Nitro lacquer wins the durability contest, but for nylon string instruments a thin coat of shellac on the top is considered the best for tone quality. I think that is because shellac cures up harder than lacquer,and has lower sound damping properties.
So, French polish already! I do, but in areas adjacent to the bridge and fingerboard that technique "leaves something to be desired". Maybe even "a lot to be desired".
So, I'm thinking once again of spraying shellac, perhaps with an air brush. Anyone have words of wisdom to offer?
Played Elvis below.
Are enjoyed in this part of the world.
Here's Cliff Richard Singing with Hank Marvin Playing a Burns 12 String!
I hope you and others very much enjoy the Burns Guitars above, as much as I do! :)
Quote: ""I'm surprised to find you asking questions here, I think of you as someone who has all the answers for us!"
- Snipped for Shortness -
"The thing that has kept me fascinated with luthierie for almost 30 years is that there is so much to learn. Hardly a day goes by that I don't think of something new to try, or that somebody doesn't suggest a new wrinkle that makes a process work better. Musical instruments have evolved over a long period of time, and it's a very long term commitment to get to the level where the old timers were."
Hi Brian, What a truly Wonderful Attitude!
Welcome and many thanks for your lively contributions to Franks Forum.
I do so heartily concur with these excellent comments, it did indeed take a long time, careful experimentation and a tremendous amount of trial and error for the Guitar to Mature.
A really brilliant colleague who was a Gifted Chemist said to me a while back, "every single day we must look at everything we do afresh and are prepared and committed to rethinking and changing what we do".
New Technological Progress was behind the remark. He Invented the Process of Spraying Clear Coat Solids, a highly efficient, very direct Spraying Process, that utilises Low Pressures with very little Overspray and Bounce Back and actually Recovers and Recycles the Unused Material as its Applied, for its Continuous Reuse.
Where in a Factory a three-shift operation is introduced working on a continuous basis. Whereas five cleaning cycles per shift are required to ensure consistent operation of a 2K liquid Clearcoat Production Line, this Process only requires one cleaning break per shift, to keep first-run capability (FRC) at the high level achieved, and leading to fewer repairs.
The ability of such Powder Clearcoat Material to apply with no sag and run behaviour results in a film build, varying only within a few microns between Horizontal and Verticals Surfaces. This Attribute in particular produces a Homogeneous and Consistent Appearance over the Entire Product.
Also, many Products, designed and produced by Companies I am associated with are Manufactured utilising Modular Technologies.
If you think it about it, this is analogous to much of your methodology and of completing the Top as far as possible, prior to fitting it to the Sides. So we are completely open to new ideas.
However, we have a tremendous respect for the design and manufacturing methods used deep down in our History, and from time to time, Manufacture Products that are a nod to Past Accomplishments.
We also build everything, all the time by hand, separate from any and all other Manufacturing Processes. This is done by Highly Experienced Experts, and Checks and Validates the Quality of Every Single Part, or Module, and Tests the Supply Chain used in Production, All the Time.
So you will appreciate that I am Open to New Ideas.
And also used to New Technologies and New Methods of Construction, especially Modular Methods that Compress Time of Final Assembly.
And, could be considered a Problem Anticipator and Problem Solver, but most of the time am Challenging Things, usually the way people Think. Most people do not think enough. A few, think too much.
But its drilling down into people heads and Understanding the Weaknesses in their Thought Processes, that really is my Main Domain. Do not misread such activity as Criticism, because Negative Criticism is an Opposite Pole, from the Positive Purpose, I Pursue.
To be able to order and run Factories better and better, not purely to compete but to lead the pack and trail blaze the future, you do need to have a Positive Attitude towards Identifying Weaknesses in Ethos, Thinking, Attitude, Design, Planning, Processes, Manufacturing, Maintenance and Capital Investment.
So if I write anything that seems to any degree whatever, Critical, it will not be a Personal Criticism at all, rather a Positively Intended Challenge to Thinking and Methodology, and meant to Highlight Issues and Expose Potential Weakness, which to those Open to Change, is I trust, a very Considerable, Genuine Help.
Brian, I have no doubt much that is written, you may already be completely well aware of, and I would never insult your intelligence. So I trust you realise that I am covering ground that will hopefully be positively helpful and informative to every Enthusiast, whether they can afford to possess the Best Equipped, Large Shops or have very Economically Equipped, very, very Small Shops.
Mainly, I try to Share Basic, Foundational Principles, If folk get the Basic General Principals right, then everything else flows well from there, and the least amount of time and money will be wasted, as most problems will be avoided, and the few they encounter, hopefully, easily surmounted. Things like...
"The Cardinal Sin of Bad Paintshop Practise, is to Sand in the Spray Booth Area."
I trust no one here does that, even if the different Working Areas are close?
But for any that might, sharing the Basic Principle, promotes thought.
Perhaps by instituting minor changes, they can avoid problems.
And by following Clear Principles, Improve Performance.
If this seems too simple, its written for Everyman.
A Top Manufacturer, or the Smallest Shop.
Serving both, equally as well.
Eliminating and Controlling Contamination is the Number 1 Issue in every Paintshop in the World.
The issue I am having with your post is reconciling the following:
Quote: " Musical instruments have evolved over a long period of time, and it's a very long term commitment to get to the level where the old timers were."
Quote: "my "techno-weenie" approach to building which requires that the bridge go on early in the process---before the soundboard is glued to the sides"
It would appear that you genuinely appreciate "the level where the old timers were." Yet also are "tied" to a modular process, via a "techno-weenie" approach.
I'm wondering if the reason for this is your desire to Test and Digitally Record the Sonic Behavior of the Top including Bridge Mass thus as close as possible to how it will Function in Practice, Prior to fitting it to the Body?
There is a tension and dichotomy here, because these seemingly contradictory statements, appear to reveal. You as a Guitar Builder, wish to go backwards and move forwards, at one and the same time. The problem appears to be, an unwillingness to compromise, at either extreme.
My view is.
That you can be fully committed to the past are far are Knowledge and Material will Allow.
You can be fully committed to the future, pushing ahead, Expanding Knowledge and Experimenting with Material and Methods.
You can try to Understand and Take from the Past as Much as Possible, Whilst being Open and Ready to Embrace the Future as Much as Possible, and Take the Best of the Past and the Most Promising of the Future to make the Best of This Moment.
There are many Analogies available.
Many people were fully committed to Analogue Tape and Analogue Equipment in Recording Studios.
When Digital Technologies were first introduced, they Sounded Awful and had a Great Many Inherent Weaknesses and Compromises.
Compared to Analogue Technologies of the time which had Matured over a long time, Digital Technologies were in their Infancy, so By Comparison Palled in Quality, Musically.
Yet Digital Technologies had their Enthusiasts, and Slowly and Gradually, the Weaknesses were Exposed, Understood and Fixed, so these Systems Gradually got Better than the Analogue Systems they Replaced.
However, contrary to what Marketing Boys would have us think, there is actually, No Such Thing as Digital Sound. All Sound is Analogue by Nature, the Digital part is simply the way in which the Data is Stored.
Therefore every Digital System has to have an Analogue Front End to Capture the Sound, and an Analogue Back End, to Playback the Sound. So, the Quality of the Analogue Front and Back and the Quality of the Analogue to Digital and Digital to Analogue Converters are Critically Crucial Elements of any High Quality System.
Thus, the Best, State of The Art, Professional Recording Systems, benefit from the Best of the Old and the Best of the New.
And it's how they Resolve the Dichotomies between the two, the Care and Attention Taken in Compromises.
That Define the Best Equipment Available.
You will draw the salient point.
For a Long Time.
People argued about Sampling Rates for Audio Recording.
You will perhaps know something about this, as you Record Sound to Analyse your Guitar Building.
The Theory was, a Sample Rate of 44.1kHz was Sufficient to cover the extent Human Hearing. Yet in practice, many Recording Engineers found a Higher Sample Rate, 48 kHz or 96 kHZ rendered a Better Sounding Recording.
How could this be? It caused a lot of argument, discussion and dissention amongst people who were all Great Experts in their Fields. The Math's based people said one thing, the Ear and Hearing based people said another and never the twain would meet.
Of course, we don't simply, Hear with our Ears, which is a surprise to many people. All our senses are in fact interlinked and interdependent far more than is realised, and we can also Feel Sound with our Bodies. This is how Profoundly Deaf Musicians like World Famous Percussionist Evelyn Glennie is able to Perfectly Tune her Instruments to Pitch by fingertip Vibration.
It turned out that, Digital Recording Equipment Manufacturers were making Recording Equipment that offered a variety of Sample Rates. Yet for the most part, instead of developing their own Digital Filters which is very painstaking and time consuming, they were purchasing off the shelf Generic Digital Filters from third party Suppliers.
These usually worked Optimally giving their Best Results at One Specific Sample Rate in Particular (which is what the Ear and Hearing Experts Detected and so used to Record with), but although they still functioned quite well at all the other Sample Rates, as they were not Custom Tailored for the Equipment they were used with, they would not render such a Revealing Recording, than at whatever was the nearest to Optimal Rate. Great Ear people were on to this straight away.
The Optimal Rate could vary from Manufacturer to Manufacturer, and it wasn't a problem with the Very Highest End Convertors, if they Designed their Own Filters, but with the most widely sold Studio Equipment around the world, it universally appeared to be a Higher Sample Rate was Superior. There were many additional issues, like Pre-ringing, Time Slur as well as the Filters that appeared to be directly improved by utilising a Higher Rate, although theoretically, that should not be the case. Gradually these issues were addressed.
But the main problem was Blinkered Thinking.
Blindly Sticking to an Mathematical Idea, when a Specific Problem was Revealing a Change was Required by Listening.
This is the Real Issue. Are we primarily Ideologically Driven or Real Listeners?
Many years ago.
I Played with a Group that was involved in Pioneering New Music in Christian Worship.
Today, certain of these New Forms have become a Whole New Genre of Music, broadly known as "Christian Contemporary".
They have their Own Chart, it's moved a long way from where we were all those years ago, but you will appreciate, I would not point Criticism towards Today's Artists.
Yet I feel sad that in many Churches I visit, whilst New Musical Expressions of Worship appear to Dominate the Service, Well Known and Greatly Loved Older Church Music, that is Fine Music, appears to have been completely abandoned altogether.
I'm sure to some degree, we all impoverished, whenever something valuable from the Past is lost, and that is all the more true when the loss occurs and the people involved in creating the loss, don't actually recognise and realise, what they've lost. They are in fact, completely oblivious, to the loss altogether, enamoured as they are and intoxicated with the exuberance of their own vivacity.
Take the Best of the Old and the Best of the New.
Make the Best Instrument you can, utilising the Best Methods of the Moment.
I'm quite sure that is WHY, Major Manufacturers like CF Martin, Gibson, Taylor as well as others use the Methods they do.
This is Really, the Solution to your Problem.
Sometimes the Problem we Experience.
Doesn't really exist as the Solution is Already Available.
The Real Problem lies inside us and to our Willingness to Change and Adapt.
Quote: "I'm now thinking that a spray gun is likely a better choice."
People use airbrushes and small airgun's because they are trying to create ART with a Spray "Paintbrush", because they are using quite small quantities of material, or because they need to manipulate the gun to apply the material in a place where it is extremely difficult to do so, thus find the small size, low pressure and gradual build up, helpful in avoiding problems.
Today, a lot of "Art" that once would have been airbrushed, can been achieved using fine brushes as well as air brushes, using heat applied stencils and by other new technological means. In one Company I am linked to, we recently flew out a man to a Middle Eastern Country to Paint a little Gold onto a Product that the customer decided he wanted, after the Product had been delivered.
It normally takes 6 Hours work to apply this detail in a Factory Production setting, and there only one guy, that does it. Years ago my Daddy did this type of work with tiny feather like brushes, and I later worked with friends that also apprenticed to do this. So what I am saying is, no matter how difficult the Finishing problem, we are used to finding ways to solve those kinds of problems, and are doing so continually. Sometimes getting Material Sprayed in Areas that can't be Sprayed!
However, from a personal point of view, although most people would perhaps find an air brush or a small hand gun, necessary for most tasks.
As Howard who is always "Sound" questioned and I myself have found, there's little that you can't do with Standard Equipment, provided you acquire the skill and versatility to use and control it, and set it up optimally to do the particular job you want, and have it properly adjusted for using the specific material you need to apply.
Of course, such liquid materials are a sort of "living thing" and you need lots of experience, (which I'm sure you are not in any way short of) but to watch carefully and be able read how the material is laying down, its speed of lay down and how its specific viscosity, is applying to the work in practice, moment by moment.
That can change by the day, hour and minute. Particularly if there is a sudden change in viscosity, humidity or temperature. So I was taught by more experienced than I to never ever take the material for granted, to always watch carefully as I applied material, watch like a hawk and always go for an even coat overall, even on the earliest coats.
Years ago I trained many Sprayers, and gave the same advice to Paint Shop Operatives whether engaged in Preparation or Finishing.
"If it were done when ’tis done, then ’twere well It were done quickly."
"Proper Preparation Promotes Perfect Paint Performance"
"Let Your Eyes do the Work!"
In regard to Sprayguns.
Today, there are many different Brands of Spraygun that will do this job well and many can now be bought relatively cheaply. I am not a Snob. They will usually work fine.
The thing is, although that is a perfectly reasonable way to go for small Workshops, and for sure economical, I would think somewhat differently about all this and I hope these thoughts may be of service to you and others.
These Economical Sprayguns are designed for the Average User and Commonly Used Materials but are unlikely to give the Professional Options of Differing Air Caps Sizes suitable many types of Less Common Material.
Certain Types of Sunbursting and Regular Stains, Water Borne Materials, a Variety of Clear Coats may be amongst those. Or if they do in a kit, it be difficult or impossible to obtain replacement parts for these purposes later on.
I would also first ask of any supplier, "do you have the spare parts readily available to service this gun?" By that I mean Air Caps of differing types, Fluid Tips and Needles, (as once the seating between the Fluid Tip and Needle wears, all kinds of problems ensue), Springs etc.
If you can't service the gun because you can't obtain spare parts for it, the gun will be fine as long as there are no problems, and provided you take especially good care of it. But once a problem does appear, something does get damaged or worn, then a cheap gun that can't be serviced because of the need of a tiny part, would need to be completely replaced altogether. Then, everything I have written, will suddenly make tremendously good sense.
A Cheap Spraygun might still be a very sensible, cost effective option, but seen from the angle of someone who has had in his time to service and maintain lots and lots of guns... (some of our Factories have over 100 Sprayguns hanging on one rack, all ready to use with various colours, at any one time, others use 1 Spraygun but with advanced automated colour selection that loads and flushes between colours automatically, and certain Brands I am associated with have over 230 different available Colours, and whilst most Sprayguns today have been almost completely replaced by Robotic Spraying Equipment by us)... then, the ability to Ideally Apply a Wide Variety of Material and the Servicing and Maintaining of all this, suddenly becomes very relevant, and what is true for Busy Factories, also holds for Professionals in Workshops, in it for the Longer Game.
As Robbie helpfully points out, it's important to strip down a Spraygun and Clean it thoroughly throughout, after every use, and maintain it to a high standard so that it will serve you well in the longer run.
Any Material that starts as Solids, will be more prone to clogging than most, normal Sprayed Materials, and will especially require a complete strip down of the Spraygun, as soon as practically possible.
A good workman looks after his tools, although I must confess to having dropped and damaged more Sprayguns and damaged more Aircaps, Fluid Tips and Needles than I could remember.
These thing happen, so if you buy a Spraygun that is a Reputable Brand, a Professional Product, its life will be extended by the ability to Service, Maintain and Replace Parts.
It's this that in part makes a Professional Product. This of course, might not be at all the way you first think, so it may be worthwhile, thinking again.
Spraying Equipment Manufacturers divide Product Lines into Original Equipment Manufacture and Re-Finishing.
Even if you are Fabricating Guitars, it will be the Re-Finishing Products that will be of interest to you.
You will need to decide whether you prefer a Suction Feed or a Gravity Feed Spraygun.
If you are Spraying vertically for the most part a Suction Feed Cup will be best, but if you are Spraying horizontally for the most part a Gravity Feed Cup will be best.
Again, if you opted for a Professional Spraygun Product designed for Professional Use, it is possible that the Spraygun could be configured to work either as a Suction Feed or Gravity Feed, but only if you consider these options from the start, as not all Professional Sprayguns can be reconfigured.
Usually Gravity Feeds are able to covert in that regard. Over the Shoulder/Belt Hang Systems are Brilliant and will work Wonderfully Vertically and Horizontally, I like them, but the problem you will come up against is that that these Systems are usually involved when a Greater Quantity of Material is Required. More than a Gun Pot, less than a Floor Pot.
Floor Pots come in Different Sizes and we have them all, but typically and usually work from Multiple Constantly Recycling Vats, in a Large Paint Mix. Each Vat has two Pumps, so one can be taken off line and completely stripped and serviced, without interrupting the Supply of Material. Hopefully you can see that the more you think and better you plan for the long term, everything keeps working, and there are less hiccups and restrictions on what can be achieved.
If you live in a Region where the Temperature and Humidity vary day to day, and that might affect the material you apply, then the Intelligent Spraygun Video below may be of interest to you. It always amazes me how so many aspects crucial to Good Guitar Building, are also highly relevant to Good Paint and Finishing.
As you will see, temperature and humidity extremes can be compensated for by utilising differing Air Cap and Fluid Tip Size Combinations (Needles?) and possibly this may be something that I trust might give David food for thought. I wondered if he may be able to simply obtain a different Set Up for his Existing Equipment, better suited to the prevailing Regional Conditions for use with Particular Types of Material?
I think it's worth looking at and understanding how the System Works, as it may spark some flash of perspicaciously helpful insight. It's a Quick, Cheap and Easy Method to Implement what may be a genuinely helpful Set Up Change that may make all the difference and be give you just what is needed.
What more could you ask for?
In regard to Compressors. I would make a number of points.
The Robotic Spaying Equipment we use, utilise Titanium Bells driven by "Turbines" to atomise the Material.
This is somewhat different from the Turbine Spraying Equipment referred to in the earlier posts from others above. It's a different kettle of fish altogether, although remarkably, neither kettles or fish are actually involved in their design and construction.
So if this seems obvious, forgive me, I am just trying to be crystal clear as people interested in Spraying will read about "Turbines" in various contexts, (Martin, Taylor and others use basic types of Electrostatic Robotic Spraying Equipment and these use Turbines) and thus may consider such Equipment addressed in previous posts, the same Turbine Equipment as is used by Major Guitar Manufacturers, which it is not.
I try to write for people who are interested in learning more, rather than simply replying to a post, because I think for everyone who posts here, there are many, many more lurkers that simply like to gain more knowledge, but are perhaps too shy to post and ask questions themselves. Whilst I have no wish to be in any way critical toward anything, particularly 3M, my concern with the Rebranded 3M Turbine Equipment, is that it is possible they introduce Hot Air into the Spraying System.
Certain Materials require a Degree of Heat so this is "not necessarily" a problem, it simply depends on what Material, you are Applying. However, as many Modern Materials applied by Spraying today of the type readers might ulitise are Water Borne (and this is increasingly the case because of Environmental Legislation), and temperature and humidity are Critical Success Factors, I would see this "System" Heat as an Undesirable and Unwanted Complication, likely to directly affect certain Materials in a negative manner, just as its being atomised, potentially affecting lay down, making it harder to predict, control and apply.
With the greatest respect, some of the 3M Systems, (I have Reps from 3M at my disposal, and very helpful they are too) seem very, very expensive in comparison to Traditional Compressors... (and although they claim highly impressive CFM Volumes I'm wondering how close to the Turbine you would need to be to retain such Volume)... But as I see it, you are limited to extremely Low Pressures at the working head of the Spraygun.
That may of course may be precisely what you want, but on the other hand it might not!
Then of course, should you ever require a somewhat Higher Pressure for certain Materials, it would appear you run into an unwanted limitation.
In practice the High CFM Volume specifications allow you to compensate for that Low Pressure with certain Materials and Smaller Products to be Finished.
The newer HVLP (High Volume Low Pressure) Sprayguns atomise coatings by employing a High Volume of Air at Low Air Cap Pressure, typically in the 1 - 10 PSI range compared to around 45 PSI for conventional methods.
This means the sprayed material has less Velocity so is less likely to "bounce back". HVLP also produces a softer spray, reduces material waste and increases transfer efficiency. However, because they require more CFM than conventional Sprayers, they need a Larger Compressor.
Just to help someone who is new to this, as I recall, if The Pressure Gauge on the Regulator is indicating 100 PSI on a Traditional Air Tank Compressor and the Air Pipe is 25 Ft long, they are likely to get around 40 PSI on a Pressure Gauge fitted to the end of that Pipe.
This is the sort of Pressure that most Sprayers will Traditionally be used to, so 1 -10 PSI must represent Thicker Material Lay Down and a Whole Different Technique of Application.
What this means in practice.
Based on my knowledge attending lectures at Spraygun Manufacturers Factories and Production Experience.
Is that they expect these HVLP Guns to be used to lay a fairly thick coat, possibly so thick it has wrinkles in it, I was told is the Correct Technique, but these smooth out.
Great for very many Products, where a Thick Protective Coat is desirable, even possibly if you wanted to initially Grain Fill with a Thick Coat, you knew would sink in, that takes forever to cure. :)
Wonderful for Furniture, Chairs, Chests of Drawers etc. and a great many Products. But to be honest, Musical Instrument are very different in many respects and with Instruments it's usually better to give lots of Thin Coats and gradually build up the Finish, applied with a Finely Atomised Spray rather than use the Typical Methodology intended for these Particular Systems, as I understand them.
Its worth noting that Traditionally, Sprayers will be used to working with Lower CFM Volumes and at somewhat Higher Pressures most often, even when using Standard Professional HVLP Equipment. So if you use this newer type of Equipment, drastic practical adjustments to working methodology may well be required, even for Experienced Sprayers.
In my experience, Sprayers of Long Standing often try to set up New Equipment, (however it is recommended to be used), to work like they are used to working, and that's, how they prefer it.
They are good enough to adjust everything to get the best out it for the Material they are Applying.
But what if you can't do that because of inherent limitations of the Systems Design?
Some years ago, a Company I was involved with was taken over by another Manufacturer.
The Paint Shop Designers of the Old Firm had built a New Shop and put in some Basic Plant, that could handle much bigger jobs than was needed. This was Deliberate Foresight!
A few years down the line, a Huge Sister Major Plant was Closed, but the Plant with the New Paintshop was Retained and today is Booming in Business. It was a much, much Smaller Plant, but was very Flexible and Versatile and could Handle Anything and Everything that could be Possibly Required.
Can you see the point?
Why buy a System Produced for High Volumes of Air and Thick Material Coating?
A System that works One Way, and thus has Inherent Fundamental Limitations to what one can do with it, By Design?
Especially, if it's a De Rigueur, Well Established Tradition, Custom and Practice that's it's better to Apply Multiple Layers of Low Volumes of Material, with the Finest Atomisation Possible?
I'm not arguing here, I'm simply trying to Promote, Profoundly Deep Thinking!
Furthermore, it has been my experience that Spraying, quite regardless of what Equipment is used, is always greatly assisted by having a most consistent quality of Air Supply.
To that end, Large Air Tanks tend to have a tremendously beneficial, Smoothing Effect on the Consistency of Pumped Air Supply, and whilst it could be argued that "Turbines" eliminate such problems and may be quieter.
Traditional Air Compressors with a Belt Driven Compressor separate from the Electrical Motor and with a concomitant Air Tank and Easily Serviced with the available Service Kits, will probably prove to be a Cost Effective, Long Lasting, Versatile Solution, and provide a Good Volume of Air for whatever you want.
HVLP Systems whatever type of Compressor is used, require Good Volumes of Air Supply however Low the Working Pressure, as do all Spraying Systems. To that end, it's worth noting as outlined earlier, that the length of Air Line, will have a dramatic effect on the Working Pressure at the Air Cap of the Spraygun.
This is something people do not take fully into account. On a link displayed on an earlier post above, we see the operator using a Spraygun with a Pressure Reading Dial at the end of his Air Line, and Before the Spraygun handle.
Some Sprayguns today, even have digital pressure meters built into their handles. This isn't meant as criticism, as I have no interest in such, and In Line Gauges as shown above, may "seem" sensible.
However, this isn't how we would normally measure the Air Pressure.
We would normally remove the Air Cap from the Spraygun and Fit an Air Cap with a Pressure Gauge adjoined to it in order to obtain an accurate reading of Air Pressure as it Atomises at the Working Fluid Tip, Needle and Air Cap of the Spraygun.
That's really the only way to be completely accurate about what the Air Pressure you are really working with. Try to think about this for a just minute. Typically, there is a Needle Adjustment Screw and a Trigger Adjustment Screw on the Spraygun.
As you know these allow a degree of fine adjustment by the operator to control the amount of Material flow and Trigger travel to limit how much Air is Atomising the Material, and balancing these, to obtain an optimum result.
If the Air Pressure is read on a Gauge, but then further adjusted, higher up the Spraygun, and after it has gone through all the small holes and the labyrinth of tunnels in the Spraygun...
(By the way, these inner holes and tunnels can be broken, squashed a little, completely crushed, blocked and affect the flow of Material and Air, and the Spraygun twisted and bent if the Spraygun flies out of the hand or is dropped on a Hard Surface..... Too often! :)
... Clearly, changes will occur between Volume, Pressure and Velocity, that will compromise a reading made on a gauge placed before the Spraygun. I visit Spraygun Manufacturers Factories and see these Products cast, hollowed out, drilled and cleaned out as they are being made.
An end of line Gauge can act as a useful guide, and tell you how much Pressure has been lost by the length of your Air Line, and also the HVLP Quick Release Connectors, (which do leak) especially with use over time, but it can't really give you a truly accurate reading of the Actual Air Pressure at the Working Air Cap of your Spraygun.
You can only get that with an Air Pressure Gauge fitted to an Air Cap. But I'm wondering whether these are specially made for us, and not easily available as otherwise Good People would not be making this obvious oversight, and simply do the best they can with what they can obtain readily and easily. It is better than nothing, much better, but don't be mislead into thinking that such a reading will give you the true Working Air Pressure, at the Air Cap.
It is useful as a Guide.
Just as at Lizard Point, Lands End, Cornwall, England.
There is a Sign Pointing Westward towards America that reads "New York 3147" indicating the distance in Miles.
Which is probably, just as accurate! :)
Brian, much of what I have written will be already completely understood by you.
However, my main concern is the Lurker, enthusiast who is keen to learn more.
The picture above, shows a Telecaster Body, Sprayed with Shellac.
For sure, it can be done!
Many Years ago, when I was a young chap, after a Steinway Piano was Blacked with Paint, a single French Polisher would spend an entire weeks work, simply applying the Final Gloss Finish, by Hand.
To be quite honest, personally, I have no problem with such a Finish. In fact, I rather like the thought of all that Hand Care.
And have seen my share of Poorly Sprayed, Weak Finish in the Centre of Modern Grand Piano Lids.
Some Manufacturers obviously haven't heard of Extension Pole Sprayguns!
Sometimes, the old ways really are best, and really can't be bettered, even if some people find fault and are dismissive of them.
But there's always a way to do, whatever job you need to do, and the optimal method, already in practise.