Not all endmills can cut downwards. Have you tried ramping into the cut, or coming in from the edge of the material?
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Well the part I was trying to mill was in the middle, so I cannot come in from the side.
I set the plunge speed to biblically slow (think it was something like 0.1mm a second) and the feedrate was set at 20mm/s. It still shattered on touching the metal.
Maybe the wrong type of bit 
Similar to this bit but 1/8"
I don’t have any aluminum experience myself, just passing along what I’ve read/seen. My understanding is that unless the cutting edges cross the centerline on the bottom, then the bottom of the bit doesn’t cut, and the bit it can’t “plunge.”
Complete armchair engineering, but that looks like it should work. You should be cutting at a reasonably slow RPM, otherwise you risk not cutting enough and overheating your bit (or worse, welding your bit to the stock), especially with a two-flute bit. And if you can, change the plunge angle to something other than 90 degrees. Let the bit work down into the stock rather than jam straight down into it. Once the endmill is fully involved in the stock, having the full cutting length of the flutes engaged will help. Or at least, the full DOC… And the trochoidal milling really will help a lot. Assuming, of course, that the pocket/channel/hole you’re milling is larger than the diameter of the endmill.
Its just SO time consuming to try and dial this in! (And expensive #BrokenBits)
I think part of the issue is the wealth of conflicting information on the Web. Some people say mill aluminium at 32,000RPM, some say at 12,000RPM.
I have not particularly noticed any difference yet between any speed.
It does make sense to me that the bottom of the bit must have a cutting ‘blade’ across it’s entire width, otherwise it simply cannot plunge into the material full stop.
I do have bits that are angled at the ends. They say they are for aluminium, but I have yet to find any use for them. Because the point is off-centre, they instantly snap the second they touch the surface to be cut.
I tried them approaching from the side and they didn’t last long at all (snapped).
Going to try a 1/4" bit this afternoon. Straight cut with a cutting face across the bottom. Nothing to lose really
I would suspect it is either your feed settings or rigidity of your router. I had no issues cutting aluminum with my older 525 version MPCNC. I used these bits:
I have tightened up the Z axis, and it seems pretty solid.
I have ordered more bits. See what happens.
What feedrate, plunge speed, DOC etc did you use for that aluminium milling in your pictures (3&4)?
Would also be interested to know how long that took to mill out.
Pretty sure slower is better when it comes to the bit speed. Soon find out!
Feed and plunge were 1 mm/s. DOC .1 mm/s
So yeah, it took like 16 or so hours to cut…
I could probably speed it up a little and shave some off the time, but it was my first cut in aluminum and it’s using an older model MPCNC (core isn’t at rigid as the Primo).
The part came out great and the piece of aluminum was like $10 shipped. A local water jetting place wanted like $100 for the same part, so I was happy to wait a long run time to cut it!
@stevolution sorry, I haven’t tried cutting aluminum yet so I don’t have any speed/feed/DOC suggestions but have you checked the grade of the aluminum that you are trying to cut? There are a few grades that are not very well suited for machining so that could be another reason.
Yes it did occur to me that the aluminium grade may be the issue, but how do you check that?
I got these pieces from my ‘stock’ of metal and no idea where they came from.
If I ever get this dialled in at all (which isn’t looking too likely!), then I really would like to make a detailed spreadsheet of cutting info.
16hrs. Trouble is, I computer program etc in my workshop and it’s also my home. That noise for 16+ hours isn’t really acceptable (to me or my neighbours).
But… that is something I didn’t realise, the length of time these things take to mill.
Also, I didn’t think you were supposed to leave these things running alone. Long day in the shop!
My feeds/speeds were very conservative - I wasn’t in a rush and just doing a one-off piece, so I wasn’t worried about how long it might take.
There is no easy way to test the grade of aluminum at home. I would either try again with a new bit and conservative settings like I used or even purchase a small piece of known grade aluminum to eliminate that from being your possible issue.
As for leaving the machine unattended, people do, but it doesn’t mean you should…
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Never leave your CNC unattended† while the spindle has power. And probably never when the steppers have power, either.
†This can include turning your back on it, or getting more than an arms length from it. It is a computer-controlled robot. Assume it a) wants to kill you, and b) either knows how, or is learning… 
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Well not leaving a CNC running powered up instantly renders any milling project over say 8 hrs impossible then 
You could say never leave a 3D printer running either, but I usually have a pair of those running overnight.
My workshop has cameras on all the 3d printers and the CNC head linked to my phone, and a smoke + heat sensor that kills the workshop power upon detection.
Anyway, I could not ever listen to that thing whirring away for hours on end.
Milled out some timber projects today… all fine. Ordered some bits for Aluminium. Have anther go with those later.
I like Easel, but these programs always seem to be something missing. You cannot set up your machine in Easel. You can make a profile called ‘other’ but you cannot input custom rails lengths etc.
Shame
Ultimately, it’s your machine, your shop, your life. But official line is to always oversee your CNC. Fires start and spread way too quickly. Invest in a decent headset if the whine is what gets to you.
3D printers are a completely different beast. There are a number of things that have to go wrong in order to cause catastrophic failure in a 3D printer, most of which are very, very unlikely, especially in the combination required to cause the thermal runaway needed to start a fire. But a spindle collet, at speed, rubbing against stock, spoilboard, or anything else, can start a fire very quickly. And unless your dust management is truly top-notch, (or you’re milling metal), you have plenty of ready tinder to get things really going.
So again, it’s your machine, your shop, and your life. But the official line is that all CNC operations should be closely supervised, and all safety precautions followed (including having proper fire suppression at hand). And yes, there are ways to mitigate the danger and threat of fire, and ways to limit any damage that may occur, but that’s like saying that double-bagging makes putting gasoline in ZipLocks safer… 
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What… double bagging gasoline isn’t safe? 
Best get those Ziplocks out of my truck 
I have ear protection. It’s just not pleasant working in the same room as 8+hrs of whirring noise.
To be honest, I would just get someone else to make it for me if it was that complicated.
It’s like my 3d printing. Simple one-off stuff I do myself, but I have a great guy who I found online years back who produces outstanding 3d prints if I need them at a brilliant cost. If it’s volume or of a large size, I just get him to do it.
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Thought I would update progress…
Got some different 1/8" bits.
https://www.ebay.co.uk/itm/313493984587
These seem to work well in aluminium. Gone all day and no breakages.
Started all settings slow ‘n’ low and worked my way up.
Router seems fine on its slowest speed, and so dialled it in with regards to noise vs time vs quality with:
Spindle 13,000RPM
Plunge speed 10mm minute
Depth of cut 0.6mm
Feedrate 900mm minute
I found you could wind the feedrate right up to 1500mm per minute and it still be fine, but it did sound a little strained at times.
Cuts a 30mm disc @ 2mm deep in 8 minutes. That is pretty acceptable.
Estlcam? Just don’t like it. Each to their own I suppose.
I found EASEL far better. Export that straight to Repetier and we are off.
LUBRICATION! That certainly helps.
I re-printed my vacuum head and added a couple of slots underneath at the edges that let the down-draft of the router blow a curtain around the vacuum head.
This works brilliantly at keeping the lubrication fluid centred and within the cutting track. Hardly any lubrication or metal particles escape the vacuum head and the fluid pools inside your part.
I also added a brass lubrication tube pointing directly at the milling target.
So, I made a quick lubricating station. Found an old car windscreen pump with metal gears in my box of pumps.
Quick bit of Arduino code and a 3d print and now I can pump a ‘pulse’ of lubrication or cutting fluid directly to the cut.
You can set the pulse length and how often using the rotary knob. Used a plant irrigation valve to obtain ‘drips’ out of the end, rather than a jet.
My only question is… attached is the 2mm deep circular cut. Not entirely smooth (few tiny ridges). Increase the step-over?
Still have some experimenting to do.
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Nice! Did you end up cutting the original aluminum or ordering something known?
Just ploughed into the stock I had 
We’ve had a few fires. One guy burned his table down. Luckily it didn’t take the shop with it. Mine blew itself out. Just be careful.
I’m standing next to it all the time… fire extinguisher on the wall to the left.
I did think of adding a second pump with a ‘Y’ piece to my lubrication downpipe.
My shop has a smoke and heat detector that operates a contactor. I could rig it to pump water directly onto the milling bit if triggered. Probably not required.