Sep 22 2016

Pocket Milling

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The combination of CNC machines and CAD/CAM software allows machinists to cut materials faster and more accurately than what is possible when cutting by hand. One of the most common types of cutting is pocket milling (or pocketing), which sees extensive use in the aerospace and shipyard industries along with the uses a hobbyist has for the technique. Pocketing milling can be used with 2D or 2.5D projects and roughly 80% of all mechanical parts can be created with this kind of toolpath. Using this type of toolpath can make a big difference in the quality of a finished project.

Pocket milling

Pocket milling

Pocket milling allows you to use an end mill and machine away large parts of your raw material in a roughing process prior to finishing your project. This process allows you to save time and money while maximizing the amount of material removed. There are several styles of pocket milling such as traditional lace or zig-zag, concentric or offset In/Out and high speed cutting paths. The type of toolpath you pick can be categorized as linear or non-linear and there are parameters that can be set in many CAD/CAM software programs to control the pocket milling process.
Linear tool paths are unidirectional and the two major types are zig-zag tool paths and zig tool paths. Zig-zag milling causes the tool on your machine to move back and forth while removing material. Cutting is done with and against the rotation of the spindle. This method makes machining faster but also increases tool wear and machine chatter. Zig milling causes your tool to move in only one direction which results in better surface quality. However, you will have to lift and retract the tool after each cut so it takes more time to finish machining.
Non-linear tool paths are multi-directional with contour-parallel tool paths being an good example of this type of tool path. Contour-parallel tool paths use the pocket boundary to derive the tool path. Using this method your cutter is always in contact with your material, allowing you to eliminate time that would be needed to position and retract your tool using other methods. This method is used frequently for large-scale material removal and there are two different approaches that can be classified as contour-parallel tool paths. Pair-wise intersection approaches bring the boundary of the pocket inwards in steps. Offset segments intersect at concave corners and intersections are trimmed off to obtain the required contour. Voronoi diagram approaches segment the pocket boundary and the voronoi diagram is constructed for the entire pocket boundary. Voronoi diagrams are used to generate tools paths and this method is considered to be efficient since it avoids the topological problems machinists can run into using traditional offsetting algorithms.
Toolpath parameters for pocket milling in your CAD/CAM software will include data about roughing and finishing tools, pattern selections, cutting direction options (climb vs. conventional), toolpath cutting angle and step over % input fields. There should also be data that allows you to control side and bottom allowances for finishing as well as depth controls for single or multiple roughing steps. Many CAD/CAM software programs allow you to define single, even cutting depths based on the overall depth and define or force depths. Finally, there should be lead-in and lead-out options to control how the tool enters and exits the cut. Some CAD/CAM software programs will offer all or at least some of these options and some will not; it will depend on what software you are using. There are CAD/CAM programs that offer explanations and tutorials on pocket milling and these programs are usually the ones that are well equipped for pocket milling operations. Examples include BobCAD-CAM, CIMCO CNC-Calc and SimCam (CNCSimulator Pro).


Sep 1 2016

Aluminum and CNC Machines

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Aluminum is one of the trickier metals used on projects made with CNC machines. Its properties are a bit different from other metals so there are usually considerations that have to be taken before you start cutting. This article will review how aluminum reacts when cut with a water jet cutter, a laser cutter and a plasma cutter so that you can be better prepared to work with aluminum regardless of what type of CNC machine you are using.
Water jets are the most common type of CNC machine used for cutting alu, being able to cut as thin as 0.001” or as thick as 12”. Because water jets are a cold cutting process you do not have to worry about heat while you are cutting like you do with laser or plasma cutters so there is no need to worry about deformation or the material hardening. The lack of heat creates a safer work environment since there are no dangerous fumes being created by the cutting process. Abrasive water jets also have the advantage of being the cheapest of the three machines discussed in this article. Almost every type of cut you could need for an aluminum project is possible with a water jet.

Aluminum and cnc machine

Aluminum and cnc machine

Laser cutting is a bit unusual for working with metals (generally mechanical tools are used for metal cutting) but it is still a viable option. Because alu reflects light and conducts heat efficiently there are considerations that need to be taken before using a laser cutter on aluminum. Due to aluminum’s properties a standard laser will not work. Instead you would need a laser with a high power setting that also uses compressed gas. Using gas during cutting is fairly common with multiple types of machines so it should not be difficult to make the modifications you need. Laser cutters supported with nitrogen can cut aluminum without any loss in the quality of your project. The downside is that the increased power usage (i.e. more electricity) and the gas that you will use are going to make cutting aluminum more costly to cut than other materials. Additionally, laser can only cut aluminum that is fairly thin; at the maximum a laser cutter can be used on aluminum that is about ⅛” thick.
Plasma cutters generate a lot of heat and are capable of cutting many materials, including aluminum, very quickly. It may take a little time for a plasma cutter to get to full power after you turn it on but once the machine is running it will do its job very well. Selecting the correct type of gas to use for the plasma is paramount in ensuring that the aluminum cuts correctly. Your choice will also determine how messy the cutting process will be (what type of aluminum you are using will also be a key factor in determining this). Plasma cutters can use less expensive gasses than laser cutters can when cutting aluminum so costs will be a bit better over a laser cutter (though they likely will not be cheaper than a water jet).
Each of these three methods has their own ups and downs when it comes to cutting aluminum. If you are choosing between all three of these methods a water jet is going to be your best bet in most cases. Not every machinist will have a water jet available so if it comes down to a plasma cutter or a laser cutter do a little research and see which one would work best on the type of aluminum you are using. Regardless of what type of machine you have access to there is usually a way to make any project work (within reason) on a CNC machine. You just may need to think outside the box a little to figure out what that way is.


Aug 25 2016

CNC Machine Power Consumption

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Electricity is not the most expensive thing to worry about when running a CNC machine. But while it does account for a small percentage of your operating costs it is still a factor that you should be aware of. For the computer you use with your machine the power usage will be negligible, you do not really need to worry about it. The CNC machine itself should be your area of concern. Looking at your motors is a good way to identify power consumption; most of the power your machine uses is going to be directed towards the vacuums, air compressor and spindle. Say that all together these devices can draw a maximum of 50 horsepower if they are all running together. One horsepower uses up about 750 watts. This means that at peak efficiency you will be using 37,500 watts worth of power. Check how much you are charged per watt to determine what running your machine costs. Also remember to run the numbers based on the amount of power you usually use. If your machine can run at 50 horsepower but you usually only run it at 30, use the number 30 when figuring out your costs. The number you come up with should not be too high; it will likely only be a few dollars per hour. However, if you are using your CNC machine for business purposes the capital you spend on power could be figured into the cost of whatever items you make and sell.

CNC machine power consumption

CNC machine

A skilled machinist should also be aware of problems they can run into when it comes to power usage. Many machine shops use a 3-phase ungrounded service or a 3-phase, 4-wire grounded service. Either of these services requires a grounding electrode conductor to interface with the building grounding electrode system. Together the conductor and system provide low-impedance paths to the ground for lightning or electrical faults, provide low-impedance fault return paths to trip breakers and reference the building’s electrical system to minimalize voltage differences between various exposed metal parts. CNC machines use a regular wire, extending from their power supply, to connect to a ground plate. The ground plate is bonded to a grounding conductor, and subsequently to the grounding electrode system. This establishes a local signal reference with the CNC machine itself and with remotely connected devices. Stand-alone CNC machines should have good grounding, bonding and shielding but machines with data links or remote devices can be vulnerable to stray currents. If that is the case, take extra precautions to avoid electrical damage.
CNC machine manufacturers may recommend, or even require, the use of a supplemental ground rod with the machine they have produced. Usually this is an 8 ft. copper rod that goes through the floor, connecting to the ground plate. Different manufacturers will cite different benefits of using a supplemental rod but on-site examinations have shown that using one of these rods can actually increase the risk of electrical damage instead of decreasing it. The supplemental rod connects the electronic controller to the grounding electrode system and can attract stay electrical currents, such as lightning strikes or electricity generated from power system failures. Potentially the rod could attract a large enough electrical current that it would damage your CNC machine. If you decide to remove a rod, double-check the relevant safety codes and make sure you are not violating any of them. The same goes for implementing any solutions that you think could help to reduce the risk of electrical damages. CNC machine manufacturers can be a good source of relevant advice; they built the machines and should know them very well as a result. Also keep in mind that not all power problems stem from a grounding issue. If you have checked and rechecked your grounding and are still experiencing problems, explore other areas.


Aug 18 2016

Do I Need a Formal Education to use a CNC Machine?

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CNC machining is a hobby to many people but it is a profession to other individuals. There are classes and schools dedicated to teaching people about CNC machines. You may ask yourself whether it is necessary to get a formal education regarding CNC machines in order to use one. While it is not necessary, it certainly helps. Operating any CNC machine is by no means self-explanatory and professional CNC technicians are required to go through training. Hobbyists can and often do figure things out on their own but if you have the time and budget to take a few classes they will certainly increase your knowledge of CNC machines.
There are a lot of technical schools out there but not all of them will offer training with the type of CNC machine you want to use. Most schools that do offer training programs will not train you in a single classes; multiple classes are taken to break the training process up into several sections. Beginning classes may not even offer any hands-on training with the machine; actually working with the machines can be reserved for later classes in the training program.

CNC router machine

CNC router machine

Beginner classes will teach students about the basic concepts of CNC machines. Remember that even if you know a bit about CNC machines the same may not apply to everyone in the class. Just because the information the class is going over is not benefitting you does not mean no one in the class needs to learn that material. It may be boring at first but you have to get past the basic courses before you can move onto the real fun stuff. These courses will frequently cover the limitations of CNC machines. You will be taught to consider factors like tool selection, spindle speed, cutting sequences and clamping and positioning before you turn your machine on. Reviewing the function of G-code and how it interacts with a CNC machine is also commonly covered. Examples of coursework in beginner classes includes establishing how you will choose the right tool for a project (considering factors like safety and efficiency), installing handling devices and tools, loading G-code into the machine’s software and producing sample parts to make sure they match specifications and operation instructions given to you.
Advanced classes are where you start to really use the CNC machine, now that the beginning classes have taught you the basics of how to operate it. Initial advanced classes tend to start with reading, comprehending and making CNC programs for basic tasks like drilling, threading and turning. Later classes will cover more complex tasks like machine adjustments, program editing and creating new command syntax. Coursework in these classes may involve things like comparing test results to identify editing needs, regulating and adjusting coolant flow, repairing or replacing damaged tools and taking steps to prevent damage to tools, the CNC machine and the material being used for your projects.
These are generalizations of how a CNC machine training program is run and each institution may do things a bit differently but most places will do something along these lines. For a hobbyist it is not 100% necessary to take classes for CNC training but you will learn any subject faster when it is taught to you, compared to just figuring things out for yourself. Even if you do not have the time or budget to attend formal training at a school you should still look up tutorials and other help videos online to get a better idea of where to start and what to do. Everyone was a beginner at some point and they all had to learn somehow; determining the most effective and efficient way of learning is up to you.


Aug 11 2016

CNC machine Attachments

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When you first buy (or build) a CNC machine your primary concern when working on your budget is likely going to be figuring out what the best quality parts you can afford are. Every machinist, from professionals to hobbyists, wants to get the best CNC machine that they can in order to make machining processes as smooth as possible. While you should certainly concern yourself with the necessary parts of the machine first, so that it can actually run, there are additional considerations you can take. Attachments (or accessories, add-ons, or whatever you wish to call them) may not technically be essential to the running of a CNC machine but once you start using them they can be so beneficial that they will certainly start to feel like necessary components.
Some attachments are so common that many machinists would likely argue that they are essential components to any CNC machine. Ruin boards are a great example of an attachment that fit into this category. Image that you have your CNC machine set up and you are ready to machine your first project on your nice, new t-slot table. With what you just paid for that t-slot table you can picture what a nightmare it would be to accidently cut right into the table and destroy it. Keeping a ruin board between the table and your material should stop this from ever happening. Ruin boards do not need to be too thick; usually something between ⅛” and ¼” will work fine. New machinists may want to use a thicker board to leave more room for error.

CNC machine clamps

CNC machine clamps

Clamps are another great, yet simple, attachment that most basic CNC machines should include. Any level of precision machining will require you to hold your material still. There are a lot of ways to do this and clamps are one of the easier and more cost efficient methods. Sometimes you may have other methods available; t-slot tables utilize t-slot nuts, step blocks, step clamps and other implementations but it can be a hassle to find pieces that fit the specific table you are using. Making a clamping system of your own can be much more effective. Be creative and try to develop an easy-to-use system that works well with your equipment and set-up.
In some cases clamps may not be a good hold-down method because the item you are machining is too small. When you find that your clamps are too large, a milling vice is an excellent alternative tool. While a regular vice could be jury rigged to your table, a milling vice is designed specifically to work with a CNC machine table and they tend to be extremely precise. There are many different types and brands of milling vices in many different sizes so determine your needs and do a bit of research before committing to anything expensive.
Once you have a hold-down system in place you can start actually machining. On any project you want to make sure that everything has been machined accurately and there is no set of tools better for this than a pair of calipers. Digital calipers are the way to go for their extreme precision; 0” – 6” calipers will work fine for the vast majority of measurements you need to take while examining the finer details of projects. Cheaper calipers work fine but like any other tool you will want to go for the higher end of tool quality and price range as your budget allows.

 air sprayer for cnc machine

air sprayer for cnc machine

During and after machining, chip evacuation will be one of your primary concerns. Using an air sprayer is the best way to clear out chips while your CNC machine is running. Any standard air compressor with a trigger nozzle can do this well. Clearing away chips during the cutting process is often a critical procedure. After your machining has been completed you will want to use a shop vac’s powerful suction to get all of the chips out of your work area, leaving everything crisp and clean for your next project. Any time you are working with chips, and when using a CNC machine in general, always remember to wear safety goggles.