Jul 7 2016

Climb and conventional milling secrets that you should know

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When a cutter moves through material it can mill up (conventional milling) or down (climb milling). Many machinists use climb milling for most, if not all, of their CNC projects. Climb milling is known for producing better surface finish than conventional milling and overall does have more advantages than conventional. However, climb is not always the better of the two options and any machinist should know that there are times when conventional is preferable, and when those times are.

Climb and Conventional Milling

Climb and Conventional Milling

Using climb milling, each tooth on your cutting tool makes contact with the material you are working with at a defined point and moves out, cutting thinner parts of the material until it is no longer touching the material. So, the width of the material being cut starts at the maximum length and decreases to zero as the cutter moves. This causes chips to be thrown behind the cutter, making chip removal an easier process while machining. Tool life is also extended because each tooth on the cutter is not rubbing against the material. One of the major downsides of climb milling is that it can potentially produce a lot of backlash. As a result this method should mainly be used on machines that can eliminate large amounts of backlash and it may not always be usable with older CNC machines.
Conventional cuts in the opposite direction of climb. Using conventional milling, the teeth of the cutter will start at zero thickness and work their way up to the maximum thickness that you are cutting. When first making contact with the material your cutter does not even cut the material; it slides across the material surface until enough pressure is built up for the tooth to dig in and begin cutting. This causes the work material to become hard and somewhat deformed and also causes cutters to dull faster than when using climb. The sliding and biting of this cutting process also tends to leave an inadequate surface finish on work materials. On the upside this process does not generate anywhere near as much backlash as climb and is a perfectly sound cutting method on almost any CNC machine. The two methods do not have to be used independently either; climb can be used for rough passes while conventional milling is used for finishing passes.
Climb does have a few distinct advantages over conventional when your machine can manage it. As mentioned before, your tool life will be longer, surface finish will be better and chip removal is much easier. Additionally, you do not need as advanced of a hold-down system. Climb exerts force downwards instead of upwards like conventional milling. You can also use higher rake angles while climb milling, saving you a little money on the amount of power needed. Just do not forget about the excessive backlash when looking at all of the positives of climb milling.
When using climb milling, deflection can causes some problems with surface finish. Climb cutting causes tools to deflect, deforming the surface finish of projects and leaving you with less than adequate results. If you run into this issue try switching to conventional cutting; that will likely make a big enough difference to correct any issues you are having with maintaining a good surface finish. While conventional cutting can help it will not always fix your problems. If you have tried climb cutting and conventional cutting and are still having issues you can decrease deflection further by reducing the depth of your cuts. Using a small amount of your cutters diameter will make it less likely that you will experience any deflection.


Mar 24 2016

CNC Routers vs CNC Milling

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CNC Routers vs CNC Milling

CNC Routers vs CNC Milling

CNC machines with a 3 Axis set-up are usually routers or mills. While both machines are similar in principle they are used for two very different purposes, resulting in them being constructed fairly differently. This article will give you a brief analysis on the difference between the two machines.

CNC Router vs CNC Milling

CNC Router and CNC milling

CNC routers are commonly used to cut soft materials like wood, foam and plastic. With the right know-how a CNC router can even cut aluminum and other soft metals. Because the materials being cut are soft CNC routers are built fairly lightly. A small CNC router can weigh several hundred pounds but that is very light compared to larger routers and mills. The soft materials cut on a CNC router tend to come in large sheets so CNC routers have big cutting surfaces but a small z-axis. Cut and jog rates tend to be high due to the large area that needs to be covered during the cutting process. For example, some routers are capable of jogging at 12 inches per second. On average a CNC router will cut four to eight times faster than a CNC mill. CNC routers can operate at 25,000 to 30,000 RPMs at high speed while a CNC mill will have a speed 3000 to 5000 RPMs when cutting quickly. The trade-off of a router is accuracy. Due to the high speeds a router cuts at there is not as much accuracy as you would get when using a mill. Usually soft materials do not need to be precisely cut to a 1/1000 of an inch so it should not raise any issues in most cases. CNC routers can be fit with a router or a spindle as a cutting tool.

CNC Routers vs CNC Milling

CNC router

CNC mills are beasts compared to routers. They are built to cut hard materials and that can mean anything from aluminum to titanium. CNC mills are often used to create (or mill) machine parts so they are incredibly accurate when cutting. The average mill is accurate down to 1/1000 of an inch, if not even more accurate than that. A CNC mill can cut with such accuracy because they are made with extremely hard materials, such as die cast iron, that will not flex under any load you put on them. This makes CNC mills many times heavier than CNC routers. A large CNC router can weigh upwards of 15,000 lbs. while a CNC mill that is just as big can weigh 90,000 lbs. Hard materials need to be cut at much slower speeds than soft materials so CNC mills do have a much slower jog speed than CNC routers. CNC mills use spindles like CNC routers can but they do not use routers since spindles work better than routers at lower RPMs. CNC mills can be used for routing but tend not to work as well as a dedicated CNC router. They also have a much larger z-axis than CNC routers because they are often used in conjunction with a rotary indexer. CNC mills are significantly more expensive than CNC routers of equal size and usually have a smaller cutting area than their similar sized CNC router counterparts as well. Any CNC mill with an area larger than 2×2 feet can easily cost tens of thousands of dollars. CNC mills can be built to handle different types of materials (horizontal, vertical, multi-axis, etc.) as opposed to a CNC router designed to handle sheet materials. CNC mill manufacturers often sell their machines with different spindle options depending on what kind of material you intend to mill.


Mar 3 2016

Laser CNC Engraving Metal

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Laser CNC Engraving Metal

In the past #lasers and metals have not mixed very well. While a laser does produce high amounts of heat suitable for cutting or engraving it is still, at its core, light. Anyone who has ever walked through a full parking lot of shiny cars on a hot, sunny day without their sunglasses knows that metal reflects light very efficiently. Many individuals know that laser cutters traditionally do not work on metal and would not attempt any kind of metalworking project using a laser. However, there are multiple types of lasers and some do work well enough with metals for engraving projects.

CNC Laser Engraving Metal

CNC Laser metal cut

One of the first gas #laser invented was the CO2 laser and it is still one of the most common lasers used today. This type of lasers work on some metals but not all, as some metals reflect the laser beam too much for it to be effective on metal projects. One type of the metals that works well with a CO2 laser is anodized aluminum. Anodized aluminum comes in several different colors and you will observe different effects depending on what color the metal is. For example, black anodized aluminum turns white when engraving with a laser while red anodized aluminum turns light pink. You can intensify the color with a second pass and get a whiter sheen but you will usually not be able to completely remove the original color created by the initial cut. Anodized aluminum should be cut at low power, high speed setting in order to generate crisp, clean engravings. Using too much power can distort engravings and result in images that have been burned too much during the cutting process.

 CNC Laser Engraving Metal

CNC Laser cut

Painted brass is another metal that works well. Do not use unpainted brass with a CO2 laser; it will reflect the beam and you will likely get hurt. The laser will remove the coating from brass that has been painted, exposing the brass beneath for appealing visual effects. You can also use brass-coated steel. Like with painted brass, you will be removing paint to expose the brass beneath. Brass-coated steel just has a thin layer of brass over steel instead of being made from pure brass. The polished brass that you expose with your #laser is protected by the lacquer, preventing the brass from being oxidized and keeping it bright and shiny for many years. If you do not know whether your material is painted brass or brass-coated steel you can test it with a magnet. Magnets will stick to brass-coated steel but not to painted brass since solid brass does not have a sufficient magnetic field to attract and hold a magnet.
For other metals you can use an Yb: Fiber Laser, a fiber laser that uses the element ytterbium. Fiber lasers have several distinct advantages over more traditional lasers. The key component that makes them suitable for laser engraving is that the light used is already coupled into a flexible fiber, allowing it to be delivered to a movable focusing element easily. This is what makes it much more difficult for metal to reflect the beam, making this type of #laser safe to use with more types of metals. Fiber lasers also have a very high power output and can have active regions up to several kilometers in length. The fiber’s high surface area to volume ratio allows for continuous output at the kilowatt level, resulting in efficient cooling. Because fibers can be bent, unlike rod or gas lasers, they are usually very compact machines. The pulses that the lasers generate operate within nanoseconds, further making fiber lasers well-suited for metal engraving projects.


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.