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Hey folks,

I spent some time testing out the Magic Probe from StewMac. Some of what I learned is below and in the video on YouTube. I’m not sure why YouTube cropped the video so the captions are off screen, but alas.

First, here is the product - https://www.stewmac.com/luthier-tools-a ... ess-gauge/

The product website has a good set of tutorials to help get started - https://www.magicprobe.net/mag-ic-probe-software-1/

The idea with this tool is that you take a birdseye picture of the instrument top, import it into the software, and take measurements. The probe has a magnetic ball which goes inside the instrument. The probe is then placed on the instrument top and the software reads the thickness of that point. You capture the thickness by clicking on screen in the same location on the virtual top as where the probe is on the actual top. Then move to the next point, measure, etc…





Of course, I immediately thought “how can I make this more accurate and repeatable?”. That’s where the CNC comes in. I used the laser on the CNC to draw out a grid of points, including the 00 shape and bracing layout, onto brown craft paper. This protected the top and gave me easy visual targets to take the measurements. Having the brace layout helped to avoid braces. The software has an offset feature where I could account for the thickness of the craft paper in the resulting measurements.

Here is a video with more detail - https://youtube.com/shorts/VMj1QWabCLM?feature=share

I think this will be a useful tool. Any questions let me know.

Brad


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I've always wondered what the guitar top actually comes out to be with all the finish sanding and so on. I've measured a few using that Hacklinger gauge before but I always wondered how accurate it was.

Very nice demo on the Youtube short.

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Measure Twice,

Karl Borum

I don't really see the point of this on a flatop guitar. I dreamed of having something like this when I was building F5 mandolins. This excels at mapping out arch tops.

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Hutch

Get the heck off the couch and go build a guitar!!!!

I have one and I have used it on “flat top guitars” to make sure that I didn’t oversand after assembly. I’ve done a couple over the years where I suspected that the top ended up overly thin. I checked and retopped those. I’ve also used it to check guitars that people have brought me. I don’t use it every day, but when I need it, it’s invaluable.

I dreamed of having one of these for years and investigated (mentally and a few experiments) ways of making something to do the job. Even though it was somewhat expensive, it was less expensive than what it would have cost me in time and effort to develop it myself.

Goal for me is pretty simple. I use the methods from the Gore / Gilet books to determine the starting thickness for the plate. I then thin the perimeter of the plate after closing the box. This lets me see that progress and hopefully dial it in and make it repeatable.


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Very professionally done Brad.

I couldn't justify one myself but perhaps some could make a few bucks renting one out!

Cheers Dave

I’m kind of with Hutch on this. Would be awesome for Mandos and arch tops. One obvious other use is measuring vintage guitars.

This is how I plan to use it for flattops - https://youtu.be/Dj5RewW11uM?t=2529

Michael knows a thing or three.

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Very cool, and the price is not much different than a hacklinger gauge. Thank you for the run down on how you use it!

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Hey Brad, this is topic-adjacent, but do you use Steve E’s spreadsheet with the calculator to determine thickness, or something else?

Spreadsheet fun
https://r.tapatalk.com/shareLink/topic? ... source=app


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Edit: I see now in the post link you share its the combined spreadsheet, that’s the one I use.

James, I have two spreadsheets. One is named “Plate thickness calculator “ and one is called “Luthier combined spreadsheet”. I got them both from past posts on the OLF. They both give the same output when given the same input, so either one is derived from the other or they are both doing the calculations correctly.

The one I use is the “Luthier combined spreadsheet”, which has some other tools in there but I haven’t used them.

I use this to get the starting thickness of the plate and then thin the edges, usually ~.005 - .010 ish. I say ~ and ish because the way I have been measuring this is to try to put calipers on a little spot in the plate that might be proud and give me some purchase. It usually works.

Would it help to put one of these spreadsheets on the Roundtable google drive to archive it?

Brad


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I'm in the process of doing something similar. Thanks for posting Brad

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Results of some experiments today on the latest 00.

https://youtu.be/iEOfjG2tbR0?si=Lh8cSzDZgdaX5R3V


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Hey Brad,
I created and posted the "Plate Thickness Calculator" shortly after the books were published.
The calculations were reviewed by Trevor himself.
The link is here: https://docs.google.com/spreadsheets/d/18ahHbj_KoVW7wiIxOkqo3r9ujJtirCso/edit?usp=drive_link&ouid=106696316853042284696&rtpof=true&sd=true.
Cheers!
Rob

Perfect. Thanks, Rob!


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