Senior Engineer at Rathburn Tool & Manufacturing

One of the most problematic concerns found in turning are stringy shavings. They are dangerous as they are extremely sharp and cause safety concerns with associates cutting themselves trying to pull those shavings out of the machine. They also create downtime when the shavings wrap around machine components.

How do you break the chips?

Some materials are more prone to stringy shavings than others but the concepts remain the same: how to overcome it.

1st—Choose a cutting insert with the proper chipbreaker for the job. All cutting tool manufacturers have charts showing what depth of cuts along with speeds and feeds to run your inserts at. I have found that shops will disregard the information in those catalogs thinking the numbers are inflated to make their inserts look better. That could have been a problem in the past. But today the information in those catalogs is accurate and will give you a good starting point.

2nd—Nose radius. Here is where people trip up. In order for the chipbreaker to work you have to have a depth of cut greater than the nose radius of the insert. As an example, shops will leave 0.05″ on the diameter for finishing and use an insert with a 0.031″ nose radius. You will almost never break the chip. Make the adjustment and leave 0.065″ for finishing and see the result. Or change the insert to a 0.015″ nose radius. Of course, changing your nose radius will also have an effect on surface finish, but that is another blog.

3rd—Feeds and Speed. As you may know, speed kills tool life. But if the above has not corrected the problem you need to play with the cutting speeds. Increasing the speed will cause more heat into the chip thus making it easier to break. On the other hand, if you get too much speed the heat will increase to the point that it will weld itself on the insert. So, you have to experiment. Playing with the speed is always the last on my list of fixes. It generally means you have a difficult material to work with. Feedrate is more forgiving. But if you start out and pick the feedrate in the middle of the chart, from the catalog, for the insert that you picked out you will be safe.

Rathburn Tool & Manufacturing has been solving complex milling and machine challenges for more than 35 years. For more information or to discuss milling issues, please contact us at info@rathburnmachining.com.