CNC machine or toy?
How do you tell the difference between a real CNC machine and a toy? This is a question many novice customers ask themselves, unaware of the differences between products on the market. Plot Electronics, with more than 20 years of experience in building and constructing CNC machines, can help to solve this dilemma. Over the years, we have learned that you cannot skimp on high-quality components if you want to ensure the reliability and precision of your equipment.
Components used: Key to sustainability
Initially, any manufacturer may find it difficult to choose the right parts, but our experience has taught us that saving on quality ends up costing more in the future. The CNC machines we build are made for production, not play. You will find many machines on the market that look professional, but in reality are just 'toys' - cheap, not very robust and prone to failure.
Traps of cheaper substitutes
Typically, imported machines that mimic professional equipment are priced low - 10% to 20% worth of machines from established manufacturers. Instead, as often happens, many sellers bump their price up to 500%, presenting them as premium products. Therefore, before buying, compare the product carefully on different platforms (e.g. Aliexpress), paying attention to key mechanical components such as the running gates.
These low-budget machines are usually based on outdated technologies, such as stepper motor drives, which have been falling out of the industry for two decades. If such equipment goes into production, you will quickly see a drop in accuracy and, consequently, a reduction in profitability.
Conversions versus real opportunities
Some companies are trying to upgrade cheaper machines by adapting them to more demanding tasks. While this may initially seem like a good option, these machines have a limited lifespan and are not suitable for reconditioning. They simply cannot withstand the intense production load.
How do you tell the difference between a CNC machine and a toy?
One test that can be carried out is the simulation of a collision. In professional CNC machines, even at full speed, a collision should not permanently damage the mechanics. On low-cost counterparts, such a situation could lead to permanent damage.
Brand trust: Is it always justified?
Many companies choose machines on the basis of the manufacturer's reputation, without paying attention to current service or warranty conditions. Meanwhile, changes in the market can affect the quality of service or after-sales service. Therefore, it is worthwhile to carefully examine the warranty conditions and make sure that the service will not take weeks in case of problems.
Summary
When choosing a CNC machine, it is useful to know the differences between the components used, which affects its durability and capabilities. Good quality components, although more expensive at the outset, can result in significant savings in the long term, minimising the risk of downtime and costly repairs.
How do you choose the right CNC machine for your business?
Determine what parts it is made of
- Servo drives
Digital servo drives - there are many classes of these and so-called pseudo solutions like stepper motor with encoder (ezi-servo) - this is the main difference. On Professional machines, these are usually AC servo drives , which are capable of taking on multiples (3-10) of overloads during operation and when idling. AC servo drives are very expensive and actually represent about 40 % of the value of the machine. The efficiency is a multiple of machine work done on stepper drives or ezi-servo - the 3D work itself takes 10-20 times faster and the results are noticeable in terms of quality to the naked eye. In the super professional series, the servo drives in the machines produced have 800% overload capacity, which in the case of cheaper machines is at the level of 300%, which is 2.6 times higher, giving higher acceleration and speed of execution of details in comparison with cheaper solutions, and 8-20 times higher than in the case of machines on constant torque stepper motors, which are classified as toy machines. Also important are the speed of response to deformation or the filters and algorithms used to control the drive, such as harmonic filters or pendulum filters. The use of advanced capabilities in terms of speed performance is essential. Modern servo drives have a balance between algorithm and direct drive response to deformation. Getting rid of the algorithms and simplifying the block responses increases speed but will not increase precision, nor will it allow correct operation for changes in the nature of the operation. Machine designs have internal stresses that can cause vibratory deformations, which are dampened by the possibility contained in algorithms that defy the laws of physics and are able to stop the accelerated mass without overshoot and visible vibrations on the workpiece. It is therefore not true that the fastest reading and response of the control system to the deformation is the best choice. It does not take into account the quality parameter of this change. There is a fast response, but is it correct ?
Linear drives, which are heavily advertised as direct drives, are also used. The drives differ in performance by about two to three times being faster than industrial machines, but they also have their disadvantages. An important parameter is energy density, which is a direct result of the components used, including rare earth magnets. This technology has been known for many years but is only just being implemented in cnc milling machines. Previously, it was used in machines such as lasers or plasma cutting machines. The components used in their manufacture have an impact on the power of a given motor and its size and weight, which is important during fast feeds. In milling work, the level of capability is only satisfactory in machines with small working areas due to the large winding cross-sections and the large currents flowing through them giving power over small distances.
In large-scale milling machines, the use of linear drives does not yet have a sufficient level of power to maintain the milling position.
- Machine frames
In order to be able to use servo drives in the machine, it is necessary to machine frames with high accuracy, which are machined to an accuracy of +/-0.01 mm, and such are also the linear guidance components of the carriages in class H and P. In non-professional machines, the level of workmanship or deformation during operation is much greater and reaches up to 1.2 mm. For the furniture industry, these values are acceptable, but pose a problem for the service life of such a construction. The given changes lose their deformation resistance properties and become bent, changing their geometry after time, or do not hold on the workpiece, deteriorating their properties with the time of the cnc machine. Machined frames may be in poorer tolerance and if the frame has larger deviations a linear guide is used in a deteriorated class - designed for sliding doors etc. The carriage class is 0.3mm, but there are usually 4 and the errors add up - this allows the machines to run because the clearances are large enough to cover the mechanical errors. The errors are only apparent when the cutting load is greater than the weight of the guide body - then you know what the machine is worth. Plot Electronics has fine-tuned the machining process and makes devices with a very high accuracy class of 0.01 mm as standard on 4 metres. Higher accuracies are possible, but time is of the essence in terms of economy. The class of components used is also selected according to machining accuracy. The design of the machine has a great influence on the quality of the workpieces, the possibility of using large tools and the service life of the tools and the machine as a whole. Welded constructions are subjected to internal forces that affect the stability and performance of the CNC machine. This process is covered by company secret and patent, but in many cases temperature, chemical or vibration annealing is used. If you do not have an annealed print, then your design has not been in a furnace and this can easily be checked by looking inside the profile. Vibratory methods have no visible signs, but you can easily hear the structure, chemical methods have similar effects to annealing, and there is also an ageing method where the structure is subjected to daily life and rests.
- Spindles
Many spindle suppliers are found on the CNC machine market and it is difficult to judge directly which ones are in a class of their own and which ones are just for fun. Depending on the needs, spindles are selected according to the operating characteristics supplied with the spindle, which guarantees stable operation after proper parameterisation by a controller called an inverter. Plot Electronics uses spindles from HSD, Hiteco and other companies whose products are characterised by exceptional quality and durability. On the market of CNC machines, you can find equivalents of HSP and water-cooled spindles used in the amateur class, commonly called Wet Chinese spindles - this is how spindles from China are described. Their power in comparison tables has nothing to do with reality - it is the power consumed and not the effective power on the shaft. The power comparison therefore makes little sense because there is no guarantee of stability.
The advantage of the professional spindles used is their non-linear working characteristic, which has a peak in power at the average value of the maximum rotational speed, giving the possibility to work in a larger range of rated speeds. Plot Electronics takes advantage of this advantage by enabling it to work at low cutting speeds and, as a result, allowing the user to work with the parameters envisaged for the process of cutting steel materials at 800-3000 rpm with a spindle with a maximum speed of 24000 rpm, which enables the user to work with many different types of materials with an advantage over other solutions.
Also of significance is the spindle control itself, which is implemented through Automation and a device called an inverter, which features inverter operation pumping energy into the motor equal to the energy consumed. This saving keeps the motor at optimum rated conditions for the load. Such a spindle is therefore utilised to the maximum and unused energy does not occur and is not converted into heat. This saves energy and offers tremendous opportunities to precisely control the torque spindle speed, but also to control the cutting motion. Spindle frequencies range from 200 to 1,000 Khz, which makes it impossible to use vector operation algorithms up to 300 Hz, whose efficiency is 1.4 times higher than scalar control; for higher frequencies, proprietary algorithms are used, the programming of which can only be performed by the manufacturer's service.
- Drive
Drive is by means of planetary gears and helical slats, also in the Z axis, which is unique among the competition. This solution protects against collisions - possible program errors - inattention, etc. On Plot Electronics machines, nothing bad will happen during such incidents - the machine will shut down. The machine is protected against operator errors. After switching off, switching on again and performing a reference run, the machine fully returns to its original settings. The machines are designed for such eventualities thanks to years of experience. The use of helical drive in Z-axis mechanics involves the use of planetary gear elements and expensive motors with integrated brakes. The solution used by Plot Electronics is more expensive but reliable and durable.
Competing machines use ball screws, the collision of which causes damage to the drive, usually to couplings and mechanical components, and to balance the weight, Z-axis booster cylinders are used, which in terms of safety and system complexity is an outdated and unreliable solution.
The Y-drive system operates independently, allowing the right-angle correction system to function - the loads during operation for extreme dimensions are different for both drives - the relevant algorithms take care of synchronisation and the angle system always positions the machine precisely during reference.
The parameters and accuracy classes in which the components are manufactured and installed are important, and this is not readily apparent at first glance.
In toothed strips, the grades used start from T6. For many manufacturers, this is not important and they use cheaper substitutes, the quality effects of which are felt on the workpiece but also in terms of durability. If the quality is poor, there are visible signs of wear in the form of scuffing on the edges of the helical strips, which causes deformation of the scale and the machine does not keep to the parameters.
- Guides
The mechanics of cnc machine building are proprietary and have an advantage over competing solutions. The X-drive slides are mounted at the top and bottom of the beam, which enables the transfer of greater forces due to the larger spacing than in competing solutions, this results in smaller cross-sections of the running beams in the machines than in competing solutions, but the axial spacing is larger, which enables the transfer of greater cutting forces, in addition the slides do not need folding guards because there is no concern about dust on the slide because from above and below the chips and dust are easily cleaned by the ball carriage scrapers. In competing solutions, the guides are bolted to the side of the beam, which results in smaller spacing and the need for larger cross-sections of running beams in addition to the folding covers, which make it difficult to reach the guides for the operator checks and cleaning that are required. Mounting Y drive guides on the machine structure is also a mistake, but is used by many machine manufacturers avoiding the impact of machining errors in the structure on machine errors. The machining of the planes on the sides of the profiles is apparent and is intended to roughen the machining so that only the tracks can be seated. The expansion of the steel in such structures causes it to push against the side walls of the profiles of which the machine is made. This causes changes in the concavity or convexity of the profile to which the guideways are attached, which in turn push against the bogies and these widen the spacing between the supports of the beam. In such cases, the 4-row carriages support the entire load of the beam on only 2 rows, limiting the service life of the carriage and resulting in relatively faster wear of the carriages. An additional problem with this design is the settling of excavated material and dust on the bearing sill, which necessitates the use of covers. One important aspect is the fact that the guideways stick to the bases, otherwise the guideways will not withstand the pressure of the weight and will fall on the bolt until it is blocked against the side edge of the bolt. The construction of the kinematics is not wrong, but regular maintenance and almost daily lubrication must be remembered.
In designs with bottom-mounted tracks, there are no mechanical faults and the tracks are not stressed and are naturally protected from the ingress of dust or chips. Cleanliness is easier to maintain in such constructions and the service life of the bogies is more than 10 years with frequent lubrication.
- Structural wishbone system
Clearances in CNC machines appear after about 2 years of operation and must be corrected by tightening the special screws that push the gears against the gear rails.
The machines offered by Plot Electronics use a proprietary solution that automatically applies pressure to the drive to prevent backlash, giving ideal operating characteristics for years to come while protecting the entire precision mechanics of the machine from operator error or collision.
In addition to the adjustment function, the proprietary solution absorbs most of the vibration and oscillation of the mechanics during the cutting process, which extends the service life of the entire mechanics several times and gives the possibility to work with unbalanced or special tools.
- Vacuum clamping system
Vacuum clamping is moving into the standard and is a popular clamping solution for boards and components with a sizable surface area. There are problems with clamping smaller components, which Plot Electronics has tackled by applying a proprietary solution and developing clamping methods in the form of vacuum antiforms. In addition, the vacuum pumps used are developed for Plot Electronics and are characterised by higher efficiency and lower energy consumption based on the use of pump speed control by inverters and programming in sinus-vector algorithms. This solution controls the operation of the motor using a vector rather than a scalar measure, resulting in an efficiency that is 1.4 times higher than nominal, which is due to the vector operation of the motor. In addition, the pump model used is in 60hz operation which increases the pump capacity by approximately 20% The use of motor control for vacuum pumps on cnc equipment is not found in competing companies.
- Technology HM+
In the case of Plot Electronics, the machine gantry and chassis beams are reinforced crosswise by interlocking bars (ribs). This is a very labour-intensive operation, but according to our research (and external studies) increases the stiffness of the entire system by about 7-8 times that of machines made on normal profiles. On new machines, the system is additionally flooded with HM+ compound (proprietary solution), which increases rigidity by about 12.5 times. Some CNC machines also use compartmentalised reinforcement and polymer concrete flooding, but in this case, after about 10 years, corrosion and weight loss occur, leading to loosening of the filling material and the creation of a cavity around it.
Based on 20 years of experience and many different cases in thousands of CNC Machines production, I would certainly recommend to buy professional machine tools from Sentinel N series. All owners of these cnc machines have succeeded. Feel free to contact us.