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MGN12H Mini Linear Rail Guide, 250/300/ 400/500/ 550mm Linear Sliding Gide with MGN12H Carriage Block for DIY Printer and CNC Machine (250mm)

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About this deal

MGN9, MGN12, and other rail names are all part of Hiwin’s naming system. This is a name you’re bound to come across when researching linear rails. Hiwin is a popular Taiwanese producer of linear motion components. Due to the popularity of Hiwin rails, many Chinese manufacturers have been making their own products following Hiwin specs, including sizes and model names. The other issue with smooth rods is deflection, which is how much the rod bends when a load is applied. Deflection is the main weakness of unsupported rods, and the reason why supported rods are always preferable for moderate and heavy load applications. MGN vs HGR linear rails Linear rails with a square section, such as Hiwin guideways, are the first choice when accuracy and reliability are needed. They are the standard on CNC machines and have been gaining popularity in hobby 3D printers and laser cutters as well. Linear rails are made of precision ground steel, and allow a carriage to travel along its length. Crucially, they constrain motion along all axes except the axis of movement. The carriage cannot tilt up/down or sideways, or roll around the rail. Tip: three-wheel gantries are preferred over four-wheel gantries to avoid overconstraint issues. Linear rails vs smooth rods

Dynamic load (C) is the maximum continuous load applied to the bearings and raceways that doesn’t compromise the service life of the rails beyond the nominal rating (which is 50km for MGN/HG rails and other ball-type rails). HGW (flanged) carriages can withstand moment load better (i.e. a load that would cause a rotation), as they are shorter and the bolts are more widely spaced.

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Linear rails are designed to resist multiple kinds of radial loads, which are forces perpendicular to the direction of movement: According to Hiwin’s official lubricating instructions , these are the recommended grease lubricants for standard applications: Manufacturer However, V-wheels need to be carefully tightened with a small wrench, and require maintenance as they loosen and wear out over time. V-wheels are very much a “save now, worry later” solution. Still, when properly installed, they do provide good accuracy.

Due to saw limitations and the hole spacing on a MGN rail, ZYLtech will determine which length rail to use for the custom length specified. There will be no “cut off” pieces from custom lengths. If you compare smooth rods to linear rails side-by-side, the first thing you’ll notice is their play, or rather clearance, as linear bearings designed for smooth rods tend to be fit quite loosely. This makes them particularly poor at withstanding loads that cause the bearing to “yaw” or tilt perpendicularly to the axis of travel. This is why they are rarely used outside of low-load applications like 3D printers and laser cutters. On the other hand, linear rail carriages are designed to have raceways with slightly oversized balls. This “negative clearance” is known as preload.I recommend using square slider nuts to secure MGN rails to 2020 extrusions, as long as you have access to at least one end of the T-slot. Otherwise, drop-in T-nuts are very convenient but you run the risk of accidentally tightening the nut against the rail itself, without the nut flanges engaging the 2020 profile. Lubrication

Let’s take a look at Hiwin rails, and by extension the many inexpensive Chinese clones available. There are many different series of rails and carriages, but the two most popular ones by far are the MGN and HG series. MGN carriages feature two bearing raceways, while the HG series goes up to four which provides lower friction. Z1 preloaded rails will not slide as freely by hand when compared to a Z0 rail. Any imperfections in the machining process become twice as apparent when higher preloads are involved with an absence of real load. Want to feel your Z1 rail's true characteristics? Lay the rail on a clean, flat, and hard surface - then push down on the face of the carriage with light force while moving the carriage around. This better simulates real-world behavior. V-wheels are the main alternative to linear rails in the hobby space, and are widespread in 3D printers and budget laser cutters (like some variants of the K40 laser cutter). V-wheels are designed to ride on V-shaped grooves of aluminum extrusions. Because of this, they are extremely cost effective for large machines since parts of the frame also act as linear guides.As mentioned before, HG carriages are taller to accomodate four raceways instead of two on the MGN series. This makes them a good choice for heavy load applications like CNC milling, and according to Hiwin it also makes them suitable to be mounted onto slightly uneven surfaces. The open-source PrintNC CNC router design takes advantage of this by using HGR rails on rectangular steel tubes instead of aluminum extrusions. Note: I have only included specs for the short CA/CC carriages, as the HA/HC carriages are much harder to find online. Tips on buying, using & maintaining linear rails Handling Z1 commands a higher preload between the rail and carriage than a more typical Z0 preload. Preload occurs after all space between two components (in this case the rail and carriage) is closed. Any further interference becomes preload, as these materials are too hard to physically compress. Linear rails and carriages have been prohibitively expensive for a long time, but in recent years their price has fallen considerably.

Having a higher preload is a benefit for our use case, but does change the way that rails feel when move by hand. What to expect:The naming of MGN rails is straightforward, with the number in MGN9/MGN12/MGN15 indicating indicating the rail width in mm. MGN carriages are available in two lengths: Weight is a big consideration whenever a linear rail is mounted onto a gantry. High mass means lower possible acceleration, is undesirable. Each tier of MGN rails almost doubles the weight: Rail size Rails can be cut to any length using an abrasive cutting method. Consider graduated shallow cuts to keep heat down and avoid warp potential. Some folks prefer to mount the rail to spare extrusion which can also help with warp mitigation. What is a Z1 preload? Aside from linear rails in the highest price tiers, all linear guide rail carriages will benefit from a proper cleaning before being put into service. See here for a great walk through on this process. It’s worth noting that MGN9 carriages are the only ones out of the three sizes that do not overhang a 2020 extrusion. This means that the carriage can ride right next to a panel, or that two MGN9 rails can be mounted 90 degrees apart onto the same 2020 extrusions like this:

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