CNC Machines

What is the different of the Gantry Part Moving Machine (GPM) and Working Table Moving Machine (WTM)?
Gantry Part Moving Machine (GPM)

 Pros: Large Processing Area, Fixed location Space
 Cons:  Not good for hard materials processing,
 noisily, not accuracy 

Working Table Moving (WTM)

 Pros: Suitable for hard materials processing,
 Accuracy, low noise
 Cons:  Small Processing Area, Variable location Space



A. Gantry Part Moving Machine (GPM)

Type 1 of machine : BORSH 9060 and WALTER 6545L


Descriptions:

The structures of the BORSH 9060L and WALTER 6545L are similar that the gantry part is supported by two guided pins with linear ball bearings installed under the gantry part! The supports of the guided pins are inserted between the base of the machine and the bottom of the guided pins. Therefore, the guided pins will not be bending during the CNC operating.
 
However, the working table of this type of machine will produce vibration and noise during the operation, because working table has not any supports between the bottom of the working table and the base of the machine at the middle of the working table. Furthermore, the maximum vibration magnitude and the maximum bending moment were found at the middle of the working table and between the supports wall installed at the front and at the rear of the base part! The vibration of the working table is produced when the tooling installed in the spindle is going downwards and processing the workpiece.

Therefore, the accuracy of the processing the this type of CNC machine as close as the middle of the working table is the worst, because the vibration and the bending moment magnitudes of the working table are the maximum. We assume that the height of the tooling installed in the spindle is constant, the cutting depth is variable and unpredictable during the operating because the working table is vibrating. Furthermore, if the cutting depth is going downwards at the middle of the working table during the processing, the feeding force produced by the stepping motor of the Z axis of the machine is applying, part of the feeding force will be absorbed by the working table which is bending at this moment!   

Type 2 of machine : BORSH 4030L and WALTER 2520L




The structures of the BORSH 4030L and WALTER 2520L are the same that the gantry part is supported by two guided pins with linear ball bearings installed under the gantry part! The supports of the guided pins are inserted into a frontal wall and rear wall of the machine without any supports under the guided pins. Therefore, the guided pins will be bending during the CNC operating.


Therefore, the guided pins will be bending upwards cause by a reaction force during the tooling is feeding and going downloads. Therefore, this type of CNC machine cannot be designed as large area CNC machine. Otherwise, the vibration and noise are extremely high.

All GPM machines are not suitable for processing hard materials, because the reaction force of the feeding force of the tooling will be absorbed by the guided pins or the working table, if the the working is hard such as copper, the  feeding force may be totally or mostly applied to the working table or guided pins directly that the effective of the processing is not ideal.

To conclude, the BORSH 9060L and WALTER 6545L are suitable for processing soft materials with large processing area such as wood product, wooden door, guitar, aircraft model, plastic, advertising board and product, composite, etc. The BORSH 4030L and WALTER 2520L are not used for processing hard materials. Processing wood, advertising board and product, composite, etc.

B.Working Table Moving Machine (WTM)

Type 1 of machine : WALTER 3040B and BORSH 3020P



Descriptions:

The structures of the WALTER 4030B and BORSH 3020P are the same that the gantry part is fixed on the base part directly, the working table and the guided pins are installed and moved together. The linear ball bearings installed under the working table and fixed on the base part! The processing location of the tooling on the Y direction is fixed and the working table can be moved alone the Y direction, therefore, the reaction force discussed on "
Type 2 of machine : BORSH 4030L and WALTER 2520L" can be eliminated, therefore, this type of machine is suitable for processing hard materials such as copper and aluminum with low vibration and low noise. 



Understanding the driving Unit of the machine

 Ball Screws

The ball screws are accurate and smooth driving unit. The normally accuracy is 0.03mm. In addition, the ball screws have high anti-backlash ability. Therefore, mostly of our CNC machines are installed ball screws as the driving units.

However, the major disadvantage is that this driving unit is heavy and high cost.
 Simple Nuts with a Spring

A economy driving unit is to use simple nuts and simple screws as the driving unit. The structural is  simply that two nuts are installed on a screw and a spring is installed between the nuts that an anti-backlash feature is created.Furthermore, a locking feature are also designed between the nuts for keeping the distance between the nuts.

However, the major disadvantage is not smooth with high friction.
 Teflon Nuts

Teflon is a tough material that is a good and low cost driving unit with simple screws. The the thread of the Teflon nuts is created as close as the thread of the screw that an anti-backlash feature is then be created.

However, the major disadvantage is that the Teflon nuts are easy to break during the shipping period.


Wrong Concepts for selecting CNC Router (Machine)

1. Working space as large as possible.
   Example: The prices and the weight of the CNC6040 and the CNC3040T are the same, I must select the
                  CNC6040 instead of CNC3040T, because the working space of the CNC6040 is large than CNC3040T.
                  I want to use the machine to make PCB and metal.
A simple discussion about different types of CNC machines is shown above. If you need to processing metal such as copper and aluminum, CNC3018 and CNC3040B are most suitable. Otherwise the processing accuracy is bad and the vibration and noise produced by the working table are series.   

Remarks: CNC6040 is the old version of the WALTER 6545L, CNC3040T is the old name of the WALTER 3040B.

2. Multiple purposes and Multiple function in one single machine.
   Example: Request to processing some workpieces of copper and wood, PCB, plastic product with tolerance 
                   0.05mm or less by one machine.
Since different types of machines are designed and developed for different proposes with different function, You should think carefully for selling a suitable CNC machine before your order. .
A interesting thinking is that most people would like to buy a professional CNC machine for processing several materials types of workpieces, for example most companies will buy professional CNC machines (about USD 3500) for making advertising board and product. The companies are not normally use the machines to cut metal! But, most of the people want to buy low cost CNC machine ( Below USD 3000) for processing steel, metal, stone, wood, PCB,etc.
This is a big problem for selecting CNC machine. Why the high cost and profession machines are normally used for few purposes, but low cost machines can be expected to do many purposes of work?   

3. Accuracy as high as possible.
   Example: Request to do a workpiece with tolerance 0.03mm or less.
Since the accuracy of any low cost CNC machines (Less than USD 3000) is about 0.08 or the best of 0.05mm, in addition, low cost CNC machines have not been designed with any feedback system for checking the actual position of each direction of the CNC system. the  low cost CNC machines cannot be used to do high precision workpiece processing.  


Steps of selecting a suitable machine for myself!

1. What are my processing purposes and objectives with using the CNC machine?
    1. Business purpose or for Hobby?
    2. Milling, Drilling, Trimming, Cutting
    3. Artwork
    4. 2D or 3D or Cylindrical workpiece?
    5. PCB engraving?
    6. Dispensing, drawing, painting, 2D/3D reserve engineering or other?

2. Which materials of workpiece will be used?
    1. Metal: iron, brass, copper, aluminum?
    2. Wood: Hard Wood or Soft Wood?
    3. Plastic, composites?
    4. other?

3. How much working space do I need or perfect?


 Model
BORSH
 9060L
WALTER
6545L
BORSH
4030L
WALTER
2520L
WALTER
3040B
BORSH
3020P
 4th Axis
 Business purposeR
R
R
N
R
R
R
 Hobby purpose (Student Project)
R
R
R
R
R
R
R
 Milling, Drilling, Trimming, CuttingR
R
R
R
R
R
R
 Artwork R R
 R
R
 2D or 3D workpiece processing
R
R
R
R
R
R
 R
 Cylindrical workpiece processing
   N
 
R
 PCB engraving   R
R
R
N
 Dispensing, drawing, paintingR
R
R
R
R
R
R
 2D/3D reserve engineeringRR
R
R
R
R
R
 Processing Material of workpiece
       
 Metal: iron, brass, copper, aluminumN
N
N
N
R
R
 
 Hard Wood
R
R
R
N
R
R
 
 Soft WoodRR
R
R
R
R
R
 Plastic, compositesR
R
R
R
R
R
R

 RRecommended
 NNot Recommended

Table 1.1
  A summarized table for selection a suitable CNC machine model for myself!

Latest update: 24 June 2011
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