fretting - rounding errors

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Robert Smallwood
Posts: 108
Joined: Sat Jan 07, 2012 7:33 pm
Location: Merimbula NSW Australia

fretting - rounding errors

Post by Robert Smallwood »

Hi.

This could probably go anywhere.

I've been fiddling with a cad programme and done myself a fret distance calculator iin Excel. I draw my centreline & step from nut towards the bridge the appropriate distance according to thr ftret number. So now errors start o creep in.I type 21.4428 when i locate or selct the point in the programme it's 21.407 that's .0358 difference (ie more than the width of a fret slot .023)

I'm guessing this is a significant error. Does anyone know the tolerance of a fret postion absolute or relative?

I have checked my excel results agansit published scales and so i belive i am typing in correct values. Perhaps my locating is too coarse.
could 'rounding' errors be as large as this? another 8.5095 true vrs 8.508 not so bad..but more than hal a fret slot. (.0015)

Thanks,
Rob.

Gordon Bellerose
Posts: 1186
Joined: Wed May 30, 2012 11:47 pm
Location: Edmonton AB. Canada

Re: fretting - rounding errors

Post by Gordon Bellerose »

If you are .015, or half a fret slot out, I believe that difference could be corrected by filing the crown of the fret in the correct direction.
If the guitar gets sold to someone else and had to be re-fretted, this will not be obvious.

The issue is how much is the intonation (correct pitch) affected by such a small amount?
I don't have that answer, but I would suspect a good tuner would pick up a difference.

A secondary issue may arise if the initial small error becomes compounded by causing error in the other fret slot placements.
I need your help. I can't possibly make all the mistakes myself!

John Sonksen
Posts: 356
Joined: Sun May 20, 2012 12:16 pm
Location: Portland, OR

Re: fretting - rounding errors

Post by John Sonksen »

That seems like more than just a rounding error to me. Are you measuring point to point, edge of fret slot to edge of fret slot, are there any offsets set up in the selection parameters? I would definitely not go forward with those numbers, you'd be better off with a long steel ruler and calipers.

Eric Baack
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Joined: Thu Dec 27, 2012 4:28 pm

Re: fretting - rounding errors

Post by Eric Baack »

measure every fret from the nut so that you don't get any tolerance stack up. if you measure fret to fret then over the course of 20+ frets, an error of .005" short turns into .1" off or more if all of the errors are in the same direction.

John Sonksen
Posts: 356
Joined: Sun May 20, 2012 12:16 pm
Location: Portland, OR

Re: fretting - rounding errors

Post by John Sonksen »

Now that I read this again, is the fret calculator generating all of them from the nut at once? If so your formula needs tweaking

David King
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Location: Portland, OR
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Re: fretting - rounding errors

Post by David King »

I'm totally confused by this question. Please, what am I missing? Why would it round at the hundredth's place and leave a random digit at the thousandth's?

Robert Smallwood
Posts: 108
Joined: Sat Jan 07, 2012 7:33 pm
Location: Merimbula NSW Australia

Re: fretting - rounding errors

Post by Robert Smallwood »

Sorry ..I wasn't very clear. I'm sure my excel calculations are on the money, and i step from the nut to each fret position individually, but on the diagram in the cad programme. ie I type in the co-ordinates. when I checked with a 'select' point in the cad programme - a sort of mouseover - the co-ordinates show and were as stated before.
So I don't know whether i'm too clumsy with the mouse - very possible - or if rounding errors on the input distances affectd the numbers and what ever the case - how big a diference would it take for a fret to sound wrong?
This is in a computer, nowhere near a piece of wood, but i would like to get some idea as to how much error it takes to be heard. i suppose relative to a fret slot width.

like if one fret was 1/2 a slot width out could you play in tune? Or if you did a zero fret rather than a nut would the tuning be out?

John Sonksen
Posts: 356
Joined: Sun May 20, 2012 12:16 pm
Location: Portland, OR

Re: fretting - rounding errors

Post by John Sonksen »

are you populating the fretboard with single points that you are crosschecking against your spreadsheet, or are you mousing over a fret slot width feature? Just trying to clarify if you're picking up the edge of one side of the fret slot versus the center of each one. Even if it were the latter it seems like your measurement issues are farther off than what would be explained by half a fret slot. I can't give you a good estimate for how far off you can be without it affecting intonation, but I'd try to be as spot on as possible. Do you have any offsets set up when you're forming a slot feature, or maybe one at the nut end of the fretboard? In the fretboards I've modeled in Solidworks I've manually entered the point measurements from the nut end and created a .023 slot that bisects the points. Kind of a pain in the butt, but it would allow you a chance to compare the result from each method and see if it's somehow a rounding error, (which I couldn't believe it would be if it's as far off as you're saying).

Robert Smallwood
Posts: 108
Joined: Sat Jan 07, 2012 7:33 pm
Location: Merimbula NSW Australia

Re: fretting - rounding errors

Post by Robert Smallwood »

I'll try inputting the slots. and see what happens. I never thought of that.
Thanks,
Rob.

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