Accurate CNC, Inc.

In the process of developing the Accurate 350 design, our goal has been to meet the demands of professional PCB prototyping. This includes exceeding the capabilities offered in mass production methods. For example, the resolution of our prototyping machine is nearly twice as high as the best that can be achieved in mass production. In order to meet our goal, we have carefully researched and analyzed the advantages and disadvantages of every piece of technology used in our prototyping machine to ensure that the Accurate 350 is most precise, reliable and convenient to use. Here we would like to offer you a glimpse at some of the considerations that have guided us in designing the Accurate 350.
	Precision Starrett® micrometric head is used to control depth limiter position. The Z axis has two modes of operation - with or without depth limiter. The force applied to the work piece can be adjusted from 3.5 to 9.5 Lbs. when the limiter is used.
	Here is how it looks before the “skin” is on. All three axes are factory pre-lubricated and won’t need service for at least 5 years of intensive use. In all three axes we use re-circulating balls linear bearings and precision polished shafts.
	We use gold plated spring needles and stainless steel contact targets in our home and limit switches. They guarantee that the zero coordinate position is exactly the same every time the machine starts.
Why choose a moving gantry? Manufacturers of similar machines insist that a split axes design is more accurate than a moving gantry design. This statement is not completely right. The right statement is that a split axes design allows you to achieve a high level of accuracy easier. However, there is a price to pay, since a split axes design also means: twice bigger footprint for the same working area constantly moving work piece, which obscures your view of the process you need expensive light weight table to get the same dynamics. We are using very tight production tolerances and have the precision needed without the disadvantages listed above. Why choose a belt driven spindle? In the last two decades, spindle speeds have increased from an average of 40-50K to 150K RPM, even 200K RPM. The race is fueled by the need for efficiency in production of large quantities of PCBs. Many mechanical prototyping machine manufacturers offer spindles with 100K RPM. Speeds above 85K are off limit for belt driven spindles, but let's see what we need for precision prototyping. The following link http://www.mitspcb.com/edoc/spindle.htm leads to a description of the relation between speeds and run out in the case of classic integral motor-spindle. Some examples of the quality of the milling process related to the spindle speed can be found at http://www.mitspcb.com/edoc/srtio3.htm. Considering the information from the above listed sources, it is easy to conclude that for the purposes of prototyping 60K RPM is a sufficient speed. Belt driven spindle is completely reliable at this speed and has some additional advantages: good mechanical decoupling (in term of vibration) between the motor shaft and the spindle shaft allows maintaining very low run out (0.005mm; 0.0002inch) in the entire speed range (8000-60000 RPM); separation between the motor and the spindle lower the cost of the system without compromising in the quality of milling process maintenance is cheaper due to simplified design and you can afford to have a spare spindle. Replacement takes less than 30 sec. We have been testing our design for more than 3 years. The belt’s life is more than 24 months of intensive usage and you can afford to change them in advance, because they cost approximately $1 each. Is this a good price to pay for the advantages above? Also, we ship our machines with 5 spare belts. Why choose a motorized Z axis? Machines on the market in our price range usually have a solenoid or pneumatic driven Z axis. Right, it is cheaper, but what are the disadvantages? hard even impossible to control the tool in feed precisely using the control program insufficient Z axis travel (solenoid driven) limits the usage of the machine requires compressed air (pneumatic driven), which is not convenient for an electronic lab. With our motorized Z axis we have unlimited control to the in feed rate. The Z axis travel makes our machine useful for more applications without the need for compressed air. We spend more than competitors to build each machine, but we still have the best price on the market. Our customers agree the price is more than justified by the quality!