Does anyone have experience cutting HDPE with a .25" end or ball mill successfully? If so, what depth of cut, RPM, feed and plunge rates did you use?
Also when using the .25" ball mill, the cutter was cutting into the part geometry. This was not a problem with the .25" end mill or a .125" ball mill. Are there something that I might be missing?
This is a picture of fillet where the ball mill cut in to the geometry of the part:
Did you check out the official Carbide 3D Feeds and Speeds Charts?
(William Adams (Carbide 3D))
In addition to the official charts, we have some numbers on the wiki: http://www.shapeoko.com/wiki/index.php/Materials#HDPE — though the largest endmill used is a 4mm.
The geometry not being honoured seems likely to indicate lost steps — check belt tension and pulley set screws? How did the preview look? (options for previewers here: http://www.shapeoko.com/wiki/index.php/Previewing_G-Code )