Milling Slots

mikey said:
Is this behavior when you use the end/cutting tips only? I have seen something like this when the cutter is dull but not when it is sharp and certainly not when side milling.
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When end cutting they dance! :) But this does demonstrate how flexible an end mill can be. A lot of people don't realize how flexible HSS cutters are, especially small diameter ones. Walking happens all the time, but is prominent and more realized when slot/key way cutting, because when cutting back and forth in the same slot/key you will leave steps in the side and if you want to clean things up, you will have to take the slot oversize to get both walls/sides to clean up. Even when you take a heavy cut (without full cutter contact/plowing) the end mill will spring/flex away from the material, it's just not as obvious. This is one reason why light finishing cuts are taken when attempting to hit a tight tolerance; to minimize the tool spring.

Think about this for comparison. One of the most flexible HSS cutting tools is the drill bit. Think about how a drill, especially a small diameter one, will flex/bend when there is a slight miss alignment. You can even push on the side of one with your hand as feel/see it move. Now, end mills aren't this flexible because of their cross sectional design, but they do flex and the small/long ones can flex an incredible amount before breaking and will walk like crazy!

Ted
 
Okay, you're talking about deflection, something of which I am well aware. What confused me was the term "walking". I've seen what I would call walking when climb milling and the end mill dug in but that is pilot error.
 
mikey said:
Okay, you're talking about deflection, something of which I am well aware. What confused me was the term "walking". I've seen what I would call walking when climb milling and the end mill dug in but that is pilot error.
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Yeah, I'm guilty of using the same terms the old timers used when I was just learning this stuff... Hey, I guess now I'm an old timer! :eek: But, as my avatar states, I will never regret it!

Ted
 
mikey said:
Okay, you're talking about deflection, something of which I am well aware. What confused me was the term "walking". I've seen what I would call walking when climb milling and the end mill dug in but that is pilot error.
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Mike I was just trying to add to Ted's post. I didn't intend it to imply that you were not aware of stiffness. Some times these posts get a little sideways.

David
 
Thanks, Guys. Appreciate the information. At least now I know what you meant and yeah, deflection is a real thing.

Dave, thank you for your comment and concern - I know you meant to augment Ted's explanation and appreciate that others who follow will need to know the information you provided so we're all good.
 
I would drill an undersize hole then chop the slot out, feeding the quill up and down as you advance the table a little at a time. We used to do dozens of parts that way, easier on the endmill because there isn't continuous contact, so less heat. You can also use underside endmill to rough out then finish with one to size. Use a good quality cutter.
 
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