How Do I Tell When ....

[Transformer]

an end mill is dull? I am really on my first project, working on steel on my Grizzly mill using HSS end mills. As I was playing around with feeds and speeds and depth of cut I realized I do not have the knowledge or experience to tell whether my setting is off or I have a dull end mill. At this point I am pretty sure my new end mill is fine, but how do I tell when it is getting dull?
Dennis

 

[Karl_T]

The first sign is heat. You need more coolant and it starts steaming more.

The corner of the EM is the first spot to go. Hold a light to reflect. A sharp EM will break from one surface to the other with no reflection. As they dull you see light reflecting off the dulled surface.

You can also feel the sharp edge with your thumb. Some use a fingernail.

This is just an experience thing. For some jobs you can push them till they burn up. others, the mill need to be perfect. small mills need to be sharper.

 

[smoa]

Another indicator is your surface finish will deteriorate. Your machine will also be under a larger load, or working harder.

 

[JimDawson]

Great question!

What everyone said above is correct. In more extreme cases of dull, the machine will actually shudder on a heaver cut (or sometimes on a lighter cut). As you gain more experience you will be able to tell pretty quickly when the end mill is done. When starting out with a new, sharp end mill, it will pretty much cut the same for some period of time then all of sudden everything will change, you can feel it and hear it. It's at that point you have to decide to continue cutting or change the end mill.

End mills have a finite life and normally, under optimal conditions, will last about 80 minutes. Excess speed is the biggest killer, as is too much or not enough feed. Too much speed and/or too much feed = excess heat. Too little feed causes the end mill to rub rather than cut, also = excess heat. There is a sweet spot for any job you are doing, and you will be able to find it pretty quickly as you gain experience.

 

[Tony Wells]

For me, other than the feed pressure if I am hand cranking it, I watch for a large burr to be pushed up at the edge of the cut. Sharp end mills leave smaller burrs. When it gets noticeably harder to push, and I see a large burr.....it's done.

 

[chips forever]

an end mill is dull? I am really on my first project, working on steel on my Grizzly mill using HSS end mills. As I was playing around with feeds and speeds and depth of cut I realized I do not have the knowledge or experience to tell whether my setting is off or I have a dull end mill. At this point I am pretty sure my new end mill is fine, but how do I tell when it is getting dull?
Dennis

Here is a trick you might want to try. It does help to keep end mills a tad sharper. Take a very fine grit stone and carefully angle it to match the flute and draw it across the flute. Do it for each flute. It is not so much to sharpen but to remove burrs that form thus keeping the end mill a tad sharper

 

[kingmt01]

Good question. Glad you asked.
I'm trying to teach myself. & when doing so you don't actually know what to ask ahead of time until you get yourself in a corner. Reading the questions of others helps avoid this.

 

[David M]

Speed/feed charts aren't hard to find, either look around on this site or an internet search. Get you in the ballpark anyway. A dime store magnifying glass can come in handy for a good look at the pointy end of your tooling too.

 

[Bill C.]

The first sign is heat. You need more coolant and it starts steaming more.

The corner of the EM is the first spot to go. Hold a light to reflect. A sharp EM will break from one surface to the other with no reflection. As they dull you see light reflecting off the dulled surface.

You can also feel the sharp edge with your thumb. Some use a fingernail.

This is just an experience thing. For some jobs you can push them till they burn up. others, the mill need to be perfect. small mills need to be sharper.

The thumb nail trick I learn from a older tool maker. I used it to test reground die sections for sharpness.

 

[Lood]

Thanks to all from me also. I'm brand new to milling and I just learned a lot from this thread.