Official Luthiers Forum!

I need some help. I laid out the fret slots in my first two today, and now I am confused. How is the best way to measure the spacing? And what tolerance is acceptable?

The method I used was to stick a template to the fret board with stensil adhesive. The template was drawn on a CAD system in the engineering department, and it checks true. After sticking it down, I used a straight edge and a Japanese marking knife. I was careful, slow, and did the best I could.

After that, i widened each mark with a razor saw, then widened again with a veneer saw. This gives me a nice slot for registering the Stew Mac fret slot saw when I put the board in the miter box.

OK, so everything was ready for the final saw cuts, so I thought I would double check the spacing. Yikes! It looks like I messed up a few, some don't line up with the template any more. Some appear to be off by as much as the width of the slot, or around .020". Unfortunately, fret number 12 seems to be the worst one. It seems to be short in that it is closer to the nut than the saddle. I tried measuring how far off it is from the template, and it looks to be in the range of .010"-.020".

So, I take calipers and measure. Fret 12 now seems OK compared to fret 11, which looks good on the template.

So I am very confused as to how to measure this stuff. Maybe it is just my eyes are not good enough, but putting the two boards together, some of the frets don't line up with each other from board to board.

If the 12th fret really is off, am I better off to scrap these and start over? I hate to do that, because they are zircote, and since the Gibson raid, the price doubled.

Any advice is greatly appreciated!

_________________
Phil

http://www.oleninstruments.com

"Those who tilt at windmills are only considered insane by those who can't see the dragon."

Paper can be very stretchy. (It looks like your printout is on paper). It also changes dimensions fairly radically with humidity. So I would suspect that the paper "moved", and you could have stretched the paper when sticking it down. Check your fretboards out with a steel rule, measuring everything form one end (rather than incrementally fret to fret) and see how you go.

At the 12th fret, a 1mm position error is ~6 cents pitch error, so ~0.020" is about 3 cents pitch error.

_________________
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

In order for that method to work, the fretboard must be perfectly flat when you lay out the lines, cut the slots, and check the slots.

If you check the slots when the fretboard has a little relief (as unglued thin flat pieces of wood don't stay flat) you'll get false readings, likewise if you're holding it againsta a surface that isn't flat (and you think it is...).

A tlerance of +-.001 inches is acceptable.

_________________
Old growth, shmold growth!

i've been doing the calculations myself for "custom" scales, in millimeters...i write the measurements down on a table beforehand...then i like to lay a strip of narrow (light colored)masking tape down the center of the fretboard. then from here i measure very carefully, and press a very sharp brad through the tape, and into the board. when i'm done i peel the tape off and there are little holes in the fretboard that indicate saw positions. sometimes the holes are hard to see in porous rosewood, but it works for me. i can then enlarge them by tapping the brad in deeper with a hammer. it is pretty slow, but i find it enjoyable. i'd say its accurate within 0.33mm or so, good enough for me. i put my face right down into the work when starting the slot, and make bloody sure the saw is where i intend it to be, till i get a good kerf set in.....
so my point is, i don't fool around with printouts or paper templates; it seems to work well that way

This.

Good thinking using spray adhesive rather than rubbing liquid water based glue on the paper, but it can still stretch while sticking it down.

I just wrote a long post on my slotting process a few days ago, so I may as well reuse it here http://www.luthiersforum.com/forum/viewtopic.php?p=517584#p517584
Not a particularly speedy way of going about it, but I haven't screwed one up yet.

Thanks for the help guys. This build is starting to seriously tax my resolve. And now it looks like I need to buy new blanks and start over.

So, where can I find a ruler both long enough and accurate enough for this type layout? I don't have anything even close. The paper printout is the best, most accurate thing at my disposal. And if +/- .001" is ideal, what is acceptable, because a ruler won't get that close?

_________________
Phil

http://www.oleninstruments.com

"Those who tilt at windmills are only considered insane by those who can't see the dragon."

Can you just fill the slots with something, flip it over, and cut your fret slots on the other side?

_________________
David Morris

find a metric tape or rule, and make life easier.....a third of a millimeter(about the finest resolution that i can "guestimate", is 0.01".....plenty close enough for rock n roll...or even classical. no matter how accurately you measure, you're not going to be able to actually place a cut with any more accuracy than that, not with hand tools and a mitre box anyway.
just my opinion of course; i know others disagree

I doubt the frets themselves are accurate to .001". Not many people can hear a ~1.5 cents pitch error, so +/- .010" is plenty accurate enough, provided you don't accumulate it by using incremental measurements, and you'd have to be really good to get that accurate using hand tools. I'd suspect that typical hand cut boards are no more accurate than +/- 0.25 - 0.5mm (.01 to .02"), as you've found.

_________________
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

That's a good question... I use a 36" straightedge with graduations to 1/64" from Hartville Tools, but as with all good things, they quit making them. Major bummer, as they were only $60, and extremely useful. Not many straightedges have graduations at all, and most long rules I've seen are only graduated to 1/16" and/or 1mm, except for the first few inches of finer marks... but that's useless for fret marking.

There's always Starrett, but their 36" rules are $2-300. And their graduated straight edge only goes to 1/32", and is over $400

Anyone else know any good sources?

I thought of that, but unfortunately I got smart and thicknessed the boards before I laid out the frets. I got them nice and flat and square. But at .190" thick, the cuts I've made will likely show. Might be worth a try anyway, since these boards are now 25 bucks a piece! Or, just save them to make box lids out of.

I thought one advantange of my paper templates was that I had them made full length, with marks for the saddle location. This includes marks for high and low string lengths per the Stew Mac fret calculator. I figured if the paper did change with humidity etc, my saddle location would be tied to the fret layout. A way to take some tolerances out of it.

_________________
Phil

http://www.oleninstruments.com

"Those who tilt at windmills are only considered insane by those who can't see the dragon."

Man, I tried making a slotting template by hand for use in my tablesaw, and despite my best efforts at accuracy, I deemed it unfit for use after cutting my first fingerboard with it. I then just drew the template out in Rhino, exported it as a .dwg file and emailed it to a guy down the road with a laser cutter. Picked it up the next day. 1/4" plexi, $20 including materials. Worked perfectly. 28" baritone scale on one side and 24.375" short scale on the other. He makes all my templates now.

_________________
Mountain Song Guitars www.mountainsongguitars.com

That board can still be used. There are ways of salvaging it providing the slots are not too far out. You do need some way of double checking it's accuracy other than a paper template. Either a known accurate ready slotted fretboard or a decent steel ruler with finely etched markings. I'm afraid the markings on something like the Ibex fret rule are pretty bad. You do not need 0.5 mm markings, 1 mm markings are good enough. It's fairly easy to divide 1 mm into half by eye. With magnification you can easily divide 1 mm into quarters, giving you an accuracy of 0.25 mm's. When I'm faced with a measurement such as 35.15 mm's I simply knife mark a mere touch above 35 mm's - so in my mind it's not quite 35 mm but it's not quite 35.25 mm's either. You can get pretty accurate using such a method. 20 years ago I didn't need the magnification either

I agree with Michael N, that is pretty much how I used to do it when I did FB's by hand. With a good steel ruler with precise 1 mm markings it is relatively easy to accurately divide a mm by 4, there are some out there that have 0,5 mm marks, but I find them less helpful. I would attach my ruler with double stick tape to a piece of wood and clamp that to a smoothly planed board (so the long edge of ruler would be vertical to the face of the 'board), and cut all the marks with a sharp marking knife. When all the marks were cut, I would mark with a single bevel making knife from each one of them, along a square. I would also saw along the square, making sure I aligned it precisely at the same position relative to the mark each time. When I measured my results afterwards, I remember 0,25 mm was as about as close as I could get it.

After getting a table saw, and setting it up with a good jig for this, I do not miss doing it this way at all, though...

_________________
Rian Gitar og Mandolin

I'm not very experienced but I've cut a few fet boards for mandolin family. I found it works for me by using a ruler divided into .5 mm have a strong light and look through a lens taken from an old projector. With a scapel I can get pretty close to divisions of .25mm. The inacurracy comes when I cut the slots with a saw. I need to work on a mitre box and jig.

_________________
We are all in the gutter but some of us are looking at guitars.

You can clearly see the difference in the markings between the Ibex and my Rabone Chesterman rule, the Rabone are much finer. Actually over a length of a typical scale there is a difference of just over 1 mm between the two rules.
The wooden 'rule' is one I made to make marking much quicker and simpler. Each mark has been made with a very fine Zona saw, so when marking a fretboard it's a simple matter to place a scalpel/knife in the Zona slot and mark the board. It has 4 scale lengths and took me a whole day to make, largely because of checking the accuracy numerous times. I guessed that if I got it very accurate I would never have to go through the whole process again.



Now for some scale lengths I use the bandsaw, so no marking required. I did use my wooden fret rule to create the indexing template though:

Metric rulers seem to be more accurate... because one mm is pretty small anyways.

If you're off by less than 1mm you can fill that slot with a dark veneer and cut it at the correct position. The fretwire will hide the veneer. I did that a few times when sawing them by hand, and I used laser cut template from Stewmac!

That stewmac fret position rule is actually quite economical, it has 4 scales on one ruler with the most common scale lengths. However I am about to go making fretboards from nothing, because I need a 17" scale and Stewmac doesn't make templates for that.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Todd, that's a lot of theory, I'm not sure how important some of those things are in reality. My experience, as I said in a previous post, is that I can mark 0,25 mm (or .25 to most of you) increments with a ruler graduated in 1 mm, as accurately or better compared to one that has 0,5 mm marks. I think those tightly spaced marks mostly serve to make things harder to read, and they're way thicker than my scored line anyways, so of no real use. For all practical purposes, I bet one could mark just as accurately in inches too, if that's your preferred unit of measure, if your ruler, eyesight, marking knife and diligence are up to it.

_________________
Rian Gitar og Mandolin

Thanks for the link Todd. It's resolved my dilemma about buying fretscale templates to try different scale lengths.
After reading it, and Rod True's post, I have just picked up very reasonably priced 2nd hand a 24"/600mm quality vernier English made from fleabay and can make any scale I want.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I have to agree with Arnt. With magnification it isn't that difficult to split 1 mm divisions into 0.25 mm or less.

This right here. I think I bought my 36', 16R Starrett for $60...it's the thick one too so it stands up on edge and is perfect for this kind of marking. It was a factory second (which they don't do anymore). You can get them used for even less, and actually the older ones are BETTER for this kind of work because the gradations are deeper and allow you to stick your knife in the groove and get a perfect mark. You stick the fingerboard up to a stop (a wall...a block of wood, whatever), stick the ruler down the centerline on edge and up to the stop, and mark away.

Hi Phil,
From the pictures you posted the boards don't look too bad. Something to keep in mind is that fret spacing is a relative thing. As Trevor mentioned, it is the percentage of error that determines how noticeable the mistake will be. 1/2 a mm at the 1st. fret will be less noticeable than 1/2 a mm at the 12th. fret. Also, with even tempered tuning some intervals are "wider" than they should be , while others are "narrower" than they should be. A slightly miscut fret may not be any more jarring to the ear of the beholder than the already "distempered" interval it falls on.
If the top of the fretwire can be doctored to bring the fret in tune, or the old slot filled, recut and the filler veneer hidden under the fret wire I would not hesitate to use those boards.

I like using a 1/100in rule. I tape it to a square block and clamp that down to the fret board about 1mm to the edge. Then wearing a 10x headset and using a brand new exacto blade I can 'pierce' the line marking on the ruler and slide the knife point town to the wood to make it's mark. I've compared these boards to ones pre-slotted and my method is more accurate. But the pre-slotted boards are accurate enough and I always use them if I am doing a standard scale.

One important thing to note is that it's better to measure from zero to the fret length to determine the mark rather than from fret to fret. This eliminates a systematic error and I believe that laying a piece of paper down could easily create a systematic error in this way.

I was wondering if one of these could be converted into a fret position marker:
http://www.waycon.biz/digitalruler.html

_________________
We are all in the gutter but some of us are looking at guitars.

Probably quite expensive. You can buy 12" digital calipers that can be used although you will have to reference from 2 points. At the end of the day a decent ruler is all one needs.