Tolerance Levels?

[Pa&Bud]

I'm completely new to this - and on my first build. I was bending my sides and test fitting - and then little imperfections in my jig (outside mold) started to bother me. I became more aware of them as I was test fitting sides. It drove me crazy enough that I am redoing the mold. I fear that a) starting by being a bit off in the body could cause problems down the line or even compound and b) I don't want to do shoddy craftsmanship and c) I have absolutely no idea what tolerance levels I should realistically be targeting.

Obviously if I could do every aspect absolutely perfect I would. However, this is my first build and I'm learning many lessons the hardway, and I'm not a genius with every tool.

I am quite anal retentive though and so when things aren't perfectly lined up - it will bother me.

I'm just curious - aside from completely aesthetic aspects (like the binding meeting together at points etc) what tolerance levels do you shoot for? Do you have a general tolerance level or is it by step? Are there particular steps that I need to make absolutely spot on?

Not looking to get flamed or start a post war - I will and I am doing my best. Just trying to learn and would like to know if my genuine best is good enough for where I'm at now - or if I would have to keep doing a step over and over and over until it is perfect.

[sunburst]

I've never really liked the Freudian term for perfectionism, but I suffer from it too. I tend to work to tolerance levels that are esoteric, so I'm not the best person to ask.
Suffice it to say, as we try to work more accurately we work more slowly, in general, and if we want to make any money building these things we need to work more quickly than we may feel comfortable as perfectionists.
Try for perfection but realize that it is impossible and accept excellent as soon as you get there, not after 15 more minutes of striving for "perfect".

[j. condino]

There are people that produce nice instruments in absolute garbage heap shops and those that produce mediocrity with extremely high tech precision equipment.

To me, the purpose of using molds and jigs should be to help you with the more difficult parts and build a better mandolin. I like as much precision as I can get with mine. If you knowingly accept a 5% margin of error (reasonable for many people) with the mold, and then the same with your top carving and the binding and the neck joint and the fret slots and the headstocks and the other 100 steps building the entire mandolin, what do you think the end result will be like?????? If you are internally wired for precision, I'd suggest you follow that path.

Having a finished mandolin is nice, but remember the journey. Spending 400 hours building your first mandolin with a process that agrees with your outlook and an enjoyable model of life will reward you with much more than just a mandolin....

j.
www.condino.com

[Marty Jacobson]

In engineering terms, nothing is perfect, right? So we look for "good enough". Knowing what is "good enough" can be very helpful.

+/- .0025" is good for planar tolerance on a "perfect" glue joint. Not all glue joints need to be perfect, but things like bookmatched tops and backs, dovetail joints, scarf joints should be.

A .0025" gap is big enough to slide a sheet of paper into. But generally it will clamp up to zero void unless it's a ragged cut.

A 60 grit sanding scratch is .016" (.42mm), for reference.

+/- .020" (.5mm) in deviation from a curve, if done smoothly, won't be detectable as a varation from the plan by most people. Maybe up to .080" (2mm) in some areas, such as in the lower bout of a guitar with a large radius.

[CarlM]

Remember that moisture shrinkage and growth can easily move your outside dimensions by 0.030 inches or more from just a few percent humidity change. And it will not be uniform. So unless you have perfect humidity control and will for the life of the instrument it just has to look good. Joints, fret slot locations and a few other features have to be held critically. The bridge is adjustable for a reason. Things move.

The best training I got for not sweating the unimportant stuff, paradoxically, was working as a tool and die maker in an electronics factory where tooling tolerances on punches, dies and mold parts were routinely +/- 0.0001 inch in critical areas. About a fourth of the stuff was critical and had no latitude for error. You learned quickly to differentiate between important and non important features. Or were invited to find other employment.

Keep in mind that unless your forms are metal, they will also move significantly with changes in humidity.

Another lesson along this line came when a cast mold building company that I was involved with at one point in my career, invested in LOM technology to make patterns for casting. The LOM equipment is a a form of 3D printing where three dimensional solid objects are built up out of laser cut sheets of paper which are laminated together. The LOM patterns were verified by coordinate measuring machines to be within 0.020 inches or closer when they were made. Within three weeks some of these patterns, complicated shapes approximately 2 or 3 feet in a cube had moved half to three quarters of an inch in a humidity controlled pattern shop and storage. The company had a $150,000 investment in a machine that was not usable.


https://www.popularwoodworking.com/t...-and-expansion

[AndyV]

I've never built an instrument, but in other endeavours have finally learned to act on the knowledge that I'm my biggest critic. If I'm not the only person who will notice minor flaws in my work, I'm probably the only one who will care.

[Br1ck]

The biggest lesson learned for me just building a kit, was that you are going to make mistakes, and I made plenty. Probably the most noticeable was somehow letting my Dremel router lean, cutting the binding channel too wide. On both the treble and bass sides. I had to cut long strips, one four inch one six, to bend and glue back to the top like I was binding with wood, then recut the channel again. Did I have a scrap box of spruce to at least match the wood? No, I had some decent redwood.

At this point I was going to have a black top to hide this. But you know what? I did a really good job, for me, of fixing my mistake. In the end I'm leaving the top clear because I'm accepting and embracing the imperfections. It doesn't hurt that I really like the mandolin. If people don't see the repair, I point it out to them.

The episode has become a fond memory of what was traumatic at the time. Do the best you can and accept that it won't be perfect. Enjoy the journey.

[fscotte]

Only the fretboard needs to be perfect.

[rowka]

If people don't see the repair, I point it out to them.

Stop doing that.

And if they DO notice it, compliment them on their good eye for noticing your subtle aesthetic design choice.

[Drew Streip]

I'm probably not the best person to ask, because I have so far only built a ukulele kit and am currently halfway through a dreadnought kit. In general I'm a perfectionist. But in luthiery, I have to check myself. Tone, intonation and durability are the main things -- all else is a display of your workmanship.

On my ukulele, I marked the bridge position according to the plan. And I stained/finished the body, according to the plan. But by the time I fitted the neck, due to inexperience, the bridge position was 1/8" forward of where it needed to be.

So I learned 1) how to finish-match 2) how to remove finish 3) how to triple-check measurements.

Nobody who looks at it would know. And even if I don't make those mistakes again, I'll make other ones. For example -- I filed a few brace slots too deep in the kerfing on my dreadnought and will need to make some creative shims to tighten the joints. But they'll be invisible inside the box. And, I would hope that my future work is not judged on the quality of my first attempt. (unless it fails to improve, in which case, commence judging.)

[HoGo]

I try to work as precisely as I can. I want the joints tight with no gap visible. When I'm cutting outlines or fitting neck or such I work to thickness of pencil line. Here are pics of neck I just glued into body. The lines (centerlines and fret opsitions) were drawn onto body and neck independently before I cut the dovetail. After work I want all the lines line up and the neck centerline project right at the line in the center of the top between f holes.