Getting a nice finish in pockets

[mrcodewiz]

I am going to be creating some parts and I want to engrave a shallow logo (.025 to .05 or so) on some of those parts. When I'm done machining, the inside of the pocket has witness marks from the endmill and I can't figure out how to clean it up and get it ready for anodizing. Here is a test of the logo that I did. I didn't get a picture of it with the witness marks but this is after I hit it with a wire brush on a dremel. It just made it rough. It also couldn't get into the tight corners and it also blemished some of the edges so this method is totally unacceptable. Is there a simpler way of cleaning up the finish on engravings like this? BTW, for scale - this logo is less than .75 inches high.

Oh, and disregard the little nips or whatever you call them. This was a test run - I need to adjust the actual size of the cutter in my CAM app.

Thanks,
Kevin

[HuFlungDung]

The witness marks should not be so rough that you can catch them with a fingernail. If they are that rough, then try a different tool. I think that a small corner radius on the endmill is important to ensure good blending.

A final cut with only about .005 to .01 depth might improve the bottom finish. Use a spray of WD40 as an experiment to see if it improves the finish.

If the witness marks are visual only, then probably Scotchbrite is sufficient to change the texture, although it looks very tedious to work in something that small.

[mrcodewiz]

I will try to reduce my finish pass. I just did two cuts each at .025. I am also using a mister for lubrication.

[Limited660]

You could probably throw it in a Vibratory Tumbler and clean it up in there, I read that they make deburring stuff and other things to put in that would clean it up and polish it if you could do that.

[Limited660]

BTW, are you doing the anodizing yourself??

[mrcodewiz]

Originally Posted by Limited660 BTW, are you doing the anodizing yourself??

I hadn't gotten that far yet. Depending on how many I made I had considered setting up an anodizing tank.

I tried it again tonight. I had to shrink the logo a little horizontally which forced me to go down to a 2-flute 1/32 end mill with a .002 finish pass and I think the witness marks are worse now. I don't know that I would say I could catch my fingernail on it but it is definitely 'rough'. Some of this could be the aluminum I am testing on. It is just a piece of channel I picked up at Lowes a long time ago and was still laying around in the garage. Perhaps I should try it on a decent piece of aluminum.

What kind of vibratory tumbler do you use? Just something like a bullet shell tumbler?

[Limited660]

I dont have one, just read about them how they can remove rust and deburr parts with special media... Have you researched the items needed for anodizing??

[mrcodewiz]

Yeah, I have read tons of articles on setting it up - home anodizing is what I was thinking. I guess I could try sandblasting it too with glass or something to see if that cleans it up. I don't recall ever having this issue with larger endmills. Just these tiny ones.

[tikka308]

are you sure you mill is perfectly trammed?

[mrcodewiz]

Well, I trammed it after I finished installing all of the CNC stuff (~5 months or so?) and haven't had any crashes since then but with the mini-mill, you never know. Good point though, I will re-check the squareness again.

[tikka308]

5 months! Wow. I check my tram probably every 6 hours of milling or every few days, whichever comes first. Granted I have a TAIG, which has a swivel-Z axis (i.e. much easier to lose your tram than a fixed square column)...

[HuFlungDung]

It must be an optical illusion, but that last picture of the part looks like furrows in a field

A 1/32 endmill is smaller than I have worked with to date, but I can imagine that it is extremely flexible. When flexed, the bottom end plane of the tool flutes will be tilted, and this will create definite roughness. I would recommend milling the pocket with a larger tool (perhaps 1/8"), then clean up the rest areas with the smaller tool. Of course, this might be a lot of cam work, depending on what you have available for software.