398
OPTIONS
96-8000
June 1999
11.7 HIGH S PEED M ACHINING
High speed machining with the Haas CNC is possible up to 300 inches per minute and up to 1000 blocks per
second. 600 blocks per second is standard and 1000 blocks per second is a purchased option. No special
programming or setup is required to get these speeds.
There are a few points to consider at high feed rates.
1) At higher feed rates interpolation accuracy will be reduced.
2) The higher the resolution you specify on your CAD/CAM the longer the program and the slower the
speed
3)When using DNC you must have a very fast computer and excellent DNC software.
In most CNC controls you have to set the maximum feedrate according to the most accurate detail you were
machining. Just as in a car you cannot make a right turn at 100 MPH so to the CNC control must slow down
in the corners in order to give the accuracy you require. Unfortunately the corners often dictate the maximum
feed rate for the entire program when that may not be desired. The HAAS control uses a special function called
Contouring Accuracy (G187) which allows you to specify the required accuracy. If the programmed feedrate is
above what the control can accurately machine the control will automatically slow the feedrate to obtain the
required accuracy. In straight line moves the feed rate will be at the programmed rate. See Contouring accuracy
in the next section.
When machining a sculptured mold you obviously would like to have the smoothest surface possible. The
higher the resolution you select (the distance between machined points) the more accurate the final part. The
downside to this is that program length is longer and feedrates slower. Beware of the relationship between
stroke length , feed rate, and block per second. If you have 1000 blocks per second and each block is 0.001
inches in length, this is 1 inch per second and 60 inches per minute. Trying to program more than 60 inches
per minute in this case will not go any faster; you cannot get more than 1000 blocks per second. Similarly a
resolution of .0001 will limit your feedrate to 6 IPM.
The best way to machine a part is from CNC memory. The HAAS control can be purchased with up to 8
megabytes of ram. This eliminates any communications problems and offers the highest blocks per second
possible. If you choose to run the HAAS control directly from your computer, you must ensure that your
computer can send data fast enough. A general purpose Windows based communication program will not work
reliably. The serial port and wiring from your computer must be of the highest quality. Beware, that when
running DNC, computer serial ports are not able to send data to the CNC fast enough to get the blocks per
second rate which you require. The fastest serial rate of this control is 115200 bits per second. This translates
to 115200 characters per second. If a typical block consists of about 20 characters, it is not possible to run
DNC at more than 575 blocks per second. If you are not experienced with high-speed DNC get expert help from
your dealer or have him recommend someone local with hands on experience.
In order to get maximum performance from large memory programs the following hints will help:
1) Eliminate all unnecessary codes such as line numbers, comments, redundant G codes, etc.
2) Eliminate all leading and trailing zeros, i.e. make X002.0000 to X2.
3) Incremental (G91) programming utilizes the least data i.e., (G91 X1 Y1 Vs G90 X2.0001 Y2.0001)
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