Lesson 12 Tasks Required To Complete A Production Run. Tasks Related Complete A Production Run

Transcription

1 Lesson 12 Tasks Required To Complete A Production Run Once a job is set up and the first good workpiece is efficiently machined, the rest of the workpieces must be run. Completing a production run is the job of a CNC operator though the same person who sets up the machine is often the person who completes the production run. A misconception exists about the difficulties related to completing a production run. Many manufacturing people feel that running out a job simply requires part loading, cycle activation, and workpiece removal. In reality, there is usually a lot more to it. With an understanding of what it takes to set up a CNC machining center, let s turn our attention to what it takes to run the rest of the workpieces in the job. Here is a list of the related tasks: Done during every cycle: Load a workpiece Activate the cycle Monitor the cycle to ensure that cutting tools are machining properly (first few workpieces only) Remove the workpiece Clean/de-burr the workpiece Perform specified measurements (if required) Report measurement results to statistical process control (SPC) system Not required in every cycle: Make sizing adjustments for critical workpiece attributes Replace worn tools Remove chips from work area (if required) Machine maintenance At first glance, the tasks related to completing a production run probably look pretty simple. And as long as everything is going smoothly, keeping the machine running good workpieces may be as simple as loading the workpiece, pressing the cycle start button, and removing the completed workpiece when the cycle is completed. This may be the case for the first few workpieces machined in a proven job (one run before). It is quite common, however, that operators must make adjustments during the production run to ensure that workpiece are produced consistently. The more workpieces in the production run, the tighter the tolerances, and the more abrasive the workpiece material, the more likely it will be that adjustments must be made. The frequency of these adjustments (how often they must be made) is also related to these factors. In this lesson, we will be taking a close look at what it takes to complete a production run once the setup is completed. As we did in Lesson Eleven, we will present the related tasks in the approximate order that a production run is completed. Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page1

2 Remember from Lesson Eleven that there are only two things that occur on a CNC machining center. The machine is either in setup or running production. In this lesson, of course, we will be addressing thing that occur during the production run. And this includes just about anything that happens between setups. Production run documentation With the setup completed and the first workpiece passing inspection, you are ready to begin the production run. We are assuming at this point that you have more than one workpiece to machine. As with just about every facet of manufacturing, companies vary with regard to how many workpieces they commonly run per job. The number of workpieces to be produced is called the lot size. Lot sizes can even vary substantially within one company, meaning some jobs may have but a few workpieces to be produced while others have many. Generally speaking, CNC machining centers are most often applied to small to medium sized lot sizes from one to about one-thousand workpieces. While there are companies that do more, dedicating their CNC machining centers to running one workpiece day in and day out, the vast majority of CNC using companies run a variety of different jobs of varying lot sizes. Your company s typical lot size has a big impact on how you approach production runs. Indeed, it has a big impact on how companies utilize their CNC people. And it impacts whether production run documentation is even provided. If a company consistently runs small lots of under ten workpieces, it won t take much time to complete each production run (assuming relatively short cycle time). A company in this situation will typically have one person setup the job and run the job out. In this case, there may not be any production run documentation. The person setting up the job and running the first workpiece will know how to run the rest of the workpieces. On the other hand, if a company consistently runs larger lots of one-hundred workpieces or more, it will take much longer to complete the production run. This kind of company tends to have one person make the setup and another (usually lesser skilled person) run out the job. In this case, special documentation should be provided for the person running out the job the CNC operator. Unfortunately, many companies expect their setup people to verbally explain what must be done to run out the job to the CNC operator, meaning they still may not provide any written production run documentation. Admittedly, many of the tasks related to running production are quite basic and very redundant if many workpieces must be produced. But adequate production-run documentation is essential to help the CNC operator understand what must be done when running workpieces, especially if several people will be involved with running out the job (like first, second, and third shift operator). The setup person may not be available to explain how to run out the job to everyone. For our discussions in this lesson, we will be assuming that one person makes the setup and another completes the production run. So we do provide production run documentation. Figure 12.1 shows the production run documentation for the example job introduced in Lesson Eleven. This documentation must answer any questions a CNC operator will have about the job. We ll be referring to this form as we describe the tasks related to completing a production run. Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page2

3 Part No. A-5487 Part Name: Bracket Program No.: O0003 Programmer: ML Machine: Mori MV-40 Date: 09/20/03 Station Tool Offsets Life/adjust 1.0 end mill 1/2 end mill 5/8 end mill #4 center drill 3/8 drill L:1 R:31 L:2 R:32 L:3 R:33 L:4 L:5 250/50 200/ Calipers Offset 32 Calipers Offset 33 Calipers Offset 31 Inspection instructions: Inspect each workpiece as follows (while machine is running). Be sure the three holes break through bottom. Using gauges provided with the job, measure the overall length, width and depth of oval pocket, and the slot width and depth. Record results with the statistical process control (SPC) system. Block delete: Not used in this job Depth gauge Offset 2 Depth gauge Offset 3 Workpiece loading: Workholding setup: Production Run Clean the next workpiece to be run while the machine is running, removing grease and grime. Be sure to clean the jaws when you remove the previous workpiece from the vise. (Wait to clean, de-burr, and measure the completed workpiece until the next cycle is started.) Clear the chips from around the vise. Center the workpiece in the vise as shown in the drawing. Use a 6 scale to confirm position. Tighten the vise, and tap the workpiece down with a lead hammer. Workpiece vise Figure 12.1 production-run documentation for our example job As you can see, this documentation is pretty concise. It does, however, touch on the most important things an operator must know in order to run out the job. After some general information about the job, the right side of this page shows how workpieces must be loaded into the workholding device. There instructions as well as a sketch showing a workpiece in its workholding device. The top of the left side of this page shows which offsets are used for the job, and very importantly, a drawing showing which workpiece attributes are related to each offset. We are also letting the operator know approximately how long each cutting tool will last, as well as how often sizing adjustments must be made (in number of workpieces produced). Finally, we re providing some instructions for how this workpiece must be measured (inspected). Tasks required for completing a production run Now let s discuss the tasks in the approximate order a production run is completed. We will first look at the tasks that must be done in every cycle. Then we will show the tasks that must be done every-so-often. Remove the previous workpiece The task of workpiece loading begins with the removal of the most recently completed workpiece from the work area. This requires the operator to understand the workholding device being used to secure the workpiece and anything special should be described in the production run documentation. For our example job, the operator must remove the workpiece from the table vise, which requires the use of a vise handle. Workpiece removal usually requires that the location surfaces of the workholding device be cleaned. In most cases, the work area near the workholding device should also be cleaned to remove chips and debris. Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page3

4 Note that some operators get into the (bad) habit of beginning to work with the workpiece just removed prior to loading the next workpiece. While the completed workpiece must eventually be cleaned, de-burred and measured, the operator should set it aside until the machine is in cycle for the next workpiece. Load the next workpiece This is a very important task since an incorrectly loaded workpiece can have disastrous consequences. The workpiece must be properly placed in the workholding devices and sufficiently secured. While loading workpieces is usually pretty simple, the setup documentation should include workpiece loading instructions, especially if there is anything special or unusual required. Notice that our example production run documentation form includes explicit loading instructions requiring the use of a 6 scale (ruler). Once the workpiece is placed in the proper position, the vise handle must be turned to clamp the workpiece. The amount of clamping pressure is determined by the size of the vise. If you are unsure about how much clamping pressure to exert, you must ask an experienced person. Once clamped, most table vises require you to tap the top of the workpiece with a lead hammer to ensure that it is properly located against the bottom surface. If you have never seen this done, ask an experienced person to demonstrate. Once the workpiece is loaded, the machine doors (if there are any) to the work area must be closed. Activate the cycle With the workpiece properly located and secured in the workholding device, you are ready to run it. If the machine has been consecutively running workpieces part after part after part activating the cycle is very easy. You simply press the cycle start button. The machine will begin running the next workpiece in the normal manner. But there are situations when you must confirm that the machine is truly ready to run the next workpiece before you activate the cycle. Maybe you have been away from the machine for a while (at lunch or on break). Maybe you are just beginning a shift (someone else has been running production before you). Maybe you know something about the machine is different since the last workpiece was run (you just replaced a dull tool). Or maybe you suspect that something may be wrong (did someone bump into the control panel while you were loading a part?). In these cases, again, you must confirm that the machine is truly ready to run the next workpiece. This involves checking (and setting) several switches on the control panel. While this may not be a complete list, here are some of the switches that must be properly set before you can continue running production. Dry run: off Single block: off Optional stop: off Machine lock (if available): off Block delete: As requested by programmer in the production run documentation (probably off) Rapid traverse override: 100% Feedrate override: 100% Spindle override (if available): 100% Mode switch: Memory or Auto Display screen: Program mode (and correct active program is shown and cursor is at the beginning of the program) Machine position: At the tool change position Again, with the machine ready to run the program, activating the cycle simply requires pressing the cycle start button. And remember our safety-related rule: Whenever you press the cycle start button, you must always Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page4

5 have a finger ready to press the feed hold button. If the machine behaves in an unexpected manner, you will be ready to stop it. Monitor the cycle This may not be necessary for proven programs that you have seen run many times before. But if you are new to a program, it is a good idea to get familiar with the cycle especially if you did not program the job or make the setup. This will help you understand the tools that are being used and the general machining order used in the program. It also helps you get used to the various sounds made by the machine as it runs a workpiece (each machining operation will have its own sound). If something changes during the production run, you will be able to recognize it. For new jobs, you will also want to confirm that cutting tools are machining properly for several workpieces. Certain cutting-tool-related problems, especially with speeds and feeds, may not present themselves when the first workpiece is being machined during setup. With new jobs, you will need to stay alert while running the first few workpieces. Some jobs have an especially troublesome machining operation that must be monitored for each cycle (if so, it should be stated in the production run documentation). You may, for example, be asked to monitor an insert drill as it machines each workpiece to watch for insert breakdown. If an insert breaks, it will cause even more damage to the drill and workpiece. Being there when it happens will allow you to immediately stop the cycle and save the drill and workpiece. Again, the need for this kind of monitoring should be well documented. Clean and de-burr the just-completed workpiece Once you have loaded the next workpiece and activated the cycle (the machine is running), you can begin working on the workpiece that has just been removed. It will probably be covered with coolant and debris. And it will probably have some razor sharp edges, so be very careful when handling it. Most companies expect their CNC operators to clean and de-burr the workpieces they produce. This is actually a pretty important general rule in any machine shop environment. Whoever machines a workpiece is responsible for cleaning and de-burring it. Never allow a workpiece with dangerously sharp edges to go on to the next stage in its manufacturing process. Cleaning usually involve wiping the workpiece with a rag or shop towel. Again, be very careful when cleaning. The wiping action you use can cause sharp edges to cut you. Think of washing a steak knife by hand. You must be very careful when washing its blade. The same is true for the machined edges on a workpiece. They can be every bit as sharp as a kitchen knife. If you use any kind of air-blowing system to blow off the workpiece (many shops have banned air blowing systems for workpiece cleaning), be extremely careful chips can fly anywhere. While you must always wear eye-protection (all shops require it), nothing is protecting your ears, nose, mouth, etc. from flying debris. Many types of de-burring operations can be included right in the CNC program. Indeed, many companies go to great lengths to completely debur workpieces as part of the CNC cycle so when the workpiece comes off the machine, it will already be de-burred. However, not all companies are so concerned about removing burrs during the CNC cycle. You must be prepared for sharp edges on workpiece you remove from the machine. A variety of hand tools is available to debur sharp edges, like files and hole de-burring tools. If any are unfamiliar to you, ask an experienced person to demonstrate their use. The next illustration shows several types. Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page5

6 On popular type of de-burring tool is used to remove sharp edges from holes. The next illustration shows it in two sizes. The de-burring edge (on the short curved end) swivels around in the handle. This allows a person to quickly debur a hole by inserting the de-burring edge in the hole and rotating the rotating it around the hole. The more times the de-burring edge goes around the hole, the more material of the burr is removed from the sharp edge. Probably the most common de-burring tool is a hand file. It is used to debur sharp corners. The next illustration shows one. Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page6

7 The flat surface of the hand file scrapes material (the sharp burr) from the corner edge. The pointed end (called the tang) is often placed in a handle that makes the file easer to hold and use. A file only works in one direction when pushing the file away from you. It does not remove any material when it is being pulled toward you. For our example workpiece, just about all machined surfaces will have sharp edges since we didn t use any special de-burring tools in the program. These surfaces include all surfaces on each end of the workpiece, the top surfaces of the slot and pocket, and the top and bottom surfaces of the three holes. Again, every machined surface will have a sharp edge. Perform specified measurements Measuring tools are described in detail in Lesson One. At this point, we assume that you understand how measurements are taken. But again, if you are in doubt about how to use a given measuring tool, you must ask an experienced person in your company to show you. Most companies expect their CNC operators to inspect at least some attribute/s on every workpiece they machine. But companies vary with how many attributes must be measured on every workpiece. Many companies have their people measure stagger the measurements. A few different attributes are measured on each workpiece. In this way, the operator toggles through all workpieces attributes after several workpieces are machined. If ten percent of all workpiece attributes are measured on each workpiece, for example, all workpiece attributes will be measured after ten workpieces are made. With many workpieces, there are a few very critical workpiece attributes that must be measured on every workpiece. This is in addition to the staggered inspections just mentioned. Which workpiece attributes must be measured, along with the frequency of measurements, must be specified in the production run documentation or instructed to the CNC operator by one means or another. This is yet another area that may involve some unwritten rules. Operators may be expected to know the logic used to determine how often workpiece attributes are measured. Most companies also expect their operators to record the results of measurements in some fashion. But again, companies vary when it comes to specific methods used to record. Recording may be done with a paper and pencil written on some kind of inspection form. More likely, recording is done at a computer terminal using some kind of statistical process control (SPC) system. For our example job, notice that production run documentation specifies that the overall length of the workpiece must be measured for every workpiece. So must the width and depth of the slot. The operator is also asked to check the width and depth of the 1.0 pocket. And they are asked to visually check that the holes break through. They must record measured dimensions using the company s SPC system. Which takes longer, the CNC cycle or the off-line tasks an operator must perform? With long CNC cycles, it is likely the operator will be able to clean, debur, and measure the workpiece during the CNC cycle. That is, the operator will be able to keep up with the machine. But with shorter cycles, and when there is a lot for the operator to do, it may not be possible to keep up. Most companies try to design their processes in such a way that the machine takes (slightly) longer than the CNC operator. This keeps the operator quite busy while the machine is running yet maximizes the machine s output. Make offset adjustments to maintain size for critical dimensions (sizing) The tasks described so far are performed in every cycle. The tasks shown from this point are performed only if and when they are required. We have been stressing the relationship between tolerance size and the need for trial machining and sizing adjustments throughout this text. You know the setup person will run the first workpiece as part of the setup. When doing so, they will size in every workpiece attribute so that when the production run begins, Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page7

8 each workpiece attribute will be coming out right at its target value (often its mean value). So when the operator takes over, all workpiece attributes will be being machined properly. You also know that as you continue to machine workpieces, cutting tools will wear. The more abrasive the workpiece material and the softer the cutting tool material, the faster the cutting tool will wear. Tool wear often has a direct impact on the position of machined surfaces, meaning surface positions will change as more and more workpieces are machined. The smaller the tolerance on a given workpiece surface, the more likely it will be that the cutting tool will not machine the surface within its tolerance band for the entire life of the cutting tool. With small lot sizes, this may not present a problem. The operator may complete the entire production run before any cutting tool gets dull, and before the workpiece attribute grows or shrinks out of its tolerance band. But with larger lot sizes, the wear a cutting tool experiences may cause the surface/s it machines to grow or shrink out of its tolerance band before the tool gets dull. This, of course, will place upcoming workpieces in jeopardy. In this case, the CNC operator must make a sizing adjustment to keep the cutting tool machining the surface properly. Indeed, several such sizing adjustments may be required during a cutting tool s life before it is dull and in need of replacement. Again, we have explained sizing and why it is done previously in this text. The previous few paragraphs contained nothing new. With our example job, there are three very tight tolerances to hold: the overall workpiece length, the slot width, and the slot depth. Say we have a large lot of two-thousand workpieces to produce. After the setup is made and the first workpiece passes inspection, each of these critical dimensions will be being machined right at its target value (its mean value in our example). As we continue to run workpieces, we will notice that the overall workpiece length is growing. It started out at (slightly smaller than its target value), but after twenty workpieces, we may find it to be After forty workpieces, it is And after sixty workpieces, it is This growth in overall length, of course, is being caused by wear of the 1.0 end mill. If this trend continues, the overall length of a future workpiece will be out of tolerance (scrap). An adjustment must be made to the 1.0 end mill s cutter radius compensation value (offset number thirtyone). If the overall length of the workpiece is currently , the current offset value should be reduced by to bring the dimension to its target. But as you know in the Imperial measurement system (inch) mode you are only allowed to make offset adjustments in increments. We will reduce offset number thirty-one by This will cause the end mill to machine more stock from each end of the next workpiece, making the overall length of the next workpiece back to a value slightly smaller than its target value. The same situation will exist with the width (and possibly the depth) of the wide slot. As we continue to run workpieces, we must be alert for sizing adjustments required due to tool wear. In order to make sizing adjustments during a production run, of course, we must know which offsets are related to each tool. In the production run documentation for our example job, there is a list the offsets related to each tool in the tool list. But to further clarify, there is a nice drawing which shows the offsets related to each workpiece surface. This allows us to make sizing adjustments without having to know which tool even machines each surface. Unfortunately, most production run documentation doesn t provide this level of clarity. Most operators are on their own to figure out which tool machines each critical surface and which offsets are related to the tool. Since the 1.0 wide pocket and the holes have no tight tolerances, the cutting tools that machine them will last for their entire lives without requiring sizing adjustments (with drills, there is nothing that can be done with offsets to change the diameter they machine). If possible, production run documentation should also help the CNC operator know when sizing adjustments are needed. This, of course, requires experience some running the job. During the first time a new job is run, the operator will learn if sizing adjustments are necessary. If they are, this information should be added to the Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page8

9 production run documentation. Notice in the tool list for this job, we include the approximate number of workpieces that can be machined before a sizing adjustment is necessary (in the Live/adjust column). This lets the operator know if sizing adjustments will be required before a tool must be replaced. Replace dull tools As with sizing adjustments, this task will only be required with larger lot sizes when cutting tools will wear out before the job is completed. Before a dull tool can be replaced, of course, the operator must recognize that it is dull. This requires some basic machining practice skill. Indications of a dull tool include a change in the sound the cutting tool makes, a change in the amount of smoke or mist generated by the tool, a change in the color of the chip being machined, and a change in the surface finish the cutting tool machines. If you do not have shop experience, you must ask experienced people for help with judging when cutting tools get dull. When a cutting tool must be replaced, many of the same tasks required for the cutting tool during the initial setup must be repeated. These tasks include assembly, measurement of tool length compensation values, measurement of cutter radius compensation values for milling cutters, offset entry, and placement into the machine s automatic tool changer magazine. All of these tasks are presented during our discussion of setup and will not be repeated here. Keep in mind that if a cutting tool requires trial machining during the initial setup, it will also require trial machining during replacement. Tools one and two in our example job (the 1.0 end mill and the 1/2 end mill) both require trial machining during setup. If they are replaced during the production run, they will require trial machining again to ensure that the surfaces they machine come out to size on the first workpiece each new cutting tool machines. All of this means, of course, that if a CNC operator is responsible for replacing tools during a production run, they must possess many of the same skills possessed by the setup person. For this reason, some CNC using companies do not expect their CNC operators to replace worn tools. Instead, they have a setup person do so. If possible, production run documentation should specify the expected life for each tool. Again, this requires some experience with the job (or at least, experience with the related cutting tools and the material being machined). In our example documentation, we specify an expected tool life for each tool so the operator will know if the job can be completed before any tools wear out. We have been assuming that the CNC operator will be responsible for determining when a cutting tool gets dull. Some machining centers have a feature called tool life management. This feature (which must be programmed by the programmer) will monitor each cutting tool in the job and alert the operator when a cutting tool gets dull. Most tool life monitoring systems can even cause the machine to stop using the dull cutting tool and automatically start using a fresh cutting tool. This, of course, requires that multiple identical cutting tools be set up and loaded into the machine s automatic tool changer magazine. Clean the machine Most companies expect their CNC operators to keep their machines clean. Every so often (commonly at the end of each shift), the operator will remove all chips from the work area and clean the machine table. Chips machined during the shift will be dumped (from the chip disposal drum). Preventive maintenance Some CNC using companies expect their CNC operators to perform basic preventive maintenance like maintaining coolant levels, way lube levels, hydraulic oil levels, and filters. If this is required, instructions must be provided that describe the required procedures and their frequency. Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page9

10 Anything else you ll be expected to do? Some companies expect their CNC operators to perform tasks that are unrelated to the CNC machining center operation. This is especially true when the company commonly machines workpieces having very long machining cycles. It is not uncommon, for example, for some machine cycles to take well over an hour to complete. Maybe the operator can complete the workpiece tasks (measuring, SPC reporting, dull tool replacement, etc.) in much less time than it takes the CNC machine to complete its cycle. In this case, the company may ask the operator to continue working on something else. They may, for example, ask operators to perform some assembly tasks related to the product they manufacture. If additional tasks are required, of course, instructions must be provided for doing so. Key points for Lesson Twelve: You must understand the tasks that occur in every cycle workpiece loading, monitoring the cycle, workpiece unloading, workpiece cleaning, workpiece de-burring, and workpiece measuring. You must understand tasks that do not occur in every cycle sizing adjustments and dull tool replacement. Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page10

11 Practice running the first workpiece Instructions: Study the following drawing, paying particular attention to the dimensions and tolerances. Note that this drawing is not fully dimensioned. Only the dimensions and tolerances that are related to this exercise are provided. Next, read the description of the process. Finally, answer the questions that follow / /4 dia. Process: Description Tool Station Mill right side 1.0 end mill 1 Mill 2 x 2.75 pocket 1.25 end mill 2 Drill 3/8 hole 3/8 drill 3 Counter-bore 3/4 hole 3/4 end mill / / / /8 dia / After measuring cutting tools, you enter the offsets as follows: # Value: (length of tool 1) (length of tool 2) (length of tool 3) (length of tool 4) (radius of tool 1) (radius of tool 2) Questions: 1) You re ready to run tool number one (the 1.0 end mill that mills the right side) for the first time. You notice that there is a pretty close tolerance (+/ inch) on the 5.5 inch dimension that this milling cutter machines. You re worried that this tool may machine too much stock on its first try, so you decide to trial machine. You increase the value of offset number 31 by 0.01 inch (making it 0.510) and allow this milling cutter to machine the right end. When the tool is finished, you stop the machine (with the optional stop switch) and measure the 5.5 dimension. You find that it comes out to What must you do to offset 31 to make this milling cutter machine properly when you re-run the tool? Be specific. 2) After re-running the 1.0 end mill, the 5.5 dimension comes out right on size (to 5.5). You re ready to run tool two, the 1.25 end mill that machines the pocket. Again you notice the tight tolerance (+/ ) and decide to trial machine. You increase the value of offset number 32 by (making it 0.635). You also notice the even tighter tolerance on the pocket depth (+/ ) and decide to trial machine this surface as well. So you increase the value of offset number two by (making it ). After this tool machines you stop the machine. You measure the pocket size in XY and it comes out to along X and along Y. You measure the pocked depth and find it to be What must you do to offset 32? What must you do to offset 2? Be specific. 3) After re-running the 1.25 end mill, you re ready to run tool number three (the 3/8 drill). Does this tool require trial machining? (yes or no) Why? 4) You move on to tool number four (the 3/4 end mill that plunges the 3/4 counter-bore). This tool machines in a plunging fashion, just like a drill. Again, the depth of this pocket (0.25) has a tight tolerance (+/ ), so you decide to trial machine. You increase the value of offset number four by 0.01 (making it ) and run the tool. After machining, you stop the machine. When you measure the depth of the counter-bored hole, you find it to be What must you do to offset number four? Answers: 1) Reduce offset number thirty-one by ) Reduce offset thirty-two by and reduce offset number two by ) No, this tool does not require trial machining because none of the dimensions it machines have tight tolerances. 4) Reduce offset number four by Copyright 2011, CNC Concepts, Inc. Machining Center Setup and Operation Page11