One last thing I’ll add to the thread is that Millalyzer is fantastic for analyzing feeds and speeds. I haven’t tried to use its “give me feeds and speeds for this material” mode but it’s amazing for understanding what exactly is going on in a cut.
Millalyzer’s online manual is also really informative.
IMO, its worse than useless for Shapeokos, Nomads, and everything else because it obfuscates and misleads.
I’ve learned a lot from hsmadvisor and it provides a fantastic starting point for me in various materials. I spend a lot of time deciding feeds and speeds for a new mill/material combination and since I don’t have any idea what values are sane, I like being able to see the ballpark wattage a given cut in a given material will take. It has enabled me to make deep & narrow adaptive cuts without being an expert machinist, and the results are fantastically better than shallow & wide on a nomad 3. Absolute game changer for a novice and it’s just a starting point IMO.
Thanks for the links, that shapeoko tutorial is golden.
My experience was that the numbers were getting into the realm of possible if you set the turtle/hare slider all the way to turtle. But where should I set the slider? I can’t go too slow, because I’ll burn or melt the material.
And even with the slider in the green (around 30-40% I think), I stalled the Nomad cutting HDPE using the GWizard settings. It was way too optimistic as to what the Nomad’s spindle can handle. Looking at my notes: HDPE, 6mm endmill, 18k, 900mm/min, slot cut with 8mm DOC. That’s an instant stall.
In the end, I realized that GWizard just doesn’t give me reliable numbers to go on. It was not a good purchase.
I am getting much better numbers from HSMadvisor. It’s not perfect: for example, I wish it took into account that you simply can’t cut acrylic with slow feed rates, or you’ll melt it. I also noticed the recommended numbers sometimes jump a lot depending on tool stickout. While that might be the case for harder materials, there are more important factors for plastics. But overall it gives me numbers that are aligned with what I’ve seen from (limited) experience.
I think you highlight a good point about these software tools, particularly with the machines we are using. You have to add a healthy dose of intuition, experience and often scepticism to their results. And maybe concentrate on the “advisor” part and take it as general advice and not strict law.
IMO “HSMAdvisor keeps getting better. Like the SFPF Calculator it now enables entry of the maximum acceptable cutting force in the “Machine Profile” settings” Cutting forces are usually the primary limiter of “hobbyist” CNC router performance. But HSMAdvisor also allows the entry (and/or download/upload) of spindle torque curves to predict when the spindle power would be the limiter. Millalyzer can do all of that and also show what those forces look like,
IMO, since cutting forces are reduced when spindle speeds and endmill diameters are increased as well as when chiploads are decreased, spindle speeds and endmill diameters should be maximized and chiploads minimized to the extent possible. But spindle speed should not exceed the endmill manufacturer’s limit for the material being cut. If the endmill manufacturer provides a minimum chipload for the workpiece, like Kennametal’s “Max Chip Thickness”, I’d use that. If not, @Julien’s recommended universal 0.001" chipload (actually IPT?) would be a good way to determine an appropriate starting feed rate.
In my experience it’s not that simple. On my machine it’s possible to take a 1mm axial, 4.8mm radial cut with a 6mm endmill (actually I can just about quadruple the depth I think) but not a 4mm axial, 0.5mm radial, despite the latter cut being all around lighter.
I agree on speeds and endmill diameters but not on chipload. I always stick to the manufacturer’s recommendation when it comes to chipload. You definitely shouldn’t go high (that’s how you break endmills) but as you go lower, the endmill edge has more collisions per unit work, which I’m guessing is bad for tool life and the chips are smaller, so can’t carry away heat.
Plus, as I said above, I don’t think cutting forces are the variable to optimise for.
I’d put the manufacturer’s recommendation in the calculator and then leave it to do the optimisation (e.g. account for chip thinning).
Can’t Millalyzer’s Machine Settings account for that?
I agree if the manufacturer provides realistic minimum chiploads, like Kennametal’s 0.0059" minimum “Max Chip Thickness” independent of endmill diameter but unlike Amana’s (overly aggressive chiploads?)
Don’t higher cutting speeds and smaller chiploads reduce cutting forces? Wouldn’t that then reduce the cutting energy (hence heat generated) per chip?
It has settings for transverse, feed and plane but they don’t appear to help here.
|4.8mm radial, 1mm axial||12.1||17.6||18.3|
|0.5mm radial, 4mm axial||8.3||8.2||11.7|
The low-radial, high-axial cut has lower forces in every respect and yet it just doesn’t work and becomes a chattery mess.
I don’t think that’s necessarily crazy, you just have to adjust the width and depth of cut to compensate. When doing adaptive toolpaths for example, I’ve pushed 3mm single-flute endmills to 2400mm/min at 10k RPM (nearly 5 thou FPT) but I did it with IIRC 0.3mm width and 0.5mm depth.
Well friction is the product of the coefficient and the force applied so yes, it should, but it also reduces the amount of heat carried away with the chip. I don’t know how those two equations balance.
But manufacturers like SECO seem pretty unanimous in cautioning against overly low chip load.
Maybe @spargeltarzan will weigh in on this.
Like this?! Probably not much heat generated when cutting at 4 Watts.
Yep! Such is life on a stock Nomad.
The most important aspect regarding chip thickness is that the edge is never perfectly sharp, but looks more like this:
h_0 is the chip thickness here, and in this picture it’s smaller than the tool edge radius r_e. The tool is kneading the material in front of the radius instead of shearing it off. What you want to happen is more like this:
Here the uncut chip thickness (t) is much, much larger than the edge radius. I think it’s fairly intuitive that the second process is more efficient in lifting off the chip from the stock.
This doesn’t mean you should go for the largest possible chip thickness (feed), but stay well away from the edge radius. Hence the minimum chipload guidelines.
True, but it is concentrated to a very small area as well. The temperature inside the shear zone, right ahead of the edge, is often 200 degree Celsius when cutting aluminium at high vc.
Yes, that’s about it. It’s not so much the heat itself (in aluminium at least), but the softened and very sticky aluminium sliding over the rake face. Every time it does that, it rips tiny tiny flakes out of the carbide - it’s visible if you have a decent microscope. So yes - tool life measured in meters cut usually goes up with chip-load. Here’s an example from Sandvik’s calculator:
Mind you, this is tool life in meters, or number of features produced for particular set of engagement parameters (recommended defaults for the tool). It gets more complicated if you start changing engagement as well.
How much tool life matters to you depends on how much you payed for your endmill, I guess.
Unfortunately cutter edge radius doesn’t seem to be available from manufacturers. What are typical values? Do most manufacturers likely use that or some other criteria for their minimum chipload (actually IPT?) recommendations? Can varying edge radius in Millalyzer be used to predict the impact? Is the argument that big chips help control heat valid?
Do coated cutters help much?
Does Millalyzer calculate that?
Would it be reliable if they did? You’d expect it to change pretty quickly as the tool wears, wouldn’t you?
(This isn’t a rhetorical “you’re stupid for asking the question”, I’m really curious whether it’s reliable)
Perhaps it generally makes more sense to measure it with an optical comparator or somesuch?
10µm edge radius:
75µm edge radius:
Yep (manual page):
If the tool is ground to a sharp edge, for use in aluminium, 3-5 µm. Some specialised coatings such as high-quality DLC add only 1 µm to that, but most are an extra 3-5 µm. Some manufacturers offer/advertise optional edge treatments, meaning larger, but well-defined radius (5-10 µm). That can have benefits (long-term consistency) for some applications where fz is very large anyway.
An endmill that is advertised as “universal” or “general purpose”, and which the manufacturer says may be used in steel will have a larger radius and a robust coating that add up to 7-15 µm. This is already painfully close to the chip thickness values that might be used in Nomads and Shapeokos.
Inserts for indexed tools have radii of 15 - 50 µm unless ground and polished.
Depends. Yes, it wears, but not necessarily quickly. If a 2-µm-radius endmill that is ground for acrylic is used in 7075, then you’re right, that edge won’t last long - and you can see that with the naked eye. That precise same tool in 5083 or 5754 (a.k.a. “dunno-which-alloy”) may well work fine for quite a while. An endmill designed for aluminium should be able to maintain its small edge radius (maybe 3, maybe 5 µm) for about the nominal tool life, and will certainly if lubrication is used.
In carbon steel, cast iron, graphite, cast aluminum alloys (Si > 5%) - absolutely. Wrought aluminium alloys - only where you can push large chiploads, so that the added radius doesn’t matter much.
Proper lubrication helps more…
Not sure. What is the definition of “control heat”?
So @Julien’s and @Vince.Fab’s empirically derived advice to not use chiploads (chip thicknesses or IPTs?) less than 0.001" is reasonable? Does increasing chipload ever help to reduce heat in either the workpiece or cutter; if so when? Is that as effective as alternatives so as flooding, cooling mists and/or lubrication?
Oh, yes, certainly.
The deformation mechanism in the first picture above (when the chip thickness close to, or smaller than edge radius) is less efficient, that is, larger forces are needed to separate the chip from the stock. Therefore, the amount of energy spent per material removed also goes up, and a fraction of that is converted into heat. So, increasing the uncut chip thickness (t or h_0 above) to a value that is a good bit larger than the edge radius will reduce the amount of heat generated per material volume removed.
However, if the reason you’re interested in heat in the first place is something like the temperature rise in the workpiece, then of course the absolute (not specific) amount of heat power in relation to heat dissipation is more relevant. Meaning cooling or reducing RPM.
No, but it isn’t as messy.
What uncut chip thickness to edge radius is required to sufficiently minimize the amount of heat generated? Is there value in further increasing the uncut chip thickness to increase the proportion of heat carried away by the chips?
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