Straight edge for necks printed for new HB electrical mandolin

[poul hansen]

I couldn't find a Straight edge for mandolin necks but found a 3D printable, so 5 hours later I could check my new HB "telecaster" mandolin.

It works but only on newer mandolins, so I measured my vintage mandolins and found out that a reduction to 95% made it suitable for those.

https://www.thingiverse.com/thing:4053758

[Richard500]

Nice idea, and good adaptation to shorter scale, and easy to flatten if necessary. Wonder if repairers only check the fret tops routinely.

[pops1]

I have 5 different lengths of straight edges., from 2-24". The smaller ones I use as fret rockers most of the time.

Like Sunburst, I don't have notched straight edges either.

[sunburst]

...Wonder if repairers only check the fret tops routinely.

Those of us with enough experience check fret height as well as straightness of the playing surface. Deviations is straightness of the actual fingerboad can be present even in instruments that play very well because the frets can be leveled. That leaves the frets of various heights, so when checking a neck, measuring fret height can reveal it. To some extent, actual fingerboard flatness is irrelevant if the frets can be leveled for good playability, and leveling the frets, until the time comes for a re-fret, (when the 'board itself can be leveled) saves the luthier time and the customer money.
Anyway, because of all this I don't own nor use notched straight edges and feel no particular need for them. It is the playing surface that matters to the player, and unless the fingerboard surface is egregiously out of flattness, a condition that is visible, the fingerboard surface is of much less importance.

Anyway, as in most of lutherie, to each his own. Material, method and tool preferences vary substantially from luthier to luthier. Some find notched straight edges useful, I do not.

[CarlM]

Anything you 3D print as a check gauge like this should be checked against a known good straightedge. Unequal shrinkage, printing conditions and environmental factors can warp the parts significantly. That is not necessarily so but the parts are not guaranteed to be straight off the machine.

[poul hansen]

Anything you 3D print as a check gauge like this should be checked against a known good straightedge. Unequal shrinkage, printing conditions and environmental factors can warp the parts significantly. That is not necessarily so but the parts are not guaranteed to be straight off the machine.

Correct
I have checked but for all practical purposes, they are straight. This is not rocket science but just for my own sake, I slightly sanded them on a fretsander block. ;-)

[sunburst]

...This is not rocket science...

True enough. When I needed a straight edge longer than any I had in the shop I ran a maple mandolin side piece over the jointer, checked it against machine tables, and penciled "straight" on it. I still use it from time to time. I could hand file fret notches in a similar one if I had the desire.

[CarlM]

It is good you recognize the concern. While this does not require hyper accuracy I have seen things come off 3D printers with 3/32" or 1/8" of warp that required some rethinking on the process to get usable parts. This is a little more simple than some of the problem geometry I have seen, but similar conditions with one side flat and the other with more notches and cutouts is prime for different shrinkage on each side and hence warp.

[Tom Haywood]

I like to use a notched straight edge to see how level the foundation (fret board) is. That can tell me a lot about the neck, the frets, and what's going on with the instrument generally. It is a triple purpose tool: set it on the fret board to check for twists and humps, etc; if it is long enough, you can check for ideal bridge height (sometimes this helps in diagnosing neck block rotation); then put it on to the frets. Not necessary in many fret level situations, but useful if you have it. I can make a useful notched straight edge for any scale fretted instrument in about ten minutes by marking a wooden ruler and cutting out roughly 1/4" slots around the marks using the band saw. Then sand the "feet" side to level using a 4 foot (or 2 foot) level with sand paper taped to the side. Always sand it to level before using it again in the future.