By scraping, I meant there was some epoxy left in some of the corners that I needed to scrape out with a sharp stick. Bead blasting doesn't do a good job of removing epoxy as it seems to bounce off it without cutting. The finishing passes were set for a .0005" maximum scallop height, and those passes were working with .005" material left from the previous roughing passes. There were two small areas near the collector flange that needed work with a needle file that my cutters couldn't reach. Other than that, the manifolds went from the Tormach to the bead baster with no other filing or sanding. - TerryTerry:
Your CNC machined parts look like sand cast after the bead blasting.
I've probably asked this before, but... What's your typical stepover and depth of cut on the final pass? In particular, the corners on the exhaust header where it bends after coming out of the head, did you do any sanding there? (You said you had some scraping and filing to do.) Or were they just machined, then bead blasted?
I do believe that you've perfected the process for simulating sand cast parts in miniature.
With my unknown grit Harbor Freight beads, I can usually bury .001" machining marks, and a little more if I'm willing to dwell long enough. I wouldn't be able to hide .004" though. What happens is that on a finished surface with .0005" scallops directly off the mill, the surface is so reflective that defects are difficult to see, and if a polished surface is wanted, then you're finished. With the matte finish of the beads, though, every defect clearly shows up. That's why I try to get the best finish possible on the mill even if I'm after a cast looking surface when I'm done because once I start filing, a bead blasted surface is unforgiving and will need time to make it right with a file. - TerryThanks Terry.
I'm thinking about casting some parts for some RC truck and construction equipment projects that I've got lined up as future projects. These would be cast using either lost wax or lost PLA 3D printed patterns. I was wondering if I could use your bead blasting process to eliminate the layer lines from the cast parts without any other post-processing. It sounds like that will be do-able as long as I print using 0.1mm layers. (That's about 4 thou-ish for the Metrically challenged.) My printers will happily print at that layer height.
I think you said that you are using glass beads from Harbor Fright, is that right? (What grit/size are the beads?)