DS Fixture
Disc Sanding Fixture
Vertical hammer shank prep.
The disc sanding fixture is for selecting an exact clearance for the glue joint. Even with batch variation in shank diameter and out-of-round conditions, hammer shanks can be dimensioned within a thousandth of an inch to a final selected diameter that gives a predictable and consistant result when gluing.
In contrast, knurling for glue clearance can cause an uneven and unpredictable pressure as the moisture in the glue swells the wood that was compressed. Minutes later this swelling action can randomly force the shanks away from the fences resulting in time lost to frequent corrections required to preserve the alignment.
Since every glue has its own unique properties and strength in gap filling, care is taken to use the least amount of reduction as possible that will still give room for the glue and prevent a glue-starved joint.