Final pass on cutout

[TomGB]

For cutting out 3/4 hardwoods (Mahogany, Cherry, Maple,& Walnut) I've been trying the "Last Pass Allowance" option to try to remove the witness lines from the various pass depths. I'm looking for some guidance on how much of an offset I can apply when using an !/8" and 1/4" endmill for the 3/4" thick last pass.

[Adrian]

So much depends on the capabilities of the machine. I do it slightly differently as I don't use the last past allowance but have two separate toolpaths merged into one which gives me better control of feed rates etc. For what it's worth my allowance is 0.5mm for hardwood.

[ohiolyons]

So the last past has an issue, even if you specify leads. It is straight down possibly leaving a witness mark.

So the solution is to do the two toolpaths.

Select the vector.
Create the first toolpath and utilize an (i generally use 0.02") allowance offset to make bigger or smaller depending on whether it is an inside or outside cut.
From the tool you selected a default number of passes will be calculated based on your pass depth in your tool database.
Use leads.

Select the same vector.
Create the second toolpath and reset the allowance offset to zero.
Edit the number of passes to one.
Use leads.

Run them separately or combine then as Adrian does.
To combine them into one toolpath select the Visible toolpaths to one file option.

Hopefully I have spelled out the way Adrian does it properly, I using my memory from previous posts he commented on.

Ramping will help reduce vertical insertion witness lines also.

[ohiolyons]

Positive Allowance Offset

No Allowance Offset

Negative Allowance Offset

[adze_cnc]

So the last past has an issue, even if you specify leads. It is straight down possibly leaving a witness mark.

Yes and no. If you use the "Ramp of Lead In", which only ramps over the length of the lead, option it appears to be straight down but that's only because so many people set such a short lead that it appears to be plunging straight. This image shows a "Ramp on Lead In" with a large lead value and a last pass of 3/16". The plunge is curved.
 

 
If you don't specify "Ramp on Lead In" it will create a normal ramp and lead in.
 

 
Also attached is an animation to show the result of that (click on "broken" attachment icon).