This is no big deal. A hundred other builders have the same thing.
This jig facilitates cutting or re-cutting a slot for a replacement truss rod. Two thirds of the vintage Harmony Sovereigns we receive have broken truss rods. We don't bother pulling the old out and replacing with an original Harmony OEM rod. (Lord knows we have bags of those.) The Stewmac #2551 is far superior in every way. We just pull the fb off and install a nice new rod. Besides, many Harmony necks need refinishing anyway. We also take the opportunity to install new fb binding.
The jig is made of two sets of three maple blocks and a 1/4 inch MDF guide. Each block set has two outer blocks which guide and align a center block. The center block in each set has a "V" cut padded with a piece of non-slip matting. Viewing the from the flat MDF guide, there are two long screws on each side centered between two other screws. These screws pull the "V" block up against the MDF guide, thereby trapping the flat surface of the neck against the underside of the MDF guide. When these four screws are tightened the neck cannot move at all.
Use a small plunge router with a Porter Cable type guide to guide the router down the part of the neck to be slotted. By far the best router to use for this is the Dewalt DW611PK with plunge base.
©2016 D.R. Hanna