Jul 28 2016

Plastics routing

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Modern plastics vary greatly throughout their manufacturing processes. The differences between various types of plastics and the different uses machinists will have for their materials cause problems for some people. A good machinist, whether you are a hobbyist or a professional, should be aware of the problems you could run into and steps you can take to get around those problems.
Not all plastics are made equal, not even plastics that share the same name when you are purchasing your raw materials. Something as simple as a change in color can alter how one plastic cuts compared to another. You need to be able to recognize and classify what kinds of categories plastic falls under when you are working with it. To start, determine whether you are working with hard or soft plastic. This is easy to determine; you can check this by seeing how rigid or flexible your material is. Alternatively you can see what type of chip is produced when the material is cut. Soft plastic chips will curl while hard plastic chips retain their solid shape. A single type of plastics is not always universally hard or soft; some plastics can be hard or soft depending on how they were manufactured. Knowing the geometry of your cutting tool is the second step to success. Tools that are best suited for cutting plastic have high rake and low clearance. These days there are thousands of different tools made for plastics cutting that you can choose from. Soft plastics tools have “O” shapes and are usually straight or spiraled in shape. Hard plastics tools can have an “O”, spiral shape or a “V”, straight shape.

Routing plastics

Routing plastics

One of the most irritating problems you can run into is the plastics material welding. This problem can happen due to the direction of your cut, using a cutting tool that is too small or having a chipload (the thickness of a chip) that is too large. Chipload is the most common cause of this problem. Your chipload is determined by your spindle speed, feed rate and the number of edges on your cutting tool. In plastic routing you want your chips to be just the right size to distribute heat correctly. Another potential problem is your finished project having poor finish. Having good finish is extremely important on plastic items, especially ones that are made to be put on display somewhere. The quality of your finish is going to be heavily affected by your chipload. Problems aside from chipload tend to come from the condition of your CNC router. You want to make sure that your CNC router is up to speed on maintenance and performance at all times. Learning to work with plastic correctly is a matter of practice and with time you will become experienced enough that you will run into these problems less and less, until you stop running into them almost altogether.
Making sure you have the right bits for plastics is one of the most important parts of preparing for projects. Your best option for hard plastics is a solid carbide router tool. If you cannot get one of those a carbide tipped tool is a good second choice but they will not perform as well as a solid carbide tool. You can use the same kind of tools on soft plastics but high speed steel tools will also work well on these softer materials. Your CNC router should be capable of speeds of at least 15,000 RPM to work on plastic. A CNC router is the best type of CNC machine for working on plastic, being the machine that is best suited for working at the high speeds your projects will require. Ideally you want to be working at 18,000 RPM, if your machine can operate at that speed, at a feed rate of 200 in. per minute. This is a general figure for plastics in general and the exact speed and feed rate you should use will vary a bit between different types of plastic.


Jul 21 2016

CNC machine for making music

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Since long before recorded history began, people have made music. From something as simple as banging rocks together to an endeavor as complex as performing an opera, people have always had a fascination with music as a medium of storytelling and a form of entertainment and we likely always will. In modern times people who think of music generally think of instruments. Having access to a CNC machine allows anyone to make a musical instrument of their very own for all musical entertainment purposes. But music is not limited to traditional instruments alone. Anyone who has seen the theatre performance Stomp or similar shows knows that even everyday objects can be used to make music. While a CNC machine is not an everyday object they too can be used to make music, in a more literal sense than machining an instrument.

Making guitar with cnc machine

Making guitar with cnc machine

Most instruments are made from either metal or wood, which just so happen to be two of the most common materials used by hobbyists for their at-home CNC machining projects. One of the most popular instruments that hobbyists seem to go with is the guitar. There are dozens of different types of guitar designs that you can choose from. Many guides exist on the Internet for making a guitar with a CNC machine. While the general process is primarily the same for most guitars it will be the customization process that is the heart of this project. You may be able to find files and just make the guitar straight away from those but you also have customization options. This guitar can look however you want it to look like. Maybe there is a guitar you like but that you wish was a bit different, allowing you to use that guitar as a blueprint and tweak the design to fit your own tastes. Or maybe you want to be really creative and design something completely from scratch to fit your own mental image of the perfect guitar. This same principle applies to most instruments, depending on their level of popularity. You are more likely to find help and support videos for more commonplace instruments, like a violin, than for rarer or larger items like a cello. Those of you who work with metal can also pursue this project by making saxophones, trumpets or other instruments constructed from metals. Regardless of what type of materials you are using you do not have to create an entire instrument either. If you already have a ready instrument you could make new individual parts to replace, repair or upgrade various components of those items.

CNC machine for making guitar

CNC machine for making guitar

Besides producing instruments to make music, CNC machines can be used to make music themselves. The key to this process is to figure out a combination of feed rate and distance along an axis that will allow the stepper motor to spin at a frequency that mimics a musical note. With a bit of tinkering you can produce chords to replicate songs or to even entirely new tunes of your own. A more in-depth explanation of this process, as well as several musical examples based on popular video game soundtracks, can be found at http://tim.cexx.org/?p=633. Another example (https://www.youtube.com/watch?v=jAWF-qhh4pQ) shows a synchronous motor that has been set up to play the song “The Imperial March” from the film “Star Wars Episode V: The Empire Strikes Back”. In the first example MIDI (mid2cnc) script is use to generate these musical results. While the sounds you generate may not be as spot on as an orchestra directed by John Williams it can be very fun to get an additional use out of your machine while getting to do something a bit different with it.


Jun 30 2016

Speeds and Feeds for wood cutting

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Speeds and Feeds

While CNC routers are not necessarily a technology you would call “new” they are newer than some other CNC machines and concepts. Older and more established CNC technologies, like mills, are able to cut metal with exact specifications regarding chip load or Speeds and Feeds. Metal has far less variables than wood so it is easy to calculate the chip load to an almost exact number every time when doing metalwork. The work conditions for woodcutting operations are not nearly as consistent. Even when you work with the same type of wood the material can vary in density based on the growth of the wood when the tree was cut down, impurities in the wood and other factors. Hold-down methods used with wood are less consistent than the methods available for metalwork. Additionally, cooling systems can almost never be used for woodworking because exposure to moisture can change the shape of the wood during the cutting process, throwing off the results of your work and possibly ruining a project completely. As a result, machinists must pay careful attention to the level of heat generated during cutting processes or else risk shortening the life of their tools and damaging their projects.

Cutting wood with cnc Speeds and Feeds

Cutting wood with cnc Speeds and Feeds

The three key variables to consider for heat control are the number of flutes on a tool, the feed rate and RPM (spindle speed). These three variables, when combined, are used to determine your chip load, which will greatly impact the quality of your work and the life of your tools. Chip load can be calculated with the equation:
chip load = feed rate / (# of flutes x RPM)
There are numerous chip load calculators that you can find online so that doing this work becomes faster and easier than if you calculate it by hand.
Because of the many variables of wood there is no go-to, easy solution for figuring out the exact parameters you will need to set on your machine. You could not just look up “best CNC settings for pine” and find the perfect settings for your machine when cutting pine. You can, however, follow a little checklist in order to determine what settings you need to make the best possible cuts that your machine can manage. Start by taking the hold-down methods you have available into consideration. Different vacuum systems and other hold-down methods will have varying effects depending on just how your system is set up. It is good to check your hold-down systems frequently as you may get changing results as your machine ages and starts to wear down. Think about how big the part you are going to machine is; smaller parts are more likely to move when the cutter makes contact. Take the geometry of your tools into account. For example, up-shear tools have great tool life but can cause a part to move if they overpower a vacuum hold-down system. Determine how deep your cuts will be to decide on the number of passes you will make. The deeper a cut the slower a feed rate should be. This may wreak some havoc on your tool life but it is that or a low-quality part. You should start at a low feed rate and work your way up. Do not start too slowly though, that can generate as much heat and cause as much damage as going too fast. Keep going until you notice a little damage in your test material, then dial the feed rate back a bit and you should have your optimal settings.
Impurities in wood (such as knots) can cause some issues and be difficult to cut through. You will generally need to cut more slowly than usual to get through trouble areas like this. Additionally, you will want to ensure that you use a particularly sharp tool and it also helps to lubricate it so that the blade will not gum up while cutting through the tougher areas of your material. Individuals who are interested in the application of high speed wood cutting may also find this article interesting and useful: https://hal.archives-ouvertes.fr/hal-00881899/document.


Mar 10 2016

Cardboard Cutting with CNC machine

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Cardboard Cutting with CNC machine

At a glance you would not think that cutting cardboard would be a very challenging task. Cardboard is not a hard material like metal so how difficult can cutting it be, right? While cardboard is not the hardest material out there it is rigid and can be just as sturdy as any other man-made material. These days there are even companies that make furniture out of it. Now you could use a pair of scissors or a utility knife to cut the material but who wants to do manual work like that when there is a CNC machine option available. There are two major options for cutting it with a CNC machine, using a drag knife or a laser cutter.

CNC machine cardboard cutting

Cutting cardboard with cnc machine

Cardboard cuts differently from most other materials that you can work with on a CNC machine so average tools like bits do not get the job done. This is where the drag knife comes into play, being about to make the smooth cuts required to work with cardboard without wrecking the material. Before you do anything else, turn off the power to your spindle. You do not want your drag knife to spin; the knife must remain in a stationary position while it is making cuts (it is called a “drag” knife, not “spinning” knife, for a reason). Because the knife does not spin at all you will have to turn it yourself to realign the cutting edge when you want the cutter to move in a new direction. If you are used to working with bits or similar tools that can turn on their own be sure to remind yourself about the drag knifes limitations when you are programming your code. You are also going to need a way to hold the cardboard down very tightly but do not use a vacuum system. If a vacuum is used air will be pulled through the cardboard and the pressure will make cutting more difficult. Not every user will be adapting a CNC machine they already have for cutting cardboard, in which case you could purchase and use a paper cutter for this type of project. Most paper cutters are inexpensive but they tend to limit the size of cardboard you can work with and are often ineffective at cutting thicker cardboard.

CNC machine cardboard

Cutting Cardboard with cnc machine

Laser cutters are easier to cut cardboard with and are more effective than drag knives. Adjusting the cutting power on a laser is simple; all you have to do is change the power settings to alter the intensity of the laser whereas with drag knives you would have to buy multiple knives of various sizes or fine tune your machine to make small cuts very carefully. Laser cutters also leave a nice, crisp edge along the cuts they make. Additionally, since lasers do not put any physical pressure on your material you do not need the keep the material held down as tightly as you do when using a drag knife. While lasers perform much better the big downside is their cost. Be prepared for a hefty price tag; if you do not need a laser cutter long term or if you want to test one out to make sure you like the results try renting one before you commit to buying a pricey CNC machine.
There are other methods to cutting cardboard with CNC machine besides using a drag knife or laser cutter but many of the other methods do not work as well, are only suited for thin cardboard and are less common than using either of these techniques. While your budget may limit what method you can use for the job you should still be able to get your task accomplished as long as you know what you are doing and have a little creativity.


Mar 3 2016

Leather CNC and Rubber Cutting

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Leather CNC and Rubber Cutting

Many of the materials that you will find yourself working with on a CNC machine can be cut using standard techniques. When you boil it down to the basics cutting different materials like wood, metal and plastic all use techniques that are pretty similar during the cutting process. Some of the less common materials that you might work with have different properties from the more frequently used materials and therefore require you to do your work in less standardized ways. Two types of materials that you need to cut differently are leather and rubber.

CNC leather cutting

Leather cutting

Leather is difficult to work with because of how it cuts differently compared to more common materials; you cannot just lay the leather down and cut it with a bit or you will ruin the material and your project will not look presentable. Hobbyists who already have a CNC machine can equip it with a drag knife in order to cut leather but there are a few things to keep in mind while using a drag knife. When getting your machine ready turn off the power to your spindle or router. The drag knife should never spin while it is cutting. Because the drag knife does not spin at all on its own you will have to manually realign its cutting edge when you want it to move in a new direction. Keep in mind that it can only move in the direction that the cutting edge is facing when you are programming your tool paths. In addition to a more specialized tool you will also need a very strong way to hold the material down. Leather needs to be held down as tightly as you can manage when you cut it. When you are selecting a hold-down method you cannot choose a vacuum. If a vacuum is used the pressure from the suction will go through the leather, making it almost impossible to cut. While a drag knife does work it is more suited for working with thin leather but it is not your only option. For any leather (thick leather especially) a laser cutter works very well. Because the laser is not physically cutting through the material you do not have to worry about how the leather will cut. Additionally, there will be no frayed edges and the leather does not require as strong of a hold-down method since the laser does not put any physical pressure on the material. Overall a laser cutter is better for cutting leather but many hobbyists do not have access to a laser cutter.

leather cut cnc

Leather cut

Rubber is a bit more challenging than leather. While rubber can be cut there is not necessarily an “easy” way to do it. First off, do not even try to cut rubber if you are using a laser cutter or a plasma cutter. It will catch fire. When working with rubber you are going to have to mill it. The key to cutting rubber is to freeze it so that it become more solid and easy to work with. To what extent you want to freeze it can depend on the type of rubber you are working with. In most cases freezing it with dry ice will work (-80° C). You can also freeze it with liquid nitrogen (-320.8° C) but that might be overkill. Once the material is frozen you are going to have to machine it very quickly before it can heat back up (especially if you are using dry ice). You will also need a tool that is extremely sharp. This can be a challenging process so do not be surprised if you cannot do it perfectly the first time. Rubber can be cut just as easily as any other material with a water jet cutter but most people will not have access to one of those due to their price. You are more likely to go with the freezing-then-cutting method.