Adventures in Milling; My machines want a new owner.

[Rbeckett]

Hmmmm, This makes me think CNC Plasma would be a viable tool for this job!

Wouldn't trade my torchmate fer anything. It's pretty slick even on really thin warpy stuff if it's dialed in well. Can be a PITA to clean the edges if your not dialed in, but nothing a belt sander won't handle well either. I love my 4X4 Small Shop machine, perfect size for what I do and not too expensive when I got in.
Bob

 

[Tony Wells]

First glance, I'd say you could improve things by feeding faster, but hardly .54/sec, even at 1200 RPM. That's a 0.00675 chip load. Too aggressive for thin stock the way you're holding it. And you should do it in one pass, not nibble on it. Hand feed and you can tell when it's right by the sound, feel, and look of the chips coming off it. You can do this dry with carbide, and air blast to keep from recutting your chips. Choose another material for your hold-down pads. Copper or aluminum. Clamp as close to the cut edge as you can, and preferably bridge all the way across it. Choke up on the end mill as much as possible, and yes, no more quill extension that needed. You really shouldn't need to worry about all this on a piece of 20g, but I don't know your machine. So, those things could help tremendously. It does appear that the majority of the cut was with a very dull edge. Dulling can happen very quickly if your feed is too slow. End mills don't like to rub. Conventional cutting direction except for a 0.020 finish pass, which should be climb cut.

You will still get burrs, but not like those. I've never been an advocate of using any sort of wood for backup, unless I was doing some machining in the middle of a piece of Plexiglass or similar.

 

[MikeAa]

I didn't read every post but you said a HSS TIN coated end mill. Is it of good quality? I got a hold of a new boxed selection of import end mills, supposedly tin coated. What an absolute joke. They couldn't cut butter and would produce the same finish as what you got after three seconds of cutting.

 

[Mark Lossner]

Hi SwarfMaker; How did you make out with your cutting problem? Were you able to finish the part?

Yes, indeed! I will publish some more pictures once the body parts are mated together.

I appreciate all of the help I got with this problem. The final cutout looked pretty good, only a little burr at the cut line and that easily cut away using a scraper.

I applied as many of the suggestions that I could: I sandwitched the blank between hardboard, cut with the side of the end mill, turned the crank at about one turn every five seconds, and even used a better quality cutter. Yep, the part came out with a minimum of filing and scraping.

Mark

 

[Mark Lossner]

...you were cutting that using the end of the cutter? I would have just cut from the side...

Yep, that is what I was doing. I followed many of the great suggestions posted here; and, the part came out pretty well. I do appreciate the avalance of help from you guys. I learned how to do this task with little headache ... thanks entirely to my team of advisors!

Mark

 

[Mark Lossner]

... a HSS TIN coated end mill. Is it of good quality?...

It is now! Those cheapies don't do well for this application. They have done OK in aluminum and different steel alloys. I suspect my toolbox will be getting better cutters from now on.

Mark

 

[DMS]

Well, there's cheap, and then there's cheap...

The ENCO brand HSS cutters are pretty decent, better than the ones you get in most of the "set of X 4/2 flute end mills" boxes. They are cheap too (~$4 for 1/4" ones). The best part about them for people just starting out is that when you break them... you don't cry too long.

I recall when I first got my CNC mill running, and I was cutting some brackets for limit/home switches out of... you guessed it 16ga hot rolled steel sheet... I broke 4 3/16" endmills in the space of 15 minutes...

Had the feed set to roughly 4x what it was supposed to be in steel, doh!
Had the feed override set to 120%, doh!
Hmm, didn't check the spindle speed with the tach, spindle speed too low, means chip load too high, doh!
Final pass, break through, cutter overheats, gets a mass of chips welded on, stops cutting, snap... doh!

Ended up finishing with a 2flute... which took forever, but it worked.