The Trifecta of a CNC Router Production

Alex Colic

Weight

Researching CNC routers can be a daunting task for many. There is a wide range of models available, and it takes time to decipher all the differences. However, there are really two main areas where CNC routers differ: features and size when it comes down to it. There are apparent tables or capacity-sized differences when discussing size, but differences in machine construction are also distinct. For instance, Anderson manufactures a wide range of CNC routers ranging in weight from 3000 kg to over 30000 kg. So why the wide range in machine weight and models? It all comes down to matching the right machine with the daily production requirements.

The key factor in cutting speed is not router horsepower or the cutting tool. These both play a role, but the most crucial consideration is the weight and design of the machine structure. Omnitech Selexx machines are produced with a cast iron gantry, and cast-iron mounting plates are known for their vibration-damping properties. Vibration plays a factor in cut quality, cutting speed, and cutter life.

An accumulation of vibrational energy without adequate dissipation can result in an increased amplitude of vibration. Excessive vibration will result in rapid cutter wear, poor cut quality, excessive wear on bearings and machine components. Many CNC manufacturers will use aluminum for their backing plate and some for their gantry. One of the reasons is that aluminum is lighter, thus requiring smaller servo drives to move it. However, as illustrated above, it is not ideal for vibration damping. Therefore, utilizing machines with aluminum and other non-damping materials will require reduced cutting speeds to prevent vibration and, in turn, required cut quality. The result is reduced production, greatly increased tooling costs, reduced cut quality, and shorter machine component life. A straightforward method to identify vibration while cutting with a CNC router is to listen to it simply. The louder the bit is during a cutter operation indicates, the more it vibrates.

The exceptionally high damping capacity of the heavier cast iron is one of the most valuable qualities of this material. For this reason, it is ideally suited for machine bases, gantries, and supports. The damping capacity of cast iron is considerably greater than that of steel and aluminum.

Machine selection is key in matching the right CNC router to your needs. For example, if you are looking for a machine to cut solid wood components utilizing large diameter tooling, there is more potential for vibration. Thus, it would be best to have a heavier machine to handle this job and dampen the vibration. Likewise, if you are looking for maximum cutting speeds while nesting at, say, 50 m/min, you need a machine with the weight and structure to handle this day in and day out. Matching the right machine with heavier built construction and heavy-duty servo drives allows you to achieve all the above resulting in a machine with more uptime, greater production, and significant cost saving.

 

Speed

Typically, when you’re trying to make things last, you take it easy on them. The harder you push it, the faster it will decline. However, the opposite is true for CNC routers and tooling. Through our extensive data accumulated from our vast installation base, we have determined that producing an optimum chip load will extend the life of your cutter.

If you want to extend your cutter life, you need to produce an optimum chip load. Most CNC operations use a ⅜” or ½” compression spiral bit to cut out parts on a nested-based CNC router, and the spindle RPM is between 18,000 and 21,000 and cutting 20 to 50 meters per minute. Machine acceleration determines the actual speed achieved to establish proper chip load. By feeding slower, you will be overcutting, which creates heat, and heat breaks down the cutter edge, causing it to dull rapidly.

To achieve faster feed rates, you need to have axis servo drives large enough to move the machine’s mass at a rapid speed. As you can imagine, you need to accelerate quickly to achieve a programmed feed rate before changing directions. Lighter machines with less horsepower can be programmed to a certain cutting speed but will never have enough power to reach the programmed speed.

 

Vacuum Holding

One may not immediately understand how proper vacuum hold-down can affect productivity on your CNC router. If an operator notices parts moving during cutting operations, they tend to slow the machine down to reduce the side force on the part. There are a few issues that arise from this decision. First, you immediately slow down your production, limiting the number of pieces you can cut in a day. Second, cutters will begin to break down quicker the slower you cut, as this will create friction. This increased friction will cause heat, which will break down the cutting edge. This leads to significantly increased costs for router bits, and as explained earlier, this amount can be pretty staggering. As the cutter dulls further, this can also cause parts to move, which compounds the issues.

When looking at efficient vacuum tables, you need to look “under the hood” to determine how airflow goes from the table through the pump. Anderson and Omnitech CNC routers employ a large plenum or void under the entire table zones. For instance, on the Omnitech Selexx series, two large diameter pipes are going to both zones of the vacuum table (4×8 or 5×10). This pipe goes directly to the plenum and does not pass through any other dispersal valves. This results in the optimum flow of vacuum with the absolute minimal restriction. On other CNC routers, the vacuum pump is typically connected to a disbursement valve with small diameter hoses coming out of it and going to numerous cavities under the table. Where Omnitech typically generates around 55 CFM from the hole on the table, other CNCs with small diameter hoses only generate about 11 CFM. Picture drinking a Slurpee from a standard straw and then getting a proper wide-mouth straw. It’s far more efficient.

In summary, with an optimized and efficient vacuum table, you can hold smaller parts at top speeds, leading to greater productivity and longer cutter life, with fewer rejects. When purchasing a CNC router, look at how the vacuum system is designed rather than only the size or quantity of vacuum pumps. Most single table operations should only require a single 9 HP Becker vacuum pump. If you are quoted more than a single pump, you need to ask questions as to why? Most likely, they are compensating for a table that is not as efficient.

 

Tips for optimum vacuum flow:

  1. Use lower quality 1″ or ¾” MDF as the vacuum will flow better; never use LFD (flows too much) or HDF (doesn’t flow enough).
  2. Surface both sides of the MDF before using it to remove the shiny surface to open up the pores.
  3. Use recessed nylon screws to hold your MDF sheet in place on the machine table; this limits the need to flip the sheet when it starts to cup. If not using screws to secure the MDF sheet, watch for cupping and flip the sheet when the vacuum can no longer pull the corners down.
  4. When replacing your MDF sheet, check that the table gasket is in the grooves and replace if the gasket remains flat and is no longer round.
  5. Limit cut-through on your material to 0.1mm to eliminate any deep grooving where the vacuum can escape.
  6. Set your small part size automatic onion skinning parameters correctly for narrow and/or small square area pieces.
  7. Surface the spoilboard after approximately 20 to 25 sheets; the more it is grooved, the more vacuum you will lose, especially on smaller parts.
  8. Ensure the spoilboard is completely covered if you are only machining a half sheet, for example. Use an offcut or piece of laminate to cover the exposed areas. Remember, this can be a significant source of leaks.
  9. Clean vacuum pump filters regularly, daily, weekly, or when you notice at what frequency they are clogging; clogged filters can quickly affect holding ability.
  10. Don’t have your vacuum pump too far away from the machine, and ensure the lines are as straight as possible to maximize vacuum flow with as little friction as possible.

This article is reprinted with permission from Akhurst Machinery. You can find the original article here.

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