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Cutting with a tangential blade
Video Cutting with a tangential blade using KinetiC-NC
What is cutting with a tangential blade?
This processing method involves working not with a constantly rotating tool but with a blade which is fitted with a positioning drive positioned at a right angle tangential to the tool path, thus the name. The blade can either be rotatable but vertically fixed or oscillating. The fixed blade is usually used to cut foils. The oscillating blade can be used to cut thicker materials, like foam materials.
KinetiC NC Software supports the automatic rotation of the blade in the right direction without the rotational angle having to be explicitly entered in the NC program. The machine type must be set to „Blade Cutting Machine“, a rotational axis for C has to be defined and some other parameters must be adjusted. This is done most simply by importing the „Tangential Knife.ini“ file which can be found in the „Add ons“ subfolder of the Standard parameters (File Menu – Import settings – Standard parameters).
There you will find all the necessary parameters for the most common tangential blade types with a stepper motor and 1:1 transmission already pre-defined.
If the machine is to be used for milling as well, don’t forget to make a back-up of the parameters before importing the Tangential Knife file.
Tangential Blade EOT-3
Inspection of knife
Before the first usage, check the resolution of the C axis and that the orientation of the blade is correct. There are blade transmissions with varying resolutions. The Tangential blade EOT-2 has e.g. 200 full steps per rotation which is equivalent to a resolution of 5.55555 steps/° at 1/10 micro steps. The Tangential blade EOT-3 has double that resolution.
First perform a reference drive of the C axis. If the coordinate display of the C axis is not at zero, move the axes to the zero position using the C+/C- spin buttons on the Settings page. Do not use the zero button as this will reset all coordinates to zero, without rotating the blade.
Check that the cutting edge of the blade points directly to the X+ direction. In a High Z machine, this means that the knife must be positioned parallel to the long axes with the cutting edge pointing to the right.
Reference switch and reference drive
If the cutting edge is not correctly positioned, turn the blade to the right angle, using the C+/C- button. Note the displayed C coordinates and take these from the „Reference Switch position“ from the axes parameters (Configuration – Machines – Axes parameters, Select Axis: C).
If for example, -55 had populated „Reference switch position“ before, and the coordinates display displayed an exact angular orientation of +3.5, then you should enter -55 – 3.5 = -58.5. Then perform another reference drive and repeat the angle check.
No CAM program is required
No CAM program is strictly necessary for tangential blade cutting. You can import the lines to be cut directly as HPGL or DXF and enter the plunge depth and the safety height for processing the material. Alternatively, you could use a | code program.
This should be exclusively 2 dimensional, i.e. it is comprised of a series of rapid traverse positioning (G0) above the material, a plunging movement (G1 with Z movements vertically from above), one or more XY movements within the material (G1, G2 or G3 without Z) and a digging motion (G1 with Z motion vertically upwards) and plenty of repetition.
Sharp corners or not
It is important that the drawing has tangentially constant transitions where it has to flow freely through. Everywhere a line meets a sharp corner, the control automatically creates an additional digging and plunging movement.
This is required when for example, a sharp cornered right angle is to be cut. It prevents that unsightly tearing of the material or even blade breakage which can happen if the blade has to perform too large an angle within the material. If the knife is not drawn up, the corners of the right angle will be rounded off with corner arcs.
It is also important that the drawing is carefully created and that the starting point of the following lines lies exactly at the end point of the previous line. Holes or overlaps do not just lead to jerky movements, but also, due to the stepped change in direction, to unnecessary digging, turning and plunging movements. The limits to be set for the angle between lines which follow on from each other, from a stop or digging/plunging movement can be entered in the machine parameters on the Special pages.
Control of the drawing
If you experience issues with frequent stops, jerky movements and unnecessary plunging processes, first check your design and whether the start and end points of the line neatly lie on top of each other and that the transitions are tangential.
The points where the blade is lifted can be detected in the path preview as vertical lines (see figure on the right at the corner of the right angle and left on the circle).
Tangential blade graphic cutting depths
If there are digging movements in places on the path where none should be, this is a sign that either small, depending on scale, almost unnoticeable holes or overlapping of the lines, or the transitions are not steady, i.e. that the angle is too big. Digging movements at (intentionally) 90° angles as shown in the image are however completely normal.