Published 11/15/2010

Are There Variations with Your Cutting Tools?

If you have jobs that are repeated on a given CNC machine, you probably want to ensure that they can be run over and over again without machine downtime. Indeed, you probably want to consider your programs as “proven” to be secure in the notion that you can consistently run them at any time without problems.

Mike Lynch

Founder and President, CNC Concepts Inc.

Any variation that occurs from one time you run a job to the next will likely cause a so-called “proven” program to fail—causing downtime and requiring something about the job to be changed.

One of the most common variations that contribute to failed proven programs has to do with cutting tools. When a cutting tool is assembled differently from one time a job is run to the next, even minor variations can cause problems with machining, including required cutting conditions, surface finish, tool pressure and tool life. More substantial variations can cause vibration/chatter and, in worst-case scenarios, breakdowns.

The more variety you have with cutting tool components, the greater the potential for variations in cutting tool assemblies and the more challenging it will be to ensure consistency. For example, consider how many ways you could build up a cutting tool, maybe a drill, that has a 0.5-inch-diameter straight shank. The drill could be held directly in a collet holder with a 0.5-inch collet. Alternatively, any number of different-length collet extensions could be held by the collet adapter first. Also, two different collet extensions could be used. I’ve even seen setup people hold a straight shank drill in an end mill holder.

If you have multiple machines that are similar to one another, it’s likely that your company has ordered many similar, but slightly different cutting tool components. It is not uncommon to order a special cutting tool component with a specific job in mind only to end up throwing it into the same drawer as similar components. The first time there’s a shortage of similar components, its special application is forgotten or disregarded. Of course, when it is needed for that special job again, it is probably being used for another job.

Another contributor to having a variety of similar, yet slightly different tooling components is related to tooling supplier deficiencies. Your supplier may be out of stock for a needed component, which requires you to order something similar that will work. Any compromises will lead to even more potential choices when setting up cutting tools in the future.

This problem is further compounded when setup documentation is not explicit about which cutting tool components must be used. I’ve seen many machining center setup sheets that specify the perishable cutting tool name (such as 0.5-inch-diameter cobalt drill), and leave it to the setup person or tool setter to determine which components (adapters, extensions, collets and others) are used to assemble the tool. In this situation, the setup person will often choose what is readily available, regardless of whether the components will facilitate the most efficient machining.

Some may argue that with certain cutting tools, the specific components used for assembly aren’t all that critical or that the machining operation isn’t difficult. This may be true for certain tools, but which ones? As long as setup documentation specifies whether a given cutting tool’s components are critical, you should be able to eliminate problems with proven programs. However, I’ve never seen a setup sheet with this kind of specification.

Again, the more potential variations you have in cutting tool setup, the more important it is to specify exactly which components are used for each cutting tool. You must also confirm that there are enough components for the number of jobs that use them, even if they are run simultaneously on different machines.

It can be difficult to specify every cutting tool component on a one-page setup sheet. A separate tooling list may be required. If you use a list with component ID numbers, be sure that they are marked clearly and that everyone can determine what they are. Alternatively, you could create a separate chart that shows a picture of each one. Again, make it easy for people to determine whether they’ve picked the correct components—right down to the pull stud.

The best cutting tool documentation I’ve seen provides a separate drawing for each tool. The entire tool assembly is shown with a designation for each individual component. It may be not be feasible to include this info with each setup, so companies that use this technique often maintain a separate cutting tool book that includes all of the drawings.

It doesn’t matter which specific techniques you use. The idea is to ensure that all cutting tools are set up in exactly the same manner each time a given job is run. If you don’t, you cannot expect to certify your programs as proven.