Operating a CNC Powered Machine Shop

8/9/2019 Operating a CNC Powered Machine Shop

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Operating A CNC Powered Machine ShopA Road Map for Efficient Manufacturing

ByTim Markoski

Senior Member - Society of Manufacturing Engineers January 9, 2012

As someone who has spent most of my adult life working in manufacturing related fields, it occurred to me thatall too often I would end up witnessing companies making the same mistakes, over and over again, when itcame to efficient operation of their CNC powered machine shops.

CNC Machine Tools

One of the most important parts of any business plan for a CNC based Machine Shop is planning the CapitalEquipment purchases. Choosing the right CNC Machine Tools is not something that should be taken lightly.Choose the right ones for your business and you’re one step closer to an efficient operation.Choose the wrong ones and you’ll be out of business quickly.

Believe it or not, cost should not be the primary consideration when determining which type of CNC one should purchase. Obviously cost is important but it needs to be placed in the proper context. We will discuss that later but for now let’s continue.

The first criteria for determining what CNCs to purchase is the type of work to be machined.Will it need to be Milled or Turned or a combination or both? Will it need Wire EDM?What are the sizes of the work-pieces to be machined? What are the materials to be machined?What are the tolerances required? All of these points need to be considered.

The next point to consider is the production quantity.How many of your work pieces do you need to produce every month?This is important because the whole point of your endeavor is producing and selling your parts.

If you aren’t purchasing enough machines to support the endeavor then your effort and money will be wasted.Whatever machine(s) you purchase, make sure it provides slightly more capability than you’ll currently need.You’ll want some room for growth to be accounted for by whatever machine(s) you put into service.

OK, You’ve done your homework and now you’re ready to select your CNC Machine Tools. Now let’s deal with the issue of cost.

Part of any business plan has to be sufficient financial capitalization to support the endeavor.To that end, the cost of the desired CNC Machine Tool is not the only cost that should be considered.Along with any CNC Machine Tool purchase, there is a fair amount of additional equipment needed to properlysupport that machine as it is put into service. This additional equipment has a significant cost.

That cost should be planned for and taken into account when any CNC Machine Tool purchase is made.

I can’t tell you how many times I’ve gone into shops that had purchased $500,000.00 worth of CNC Machines but wouldn’t allocate funds for additional support equipment. They essential paid for expensive boat anchors.It makes no sense to buy a new CNC and then not purchase tooling and equipment to maximize the efficient useof the equipment. The Rule of Thumb that I use with clients is to budget 30% of the base cost of the machinefor support tooling and equipment.

Let’s lay out a quick hypothetical example.A shop owner is getting ready to purchase a $250K Horizontal Machining Center.



Using our 30% rule for additional equipment, the shop owner will need approximately $75K for supportingequipment. Now let’s take a practical look at what he will need to support the machine.

$250K Horizontal Machining Center , 630mm Pallet, 40 Tool Carousel CAT-50 – Supporting Equipment 8 Additional Tombstones - $38,000

o 2 - 4-sided –Blank $4000.00 eao 2 - 2-sided –Blank – Window Frame $4000.00 eao 2 - 2-sided - Window Frame-Modular $5000.00 eao 2 - 4-sided -Multi-purpose-Modular $6000.00 ea

80 CAT-50 Tool Holders - $12,000.00

Let’s take a moment and look at the above.We have just started tallying our required equipment and we’ve already used up approximately 2/3 of our

budgeted $75K for additional equipment! We haven’t even accounted for the actual cutting tools yet!As one can plainly see, there are additional costs associated with any CNC Machine Tools purchased and thosecosts need to be accounted for. It’s been said many times, “The Devil is in the Details.” .

The next important part of the CNC Machine Tool selection process is a question.

How will the machine be programmed?The question is somewhat rhetorical as there is really only one correct answer – with a CAM system!

At first blush, that claim may shock some. Allow me to explain why.CNC machine time is the most expensive time in any machine shop. There’s an old saying that “if the spindleisn’t running, you’re not making money.” Meaning, your machine must have the highest spindle utilization

possible. While that may sound simplistic to some, it’s absolutely true.If you are programming at the machine control, the spindle isn’t running and the machine isn’t making a part.While it is true, there are conversational programming systems built into certain CNC controls, it is foolish toexpect these systems to handle all of your work in an efficient manner.

Again, as obvious as this may seem in hindsight, it never ceases to amaze me that I consistently come acrossshops that don’t understand this. There is still a mindset amongst certain managers that a CNCMachine Tool is essentially a “Magic Box” that is no more complex to operate than a television set.

Nothing could be further from the truth. A CNC Machine Tool is just that, a tool. It is an inanimate object.It is only useful in the hands of qualified CNC Programmers and Operators.

This leads us into a discussion of both CAD and CAM. While these are separate and distinct disciplines,there are unified systems that can do both. There are systems that offer elements of both. These are referred toas CAD/CAM Systems. Generally speaking, any CAD/CAM system will have weaknesses in several areascompared to either dedicated CAD or CAM systems. These systems have a significant cost that must also beaccounted for.

However, before we can discuss CAM, we really need to discuss CAD as a separate entity.CAD lays the foundation for what we ultimately need to do with CAM.

CAD – Computer Aided Design

Part design is generally the purview of “Engineering”.Because of this, there is a tendency, especially in the US, for managers to view Design Engineering andManufacturing as two separate, distinct and mutually exclusive areas. Because of this, there is generally poor communication between Design Engineering and Manufacturing.



This should be avoided at all costs. Without open communication between Engineering and Manufacturingdepartments, along with a bi-directional feedback loop, companies will find themselves constantly re-inventingthe wheel. To avoid this, engineering departments need to embrace the concept of “Design for Manufacturing”.

Simply put, the concept of DFM (Design for Manufacturing) takes into account the manufacturing processesas well as part functionality, when designing a part. Too often, engineers deal with the theoretical and ignorethe practical. Some examples of this would be sharp internal corners in areas that must be machined or sharpcorners in high stress or load bearing areas. When it comes to drawings, over-tolerancing and inconsistent data

relationships are among the most egregious and problematic errors in the use of CAD for manufacturing.

To help eliminate these errors in the use of CAD for DFM, consider implementing the following rules as part of a guideline for overall CAD implementation.

1.) Standardize all 3-D models and 2-D drawings.The importance of standardization cannot be understated. When more than one engineer is involved in a partmodel and drawing, documented methods and procedures for modeling and drafting can ensure thatmanufacturing maintains both design intent as well as a benchmark for quality. Simply put, it is impossibleto measure and quantify data against a moving goalpost.

The one overriding rule that should never be violated is that drafting dimensions must always reflect thevalues of the geometric entities dimensioned at the scale shown. It should never be permissible to manuallychange a dimension value without also changing the actual geometric entity dimensioned.The importance of adhering to this rule becomes clear as manufacturing uses the CAD file data provided byengineering.

2.) Use Part Configurations for Families of PartsIt is quite common for part designs to be used multiple times with minor changes. The basic part design will

be the same across all members of the part family. The differences will be in the values of certaindimensions and features. These types of parts are called Families of Parts. All modern 3D MechanicalModeling Software applications have a tool for managing these types of parts called Configurations.

Configurations allow for all iterations of a given part to be handled within a single 3D CAD model. This isdone by specifying the specific parameters of a given part iteration in a specific grouping. Configurationsare the specific grouping of the defining parameters. Part configurations are the 3D equivalent of 2DTabulated Drawings. Part configurations have the added benefit to manufacturing in that they allowmanufacturing to create a single process for handling them.

3.) Use a PDM/PLM (Product Data Management/Product Lifecycle Management) system to manage theCAD file data. (Document Control)While it may be tempting for some managers to attempt to manage CAD files manually with an ad-hoc, fly

by the seat of your pants approach, this temptation should be avoided. Inevitably, version control becomesessentially non-existent because there are simply too many copies of a given file “in the wild”.

This lack of control inevitably leads to errors in manufacturing and an associated NCR (Non-ConformanceReport). PDM/PLM systems eliminate this problem as all data is in a “Vault”.There is only one copy of a given CAD file, at a given revision number, stored in the vault and its status can

be viewed at any time. Assembly structures and Bills of Materials can be viewed and maintained directlythrough PDM/PLM. Manufacturing can instantly view that a part is currently in an ECN (EngineeringChange Notice) state before starting work.

4.) Make sure Manufacturing has access to all CAD data through the PDM/PLM system.All modern CAM systems have the ability to use the native CAD data from the system that created it.If CAD data exists then it should be shared with manufacturing. As self-evident as that statement may be, Ihave seen time and time again where engineering refuses to share CAD models and drawings with



manufacturing. There is simply no logical reason to keep CAD data from manufacturing. Doing soessentially forces manufacturing to reinvent the wheel. Forcing manufacturing engineers and CNC

programmers to re-model or re-draw parts in order to program them is introducing risk and a likely failure point into the manufacturing process.

Now that we have established a basic guideline for CAD, we are ready to discuss the subject of CAM.

CAM – Computer Aided Manufacturing

While the use of CAM software has become ubiquitous in today’s manufacturing, too often the selection of aCAM system is done without proper consideration of the practical applications of its use. This problem is thenexacerbated by poor deployment and implementation of a given CAM system within a manufacturingdepartment.

When selecting a CAM system for use in a manufacturing facility, several key elements must be considered.As I’ve previously stated, cost is important, but it needs to be placed in the proper context. It should also benoted that many of the selection criteria for choosing a CNC Machine Tool will also apply to the selection of aCAM system for generating NC programs.

First and foremost, any CAM system you select must be capable of generating the required tool path operationsas well as the required NC code for the CNC machines being used in production. As a starting point, any systemchosen should be able to handle CNC Programming for both Milling & Turning operations. If a given systemdoesn’t support both Milling and Turning independently, then it will be worthless to consider it if you haveintentions to ultimately move into Multi-task Machining (Mill/Turn).

The second most important criteria for selecting a CAM system deals with product support. The company thatactually develops the CAM software should also have a Users Technical Support Forum for end-users to shareand help each other. The company should also have a mechanism for users to report bugs directly.Any CAM system selected should have both technical support and training available in your region through aVAR (Value Added Reseller). Ideally, both technical support and training should be available locally but that

may be impractical, based on the location of your specific manufacturing facility. Additionally, one must alsoconsider the pool of qualified labor available for any given CAM system.

Another factor that should be considered when selecting a CAM system is the ability of end-users to automatespecific CNC programming tasks. This may be possible via a proprietary Macro Language, integrated CADFeature Recognition (commonly referred to as FBM - Feature Based Machining), or via an API (ApplicationProgramming Interface). A CAM system API allows users to develop custom software applications thatintegrate with and operate directly within the CAM system. These may range from relatively simple automationroutines using a language like VB Script to essentially full-blown, professionally developed, independentapplications that simply use the CAM system as the engine or host.

This brings us to the subject of cost.Selecting a CAM system, based solely on cost, is a recipe for failure.The question to be asked is “What value or benefit does this system provide, at the price offered?”Before committing to purchasing any CAM system, make sure that a detailed Cost/Benefit analysis has been

performed. This is the only way to get a true measure of the value that a particular CAM system brings to youas a manufacturer.



When you are ready to actually submit the purchase order for the CAM system, the next two points are criticalto a successful deployment and implementation.

1.) It is critical that your selected CAM system vendor is capable of creating Post-Processors for eachmachine you will be supporting with the system.The Post-Processor is the last link in the chain. It takes what is done in the CAM software and creates thespecifically formatted NC code to drive the CNC Machines as required.

Any CAM system that cannot provide a Post-Processor capable of generating edit-free NC code is, for allintents and purposes, worthless. Post-Processor requirements MUST be included in a purchase order asa condition of the purchase.

2.) Get all commitments from your CAM vendor IN WRITING and make them part of the P.O.requirements.Do your homework and don’t get buffaloed by a flashy demo and vague promises.Make sure your P.O. has clearly defined terms as well as clearly defined penalties for non-conformance.As much as I hate to say it, if you do not get commitments in writing, you will end up spending morethan is necessary to have the system properly deployed and implemented. Any ethical vendor will not havean issue with making commitments and guarantees in writing.

Once you’ve made the purchase commitment for a given CAM system, you’ll want to prepare for a successfulimplementation.

CAM Implementation

1.) Standardize and document all CNC Programming methods, procedures and NC Code output.Companies will have changes in personnel over time. It is critical that these changes in personnel do notcreate an impediment to production. Standardization helps eliminate mistakes based on assumptions,ignorance or lack of experience. By standardizing things as mundane as screen background color, layer names and entity colors, new users will become productive much more quickly.

Standardization of things like Tool Path Lead-In/Lead-Out with CRC (Cutter Radius Compensation) ensurethat, if needed, users are able to generate NC code for a complete different CNC Control by simply selectinga different Post-Processor.

Make it easier for machine operators to read the NC code by standardizing the output from the CAM Post-Processors. By using consistent methods for Tool Change Sequences, Commenting, Rotary Positioning, etc.,machine operators will become accustomed to a single, unified output style.

A Post-processor should NEVER create tool path coordinates, in the NC code, that do not exist in the CAMfile itself. I actually had an experience with a major energy company doing just that. Their CNC Supervisor

modified all of their Post-Processors because he didn’t understand how to properly apply CRC (Cutter Radius Compensation) on a Fanuc Control. Needless to say this led to scrapped parts and machine crashes. Post-processor modifications should only be made by qualified personnel and load- tested beforedeployment!



2.) An important part of CAM Standardization is Tooling Standardization.This determines how many different cutting tools are required for machining a given part.Standardization of tooling brings huge benefits in the practical operation of a machine shop as well assignificant cost savings. A short tooling standardization outline is as follows:

Analyze and document the current tooling being used.Using the 80/20 rule, Prioritize their usage and determine the tools that perform 80% of the work.Communicate with your machine shop management and tool suppliers to determine tooling preferences.Link your common tool selection with common part selection to standardize manufacturing processes.Create tooling libraries for each CNC Machine based on the common tool selection.

3.) Use Templates to speed up dedicated CAM based CNC Programming.Simply put, CAM templates are the basic skeletons of a CAM file. They establish and contain the basicrequirements for each new part to be programmed. A sample of a CAM template could be a file thatcontains all the required fixtures and tooling for a given HMC (Horizontal Machining Center). It might eveninclude all the basic Work Coordinate Systems and Work Planes for a typical 4-sided Tombstone.

4.) Automate tasks within CAM whenever possible.Use the power of your CAM system API (Application Programming Interface) to handle the repetitive tasksthat are part or your manufacturing. This could be as simple as automating the creation of your setup sheetsor as complex as integrating into a company MRP/ERP system.

5.) Provide documentation for all CNC Programming work product provided to your machine shop.Make sure that your documentation includes all the necessary directions and information for the machineoperator to begin the fixture setup, set the tools, establish work offsets, load the program and run the parts.Providing detailed documentation helps eliminate mistakes based on assumptions or inexperience.

6.) Make sure that CAM Files, Post-Processors and NC Code files are all managed by the samePDM/PLM system that you use to manage your CAD data. By keeping the manufacturing data linked tothe engineering design data, part revisions can be handled more efficiently. There is an ancillary benefit inthat this keeps open communication between manufacturing and engineering.

The ideas presented here are simply my thoughts based on my experiences over the years.They are meant to give the reader insights into processes and methods that allow a shop run efficiently.All the areas discussed overlap and are interdependent. Meaning, one can’t deal with one area without beingaware of the consequences and effects that area has on another.

By no means are these to be taken as the only definitive and correct methods.These are provided to assist the reader in avoiding the pratfalls that they otherwise might not see.By being aware of these points, readers will have additional information to assist them in the pursuit of

continuous improvement.

About the Author:Tim MarkoskiCNC & CAD/CAM Applications Professional ( 25+ Years)Senior Member - Society of Manufacturing EngineersCertified Mastercam Instructor Original Developer of the Machinist ToolBox™ utility software.http://twitter.com/MTBSoftwarehttp://www.linkedin.com/in/timmarkoski

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Operating a CNC Powered Machine Shop