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Fretting, backbow

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Fretting, backbow

Postby Craig Bumgarner » Wed Nov 30, 2016 5:26 pm

I seem to get a an unpredictable amount of back bow in my necks after fretting. I recently noted that one of my favorite fret wires was designed with a .025" tang and I was cutting a .022" slot, so I switched to a fret wire with a .022" tang and the first one resulted in more back bow that ever. Hunh????? Thoughts on this? Is a certain amount of back bow normal when fretting? Do you allow for it somehow? I can take care of it after the fact either with truss rod or fret leveling, but would rather not. I've been working a compound relief into the fingerboards and would prefer it stay where I put it. :D
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Re: Fretting, backbow

Postby Aaron Helt » Wed Nov 30, 2016 6:11 pm

For me, I've found that there is always at least a small amount of backbow. That's why I fret the board prior to gluing to the neck. I fret, then clamp the fb flat on the counter for a couple of days. Then glue to the neck.
I've had very little issue since using this approach. But, then again, a guitar I build this way (recently) just had a neck that wanted to move backward and nothing could straighten it up. I've always said that wood does what wood does sometimes.
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Re: Fretting, backbow

Postby Barry Daniels » Wed Nov 30, 2016 7:50 pm

I use Mario's method of fretting before attaching to the neck. And then clamping the fretboard in a fairly severe arch by placing 1/2" thick wood blocks under each end and pressing the center of the board down to the bench for 24 hours. This allows the fret tangs to seat and the glue in the fret slots to cure. Afterwards the fretboard is very flat and it will place no backward force on the neck, especially if it is glued with epoxy.
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Re: Fretting, backbow

Postby Gordon Bellerose » Wed Nov 30, 2016 7:52 pm

I usually fret the board before gluing it to the neck also.
I also use 2 way truss rods.
I need your help. I can't possibly make all the mistakes myself!
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Re: Fretting, backbow

Postby Mario Proulx » Wed Nov 30, 2016 11:56 pm

I pretty much only ever skim the thread titles here these days, and was going to respond with exactly what Barry said.

As Deb was fond of saying check the archives.... :)

I still do it this way. I don't have a single instrument in my possession with an adjustable truss rod, BTW. For my personal instruments, my results are so consistent that I find the adjustable truss rod to be moot. My clients almost all opt for one, but I only offer a one way rod. No issues...

Glue a perfectly flat, fretted fretboard to a perfectly flat neck, using an adhesive that doesn't induce a backbow. K.I.S.S.
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Re: Fretting, backbow

Postby Craig Bumgarner » Thu Dec 01, 2016 12:04 pm

Interesting, thanks all. I used to do it that way, fret the board, then glue it. I switched away when I started using compound relief (different relief amount and location worked into the board for each string), something I'm happy with, but started noticing the backbow issue at the same time. Humm.... Well, I'll just have to think about that. Thanks again.
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Re: Fretting, backbow

Postby Doug Shaker » Thu Dec 01, 2016 3:29 pm

Barry Daniels wrote:I use Mario's method of fretting before attaching to the neck. And then clamping the fretboard in a fairly severe arch by placing 1/2" thick wood blocks under each end and pressing the center of the board down to the bench for 24 hours. This allows the fret tangs to seat and the glue in the fret slots to cure. Afterwards the fretboard is very flat and it will place no backward force on the neck, especially if it is glued with epoxy.


Barry- What type of glue do you use on the fret slots?
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Re: Fretting, backbow

Postby David King » Fri Dec 02, 2016 11:01 pm

I use a Stewmac TS blade but regularly set the teeth left and right to get a .024" slot. This is important with harder fretboards like African blackwood. I try to stick with fretwire from Jescar with .020 or .021" tang and often resort to filing down the barbs slightly if they are causing the problem. Where I see folks going wrong is when they infiltrate thin CA into the fret ends BEFORE they deal with the back bow and thus lock it in.
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Re: Fretting, backbow

Postby Barry Daniels » Sat Dec 03, 2016 10:35 am

I use Titebond Original and I place the fretboard into the forward bend as soon as the frets are inserted. The Titebond gives you a bit of time before it cures hard and takes a set.
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Re: Fretting, backbow

Postby Steve Sawyer » Mon Dec 05, 2016 12:55 pm

I've been reading this thread with interest, having a guitar neck that is slotted and awaiting shaping and fretting...

The frets were cut with a 0.023" fret saw, and the fret wire is StewMac narrow/medium.

I've seen a technique whereby the fret is pressed in off-center to the neck, then guided by a caul, driven in from the side. You can see Dan Erlewine doing this in this video.

Has anyone tried this? I know Dan was working on an historically significant guitar (once belonging to Mike Bloomfield - one my three or four personal "guitar heroes") so he was taking unusual care with this refret, but an interesting approach nonetheless.

By the way, if you watch the video to the end, you're treated to Dan laying down some licks from "Got My Mojo Working" which is fun... :D
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Re: Fretting, backbow

Postby Stephen Neal Saqui » Mon Dec 05, 2016 3:26 pm

Driving the neck into a back bow is simply that you haven't matched the frets to the slot.
Before you commit to fretting always test the 1st fret you put in. If it feels tight then you must cut the fret down. Stewmac has a brilliant tool they call the Fret Barber. It's probably the single most important tool they have for fretting. You can easily make you own...I made mine out of maple and it's just like theirs.
http://www.stewmac.com/Fretting_supplie ... arber.html

Develop the sensitivity of feeling the fret as it goes in and get to know too tight and too loose. Once you've got this you'll never have the problem again.
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Re: Fretting, backbow

Postby David King » Mon Dec 05, 2016 3:47 pm

The easiest way to cut up files for all manner of fretting tools is with a 4" right angle grinder and a thin cutting disc. I find that scoring both sides of the file about 1/3 of the way is enough to easily snap the file in a vise with a gentle whack with a block of wood or shot filled hammer. I do the shaping on a pedestal grinder and keep the metal cool with regular dips in water. Files being high carbon steel are very sensitive to high temperatures. Once the metal turns blue you've probably wrecked the hardness for good so don't let that happen near the cutting edges you intend to use. A refinement to the SM fret barber is to add a little bit of taper between the files, about .002" for one end to the other should do it. Lastly when the files get dull after a few years you can grind off a couple of mm to expose fresh cutting edges.
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Re: Fretting, backbow

Postby Craig Bumgarner » Mon Dec 05, 2016 4:05 pm

Stephen Neal Saqui wrote:Driving the neck into a back bow is simply that you haven't matched the frets to the slot.


That makes sense! I ordered the Fret Barber and we'll see how it goes! Thanks.
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Re: Fretting, backbow

Postby Craig Bumgarner » Tue Dec 06, 2016 9:20 am

So. the next question is what IS the proper fit for fret tangs and barbs? I've gone on the assumption that the slot should be the same width as the tang and the fret wire manufacturers made the barbs to the "proper" width. How naive of me! :-) Assuming the first part of my assumption is still correct, that is the slot should be the same width as the tang, how do you judge the width of the barbs?

In the instructions for the Fret Barber, it suggests trying short sections of fret in the slot as the barbs are trimmed. Trim a little, check a short piece, trim some more, test again. But no guidance on when it is right. In the Dan Erlewine's video, he shows the fret being easily driven on the fingerboard extension over the body, an area he says do not require the frets to be as tight. This is helpful, but how tight should they be over the neck shaft?

I realize this may be one of those "experience" things, but would be interested in any guidance. I would think there would be some guidelines, such as, if the slot and tang are .023" and the fingerboard is hard like ebony, the barb should be .030" (just a guess for the example). For softer fingerboards like maple, .032" (again, just a guess). Thanks,
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Re: Fretting, backbow

Postby Steve Sawyer » Tue Dec 06, 2016 10:09 am

David King wrote:The easiest way to cut up files for all manner of fretting tools is with a 4" right angle grinder and a thin cutting disc.


That's how I made a tool for filing the fret ends to a 30* angle. $6 for a small file, a few minutes with an angle grinder and a scrap of oak and I was good to go.
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Re: Fretting, backbow

Postby Stephen Neal Saqui » Tue Dec 06, 2016 12:15 pm

The beauty of Stewmac's Fret Barber is that you control exactly how much fret you remove by using mechanics metal shims measured in the thousandths! AND its fast! You can pull a whole strand of fretstock through or chose to use short sections.

The most important thing about this conversation, in my mind, is that one should NOT mess with the fret slot. Techniques like routing the slots do irreversible damage to the fretboard. It's stupid because the solution of controlling fretting with regard to relief and proper fret width is so simple to do. I'm not a fan of Stewmac but they do have a few important products and Fret Barber is near the top of the list.
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Re: Fretting, backbow

Postby David King » Tue Dec 06, 2016 1:10 pm

I've found that a lot of fret tangs are often a little thicker than advertised. You need to start with a caliper to measure the tang and a set of mechanic's Feeler gauges to measure the slots. On harder woods the slots will often end up narrower. On softer woods it's very common for the slots to start wide and end narrow as the wood dampens the blade's vibrations. I find I need a good .001-.002" of clearance between the tang width and the slot width. The barbs shouldn't matter at all in softer woods like maple and rosewood as the end grain can easily be crushed as you force the fingerboard into forward bow after the frets are in.
That's less likely on the truly hard woods and especially on composite finger boards. Knowing a wood's supposed Janka scale hardness is a useful relative measure. Snakewood is going to be way harder than any ebony etc.

How much barb to file off is going to depend on not only the height of the barb but also it's volume and how close the barbs are to each other in addition to the hardness of the fingerboard end grain. A typical barb might be .036" side to side and you might want to drop that down to .030".
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Re: Fretting, backbow

Postby Craig Bumgarner » Tue Dec 06, 2016 1:59 pm

Thanks David, lots of good advice there.

David King wrote:I find I need a good .001-.002" of clearance between the tang width and the slot width.


How does one enlarge a slot by .001"-.002"? Set saw teeth a bit wider than needed and dress it down to the exact dimension in the Fret Barber? Sticky back sandpaper on a feeler gauge?
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Re: Fretting, backbow

Postby David King » Wed Dec 07, 2016 2:16 am

I keep a cheap Japanese style pull saw for widening the slots to .025" when necessary. I just tape a depth guide to the side of the saw for the tang depth. I set the Stewmac blade but the set gets beaten out of it pretty regularly in the hard woods, also it's tedious setting 150 tiny teeth with a pair of needlenose. If your slots are starting out very wide at the leading edge just put a strip of sacrificial board in front of your fingerboard.
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Re: Fretting, backbow

Postby Todd Stock » Wed Dec 07, 2016 8:20 am

Since I've switched to Jescar wires, no more issues with inconsistent sized tangs and slot/fret misfits. I assemble neck and body after finishing, then do final level/prep/fretting after that. Even on T-bar necks, there's no drama and no issues with back-bow, etc. Used to use Mario's approach to fretting board off the neck, and that works as well if you understand what final geometry you want and how to set it up before assembly.

One thing that helps to get a straight, stable neck is gluing the fretboard on using a strong back and shaped caul with at least 48 hours of drying time to dump excess moisture - I know some builders have success with simply clamping board to neck, but with water-based glues like hide and fish, the strong back prevents transient movement and possible permanent distortion due to excess moisture.
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