Tool Fundamentals

Lapping tools

Lapping tools from Helical Lap & Manufacturing Co. provide a simple and economical solution for producing extremely fine tolerances and accuracies in bores and cylindrical parts.  Helical Laps can adapt to be used on almost any machine with a rotating spindle, such as a lathe, drill, or honing machine. Helical Laps are highly versatile tools that can be used in a wide range of materials and applications. Helical ID and OD Laps are manufactured from a proprietary grade of annealed grey cast iron with a grain structure designed to optimize the abrasive charging of the tool.  The lap incorporates a helical slot to allow for expansion and contraction of the tool. Helical Laps are primarily finishing tools to bring parts to size, reduce the rough peaks of a surface, and correct common imperfections in bore and cylinder geometry such as roundness, bellmouth, and barrel shape. The tools are used with a lapping compound (diamond, aluminum oxide, silicon carbide, boron carbide, garnet) and typically, only a small amount of material is removed. The tools should always be ordered to the true ID or OD of the part to be worked, and then they are manufactured with the correct starting size.

Helical Lap Uniform Expansion

barrel lap

Expanded Barrel Lap

Internal Laps

Internal laps mount on a tapered arbor or mandrel. The tool expands as the lap is moved up the tapered arbor. Because the internal taper of the lap is closely matched to the taper of the arbor, unlike barrel laps which only expand in the middle, Helical Laps expand uniformly across the entire length of the lap. This is a unique and key feature for achieving precise bore roundness and straightness. As stock is removed, simply tap the lap up the arbor. When Helical Laps are used in combination with our tightly graded, high quality lapping and polishing abrasives, exceptional bore surface finishes can be obtained. Standard lap diameters range from 3/64” up to 3”. Other diameters (including metric) and lengths are available upon request. Standard size tools are generally in stock.

External Lap

External lap insert sleeves are made slightly oversized to allow for starting clearance and are also designed to uniformly contract as the external lap holder is tightened. Worn lap inserts can be quickly replaced.


A special note about abrasives. It is possible to use Helical Laps to produce desired finishes easily and quickly; however, if more than one abrasive size is used, in order to achieve the desired finish in the least amount of time, it is highly recommended to keep separate laps dedicated to each abrasive size used. By following this recommendation, you will avoid having to go back to remove scratches produced by larger size abrasive particles.

Tool Demonstration Video


barrel lap
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