New Endmill Chatter/Dimensions - Break-in needed?

[HPFStrawn]

Is it common to have brand new endmills chatter and vary dimensions? I'm not sure if maybe this specific endmill just acts weird when new, but both times I have tried this particular endmill (OSG 3/8" Flat 3 Flute 45° Helix) new it has had chatter for the first few parts. I try to reduce the rpm and that helps, but once the cutter gets through a few parts the chatter disappears.

Today I also noticed that the cutter shrank a few tenths during this process. The first 2 parts came out about the same size (also during the chatter), then parts 3-6 (chatter cleared up) ended up consistently oversize by ~.0005. I have adjusted my cutter comp for the new results. But this makes me wonder if people do any kind of break in period with new endmills? Reserve the endmill for roughing duty for a certain time until it is "broken in"? Or are there any other tricks to get around this?

 

[Orange Vise]

It's common. The endmill lacks edge prep. As you cut a few parts, the sharp edges break down and the chatter goes away. It also affects dimension as you've noticed.

This happens with lathe inserts, too.

 

[Mtndew]

Take a small stone and LIGHTLY stone the cutting edges.

 

[DouglasJRizzo]

Take a small stone and LIGHTLY stone the cutting edges.

Dad used to do that all the time. Fine grain stone, too.

 

[Nerdlinger]

^^^^^^^what these three said. We either stone them or deal with the squealing for a few parts. Fun fact - a custom tap we’ve been using forever started either breaking right away or they would last for thousands of holes. It took us forever to figure out they stopped smoothing they edge out. So if we were lucky enough to get last a few parts the edge would have been “broken in” by then and then we see good to go for the normal life of the tap. So now we stone them and the problem has completely gone away. Good luck!

 

[MaxPrairie]

I have a tote full of broke in endmills if you are interested.

 

[CarbideBob]

Why the "break in"?
Why stone it a bit?
Dull is better? How can that be right?
Welcome to the rabbit hole. Do you want to go down it or be happy to make it run.

 

[mhajicek]

I've never seen anything like that, but I cut mostly Ti and 17-4. In my world, cutters cut best when brand new. How's the rigidity of your setup?

 

[Scruffy887]

Well we all remember saving up and buying our first new end mill. Open the plastic box, the nice pungent smell of grinding fluid. Careful not to cut our fingers. New ones did not stink like the rancid residue on the ones we pulled from old coffee cans.
Just funning with you.

 

[Nagol]

To those wondering if "dulling" the edge makes sense, think of an insert for a cutting tool. They are never razor sharp, unless made for aluminum, because it makes it brittle and in the case of the sharp endmill the sharp edge may suck it into the cut more than desired making it deflect into the cut and back out when it leaves the cut. I'm not sure if anyone sells endmills for aluminum with an edge prep because you generally want minimum friction to keep the material from welding to the tool. I use Gorilla brand Yeti line endmills in aluminum to great success when it comes around because we don't cut aluminum that often to make it worth keeping the dedicated tools around, nor do I have the RPM to use them right. They are a steel cutting endmill but the coating they use is really slick. I use them to slot 1XD deep at about 1000 SFM and 0.01 IPR with a 1/2" tool. Maybe worth giving it a try if you are going to cut steel too. Very affordable and last a long time.

 

[crossthread82]

I've experienced this before when using some cheaper endmills in steel. They would ring but not quite chatter on the first part or two, then as it lost its razor edge it would quite up and cut silent. A trick that I learned is to take a copper penny and drag it along the flute edge, almost letting the endmill cut a line in the edge of the penny. That would "dull" or rather hone the edge enough to let it cut quite right from the start. Its a similar process to what others described with a stone, however I find it a bit safer since the copper is soft and you have less chance of over dulling the edge.

 

[CarbideBob]

To those wondering if "dulling" the edge makes sense, think of an insert for a cutting tool. They are never razor sharp, unless made for aluminum, because it makes it brittle and in the case of the sharp endmill the sharp edge may suck it into the cut more than desired .

Not quite that simple and do not think you have made and shipped a lot of "sharp" carbide inserts.
To shave hairs on your arm very high rakes are needed not sharpness.
I like to show this off to people shaving the back side of my wrist or arm with my tool but it is PT Barnum.
I do tell almost all that this is niffy cool but means shit for you application if they will listen for a bit.

Why the less chatter after a break in or hitting with a stone. What changes? Why is the chip formed differently? How is the load to the endmill changed?
We all know it happens.
Bob

 

[mmurray70]

Many tools have a honed edge right from factory. Very common with steel specific endmills. Tools designed for stainless/titanium have sharper edges. Aluminum tools have razor sharp edges.

If you find the "broken in" tool works better, I would try a find a tool with the proper edge prep from factory. This way the edge you like has proper coating on it, and will likely last much longer then the edge you got from wearing down a sharper edge.

 

[HPFStrawn]

Sweet, thanks all for the pointers. I will definetly give the edge prep techniques a try on future tools.