Need Help!- Having trouble with capscrew counterbore in brass

[Grindhouse]

Greetings. I recently purchased a CNC router, and one of the projects I am working on requires a counterbore for a capscrew in 1/4" thick brass bar. I'm machining with a counterbore of roughly 3/16" (pilot) and 5/16". I set my spindle speed at about 3500 RPM and I slowed my plunge rate right down to the slowest setting. The steel tool that I used went about 1/16" in and then started to deteriorate. I don't know if I'm just trying to do something that's not meant to be done with a CNC router, or if maybe I was steered in the wrong direction by the company that sold me the tool.

Any advice would be greatly appreciated, as this is the final step before I can test my product for production and then begin selling it. If you think it's just the tool, any reccomendations of suppliers that sell counterbores, preferably with dealers in Ontario, Canada? Thanks in advance.

Dan

[ger21]

I'm guessing your cutting it dry? You probably need a lot of coolant to do that.

[Eurisko]

Sounds like the tool is overheating. Try a spindle speed of 1000 rpms, and a feedrate of .013 feed per rev. (13 ipm).

If possible, use a lubricant (WD-40, mineral oil or coolant).

[HuFlungDung]

IMO, counterbores suck. The few times I've used them on manual machines, they seemed to require a bit of man-handling, like to the point of being a bit rammy with them. The requirement seems to be high feedrate to induce lots of cutting pressure.

The gentleman's method of doing a counterbore is to interpolate a circle with the cnc.

Brass can be difficult to work because it wants to hog onto positive rake tools (like drill type counterbores). And a dwell mark on brass serves to harden that spot locally. The harder spot then requires that you boost the feed pressure to break through, which inevitably happens, then the tool gets a good bite immediately into the soft material beneath, and bam, it hogs in and rips the part out of the vise

[Belding]

Originally Posted by HuFlungDung they seemed to require a bit of man-handling, like to the point of being a bit rammy with them.

Comment made me laugh. I like the term "rammy". Going to have to remember that one.

[Grindhouse]

Thanks for the speedy replies. There is a lot of really helpful information and I'm confident that I can now get this going. And if I don't, you'll all be the first to know. Well, maybe my wife will know first due to the excessive amount of swearing that will follow any further problems . Thanks again everyone!

Dan

[MrWild]

WAY too fast with a counterbore. Counterbores like speeds below 450rpm.

[Cut It Out]

I also have a flatbed CNC.
Never had problems machining brass. Use only engravers brass, it is a lot harder and self lubricating so no need to lubricate. Any other brass is too soft and will bind to the cutting tool giving a poxy finish, tool breakage, and swarf build up on the component.
Hope this helps,,,

Jon (Cut It Out) Australia