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

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.

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

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.

BTW, are you doing the anodizing yourself??

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?

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??

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.

are you sure you mill is perfectly trammed?

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.

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)...

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

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.

If all the components are in aluminium you could mix up a strong solution of caustic soda and carefully fill the cavity and let it etch the surface for about twenty minutes or so. This will give a nice even matt finish although you have to careful not to get the solution on the top face as it will stain. You could use a syringe to fill the logo and then just wash it off with water when its done.

flannnman - you've got my interest. I have no experience with caustic soda; any recommendations based on your experience? Does something like Dow's caustic soda work? (http://www.dow.com/causticsoda/index.htm)

Caustic soda is found in commercial drain cleaners and can be found in most DIY stores. I live in the uk and there are many brands available but I believe in the States a popular one is called "Lye". You will need to experiment with the strength although it should be quite strong as it wont take very long to etch then although you have to be careful not to leave it overnight as it will do some damage. I have done exactly what you are trying to do in the past and if you are careful you can get a really nice matt finish which when anodised the same colour as the rest of your machined component will give a very good transition effect that will make your logo stand out. Hope this helps and let me know how you get on.

Looks like you are trying to push it too hard. There does not appear to be enough overlap onthe cuts. I would overlap the cuts by at least half. Rough out with a .125 or .093 mill first and only use the 1/32 for the final passes. Looks like you final passes on the outside were heavy and too fast.
Did you cut from outside to in or the opposite. Did you climb mill?

mc_n_g

Try perhaps using a solid carbide endmill. They will be stiffer than HSS you should be able to rough and finish with the same tool. I don't know what machine you use but some of the little machines toolchanges can be a pita, and you want to do as much with one tool as you can.

I agree with MC, looks like the stepover for the end mill is set way too high. I would try about a third of the diameter. it will take more steps but is should smooth out alot.

Dan

Personally for productivity sake, I wouldn't go any less than a 50% step over, unless of course you are try to maximize your DOC then you may go down to some thing like 10% but then you better be using a 1x Ø DOC!!!!!;)