End Mills, The Nitty-Gritty: Cutter Geometry

[Music] hello everyone and welcome back to at man unlimited we're continuing our dive into the rabbit hole and as one of our viewers said a rabbit hole with bees in it in our first video we're talking n Mills was received quite well so in this video let's talk about the actual cutting edge geometry so with the lathe tool you are typically only engaging one face of the workpiece at a time but with an end mill you're going to mostly engage two faces of the work at one time for example picture this as my flute of my end mill so I've got a flute and it's going to have a cutting edge down its side so that we can cut the peripheral apart now it's also going to have a cutting edge a little bit on the bottom here so that we can cut the bottom of the part because typically when we're milling we're milling a part that kind of looks like this okay so we're going to have a bottom and we're going to have a wall so the nml comes in and it's scooped material out and it goes like that and you know prise their material up so with that we need to have to cutting faces that are engaged in the material at the same time so that means we have to have two sets of geometries now most end mills that you normally buy for softer materials and aluminum are positive positive rake angle that means that the rake angle on both cutting faces are positive you can buy all different combinations of positive negative and neutral rake angle cutting tools depending on the material you're cutting okay so let's go into rake angle if you've never been exposed to again so rake angle is the angle of the cutting face relative to the material so if I have a neutral rake angle that cutting cutting edge is going to come in at a ninety degree angle to the material uncut if I have a positive rake angle that cutter is going to come in at a positive angle relative to the material so it's going to come out and kind of scoop the material out okay I'm going to cut it like a knife now if I have a negative rake angle tool that means that the cutting edge is going to lag the material and it's kind of kind of scrape it out okay so why would we want all these different cutting angles well I have to do with the geometry of the cutting angle and the strength of the edge so a positive rake angle tool will typically take less horsepower to run however because of the geometry of it it's going to be thinner at the cutting edge and be weaker so it's not going to last as long that is why we use positive R and angle tooling typically on softer materials a negative rake angle tool is going to be a lot stronger because it's going to have more material behind the cutting edge so we typically use negative rake angle tooling for materials that are harder to cut but they take more horsepower to run because instead of having a cutting action they generate more of a shearing action of the material okay so notice with our example here we can change the helix angle of the end mill without changing the rake angle of the perfum and then depending on how the manufacturer does the the bottom cutting edge you can also you know make a little hinge so that you can change it without changing the bottom cutting geometry so the bottom cutting geometry is the thing so right here this would be a positive rake angle if we straightened it out like so that would be a neutral and then if it lagged it like that cardboard sort of been that would be a negative rake angle see it's kind of scraping material off okay so we have positive positive cutters and then typically you'll see positive negative cutters where the bottom portion of the cutters positive angled and then the side peripheral cutter is negative angled okay so that's one thing to consider when you're looking at end mill geometry so let's go down to the office and we'll take an up-close look at an actual end mill and let's go over more of the geometry because there's also relief angles we've got center cutting non Center cutting and we also have the hook and the flutes so let's take a look at the rest of the geometry involved in the end mill cutting edge so what we're looking at here is the end of a half-inch for flute standard square and mill okay now this is a center cutting end mill and the way that you can tell that it's Center cutting is if you look in the center here you'll see that there is a cutter face that goes from the edge all the way to the center and then it repeats on the opposite side now even though this is a for flute end mill when we get near the center notice that only two of the flutes are going to cut in the center the other two flutes are ground relief so they don't go all the way to the center okay now with the end mill at with the end of the mill just like with the sides we have to have some place for the chips to go for chipped evacuation and that's what this groove is right here okay so this groove right here is what they call the gash and that is where the chips will go to to be evacuated now everybody says that you shouldn't plunge with end mills and the reason why you shouldn't plunge with end mills is because they're not meant they're not designed like drill bits are okay so notice this gash there isn't a good lead-in in to the flute the only distance you have to get into the flute the nml which is right here on the side is this little pocket area here so the chips have to migrate all the way from this whole edge all the way out to get to the flute to then make it up and out of the hole so that's why n mils don't plunge very well typically you want a helix I'll do a helix will cut into the material and kind of you know spiral down into it okay so this is the gash now also at the end mill we talked about having a rake angle so this end mill is a positive raked end mill the leading edge of the end mill is leading into the material a little bit so it's going to try to slice the material off okay so that's a positive raked end mill now we've got the gash and the rake angle on the cutting face now after that we need to relief angle because we don't want the end mill to rub on the material after it's cut so and they'll have typically to relief angles they'll have a primary relief angle here okay and typically this is called land and then they'll also have a secondary relief angle after that and the reason for that is all about this edge strength we want a small relief angle here so that we can leave material to make the edge of this cutter stronger and then after that we want to taper off the relief angle especially on the side so that we can get into the flute and make bigger flutes for chip evacuation okay so that's the end of a standard square and you can see it's square here this is a very sharp angle there's almost no radius in here now you have to be careful when you don't have any radius because these corners tend to chip but if you want to make a pocket that has very sharp inside corners and you need to use a square end mill and we'll I'll show you a couple of different end mills that have different corner radius profiles on them okay so now that we've looked at the end let's look at the peripheral the side of the un-- mill so this is going to be the axial rake angle and the axial side this is the side of the unknown okay now just like the end of the end know that we talked about we have this rake angle here okay and again this is a positive positive end mill so this angle actually kind of comes up and and wraps around so that when it's cutting into the material the angle is positive okay then once we get into the once we get past the cutting edge then we're into the flute so this part here is the flute and that's where your chips are going to go for your chip evacuation okay and then after the flute way down here on the bottom this is called the gullet okay so we transition from the cutting edge into the flute and then into the gullet so then also on the backside of these you'll notice you can see there's also two relief angles on here we've got a primary relief angle so you can see here in another land okay and then we've got a secondary revues angle here that's much more obtuse okay so again we want this primary relief angle to be enough just so that we don't rub the cutter on the material we just cut but we don't want it so obtuse that you know we sacrifice edge strength so we want to leave enough material behind the cutter edge so that it stays nice and strong and then we want to back off the relief angle a lot so that we can fall in and make a bigger gullet and flute so we get get good clean chip evacuation then in addition to that the more common things that you hear of is length of cut so n mil from the tip of the end mill to where the flute grind is done that's the length of cut that is the deepest you should ever cut with the end mill then after the length of cut you'll have the overall length of the end mill which is obviously from end to end and then you'll have the shank diameter now the shank diameter can be a different diameter than the cutter okay sometimes you'll get larger shanks so that you get more rigidity in the shank and then the cutter is smaller than the shank diameter in some occasions what you might to do is you might want to have a real short length of cut and then have a little bit smaller shank diameter a necked down end mil so then what you can do is you can cut a really deep pocket and only use a small amount of the end mil for your actual cutting but then you have a long shank that's a little neck down so that you can reach deep into that pocket what that does is that will increase your rigidity because you don't have all this material missing from the flutes so then let's take a look at another end mill we'll take a look at a non Center cutting end mill and see what that looks like so here's another example of an end mill now this end mill is going to be a non Center cutting end mill so notice we have this huge hole in the center here and there's no flutes in here so you cannot plunge this end mill if you do so it will bind up on the material here because there's nothing to cut it okay now notice we've got these axial cutters here so it will still cut the bottom of your material if you want to plunge these end mills you must use a helical ramp and you have to make sure that your feed rate and your helical ramp angle are shallow enough to where you can allow this this cutting edge to rotate around and cut the surface away before the material builds up and gets into this little pocket here so you have to use a kind of shallow wrapping chol when your helix in these end mills into the material now this is also a roughing end mill or some people call it a corncob end mill but it still has all the same geometry if you notice we've got the axial rake angle here followed by the primary release in the secondary leaf and then we have the radial rake angle and then these are relieved a little differently okay because these are roughing in though now the reason why we use these roughing end mills is about chip evacuation chip buildup so if you've ever used a standard end mill and you've done a real deep depth of cut that takes up almost the whole flute or the whole length of cut here what will happen is you'll get these chips that are really long and needle-like and they tend to bird's nest up on you so they're really hard to evacuate even when you're using full flood coolant they can still build up so by putting these serrations in the flutes on the radial cutters here what we do is we make it so that this ends up being like a chip breaker okay so the chip of this end know the maximum chip size is typically only going to be from the bottom of this cut to the bottom of this cut so you get these little tiny and curly chips that come off of these and they're easy to evacuate with your coolant or your you know your mist or whatever you're using so you don't get the long stringing needle chips that are you know the full flute lengths like you would on a standard end mill so they're easy to clean so they're easier to evacuate the chips okay so again same stuff we've got a radio a creek angle and then we've got a flute a gullet so that's our chip evacuation so these are the exact same they're just serrated like this okay so let's take a look at what they call a bowl nose and mill okay so these are n mils that have a radius on the corner cutting edge okay so notice on our other end mills this corner was sharp and it left a sharp corner in the bottom of a pocket or along a perf you'll that were cutting now this one has a nice radius to it okay so now this end mill will leave a radius corner at the bottom of our pocket rather than a sharp corner now these angles are actually preferred when you're roughing or doing other any other heavy cutting because this radius in here really makes the corner of this cutter very strong so it's less likely to chip or break on you the other thing that bowl nose and mills are really good at is shallow angle 3d profiling so if you have like a ramp angle on a part that needs to be cut you may not need to use a ball mill and you can use a radius 10 mil instead and then the radius end mills typically are a little bit more efficient at removing material than a ball and Mel would be okay so that's a radius 10 mil all the other geometry is exactly the same they just put a little radius on this corner rather than have it sharp so let's take a look at a fallen mill so here's a ball end mil now a ball end mil is going to be used anytime that you want a machine material off that is not at a perpendicular angle to your end mil so you can machine slopes and curves and inside radiuses and all kinds of weird stuff with ballin those as long as the ball will fit within the radius that you're trying to go after so a ball end Mills again they are exactly the same as our other end mills they have the same pipe cutting geometry except with ball end mills they pretty much just wrap the flute and radial geometry right or wrong long into the axial side of things okay and again looking at the end these two flutes are doing the center cutting and these two flutes are relieved okay so we're only cutting with two flutes in the very center now the problem with ball mills and what you have to be careful of is you've got this point in the center here that's basically a zero feed so remember the smaller the end mill you have the faster you need to spin it to keep the chip load the same so you've got this area in here that is not moving but you're still feeding it so it's got a really high chip load in the center so you want to try not to cut with the very center of the ball mill if at all possible and also think about while you're doing a profile if you're doing a ramp and you ramp from the high side to the low side that's going to force this ball to cut on its center because it's kind of plunging it right so what you want to do is you want to cut from the low side to the high side and then we're only going to be using you know up to whatever ramp angle we're cutting it so it's always better to cut from low to high when you're trying to do profiling to avoid cutting on this Center whenever possible there are situations where you're not going to be able to avoid cutting on the center you just want to be mindful to minimize them as much as possible okay so that's a at the ball end mil you can see that the cutting geometry for an end mil is pretty complex we've got all these different angles and all these different relief cops and Hulk and the flute clearance and the rake angle so there's a lot more to the end mill geometry than there is to a simple lathe insert typically you just have you know your rake angle your relief angles and then maybe a chip breaker okay with end mills typically we don't need a chip breaker because by nature milling is an interrupted cut we come in enter the material and then exit the material so that automatically breaks our chip for us so you you typically don't see chip breakers when you're selecting end mills okay so thanks for watching I hope you found this informative like all the videos please feel free to comment below and I always try to read all the comments and will take into consideration if I miss anything or anybody has something to add we'll we'll make another video on it so that we get you know the best library is possible on the next video I'm going to specifically concentrate on flutes and helix angles so helix angles is pretty cool and I don't think a lot of people give thought to helix angle so stay tuned and we'll see on the next video thanks for watching [Music]

Channel: At-Man Unlimited Machining

Views: 31,107

Keywords: At-Man Unlimited, At-Man, At Man, AtMan, Machining, CNC Machining, CNC, Machine Shop, Job Shop, DIY, How to, VMC, Fadal, Vertical Machining Center, Milling, End Mill, Geometry, Cutting Tool

Id: eH50t7kUx6c

Length: 19min 3sec (1143 seconds)

Published: Fri Feb 03 2017