Scale length and working out fret spacing

[bongomuffindan]

Hi,

This is my first post here – I am one of those lurkers who loiters and poaches knowledge from you fine people, for which I apologise and am immensely grateful. I am stuck into my first build from scratch (F5 and its going pretty nicely!). I have been using Siminoff’s book as a base and adapting with the things I read here. I have finally reached a point where I am really scratching my head a wee bit – I am ready to slot the fretboard.

Roger Siminioff advises that you measure the scale length to ensure that you slot the fretboard accurately to achieve correct intonation. I have read a great deal about scale length, both on this site and beyond, but am still struggling. I can’t work out where exactly I am measuring to given the compensation of the bridge. For example, if I follow the concourse of the E strings from nut to contact point of bridge I measure 13 6/8”, whereas if I run down the G or A concourse I get 13 7/8” (Roger’s plans aim for scale length of 13 17/18” – so gone wrong either way!) Does this mean my scale length, and therefore fret slots should be worked out from a scale length of 13 7/8” or 13 6/8” – or have I missed something completely?

So essentially I am asking, at this stage of a build, when you can’t measure to the 12th fret, I am measuring from the nut to which point of the bridge?

Please forgive me if this is a silly question.

On a final note, I love this project, it will be the first of many, and I am grateful to this site and all who reside here.

With very best wishes

Daniel

[sunburst]

Standard scale length for most mandolins is 13 7/8". In order for the instrument to play in tune the actual string length must be slightly longer to compensate for the strings stretching as you press them to the frets, different strings stretch differently, so the bridge has the "compensation" cut into the top. That will all make more sense later, for now you just need to cut the fingerboard accurately for a 13 7/8" scale, assuming you want to use that standard scale length.
Those measurements can best be found here http://www.buildyourguitar.com/resou.../jscrptclc.htm, or at other on-line fret scale calculators. Measuring and cutting your own 'board is a challenge, and buying accurately cut fingerboards is much easier than it used to be, so buying a pre-slotted fingerboard is not a bad idea.

[bongomuffindan]

John, thank you.

My understanding of what Roger is saying is that you measure from the nut to the bridge so that you can know the scale length and cut the fret slots accordingly – therefore you can compensate for any construction inaccuracies: for example his plans say that that measurement should be 13 15/16” but he provides other fret calculations for arriving at a measurement shorter than that (as I have).

The logic, as I understand it, is that if the body somehow came out a bit shorter than planned, you need to change the scale length and fret intervals because you want the bridge to be positioned between the f-holes. So if I planned a 13 15/16” scale length but when I measure it comes out to say 13 7/8” or even 13 6/8” would I not have to change the fret intervals to keep the bridge in the right place and maintain intonation? Or putting it another way, If I had a scale length of 13 7/8” and cut the fret board using calculations for a 13 15/16” scale length, would the bridge not have to be in an odd position to maintain intonation?

I understand the concept of string compensation and hence why the bridge is designed as it is (superficially of course). What I am confused about is, assuming the logic above is correct, which point of the bridge to take this measurement from? Do I take it as the distance from the nut to the contact point of the bridge of the e string (13 6/8” in my case) or to where the A string would run (13 7/8” in my case)?

I agree it would be far easier to buy a alotted fret board – but it would have been much easier and cheaper to buy an decent mandolin – but (occasionally very annoyingly), for good or ill, I am determined to do this all myself, and am loving the learning, and am thus far very proud of the result. No doubt I will live, learn and regret!

Again, please ignore any/all of this if it is potty or I have completely missed the point...

Many thanks again

[Dale Ludewig]

I think you're approaching this from the wrong direction. The scale length determines where the bridge sits. It really doesn't matter if the bridge is centered in the f-holes. And it's highly unlikely that it's going to be, no matter how hard you try. It's a good idea to start with the fingerboard before you do anything else. Accurately cutting fret slots is difficult to do by hand and if they're not perfect you're going to hear it all the time. Because a mandolin is so much shorter a scale length than a guitar, it becomes even more critical. I highly recommend buying a preslotted one.

[amowry]

Yes, it's far easier to build the body to the scale length rather than vice versa. If this helps, I usually find that the front of the treble side of the bridge on a 13 7/8" scale mandolin is 13 7/8" from the nut (even though all the strings cross the bridge beyond this point). So, if you add half the bridge base thickness to the scale length to determine the position of the f-holes, you should be in the right ballpark. Also, to take neck angle and action into consideration, remember that you need to use a side view of the instrument, not a plan view, when you're determining these distances.

[John Kelly]

Daniel, good advice all round, here - as we come to expect from the Cafe and its contributors. Dale's point is very important in that the scale length will determine where the bridge sits (remembering the small addition for compensation as has been mentioned). I use a free program called Fretcalc to calculate my fret spacing; here is a link to it - www.dougsparling.com/software/fretcalc/ I work in metric sizes, being over here in Scotland and I just find metric easier than all the fractions in the Imperial system. Fretcalc allows you to work in either and it also lets you decide on the accuracy you require in that you can decide how many decimal points you want for your measurements.

The points about buying a ready-slotted board are very valid, especially for a first instrument, but then again there is the pleasure of having done your own board when the instrument is finished.

If you decide to have a go at your own, and I think you will, remember that it is very important to have an absolutely accurately planed edge to the fretboard blank and an exact right angle from this to the nut end of the fretboard so that you can get your marking done accurately. Do not taper the board before you slot it! I use a steel engineer's square to mark the slots and a marking knife rather than a pencil; the knife gives a more accurate measurement than a comparatively thick pencil line and it also helps to guide the saw when you get round to making the actual slots. For slotting I use a Japanese pull saw with the StewMac guide which I took from an old StewMac saw; they now offer the Japanese saw on their catalogue and to my mind it is just a much better tool.
Good luck with the project.

[grandcanyonminstrel]

I highly recommend buying a preslotted one.

I agree with Dale on this. Have the fingerboard on hand while working out the body geometry issues during the build. I always cut the soundholes after the entire body is assembled and strung up in the white. That allows you to get a perfect visual orientation and to tune the voice according to your ears rather than an abstract idea on an unassembled plate.

It is important to remember that while Roger and his book are the Grandaddy model for 1000s of mandolins and builders, it is also just one person's approach and opinions.(No disrespect intended- Roger is a friend and a great guy). If you see a different approach that makes more sense to how you look at life and mandolins, don't be afraid to try it.

j.
www.condino.com

[Graham McDonald]

A couple of websites which may help explain the theory of fret placement.
Musemath
and RM Mottola's site.

cheers

graham

[Bill Snyder]

Remember that these have a FLOATING bridge that can be moved anytime you need to. If the bridge were to be glued down it would be critical but the bridge is not glued in place.

[Tommando]

Good advice here from folks with far more experience than me, but having just made a fret board by hand for an old bowl back because no one is set up to do an exact 13" scale, I want to suggest a couple of things. I suspect you can go with the standard scale of 13 7/8". If so, you will be happier in the long run with the intonation of a fretboard made on precision equipment. It is more tedious than it is difficult to do by hand, and there is plenty of room to make mistakes and mess it up. If you must do it by hand, John Kelly's advice is excellent. No matter what, the the bridge is not likely to sit exactly at the distance you intended. Measure the scale length from where the nut and fret board meet, straight down the middle of the neck. 13 7/8" will show you approximately where the front edge of the bridge (or, more accurately, the front edge of the saddle) will be. If it looks good, then use that scale length. The bridge will actually sit a tiny bit further than that as part of setting the intonation when you string it up. "Straight" and "square" are critical concepts in your measurements and cuts. Go to a web site such as RM Mottola's that gives the math for calculating fret spacing and set up a spreadsheet to do the calculations based on your chosen scale length. I found errors in some of the online calculators. I recommend using a good steel ruler with millimeter markings because you will be guesstimating some fractional distances when you scribe the fret lines. Millimeters are smaller measurements and easier to count.

[bongomuffindan]

Thank you all for your time and advice - it is thoroughly appreciated. As John and Dale said, it seems I have been approaching this issue from the wrong direction and I'm grateful to all for the above and for the nudge to look at it the other way - all much clearer and I have a way forward.

I have completely taken on board all the recommendations for buying a pre-slotted board, but John is right - I am determined to attempt to cut my own. I am very grateful for all the practical advice from John, Andrew and Tom and have taken it all on board. And thanks for the links Graham, I will do some further reading.

Thank you again to everyone, and very best wishes from sunny England.

Dan

[John Kelly]

Dan, just to reassure you a bit. Today I was working on a tenor guitar I am building and it is near the stage of fitting the neck to the body. I had made a rather lovely fingerboard from maple for this guitar and had it tapered and added a bevel to increase playability - and added in the position markers and even the frets which go in to the extension beyond the body join. On looking at the board this morning I suddenly realised that each abalone dot was one fret too high! I had them at 4, 6, 8 etc. and my only excuse is that I had a friend round when I was putting in the dots a couple of days ago and my attention was not what it should have been.
The dilemma - to continue with this otherwise rather well-made and attractive board or make another? I decided to make a new one and this morning spent a couple of hours on this task. A good lesson and some more practice in marking and slotting a fingerboard, but the right thing to do, I am sure!
Oh, Well.....