I have been using 45 degree helix TiCN end mills for a month now but I have to confess I have wimped out and only done a maximum 1 mm DOC on adaptive on 6061T6 with decent results. One day when I am feeling more reckless perhaps.
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Lets add some variable flutage to the discussion. I use a three flute 1/8 stubby VFA and it rips well if given appropriate chip evacuation area. Its cut anywhere from 8-100% flute length and 10-95% diameter depending on the needs.
Does “reduced side loading” = increased axial loading? I mean, nothing disappears, it just gets transferred in a different direction right?
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Link is to 1/4", not 1/8".
That’s a good question, I kind of thought that too until I saw the linked snow plow analogy and started thinking about helical cutter heads in jointers and planers and hand planing at an angle.
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It’s more towards the reamer end of the spectrum, so no, more chatter. That said, the material is software, the frequencies are different. It’s a lot like a saw blade - you want multiple teeth engaged (flutes) - more flutes = more better, but in something soft like aluminum, chip clearance is a huge deal, so bigger gullets are needed…so fewer flutes helps on that side more. The reason a reamer doesn’t chatter is because most of it’s flutes are always engaged.
If the balance was easy to find, there wouldn’t be hundreds of different flute/gullet/helix angle/coating materials, and cutting edge geometries, with each vendor claiming the best.
Sure, if it’s the right material and you have the power for it. d ~ 2 is about as far as I would personally go, but I’m not a production guy chasing an extra buck by getting one more part out the door. You can slot (WOC == D) but the 100% engagement can be really chattery unless you unload it with some slower speeds. I usually use a helix entry and adaptive from there specifically to avoid a slotted entry.
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Which is it then - more or less chatter? What’s a reamer?
Smaller chiploads are easier to clear and you get bigger gullets with larger endmills.
That is definitely true, this thing throws chips across the room and goes through the wood ridiculously fast at 22,000 RPM, I’ve no idea how big a cut it will take yet because it’s just scary and holding the workpiece solidly enough has become the issue. Plywood at 10mm DoC 5mm WoC and 2,000mm / min (0.05mm per tooth) and it wasn’t bothered. The workpiece on the other hand was vibrating despite being clamped flat on the spoilboard so maybe that 0 degree helix vibration theory…
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For the same size endmill, fewer flutes = bigger gullets = better clearing, but again, feed rate is different because the # of flutes is lower as well.
They look like this:
They are specifically for making drilled holes both round and on size, which a drill won’t do (they’re never accurately round, and usually undersized by a few thousandths). Note they are not end cutting.
A reamer is 100% (mostly, remember I said the whole wasn’t round until reamed) engaged with the hole, so they can’t effectively chatter, if you used one to side mill something, it would chatter like crazy. They obviously have a crazy high helix angle (ie 90 degrees).
There’s way more to chatter than just the flute arrangement and helix angle, the feed rates with the size of the overall cutter makes a huge difference - a bigger cutter is obviously (of the same material) stiffer than a small one. Less stiff = more chatter, all other things being equal. Unfortunately, we’re deep into a highly multivariate here.
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Kind-of like it would on a router table where you’d likely use 24,000 RPM for anything less than 1" diameter in the “New World” (where most router bits only have 2 flutes)? I’ll bet you didn’t get much tear-out on the faces though, right? Even if you were cutting Baltic Birch, your cutting forces probably wouldn’t have caused a router table user to slow his feed rate.
Your Chip Thickness was 0.0012", which should make @Julien happy. Measure/log spindle currents and try it again with 45 degree helix up or down cut?
Measure noise too?
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The helix angle for your posted endmill image looks like 0 degrees to me.
There was very little tear out, a little fuzzy but the finishing pass dealt with most of that. It wasn’t super high quality ply and no, the spindle didn’t even blink. I was watching the output Amps on the HY VFD and it went from 1.9 to 2.2 during the cut so the spindle was basically idling.
This is that bit doing a slightly slower adaptive clear in a pocket;
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When/how much do you sleep (assuming that you do get some sleep)?
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After a lifetime of working with US employers and customers I am roughly on EST 
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Interesting question. And yes, you’re right, you can pick the helix angle to ensure full axial engagement even for a radially narrow cut, so that the cutting forces are essentially constant. Here’s some data:
Forces (Newton) for one revolution for the SECO JH40060, which has a very sharp edge at low helix angle (25 degree):
Keeping everything the same, but changing the helix angle to 40 degree:
And finally 55 degree:
This last would be close to what you suggest, forces practically constant. Iff, and that’s the problem on a Shapeoko, if you can keep the chips from clogging up the flutes (just my impression with higher helix angle endmills).
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Interesting,
Could you explain the force directions on the chart a little more pls?
I think I get axial, this would be vertical forces up and down on the cutter.
Feed is presumably in the feed direction, i.e. the direction the spindle is moving.
In plane and transverse though?
Also, what software did you use to get this data from?
Thx
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Yes, positive feed force pulls the tool “forward”, sort of supports the steppers, negative holds back. Transverse is perpendicular to the toolpath, positive to the right when looking into the direction of motion - in this example here, negative transverse force means the tool is pressed away from the workpiece (climb cutting). Axial is positive when the tool is pressed into the spindle, negative here.
In-plane force is the magnitude of the vector sum of the feed and transverse forces. This is what your weakest axis motor needs to drive/hold in the worst case, a very critical value for the shapeoko, as I have found out (ouch!).
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Thanks,
That is really interesting.
From some previous discussions I believe the received wisdom is that the Shapeoko is better at cutting harder materials using a shallow depth of cut with a higher width of cut. Would it be possible for you to show a comparison of two equivalent removal rate cuts but trading width for depth to see what happens to the forces? e.g. trading 0.5mm DoC at 3mm WoC for 3mm DoC at 0.5mm WoC
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Here’s the comparison you were asking for (harder material? let’s go 7075; tool this time is WNT 53501060. But please read to the bottom of this post…
0.5 mm axial by 3.0 mm radial
3.0 mm axial by 0.5 mm radial
So, for your constraints, it’s a wash, more or less. However, is this the question you should be asking?
More often, we may want to know which parameters to choose to reach the highest removal rate given the limitations to the machine - and that’s not the same problem, because this stuff is not very linear: you can’t always simply scale. So the answer is … it depends.
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What calculator did you use?
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That’s interesting.
What I was wondering was whether there was some sign in the data of why the machine was less happy with the total MRR when taken as a deep narrow cut rather than a shallow wide cut. It’s quite frustrating to only be able to use 0.5mm of each cutter.
As you say the forces are quite similar, also they both show as pulses of similar width. Once machine deflection is taken into account things may change.
We might reasonably expect in the region of;
- 0.25mm lateral deflection for the 3mm WoC given the 41 N peak lateral load
- 0.2mm lateral deflection for the 3mm DoC given the 33 N peak lateral load
But these deflections would change the effective cutter engagement and therefore the forces (in the first pass, in the second we’d end up having to take that extra material if we’re stepping over by the WoC)
- 0.25mm in the shallow cut is subtracted from (correct sign?) the existing 3mm width of cut to give 2.75mm (92% of original) and the cutter pulls about 0.08 in the feed direction
- 0.2mm in the deep cut is subtracted from only 0.5mm width in the deep cut giving 0.3mm (only 40% of original) whilst the cutter pulls 0.16mm in the feed direction
So whilst the initial deflection is smaller in the deep cut the total engagement change is quite a bit larger, this might be a pointer to what’s going on when we try to swap radial for axial engagement, larger changes in forces giving us a stronger vibration input to the spindle.
There’s a bunch of simplifications in there, we know the Shapeoko deflection is not symmetric in the X and Y axes at all and there’s a bunch of coupling in the Y and Z deflections too. Also those cutting forces were calculated assuming a rigid machine?
Thoughts?
@gmack have I completely jumped the shark?
I’m assuming there’s existing research already done on how machine and cutter deflection impacts cutting forces and how those variables interact to impact overall machine behaviour, but I haven’t seen any of it.
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Maybe because people aren’t using enough of the endmill helix to smooth out the cutting forces as shown feasible in @spargeltarzan’s first post? Note that he apparently used an axial DOC equal to the endmill diameter. Many endmill manufacturers recommend 1.5 - 2 times that for side milling (enabling lower helix angles).
LOL - I had to look that one up even though I used to watch Happy Days! But, this is exactly the kind of input/feedback I was hoping for. 
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