Steps in Arc

[jim1960]

I am having a problem with steps in an arc.

I am milling on a VF 2 using MC 2021 using a contour on the inside of  a line loop.  I got the outside of the loop to work by playing with the Arc Filter. 

I a unable to the inside of the loop to make a nice arc.

Any ideas?

 

 

[gcode]

Your chain is a bunch of lines or small splines

Turn the whole chain into one spline with the Spline/chain command

Then use the command Break Many/  arcs with a .001 tolerance

The other option it to drawn your chain the old school way

[jim1960]

I can not find this Spline/chain command .

 

 

[gcode]

[Colin Gilchrist]

On 3/11/2021 at 6:52 PM, jim1960 said:

I am having a problem with steps in an arc.

I am milling on a VF 2 using MC 2021 using a contour on the inside of  a line loop.  I got the outside of the loop to work by playing with the Arc Filter. 

I a unable to the inside of the loop to make a nice arc.

Any ideas?

 

 

The absolute first thing you should do, is check your geometry. As Gcode mentioned, you can create a single spline to make it a single entity that describes the shape you are trying to cut.

However, if you look at the geometry, it should really be a series of lines and arcs, which are properly trimmed and connected.

If you are starting with a 'Spline' Shape, your toolpath will always 'linearize' the path. Full Stop. The path is a series of point-to-point moves (offset to the cutter centerline), that describe the 'wall' that your cutter is following. Since the 'input' geometry to the path is a series of points, you would be relying 100% on the Line/Arc Filter to generate any arc motion in your path. Using a Spline for this is not an ideal scenario.

The 'linearization' of the path doesn't necessarily apply if your chain is made up of lines and arcs, which are properly trimmed together. You can create a contour path without the Line/Arc Filter enabled, and if the 'input' chain geometry contains arc moves, you'll see arcs in the NC cutter path.

If your geometry is truly 'free-form curves', then a spline is required to make up that shape. The biggest issue with machining a Spline is your Cut Tolerance. This is not linear. The Cut Tolerance is a Chordal Tolerance, so the step distance 'along the curve' will vary with the change in 'curvature' of the spline itself. This is likely why you have facets that are different lengths. (This also depends on the quality of your chained geometry, and if it is a series of small entities, or a single entity, in those areas.)

So, when machining a Spline, you need to crank that Cut Tolerance down, so your path has many points, which then creates a more accurate shape for the Filter to work it's magic on. Set your Cut Tolerance to 10 millionths of an inch (0.00001), when machining a spline shape.

After cranking down the Cut Tolerance, you still need some "room" to get the filter to generate arcs. However, there are two components to the Filter itself. There is a 'Linear Filter', that attempts to remove 'small line segments', and the 'Arc Filter', which attempts to convert circular sections to arcs. But, there are also two 'radio buttons' on the dialog box, which allow you to choose 'how you want to split the amount of Filter Tolerance, between 'line moves' and 'arc moves'.

Set your Total Tolerance (1st) to 0.0002.

Enable the 'Line/Arc Filter' checkbox. Disable 'smoothing', if it was active.

Set the Cut Tolerance to 5% of that value. 10 millionths.

Set your Line/Arc Filter to 95% of the Total Tolerance. (0.00019)

Now, set the radio button to the 'Tighten Arc Filter Tolerance' radio button. Adjust the 'slider' to 75%.

Using 75% of the Arc Tolerance, also limits the amount of 'linear tolerance' that gets applied to the path as well. We are reserving most of the tolerance value for creating arcs.