Extrusion from Image Issues

I am opening an image file (jpg and many others tried) and creating an extrusion using the image (a corporate logo). When i create the toolpath I’m using a .125 endmill for my roughing tool then stepping down to a .043 endmill for my finish and pencil line. The problem that I am having is that when I change to the finishing tool the first plunge cut is going WAY to deep, I have not put a gage on it but I would eyeball it at .125 or more when the stepdown is substantially less than this (in the realm of .009) in the tool definition itself… any thoughts? This is trivial for me to reproduce anytime I import a file and attempt to do this, I think that it’s an issue with MeshCam but unsure…

Finishing toolpaths by definition follow the surface of your workpiece. You will need to create your roughing toolpaths to remove the bulk of the material so that what is left will be within the finishing tool’s capability to cut through.

With input from bitmaps it can be tricky depending on the complexity of the image. Sometimes it helps to create two or more finishing toolpaths, with successively smaller tools. The first tool(s) will remove the bulk of the remaining material, leaving only “pockets” of material in the concave areas of the workpiece.

But it sounds like you are talking about both parallel and waterline finishing. Parallel produces “lawnmowing” toolpaths that cross the workpiece linearly back and forth, and are defined in terms of stepover. Waterline toolpaths are where you specify stepdown, and they will trace successive “terraces” at increasing depths (stepdown) like contour lines on a topographic map.

Maybe all you need to do is to do the waterline machining before the parallel. Unfortunately MeshCAM doesn’t have a facility to specify this. The procedure is to calculate all the finishing steps, uncheck the parallel finishing so you are only writing out the roughing and waterline, then without closing the dialog uncheck the roughing and waterline, check parallel only and write out a second file. It is usually best to leave pencil finishing for last of all.

A small point, but bitmap input really isn’t extruding. It creates a heightmap based on the equivalent gray level of each pixel. Bitmaps will not produce vertical walls–there is always a one-pixel-wide slope even between adjacent pure white and pure black areas. But MeshCAM takes that in stride. Waterline finishing will inch its way down the sides of the geometry at the stepdown you specify.