Gartech Quick Ref: Tab Knife Holder

One of the simpler, more basic items we incorporate into our designs is the adjustable tab knife holder for leading and trailing chop-out blocks (or tab blocks). Mounted on the lap (or glue tab) head, the chop-out block is often a two-piece design. The chop-out block mounts to the head and gear ring. Mounted to the chop-out block is the tab knife holder. We’re betting you can guess what this part does.

Tab Knife Holder details

The common design of the tab knife holder includes (2) setscrews and (1) socket head cap screw (bolt). The bolt applies side pressure against the tab knife. We design our tab knife holder to provide a clamping function, to maximize pressure against the knife. This function is the same on the leading and the trailing chop-out blocks.

The setscrews allow for setting the height of the tab according to your needs. You’ll want to use setscrews that are long enough to provide stability, yet short enough to keep from digging into the tab from the top of the tab knife holder.

Another feature in the tab knife holder is that the setscrews allow for changing the parallel height. If an anvil is worn or the board warped, adjusting the angle of the tab knife sometimes helps to offer a better cut. The tab knife holder is limited by the male knife, but a slight angle can still be achieved by adjusting one setscrew more than the other.

Our last point in this entry, please notice the tab knife. Along the serrated edge, you might observe that one corner has been notched. In our design, this notch allows clearance from the 3/32″ female knife on the lower lap head. Depending on your tab knife manufacturer’s specs, the tab knife might have a bevel on that notch that further cuts the last fiber of paper. If you notice the corner of your tab knife has become bent, double-check the height of the tab knife holder and ensure the notched corner of the tab knife still clears the 3/32″ blade.