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Brad,

You recently posted somewhere about center-finding bisecting calipers which has me interested. Looking at the pics in the link I saved, https://goldenmeancalipers.com/product/bisecting-calipers/, has me wondering about their accuracy, especially with narrow objects. How's the accuracy for our uses?

Thanks,

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

Hey Pat,

I saw them somewhere too and thought, now that's what I've been looking for with all the center finding work guitars bring us. So I ordered a set a few weeks ago. Everyone's idea of accuracy is different so here's some pics for you. I think there is a range where accuracy is probably good but over all, they aren't good enough for me and I expect they vary tool to tool. However for consistent accuracy I think they would have to be made out of stiffer heavier stock.

I think if I used them I'd be double checking everything with the 6 inch centering rule so what good is that.

The pics show that in the narrower range the error is visible without even having a rule for comparison.

Another example of sounds good in theory, not so good in practice. Of course mine could be the exception. More a novelty than a Starrett level measuring device IMO.

I have one with a very nice custom plastic case I'd let go of for $50.

First pic looks off more than it is cause of camera angle and in that range it is probably serviceable.



At narrower measurements, not so much.

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Brian R, Wood Mechanic
N8ZED

Hey Pat, it wasn’t me who posted about those. Maybe Brad Goodman?


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https://sqwayretools.com/shop/ols/products/the-orignal-centersqwayre

I have one of Tim Sway's center finders and it works very well. He's a guitar builder too.

Dave

Dang Brad, I was sure it was you! Guess the ol' brain cells aren't what they used to be.

Brian, After looking over the pics, I can see where the geometry in the design would have the least accuracy at narrow settings. Thanks for the feedback.

Dave, That looks like something I'd be interested in. I saw something similar that had six legs, used for laying out classical guitar nuts, being that they're spaced equally.

Thanks, gentlemen.

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formerly known around here as burbank
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http://www.patfosterguitars.com

That's pretty cool! On the subject of interesting tools, someone introduced me to this tool while I was in Austria. It will find the center of, and give you a square edge to, a tapered board such as a fingerboard. I used it to layout and slot a fingerboard and it worked very well (normally I'm using a miter box, or buying pre-slotted).

We couldn't figure out what it was called, or where we could find something similar. From what I understand it was made by a retired guitar maker in Germany, so he contacted him for me and there was one left over and I bought it.

Anyone familiar with this?

Here it is closed:



And here it is opened. There's a notch and hole to mark the center:

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Thanks Josh

So far, from a design aspect, I'm liking that one the most.

Thanks for posting it.

Brian

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Brian R, Wood Mechanic
N8ZED

Am I missing something…. What’s wrong with a center finding rule?

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Steve Sollod (pronounced sorta like "Solid")
www.swiftcreekguitars.com

"Am I missing something…. What’s wrong with a center finding rule? "

Nothing at all and the gold standard. Just the older you get the harder to split those 32 and 64ths graduations by eye, over and over again.

So looking for a mechanical advantage, nothing more.

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Brian R, Wood Mechanic
N8ZED

Centerlines are overrated.
I find it ironic that we strive for mathematical perfection for systems that only provide an approximation (with known inaccuracies) of what things should be.

I'm always perplexed that violinists/makers, are always measuring the body to nut measurement, and the body to bridge measurement (the notch on the f holes) to be sure that it matches with the gold standard that they want. Yes, you want a 2:3 ratio between the neck length and the stop, and somewhere around an average number should be normal.

But.

How do you even really KNOW the body is within a mm or less? When playing at the end of the body, your fingers are 15mm or so above the body, and the body is curved!

Besides that, there are no frets, and the notes are ALWAYS adjusted individually to temperament, or to what is being played by your neighbor, or the other sections. It is a finger to ear placement, and even a +/- 5mm difference in scale length, or a 2 mm longer neck would seem to be the least of your concerns.

If the 12th fret was half fret short of the body end on a guitar; would it be the end of the world if the frets were all in the right place for equal temperament? On an arch top, would you ever know? On a flat top you could see it; but would it matter? It's a 12.5 fret neck, so what?

Yes. It boggles my mind.

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Why be normal?

Interesting thing I've observed with people who build things is that many of them obsess over how accurate their measurements are without considering what accuracy is required for that particular task. When I started working as a carpenter I quickly learned that the accuracy required for framing wasn't near what was needed for finish work. That translates to pretty much anything including guitars.

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Steve Smith
"Music is what feelings sound like"

Centering and locating centerlines or markers is something the human eye is pretty darn good at when borders are established in somewhat close proximity. The brain notices centering and even does a pretty good job of estimating progressive changes like fret placement.

Whether a soundhole is perfectly centered in a top is harder to notice by eye. But areas that stand out like fret markers, headstocks, logos, whether strings are equidistant from the fingerboard edge, side markers, back stripes meeting end graphs, neck center lams following the center of the heel, etc are easily noticed by most people. Failure to meet centering at the visual level doesn't scream professionalism. There are lots of areas where splitting 64ths or even using calipers to the thou is important.

There's a point where the eye can't see it and centering matters less but to not strive for your best effort is a mistake IMO.

Sure, a lot of the centering effort is cosmetic and has zero effect on playability. But if you are selling a multi thousand dollar instrument and the customer says, that fret marker isn't centered or "I put a straightedge down the middle of the fretboard cause it looks crooked and it misses the end graph by a mile", or "why does the neck meet the body between frets?" Well, I'd find that rather embarrassing. I'm often surprised what some customers notice in the details.

I don't know where centering becomes a visual hallmark and it depends on object relationships, but it can be pretty small. I find myself doing the Hesh thing with measurements like 7/64ths and a half just cause it makes sense to my brain. 64ths is about as fine a graduation as your going to get with a rule but I'm always refining those measurements with calipers. So I think my eye looks for errors in the 5 to 10 thou range. Just makes me feel good to try and meet the challenge. A centering veneer caliber measuring to the thou would be something I'd invest in.

I guess we all draw the line somewhere that works for us. (pun intended)

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Brian R, Wood Mechanic
N8ZED

Just to clarify, I wasn’t saying we shouldn’t do accurate work, just be aware of what tolerances should be. After all I’m one who typically finds centers by measuring the overall width with a caliper, dividing by 2 then setting that on the caliper so I can mark the center. I also use 0.3mm pencils for marking.


Steve

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Steve Smith
"Music is what feelings sound like"

I also use a caliper for critical centering tasks and have a feeling that even with that nifty centering jig I would always be double checking it with the caliper.

That is a really cool jig though. I’m tempted.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Yep, I almost hit the button too


Steve

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Steve Smith
"Music is what feelings sound like"

Is this what you're looking for Uncle Pat? Ken Timms from the UK makes these.

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Wasn't me...

Here's one of the reasons I need to get stuff centered. Using the old method with a solera, fretboard placement and the soundhole need to be set up dead on before the FB is glued on. If it's off, all kinds of stuff doesn't line up with the circles in the rosette. Some builders don't make the end of the FB symmetrical, so it's not so critical. I haven't gotten there yet.






That's one of them.

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formerly known around here as burbank
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http://www.patfosterguitars.com

Well I guess it's a mystery.

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formerly known around here as burbank
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http://www.patfosterguitars.com

Is the measurement to the inside of the line or the outside?

My dad is a civilian carpenter at an Air Force base and used to say “close enough for government work”.

One thing I will say, early on I used to obsess over everything. I still do, but I used to, too.


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Steve Smith
"Music is what feelings sound like"

When I worked on industrial robot gripper mechanisms, some dimensions might be specified something like +0.0000 -0.0005. I love guitar tolerances!

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formerly known around here as burbank
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http://www.patfosterguitars.com