Line-boring for adjustable shelves
by Jon Elvrum
Beginning with the ridiculous, I know of companies that rip strips of pegboard, clamp them top and bottom and drill through to establish a line of holes. The result is visually acceptable, and works, and the labor bill is horrific. Permanent jigs can be purchased or fabricated, which are simpler than the ripped pegboard and reusable, but the labor bill is still huge.
Hinge machines offer 5-7 spindles (geared heads which can be alternately used when not hinging doors). These machines have fencing and stops and integrated indexing pins. This is the beginning step of serious line drilling.
You need to recognize that there are 2 types of line drilling: simple line drilling and SYSTEM line drilling. The difference is subtle and profound.
SYSTEM drilling demands that all registration occurs from the same edge reference (the distance from the edge to the parallel center line of the drill head).
Line drilling allows for the panel to be rotated and drilled from each edge by a single head.
Given the normal inconsistency of panel processing (non squareness, and tensioned panels), in line drilling exact hole location CANNOT BE ASSURED, whereas in SYSTEM line drilling, once reference edges and offests (stops) are set and locked down, proper joinery cannot be missed.
There are also single-head system drills. The head will move at a right angle to and from the fence on a secure stop system and all drilling will honor the single edge.
System drilling is automatically achieved with a two head machine drilling with rigid first stop control followed by secure index pin advance for longer panels. Any other system has the possibility of panel flexing, producing relatively minor, but very troublesome variations.
Jon Elvrum, Director of Distribution and Sales at Ritter Manufacturing in Antioch California, is also a well known author and consultant to the cabinetmaking industry. He has written numerous articles on the 32mm cabinetmaking system and production woodworking in general.
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