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The firearms industry is currently a robust sector of the U.S. industrial economy. To assist manufacturers of small arms with growing volumes of barrels, Precihole Machine Tools, distributed by Absolute Machine Tools Inc., has introduced a dedicated manufacturing cell to improve the efficiency of producing barrels. This cell consists of equipment to perform all necessary operations on the ID to convert a bar of metal to a barrel, e.g. gundrilling to get the basic hole, pull reaming to improve the concentricity and finish of the hole, and button rifling to carve the grooves needed on the barrel.
Depending on the needs of the operation, the Precihole barrel manufacturing cell can be configured to be scalable to handle manufacturing 2500 barrels to 15000 barrels a month on a two-shift basis. A single dedicated cell requires minimum operator input, guarantees performance, and maintains high quality output.
Each machine in the cell performs a specific function. The first operation is gundrilling which produces a concentric hole to the barrel centerline for all small arms calibers such as 0.223, 0.308, and 0.45. Length of drilling can be up to 40 inches. The Precihole gundrilling machine model GVN 12C/4-100 has four high precision spindles powered by high torque spindle motors. Part counter rotation improves the drilling axis, resulting in extremely straight holes. The tool RPM and feed rate are controlled by a Siemens PLC System that has sufficient memory to store up to 100 programs. The coolant system is re-circulating and incorporates a magnetic separator, chip conveyor, bag type 25-micron filtration unit, and an oil chiller which maintains the oil at room temperature.
After gundrilling, the barrels are pull-reamed on a four spindle pull reaming machine. The pull reaming operation generates a straight axis and improves surface finish. The shank is passed through the barrel. Then the reaming tool is attached and is pulled through the barrel. By "pulling" rather than "pushing" the tool, concentricity of the barrel is high. The coolant system is the same as the gundrilling machine and provides chip separation and chilled coolant.
The last operation in the cell is performed on a single spindle button rifling machine. The barrel is loaded in a chuck and a carbide button is pulled through barrel while the barrel is rotating precisely at the certain RPM by a servo motor. Rifling twist ratios are adjustable from 1-5 to 1-60. This is a very quick operation compared to the drilling and reaming operations.
Related Glossary Terms
- chuck
chuck
Workholding device that affixes to a mill, lathe or drill-press spindle. It holds a tool or workpiece by one end, allowing it to be rotated. May also be fitted to the machine table to hold a workpiece. Two or more adjustable jaws actually hold the tool or part. May be actuated manually, pneumatically, hydraulically or electrically. See collet.
- coolant
coolant
Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.
- feed
feed
Rate of change of position of the tool as a whole, relative to the workpiece while cutting.
- gundrilling
gundrilling
Drilling process using a self-guiding tool to produce deep, precise holes. High-pressure coolant is fed to the cutting area, usually through the gundrill’s shank.
- inner diameter ( ID)
inner diameter ( ID)
Dimension that defines the inside diameter of a cavity or hole. See OD, outer diameter.
- shank
shank
Main body of a tool; the portion of a drill or similar end-held tool that fits into a collet, chuck or similar mounting device.
