About Duplicating


What is "duplicating"?  How is it done?  Is a duplicated stock still 'hand carved'?
Many factory stocks today are cut from 5 axis CNC machines from a CAD drawing.  The original Cricket stock is an example of this kind of product.  Laser precision, recessed cuts, minimal sanding required to finish.  This is not duplicating.
Duplicating refers to using a pantograph like machine to carve a copy from a 'master'.  A duplicator is very much like a basic router pantograph machine, but with the ability to move vertically as well as back and forth, and the ability to travel along the long length of a gunstock.  As well, a gunstock duplicating machine has the ability to rotate the master and the work together, and lock them in place at any point of rotation.
Some duplicating machines do not allow the stylus (the thing that follows the master) and the router to move laterally and instead the master and the work continually rotate under the stylus and router.  The carriage with the stylus and router move slowly along the stock from one end to the other.  The significant advantage of machines like this is the push a button and walk away nature of it.  A disadvantage is the master is not supported along it's length and can flex.  This flex needs to be accounted for in the shape of the master so the stock gets cut to the dimensions intended.  Also, this type of machine is not well suited for complex shapes or near-vertical pistol grips.  Many very simple stocks that come on lower priced airguns are cut by this round-and-round method.
Some duplicating machines are massive multi station machines powered by a large central motor driving belts to router heads with counter rotating cutters to minimize cumulative torque effects.
My duplicator is my own design of a blend of several types of machines that have been used in the past, with a few of my own ideas thrown in.  The one I'm currently using is my second design.  It is a single station duplicator and uses a 3 1/2 hp variable speed router.  It has 5 axis of movement: the work and master rotate keyed together, the router/stylus move left and right, forward and back, up and down, and tilt.
Using a duplicator to create a gunstock is a hand carved operation. I make a master by hand for every project with wood and Bondo (a thermo-setting clay).  Basically I'm a clay sculptor, and copy what I create into the final piece of wood.  
But the hand carving is not finished when the master is jigged in the duplicator, because using a duplicator like mine is absolutely a hands on skill.  I manually carve every bit of the stock, sitting at the machine, carefully, painstakingly, carving the entire stock.  There are still plenty of mistakes that can be made.  It is by no means 'easy'.  The master gets braced in three dimensions to prevent flex.  Every time the stock and master are incrementally rotated the bracing gets adjusted.  The rotating capability gets locked at every incremental rotation.  Cutting only occurs perpendicular to the work, so for every rotation, there is only a limited area that gets carved.  Inletting is an important detail oriented task.  Aligning the master so as to fit the blank and it's figure is another detail oriented task that is super important with little room for error.  You don't want to carve the stock and find out the bottom edge of the cheekpiece is outside the blank, or you missed the most interesting bit of figure!