Post subject:  Re: Altering Scale Length?
No issues adjusting the scale length a bit. 0.16" longer isn't much. Moving the bridge 0.08" will hardly be noticeable and probably won't need any changes to the bridge patch or braces.
These plans are only approximate anyway. By the time you print the plans, make the mold, bend the sides and glue in the blocks you'll get some deviation. The rim may come out a bit longer or shorter than the plan...no one will notice in the finished guitar. Trace the rim onto the top and measure your bridge placement from the actual body.
Scale lengths are only approximate too. True scale length is the distance from the nut to the 12th fret X 2. But some people round off or include the compensation in the sales specs. (Check out some of the debate threads on Martin's 25.4" scale length)
If you're buying a pre-slotted fret board....make sure you measure the actual scale length on the fret board when placing the bridge.
Author:  meddlingfool [ Tue Mar 31, 2015 10:32 am ]
Post subject:  Re: Altering Scale Length?
Dang decimals.
Author:  johnparchem [ Tue Mar 31, 2015 10:38 am ]
Post subject:  Re: Altering Scale Length?
There are decimal rulers.
Author:  Jimmyjames [ Tue Mar 31, 2015 11:07 am ]
Post subject:  Re: Altering Scale Length?
Yep, decimals don't even deserve to be called numbers.

I didn't realize they made decimal rulers. Now that you tell me it seems obvious but a lifetime of fractions has me spoiled. Thanks.

I'm just going to do it and see what happens.

Thanks,

-j
Author:  Bryan Bear [ Tue Mar 31, 2015 1:55 pm ]
Post subject:  Re: Altering Scale Length?
Jimmyjames wrote:
Yep, decimals don't even deserve to be called numbers.

I didn't realize they made decimal rulers. Now that you tell me it seems obvious but a lifetime of fractions has me spoiled. Thanks.

I'm just going to do it and see what happens.

Thanks,

-j


A lifetime of fractions has you brainwashed more like. Decimals are superior in every respect unless you already invested your life learning to work in fractions. Like Roman numerals, fractions are all well and good until you discover how much easier math is with Arabic numerals/decimals. beehive
Author:  Jimmyjames [ Tue Mar 31, 2015 2:19 pm ]
Post subject:  Re: Altering Scale Length?
I was just joking about decimals, I've always thought it to be a superior system but I live in America and most things aren't decimals so I just live with it. I agree completely but wouldn't I have to buy new rulers? Point me in a direction and I'll consider it for this guitar making thing. I've been meaning to buy a new 18 inch Starrett rule for my protractor square, my old 12 inch is getting too dark to see and the extra length would benefit this endeavors accuracy. I have metric/inch digital calipers. What do I need to know?

Thanks,

-j
Author:  Clay S. [ Tue Mar 31, 2015 4:37 pm ]
Post subject:  Re: Altering Scale Length?
Look for one of those small (6") metal rulers machinists commonly have in their tool boxes. The ones that have a ruler on one side and a conversion table on the other that converts fractions to decimal inches (thousandths).It will give you the answer to the closest 1/64th in., which is close enough.
Author:  dzsmith [ Tue Mar 31, 2015 7:19 pm ]
Post subject:  Re: Altering Scale Length?
I bought a digital caliper and took a measurement.
It read 63/128. I almost threw it into the pond until I realized I could switch it to mils.
Thank goodness it does not have a Roman numeral switch on it. Now that would be confusing!
Author:  Jimmyjames [ Tue Mar 31, 2015 7:51 pm ]
Post subject:  Re: Altering Scale Length?
I've worked out all my math using a broken toaster oven and an abacus. I laid out my lines and am currently cutting the truss rod slot by hand, Cumpiano specifically says not to but I don't want to go get a router. I'm about three quarters through the process and it is going very well.

Does the truss rod slot STOP and the beginning of the nut? Cumpiano isn't clear.

Thanks,

-j
Author:  John Arnold [ Wed Apr 01, 2015 1:50 am ]
Post subject:  Re: Altering Scale Length?
Quote:
I will also have to move my heel block .08 as well.

Totally unnecessary, IMHO.
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