There is sometimes confusion over the difference between Knurl Cutting and Knurl Forming and what is the best application to use for each method.  Here's a quick synopsis of the differences and ideal application solutions. 

For a Cutting Knurl, the knurl wheel’s axis is rotated to provide a leading edge, where the sharp edge will cut the knurl pattern into the work piece. Additionally, with a Cutting Knurl, less pressure is required for the operation and higher speeds and feeds can be used (use the same cutting data of High Speed or Cobalt turning tools). When Knurl Cutting, use full faced knurl wheels with a sharp edge, to penetrate into the work piece and cut the knurl pattern.

In Forming Knurl, the knurl wheels axis is set parallel to the work piece axis, and forced against the work piece, displacing the material to form the knurl pattern. A large amount of pressure is required to displace the material that forms the knurl pattern. When Knurl Forming, use beveled edge wheels to protect the edge from chipping which will create a smooth surface finish.

Double Tracking means that the knurling wheels are not tracking properly. In this situation, the knurling wheels will create a different pattern than the original design and may overlap or "double die"

There are two main causes of a knurling tool double tracking: 

1. The knurl wheel isn’t set deep enough into the workpiece.  Dorian Tool recommends increasing the depth. The knurl depth should always equal 35% of the knurl pitch.
2. The circumference of the work piece blank is not a multiple of the knurl pitch. To correct this, you must change the before-knurl diameter of the part or select a knurl wheel with a different pitch.

Dorian Tool  has developed a “Knurling Calculator Spreadsheet” that can calculate all of the parameters to avoid double tracking.

If you would like to request an electronic copy send us a note in the comments section below or, for faster results, in the form you get when you click the button below.  We'll quickly get a spreadsheet sent over to you!

Tech Tips: Dorian Tool

The lathe is one of the oldest and most versatile machine tools. Few shops can do without the processing capability offered by the CNC lathe. Long before automatic toolchangers were applied to milling machines, the lathe had a multiple-tool configuration. The tool post gave lathe users the ability to select from several mounted tools and index them as needed during a turning cycle.

Many CNC lathes are still offered with the manual tool post design. Shops can generally purchase these machines at very reasonable prices. Some shops have found a need to increase the flexibility of these lathes by adding an indexable turret in place of the manual tool post.

Installing such a turret can give a real productivity boost for shops running on Colchester, Harrison, Nardini, Bridgeport, Southwest Industries and other popular combination CNC lathes. With a CNC turret, more tools can be carried at one time. Programming the turret brings the right tool into the cut at the right time automatically. No stopping the machine to index a manually operated tool post is needed so cycle times are reduced for applications that use more than one tool.

For many turning applications a manual tool post has sufficient capacity. But any shop that is looking for a through-put gain in their turning operation without a major investment in new machine tools, can benefit by considering installation of a CNC turret.

The issue is more about processing efficiency than tool capacity, says lathe accessory maker, Dorian Tool (East Bernard, Texas). A turret configuration allows the machine tool to carry tools mounted in operation sequence. Sometimes turret tool capacity is sufficient for more than one job to run without a tooling setup in between. But significant production time is saved by the ability to automatically index the tool turret as part of the lathe's part processing program.

The turret offered by Dorian Tool is a bi-directional unit. Indexing therefore takes the shortest part from one tool station to another. It's operated by a three-phase 220/380 volt 50/60 hertz electric motor through an anti-backlash gear drive. Tool position is controlled by an absolute encoder which tracks actual position of the tool station. The working position of the turret can be right or left hand depending on the unit location ahead of or behind the lathe's spindle axis.

A proximity switch detects tool position and verifies turret lockup before a go signal is sent to the CNC. A three-piece Hirth-type coupling is used to hold the clamped turret radially. The turret indexes, station-to-station under one second. Fast index is achieved by not lifting the turret face. The entire indexing mechanism is housed in a Meehanite grade casting that helps damp cutting induced vibrations.

Four standard sizes of turrets are available. They are 100, 120, 160 and 200 mm respectively. Toolholding capacities of eight or 12 stations are available in ID, OD or combined tooling configurations.

Tool capacities range from 12 to 32 mm (1/2 to 1-1/4 inches). A VDI turret disk is available. Both turret disks have an integral coolant delivery system.

Simple electrical and coolant connections easily interface with the lathe. If an indexable turret is the difference between a CNC lathe and a CNC turning center, then this accessory is a cost effective way to up-grade your lathes.

Tech Tip: Dorian Tool