What you do in R&D matters when it's jig time...

Okay, you're working on coming up with your own design...  What should you keep in mind?

Here are some deep thoughts from a shallow mind :D   Some of it, may not be all that palatable, but its the truth.  You've heard the saying, "garbage in = garbage out"?   Yeah, usually it is used in the context of computers, programming. and data analysis - and you're making a call with a file and sand paper,  and your hands, eyes, and ears... not some computer right - so why does it matter?   True, you aren't using a computer, CNC, or a program to make your prototype, but when it comes to me for a custom jig, none of those things you used are available to me (your hands, eyes, ears, thought process, opinion, etc...) so I have to rely on what?   EXACTLY!!!   Computers, programs, and measuring devices.   So "garbage in - garbage out" really does apply to call making, especially when we're talking custom jigs!

Overview:  What you are doing now, in the process of coming up with your own design, is tedious, time consuming, frustrating, confusing, exciting, maddening, rewarding, and a ton of other words...    But one of those words is definitely not "easy".  Don't sabotage your efforts by cutting corners in the beginning!  Just because it may not pan out doesn't mean it wont pan out.  Much of what you do before you ever even start on the tone board is going to have a direct impact on the making of a custom jig.   Having done custom jigs for a lot of years (over 20 years now - holy crap!), I can usually come up with something decent, even in the worst of conditions, but man oh man, why risk something you have worked so hard on, because you were in a hurry at the start.

Let's go over the main issues I see the most.

The Tenon of the keg:   Are your tenons accurate?  Cylindrical?   If they aren't - you are directly effecting the potential accuracy of your jig.    The tenon is the base line or locator point for measuring the tone board.  Any imperfection here will be translated into the mapping of the tone board.   If your tenon is tapered, I may, or may not, be able to identify it and attempt to account for it with shimming during the mapping process.  But it is an absolute "best guess" situation.   I can't measure every spot along the tenon to check what your diameter was prior to cutting the tone board.   Any place that the height (measuring from the bottom of the tenon to the surface of the tone board) is less than half of the diameter - it can not be easily checked for diameter.   That means the one place that is key for the tenon to be straight and accurate - the tip of the board - can NOT be checked.   Same with back under the cork notch... and back there - its not only important, its hard to be an accurate height of the board under the cork tang.

Taper of the tenon, whether consistent or not, is a huge influence on how good your custom jig will replicate your prototype.   Same if its a "wavy" tenon.  A wavy tenon, where the diameter changes willy nilly without regard to anything can be huge drama - particularly the areas that are larger diameter.   If you have one spot in the middle that is notably larger than the rest - now you have a pivot point and whose to know where and how much to shim either side of it to make the tone board sit in the correct rotational position (think tip rotating up or down vs sitting parallel)

Size of the tenon is much much MUCH less important than the fact that it is straight, not tapered or irregular.   But, the size will come into play...   If your prototype tenon is larger than the bore of the jig (this happens sometimes, since many barrel bores are oversize and the keg gets fitted to the barrel before the tone board is started), then the prototype will NOT fit in the jig to do a final comparison check.   If your tenon is undersize, it can create multiple issues.  The main issues with an undersize tenon (irrelevant of your choice of option 1 or 2 for locating the board on the jig in the questions on the jig page) is fit of your tenons to the jig, and the ability of that tenon to move in the jig when you are cutting the tone board.  Not only side to side, but also increased movement of the tip compared to the back in the up/down direction.   Add in some taper to this, and your set screw in the jig could move the tenon around a ton!

Bottom line...  Focus on good tenons now!  Not only will you get better and faster at it as you learn, but the end result, will be nothing but a benefit!

The Tone Board Surface:   There are multiple things in play on the tone board surface - and they all affect the mapping.

• Tone Board Symmetry:   One side of the tone channel compared to the other - right and left if you will.  Yes, there WILL be some asymmetry in a hand made board.  But the more attention you pay to keeping it flat and even across the board, the more representative the jig will be.   The mapping process includes some "calculations" for asymmetry and weighing in the amount and its location.   The result is usually quite good - but it opens the door for differences and differences equal changes and there is no way to know what the changes will be until its done.
  
  In hand filing, the tendency is for the tone board to be lower at one end on one side and higher on the opposite side and end.  Its how physics and your body work... and it takes practice and skill to avoid falling into the traps that it can create.  The most notable is the "rotation" that gets created when this happens.    During the mapping process, I see that "rotation" and the calculations that go into the mapping attempt to "average" (for lack of a better word) it out since the jig can not have that rotation.   I don't think there is any way for a person to NOT have any asymmetry in their tone board...  but they sure can try and keep it to a minimum.
  
  
• Smoothness:   I see a lot of boards with gouges, nicks, dings, and other assorted cuts that didnt clean up in final tuning.  Be it from the band saw kerf, an errant file swipe, or what have you, if its there on the board, its going to be in the mapping data.   I can correct some if its obviously unintentional, I am instructed to "fix it", or necessary for the making of the jig - but I tend to err on the side of caution - if its on the board it stays in the mapping, and thus, cut into the jig.  The better the surface of the board, the better the map.
  
  
• Grooves:  Spit grooves as they are commonly referred to are usually fine...  But if they are on the prototype board for mapping, AND they are extremely close to the tone channel, it can force the mapping area to be moved to the outside of the grooves instead of up close to the tone channel.   And if you think about the symmetry mentioned above coupled with physics and human nature, its pretty easy to see that the closer to either edge of the tenon you get, the more inherent variation you are likely to see.   Its easy to irregularly remove material out at the edges than it is in the center right next to the tone channel.   When placing grooves in the tone board, keep that in mind...  leaving an extra .030 of board surface next to the tone channel on each side could be the difference between mapping in the sweet spot or being forced to map out on the edges.
  
  
• Cork Notch:   Often overlooked, regularly ignored, and seldom focused on - the cork notch does some important things...  and in the mapping process, it becomes a key point.  If the back of the notch is not squared up, and the corners cleaned up to a nice and tidy corner - the location of the back of the cork notch becomes a bit of a fudge factor...   I just have to do my best approximation.   In the grand cosmic scheme of things, it is not end of the world stuff... but it can matter.   When mapping, I use the end of the cork tang (face that is typically flush with the part of the cork that faces out) as the main locating point.   That leaves the wiggle room back under the cork where it has much less of an effect.  But, the sharper your corners are, and the flatter the back of the notch is, the easier it is to get good dimensions during mapping.

Shape and Features of the Keg:

There are a few places on the keg that need to be clean, true, and smooth for reference measurements, and I can see why some of them are easily overlooked - so Im mentioning them here.

• End face of the keg:   The exhaust end face - the face that would sit on the table if you were to stand the call up on the keg.   Occasionally Ill see prototypes with the end being saw cut.   They are never perfectly square, usually rough, and that causes problems.   I measure from the exhaust face to get multiple dimensions - and have to do it in different positions in relation to the end face.   If that surface is not perfectly square and smooth - one measurement could be way off just because of a groove from a saw blade or being out of square.  Luckily, the solution is super simple!!!   Just be sure to true the face on the keg when its on the lathe.   As long as the entire face gets the sawn edge cut off, by default, it will be square to the centerline of the lathe - irrelevant of the shape.
  
  
• Shoulder on the keg/Using a spacer to locate in the jig:   Some use an o-ring and a shoulder on their keg to locate the keg in the barrel.   This is just fine!  But remember... to get that dimension - it has to be measured!  It needs measured to figure out the size of the spacer, and if that surface is not clean cut, and square to the tenon, then now its a crap shoot as to where along the irregular surface I should measure to.   Best practice is to be sure that your shoulder face is turned, cleaned up, and as square to the tenon as you can make it.   It only makes things easier and better when it comes to the jig and spacer.
  
  
• O-ring Grooves:   Pay attention to where you put your o-ring grooves!   Remember, the jig is going to have a set screw to hold the keg in while being cut - watch where you put your o-ring.   The absolute minimum distance for the pedestal (area between the back of the jig and the back of the cork notch) is 0.200" - we will not warranty a jig with any narrower of a pedestal due to strength issues of the jig itself.  As well... keep in mind the integrity of your keg!   The closer the o-ring groove is to the back of the cork notch, the weaker the cork tang will be (cork tang is the top portion of the cork notch).   In our years of experience, 0.200" is the point at which the groove is as close to the back of the cork notch without compromising the strength of the cork tang.  

Hopefully that helps in your trip down the rabbit hole!!!   Remember to have fun while you're at it!