Stringy Chips Cured Easy

     Everyone knows that stringy chips are a nuisance. Ductile metals, like unleaded brass, can be nasty due to their propensity to form a continuous chip.Today's carbide tooling and higher cutting speeds can create the rapid formation of a "birds nest" of stringy chips. This can quickly overwhelm the screw machine's tooling zone and require a stoppage to clear the mess. STOP and figure what this may be doing to your bottom line profits.

Machine Stoppages Add Up Fast

If you assume a shop rate of $50 an hour, assume stringy chips are causing an operator to shut his machine down three times an hour for five minutes at a time...it's costing you $12.50 an hour. That's $100 in an eight hour shift. Five days a week! You can observe your own situation, plug in your numbers and you'll probably be surprised at what the lack of chipbreaking is costing you. What can you do about this?

Pick the Low Fruit First

First, pick the low hanging  fruit. Experiment with  the tooling geometry, feeds and speeds, targeted coolant, and high-speed vs. carbide tools. If these things don't work, turn your attention to a Non-Plunging chipbreaker cam. Plunging chipbreaker cams aren't new. There has been a long established practice of using a bench grinder to carve "divots" in the cam path. The intended consequence is to get the tool to pull back or hesitate long enough for the chip to break.

Pecking LIke a Woodpecker isn't the Answer

The problem with this approach is twofold. First, the case hardening of the cam is ground out leaving a soft spot in the cam track. This area of the cam will quickly deteriorate with each revolution of the roller. Second, the manual approach to inserting the chipbreakers into an existing cam rise creates a plunging chipbreaker. By notching a previously milled cam path (see Figure 2), the roller has to climb out of the chipbreaker higher on the cam path than where it dropped in. The result is that the tool is forced forward and jams back into the part in a sort of pecking action. This is hard on the tooling, hard on the cam and hard on the machine.

Non-Plunging Chipbreakers Equal More Parts per Hour

Modern Cam has successfully solved this problem with our Non-Plunging chipbreaker cam (see Figure 1). Our cam milling program incorporates the rise and chipbreaker so that the chipbreaker has an exit point for the roller to climb out lower than where it dropped in. The effect is that the tool returns to its cutting action without the pecking. One benefit is that the chip is more effectively broken and tool life is extended. But the major benefit is that more parts per hour are dropping off the machine. In addition, the Non_Plunging cam path and chipbreakers are flame hardended to prevent the cam track from wearing prematurely, thus extending the life of the cam.

 MCT Non-plunging Chipbreaker Cam:

 Figure 1.