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.


Jul 9 2015

Building a Wooden CNC Machine

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Building a Wooden CNC Machine

            For most CNC machine hobbyists the first and most important factor to consider when building a machine is cost. Setting your budget determines what you will and will not be able to look at when you are choosing each piece of your machine. Most CNC machines are metal but even the basic frame of your machine can factor into what quality of parts you can afford for the other components of your machine. You can trim a little off the cost of your machine by using a cheaper material and in most cases that means wood, generally composite wood since that tends to be cheapest. While it is a bit unconventional to build a wooden CNC machine it can be done and your machine will work just as well as it would if it were built from a more common material. Continue reading