All Shop Floor Operations References

Preset, Quick-Change and Adjustable Tooling for Turning Machines

Thursday June 01, 1995
Introduction

Ideally, tooling should attach to a machine like the bayonet on the end of a rifle -- quick, sure, and precise. Preset, quick-change, and adjustable tooling can achieve this ideal to a greater or lesser extent, depending on the specific application. Use of this tooling can result in cost savings through such things as:

  • Reduced labor hours
  • Increased machine hours available for production
  • Reduced skill and training requirements for shop people
  • Improved quality
  • Reduced operator error
  • Reduced scrap

All this comes at a price, however, and applications should be carefully evaluated to assure that the investment can pay for itself.

Preset Tooling

The key attribute of preset tooling is that its location in the machine is known with a high degree of precision. Once such a tool has been attached to a machine, it will produce the desired predetermined dimension without adjustment. Presetting is done off the machine, and requires that tools have a means of adjustment. In addition, the method of attaching them to the machine must be repeatable and highly accurate. Presetting is often employed on end-working tools, but can also be used for cross-working applications.

Preset tooling saves time during setup, as well as when tools are changed during the job’s run, by reducing or eliminating test cuts, measurements, and adjustments. On screw machines in particular, where the “brass hammer method” is often used, these adjustments require either substantial skill or substantial time. The amount of time saved through the use of this tooling has to be balanced against the time required for presetting. However, even if there is no apparent reduction in labor hours, there will be an increase in the number of hours available for production on the machine. This is because presetting is part of “external” setup or operating time. That is, it can be done while the machine continues to make pieces. Whether the benefits of this type of tooling come in the form of reduced labor or increased uptime, they may be most significant on newer, more expensive, advanced technology machines which carry a higher machine hour rate.

In this report, preset tooling has been handled separately from “quick-change,” which has been handled separately from “adjustable,” etc. The purpose of this is to be clear about exactly which benefits are inherent in each type of tooling. However, in actual practice these types are commonly combined, with examples such as “preset, quick-change tooling,” or “quick-change, adjustable tooling” coming to mind.

There is a question regarding the feasibility of this tooling on some cam machines, since the end points of tool slides are not necessarily predictable on a given job, or repeatable from one run to the next. In some cases this is due to small differences between “identical” cams which are used interchangeably. In addition, on single spindle machines the high and low points on the lead cam may not be exact, although some presetting systems can correct for this. These problems can be overcome by purchasing new cams to closer tolerances; but for the shop with a large inventory of existing cams, this may not be cost effective. Another option is to provide a means of making a graduated fine adjustment on the machine, either with an adjustable tool holder or with an integral adjustable slide, although this will reduce the benefits of this tooling somewhat.

Pre-Gaged Tooling

Pre-gaged tooling is a variation of preset tooling, but lacks its ability to be adjusted off the machine. It is made to close tolerances with only small differences between “identical” tools. Prior to being set up, this type of tool is gaged and variations from its nominal dimensions are noted. Generally it is used on CNC machines, and adjustments for these variations are handled by the tool compensation offsets, in many cases without the need for trial cuts and subsequent adjustments. While not common, this concept can be applied on cam machines as long as there is a way to make graduated fine adjustments, either within the tool holder system, or on the machine itself.

Qualified Tooling

Qualified tooling is another variation of preset tooling. All of the components that comprise a qualified tool are made to close tolerances; and because of this, it will cut very near to the desired dimension. One of the most common types is the carbide insert/insert tool holder combination. Installed in the machine, any combination of “identical” inserts and tool holders will generally be located within ?.005” of their nominal dimension. Like the pre-gaged type above, this tooling is not adjustable; and there must be a way on the machine to compensate for these small variations, following a trial cut and measurement.

Quick-Change Tooling

The primary characteristic of quick-change tooling is the ease, speed, and convenience it provides in terms of removal and replacement. In addition, it generally fastens to the machine in a repeatable fashion. The very fact that it is quick acting allows this tooling to save time both during setup, and when it needs to be changed during a run.

Unlike quick-change collets, most quick-change tooling can also be preset, pre-gaged, adjusted, etc. With this combination of qualities it is possible to exchange a new or “renewed” tool with one that needs sharpening, and have the machine producing again in a moment or two. In some instances it may even make sense to replace a slightly worn tool in this way, rather than taking time from production for a trial-and-error, on-machine adjustment.

Adjustable Tooling

Adjustable tooling is capable of shifting the cutting edge (or other functional surfaces) of the tool in one or more directions so that the desired dimension is produced on the workpiece. The means to do this must be graduated so that any shift can be made accurately and with predictability. This permits the number of trial cuts, measurements, and adjustments made during setup or operation to be reduced. Adjustable tooling is often a more practical alternative for traditional cam-type machines. It is more flexible, and can accommodate the variations in cams noted earlier in this report. Also, it may be the most practical way to adjust for tool wear in some situations, or compensate for deflection of the part or tooling. Some tools provide an adjustment to correct for taper in the workpiece.

Selection/Cost Savings

There are a huge number of variations in machine design, workpieces, tooling design, etc. that make it difficult to come up with useful generalizations for selecting this kind of tooling. Instead it is recommended that each shop evaluate its particular situation and select the tooling which offers the greatest cost savings. The first step is to study what is currently being done to make sure it is really understood by everyone involved. (Members who have done this note that it can produce surprises.) This is also a good time to note such key selection factors as the type of machine, its condition, how it is currently tooled, investment in that tooling, machining requirements for the parts being produced, workpiece material, and lot sizes. Also look at plant personnel, including the level of their existing skills, ability to implement new concepts, and at what point they will be retiring and need to be replaced by younger workers.

Next develop accurate and complete costs for several typical parts the way they are currently set up and run on the machine being studied. Be on the lookout for potential savings, using the list at the beginning of this report as a guide.

Evaluate the tooling alternatives described in this report, as well as any others available, and select several that appear promising. Then make realistic estimates of what your costs would be to produce the parts studied above using each of the alternates you selected. Try to put a dollar figure not only on direct labor savings, but also on the other benefits mentioned earlier, especially reduced skill and training requirements, reduced scrap, and having more machine hours available for production. Weigh the purchase cost of each alternate against the savings in manufacturing costs it can produce to decide which one is best, and whether or not it is a good investment.

Undoubtedly, it may be difficult to quantify the benefits of things like reduced operator error, or reduced training requirements. Nevertheless, try to take them into account. Other potential benefits, perhaps even less tangible, should also be given some weight. One example might be the ability to satisfy a customer's Just-in-Time requirements. Another example would be taking the skill and art of “brass hammer adjustments” out of the process, and replacing it with the science of a graduated dial. This is something that may be essential with the younger, less skilled workforce many companies will depend on in the next few years. Finally there is significant value in new technology itself, the progressive message it sends to people both in and outside your plant, and the positive response they can have to it, whether they are customers, potential recruits, or existing employees who believe in the company they work for and want to make it successful.

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