Tumbling Media for Hardened CPM 10

[thatengineermike]

I've been playing off an on for a while now trying to determine the best process(es) and media for putting a gentle radius on some parts we cut out of hardened (62-65 HRC) CPM 10 and also subsequently polishing them to a fairly high surface finish (10 Ra or better). We have an external vendor that we send parts to for now which works but I am curious what others with more experience would recommend if I was to set up a small cell for our odd ball or expedite orders.

To date I have used several different manners of ceramic/porcelain media in a tumbling bowl (Burr King) which doesn't really radius edges so much as knock off any reside from the cutting process. I can absolutely shine parts up no problem with media, provided I put like 10 parts in for 30 lbs of porcelain 1mm media and leave it for three days.

Dry, soft, multiple steps, I feel like I've experimented with them all and haven't found a solution that does this efficiently. Ideas or thoughts are all welcome!

 

[sfriedberg]

If you want to remove noticeable amounts of material, especially hardened material, use a really coarse grit. Maybe plastic media. (Worth getting advice from one of the main media/tumbler vendors.) You'll then need multiple intermediate grits to get back to the polished condition.

[Added in edit] On re-reading, I'm not sure if you have having difficulty with the "gentle radius" bit, which would be material removal, or just wanting to accelerate the polishing bit.

 

[thatengineermike]

@sfriedberg Thanks! I had tried a real coarse grit media, though not plastic but that is a suggestion I will look into. Yeah, basically the parts get EDM'd and I am just wanting to knock off the sharp edges and then polish up the surface a bit. Our vendor can sometimes turn them around in a day so I'm just trying to figure out how to replicate their black magic on a smaller scale for when I've got more custom small quantities that don't make sense to send to them.

 

[Conrad Hoffman]

I used to work for a company that ran a lot of parts through a medium sized Sweco machine. We used ceramic media and it could take a couple days to do what you're describing. Also took a lot of water and special soap to keep the parts clean. I could make a good case for just having somebody else do it! If time is money, look into Harperizing. It's basically a spinning tumbling process that applies a lot more force to the media than gravity can. It can reduce times from days to hours or even minutes. Not cheap and not that many people do it, but you should be aware of it.