Motion - Blend

When selected, blending of Backlash compensation moves is disabled.

When selected, blending of backlash moves is enabled, motion is well inside the CAM tolerance values.

When selected, blending of backlash moves is enabled, motion is not restricted by CAM tolerance values.

If imported gcode program uses internal blend tolerance values, this option, when enabled, will enforce the use of blend tolerance value set here in settings.

XYZ axis tolerance(maximum distance) that blended toolpath can deviate from toolpath.

Angle value of changed direction between machines current and next move. If angle is greater than this value, motion between these two moves will be blended. Set at 0 by default.

Angle value of changed direction between machines current and next move. If angle is greater than this value, motion between these two moves will not be blended. Set at 135 by default.

ABC axes tolerance (maximum distance) that blended toolpath can deviate from toolpath.

Angle value of changed direction between machines current and next move. If angle is greater than this value, motion between these two moves will be blended. Set at 0 by default.

Angle value of changed direction between machines current and next move. If angle is greater than this value, motion between these two moves will not be blended. Set at 135 by default.

UVW axes tolerance (maximum distance) that blended toolpath can deviate from toolpath.

Angle value of changed direction between machines current and next move. If angle is greater than this value, motion between these two moves will be blended. Set at 0 by default.

Angle value of changed direction between machines current and next move. If angle is greater than this value, motion between these two moves will not be blended. Set at 135 by default.

Blending is technique used to maximize cutting speed and minimizing machine stress. Machine stress that is discussed here is caused by forces that are result of accelerations.

Most are probably familiar with linear acceleration and deceleration limits that are set for each motor on machine. Settings “Motors/Acceleration”. These settings prevent stress to machine motors. On machine with stepper motors this is known as “lost steps”. But this is not only stress on machine.

When direction is changed, forces act on machine which cause stress and can ruin your workpiece. To prevent this it is possible to set maximum allowable acceleration that machine can handle.

Any sudden direction change at speed causes huge acceleration spike, therefore creating huge forces. That is why machine must slow down or even stop before such change. This causes longer machining time. Lower speed is also not good for tools which can overheat.

To deal with this issues we use path blending. Small arc is added to sharp corners and as a result, toolpath is much smoother and machine can run faster. We call this arcs “blends” because that is what they do. They blend toolpath segments to single smooth toolpath.

Here are 3 examples of direction change. For first one, direction is changed for 5°, for second one for 45° and third one for 135°.

It is not beneficial to add blends to all direction changes. So it is possible to specify range of direction changes where blends are added by setting “Join angle” and “Break Angle”. Only direction changes that are between these values are blended. By default “Join Angle” is 0 and “Break Angle” is 165.

Because blends alter toolpath, it is important to set allowable toolpath deviation from programmed toolpath. This is called “Blend Tolerance”. Tolerance is maximal allowable deviation from programmed toolpath.

Here are three examples.

You can see that greater tolerance and/or smaller angle generates larger blend arcs. Moving on those arcs generates forces because of radial accelerations. Maximum radial acceleration is limited with settings “Motion/Max Acceleration” and “Motion/Max Deceleration”.

In most cases, specially with smaller angles, machine speed is not high enough that such big blends are needed. In these cases blends are smaller. Just big enough to allow maximum possible speed. This means that deviance from programmed toolpath is much smaller.

Blends are enabled by default and can be controlled with g-codes G61 and G64. For roughing operation blends are usually enabled with G64. For finishing operations blends can be disabled with G61 or tolerance can be set tighter with G64.

Here are two examples showing deviance with red color. Programmed toolpath is black, blend arc is green: