Unwanted lines appear for no reason? Or some reason?

[iampapabear]

First, the equipment.
Shark Pro Plus HD, Bosch 1617, Precise Bits 1/8 tapered ball end bit.

Feed rate 100 inches per minute, plunge rate 15 inches per minute, router speed about 20K rpm.

Ran as "offset" with a climb cut.

Tool Data base shows pass depth of 0.125, stepover of 0.0124 (10%)

Post Processor: CNCShark- USB NewArcs - (inch) (*.Tap)

The material: MDF (termite barf?)

The file: a purchased 3d model from VectorArt3d

The software: Aspire 3.5

Have cut this file twice. The first time things were OK, no strange artifacts. It didn't look good , but that was me , not the machine, the software or the file.

The second time I got some strange lines in the carving. They form an "X" centered on the project, with a square box line centered on the "X". They are shallow, but very ugly . (see attached photos)

I am new to this and, frankly, have NO clue as to what might have happened. So, I ask you experts a highly technical question.......Duh, wha happ'n?

[jeb2cav]

Every now and then I see this and in my case it is usually an issue of lubrication - I use a silicon/teflon spray. In talking with folks at the Vectric conference, I find that for 3D work and the finishing pass most of them use the Offset, Climb strategy vice the Raster strategy as 'it seems to minimize' artifacts like you found.

I use Offset, Climb for all of my 3D work as a result of that tip - and I really can't say that Raster is 'not as good', but I know it works for me (if the machine is mechanically sound and the speeds/depth of cut are fine).

Not definitive answers, but some things to try/think about.

[sk8nmike]

I've seen 3 things cause this on the Shark and other CNC's. First as Jeb pointed out keep the rails and lead screws clean and lubed, Silicon with Moli is my choice. Second excess play in the system, if you can move the gantry or router mount by hand and this is normally only a fraction of an inch in either direction you'll get lines. And the third one is movement in your carving material make sure it's firmly clamped.

Mike

[Buc]

Joe,

Thanks for the tip on using the offset and climb options for finishing a 3D project. Making a show'n'tell dinner plate with Mamma Bear and the twins for a wood turners group meeting. Now I have a betcha-can't do that project to show. I needed to take an extra .020" off the top for a finish cut. worked great. The machine maybe a bit dizzy going around in circles for 3 hours. Julie wants me to send you money....

Thanks Buc