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Author Topic: CNC-If you're struggling with Aluminium milling  (Read 230 times)

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Offline Nemezis

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CNC-If you're struggling with Aluminium milling
« on: December 03, 2020, 02:11:48 AM »
If your aluminium milling looks like this, this post might help you.



For my next build, I've been experiencing in different material milling.
My CNC is a custom build originally made for wood. So I was not sure about metallic parts.

On copper and brass, it was not too bad.. (depending on what you call "not too bad") But Alu was just a giant mess.

At first, I blamed the stability of my CNC but really.. that was not the problem.

After a short discussion we had with Darth Chasm about Acrylic milling I decided to investigate a little bit further.

I will not go into too much details and just jump on conclusions: (Sorry, metric system in Europe)
  • The less flutes on bit the better. -> Single flute upcut carbide bit.
  • High RPM -> for a dia of 2 to 3mm -> 9600 RPM gave the best results. For larger dia, you will have to slow down your RPM accordingly as "cutting part" of the bit will go faster.
  • Slow feed rate -> 200 to 250 mm/min is nice.
  • Plunge rate -> 30mm/min to avoid stressing/breaking bit.

That's it for the settings.. BUT that's not enough.

If you directly cut to size, you won't have a nice and sharp result.
I may plunge at 1/2 of bit dia.. (1mm per pass). Instead, I plunged @ 0,7mm per pass (Once again to avoid stressing bit too much).
Don't go too shallow either or you won't cut enough and burnish your tool.
And per depth, use at least 2 passes to go to your final dimensions -> I used 0,3mm between passes.



Note the difference in sharpness between the outer part of the cut (waste part) and the inner part (product) to see how important it is to go into progressive passes to the final dimension.

Well, I hope it might help some on you.

All of the above is TRY and ERROR results
For those who have more experience in metal milling, don't hesitate to correct my settings since I'm really new at this.


Offline SirRawThunderMan

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Re: CNC-If you're struggling with Aluminium milling
« Reply #1 on: December 03, 2020, 03:38:07 AM »
I've got one word for ya, Nemezis: Coolant.

And a second: Enclosure.

Let me tell you a story.

A couple of years back, I joined a hackspace. Mainly because they had a laser cutter that I could use to make custom acrylic chassis disks on, rather than buy the ones from TCSS. They also had a 3040 desktop CNC engraver, which they found out could cut aluminium, because the bed was aluminium, and if you got the z axis depth wrong, the bits would go right through it.

So, I heard that, and I figured "well, now not only can I make my own chassis disks, but soon, I can make my own MHS-like parts! I'll be free from TCSS!"

I spent a few weeks playing around with this not great CNC machine and fusion 360. Learned the basics, feeds and speeds, flutes, etc. And if I remember right, my numbers were very close to yours. But, the spindle on the machine couldn't go past 7500RPM. The 4mm, 2 flute cutter was using just wasn't cutting well at that speed, and the machine really wasn't designed for cutting metal, so larger bits with slower RPMs would make the whole thing vibrate and cut worse.

And then I tried applying a lot of 3-in-1 Machine oil on my work, and the quality of the machining went through the roof. so, I bought a few cans of 3-in-1, and started trying to mill it into a copy of a ribbed-grooved MHS extension. it took about two hours, was ridiculously noisy, I went through three whole cans of oil, and in the end the piece was a fail because I'd got the mirroring wrong.

and then came time to clean this pool of machine oil and chips off the workbench. and the CNC. and the machine room walls. and ceiling. and the toilet next door.

I didn't do a great job of it. I thought I did, but what I failed to account for was that there was still plenty of oil that had accumulated in the nooks and crannies of the CNC, which seeped out during the night.

Did I mention we had a fire inspection the following morning? Surprisingly, the firefighters take a very dim view of pools of flammable material under machines powered by electricity.  :wink:

So, that was the end of that, and as we've yet to figure out a proper, DIY recirculating enclosure that won't get in the way of using the CNC for other materials (wood, plastics, etc) I haven't gone back to it. Besides, I'm having more fun with 3D printing.

But if there's to take from that pointless tale, it's 1: cooling will improve the quality of your cuts in metal, 2: it'll make a huge mess, so try and keep it as enclosed as possible.

also 3, never apologise for using the superior system of measurements.  :wink:
Better late than never.

Offline Nemezis

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Re: CNC-If you're struggling with Aluminium milling
« Reply #2 on: December 03, 2020, 04:03:50 AM »
Hey mate.
Fully agree about coolant.
But let's face it: You're bringing milling at an all different level when you speak of safe and efficient coolant system.
My aim for the moment is to stay at a DIY level however I would love to have place and money to get a pro CNC machine.
But RPM is definitely the key. initially I tried at 7K but result was messy and I had lot of vibration -> lot of tool break and improper finish.
My spindle is a G-Penny 1,5kW air-cooled and rated up to 24000RPM. Not too expensive but pretty stable for DIY.
Not sure if you can fix it to your 3040 since it's pretty heavy but you might give it a try.

 





Offline SirRawThunderMan

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Re: CNC-If you're struggling with Aluminium milling
« Reply #3 on: December 03, 2020, 04:15:12 AM »
Not sure if you can fix it to your 3040 since it's pretty heavy but you might give it a try.

Honestly, I wouldn't fix anything to that machine, I'd replace it. It's quite old now (2008-ish), and like much of that hackspace's equipment, was donated to us by someone who didn't want it any more, after they'd rewired a lot of the control hardware because the chinese wiring "didn't make sense."

But, we're a small not-for-profit, so our budget for new tools is always limited.
Better late than never.

Offline Nemezis

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Re: CNC-If you're struggling with Aluminium milling
« Reply #4 on: December 03, 2020, 04:35:09 AM »
Well, my budget was limited too.. So I build mine from scratch. I got X700 Y800 Z320 range and it cost me 1/3 of the price I would have paid for a commercial one.

Ok, cost me some extra sweat and headache though  :cheesy:

Offline jbkuma

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Re: CNC-If you're struggling with Aluminium milling
« Reply #5 on: December 04, 2020, 09:23:28 PM »
It seems counter intuitive, but if you are tapping, cutting, sawing, milling.. pretty much any sort of machining operation.. lubrication and cooling will go a very long way in improving quality.  Even giving a few drops of the 3-in-1 every few minutes will make a huge difference.

Offline Nemezis

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Re: CNC-If you're struggling with Aluminium milling
« Reply #6 on: December 05, 2020, 02:42:32 AM »
also 3, never apologise for using the superior system of measurements.  :wink:

Lol, I missed that last advise at first reading..

Wonder if you will get banned for this.. And me too for lol'ing it  :cheesy:

Offline Nemezis

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Re: CNC-If you're struggling with Aluminium milling
« Reply #7 on: December 05, 2020, 03:25:55 AM »
It seems counter intuitive..

I wondn't say counter-intuitive.. It definitely makes sense that lubrification WILL improve your cuts whatever tool you're using.

But:
1. It's messy. Depending on machine you have, you might spend a lot of time cleaning it afterward
    Mine has an MDF bed, which is pretty easy and inexpensive for levelling / beating / changing but it really hates oil stuff.
2. If you spray, you might have metal dust/shavings cloaking your pieces and cutting bit which will also bring some flows in your finish.
    The best way would be to flood it to allow proper shavings / residues to be evacuated but this requires a total different machinery / pumps / filters..
3. As SirThunderMan was mentioning: You might face security issues with oil + electrical component which might be far beyond most DIY'ers knowledge.

So don't get me wrong: Both of you are fully right about lubrification and it's very nice you mentioned it.

Also, the title of my post is probably not perfect since I was aiming ppl like me with low cost machinery and which are not working at Pro or semi-Pro level.

I also forgot to mention that you really have to install sufficient suction system to avoid shavings to get stuck between your pieces and cutting bits as it would definitely scratch the finish.



Offline jbkuma

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Re: CNC-If you're struggling with Aluminium milling
« Reply #8 on: December 06, 2020, 08:36:09 PM »
I do almost all of my work with hand tools and a drill, so it doesn't get much more low tech than that :D I lived in NYC the past several years and now just right across the river, so it isn't really conducive to having noisy tools.  Considering trying to find a budget friendly workspace next year..

The reason I say counter intuitive, is people often think "if I put oil on it, it will slip and it won't cut."