Newbie - poor auminium cutting, but why?

Hi,

I have just started with an eShapeoko, which I have been using successfully to cut balsa and styrene shapes using a cheap motor for a spindle.

I am now starting to cut aluminium, but my first attempts leave an unsightly ridge around the edge of the cut. This was not a problem before with wood or plastic.

I assume that this is going to be something to do with feed rates or speeds, but I don't know whether to go higher or lower. Perhaps it's the end mill I'm using...

I enclose a picture to show what is happening. This is cutting at depths of 0.3 to 0.5mm, using a 1mm twin-flute mill. Feed speed was between 20 and 10, and spindle speed was around 13,500rpm. I put a bit of cutting oil on the mill and aluminium surface. Can anyone advise what my next settings ought to be? What I am doing wrong? Or what I should do next to diagnose the problem?

Attachment 29363

No direct experience here as I mainly do woodwork.

But, looking at it I would say that the bit was either blunt, the wrong type or the feed speed was too slow and it has melted/ welded the cut rather than cutting cleanly and clearing the chips.
A 1mm endmill with 2 flutes leaves little room for clearing waste maybe try a single.

What does the endmill look like now, does it have aluminium stuck to it ?

I am sure someone will be along with a comprehensive answer shortly.

Ollie

Thanks very much for taking the time to input!

The end mills are new but I did run with a slow feed speed and a fast RPM. I oiled the surface to try to prevent sticking - but your comment makes a lot of sense. It's a bit dark and cold in the shed at the moment, but I will look at the mill tomorrow, and perhaps try a faster feed and a slower rpm....

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Originally Posted by Dodgy Geezer

Thanks very much for taking the time to input!

The end mills are new but I did run with a slow feed speed and a fast RPM. I oiled the surface to try to prevent sticking - but your comment makes a lot of sense. It's a bit dark and cold in the shed at the moment, but I will look at the mill tomorrow, and perhaps try a faster feed and a slower rpm....

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What grade of Ali are you using

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Originally Posted by Dodgy Geezer

Thanks very much for taking the time to input!

The end mills are new but I did run with a slow feed speed and a fast RPM. I oiled the surface to try to prevent sticking - but your comment makes a lot of sense. It's a bit dark and cold in the shed at the moment, but I will look at the mill tomorrow, and perhaps try a faster feed and a slower rpm....

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So you essentially tried rubbing/melting your way through the material.
Cutting any kind of material is all about ensuring you take a suitably sized cut. Too small a cut/feed, and you just end up with the cutter rubbing against the material, which causes it to heat up, melt and basically turn into a mess like what you managed.

I'd very much doubt any form of Shapeoko will manage to cut aluminium well, as they just don't have the rigidity.

To give some idea of required feeds in 6061 alu, Suggested feed rate for a 1mm two flute endmill is 100mm/min, at 10'000rpm, for slotting with a depth of cut of about 0.75mm
If you want to juggle figures for yourself, check out https://zero-divide.net/?page=fswizard

What grade of Ali are you using?

The shop said it was 1050. It's very soft...

I'd very much doubt any form of Shapeoko will manage to cut aluminium well, as they just don't have the rigidity.To give some idea of required feeds in 6061 alu, Suggested feed rate for a 1mm two flute endmill is 100mm/min, at 10'000rpm, for slotting with a depth of cut of about 0.75mm...

We are only talking about shallow cutting here - but I can see that I need to up the feed considerably! Thanks for the calculator reference....

1050 is pure aluminium and is very gummy. Lots of WD40 or cutting fluid required, verging on a continuous supply, and expect a bit of cleaning up with a debur tool after.

Thin sheets are usually 1050 (as it bends nicely), thicker sheets say >5 mm are often 6061 which is much nicer to cut but depends on what you are making. 5000 series also cuts OK but will again be thicker (in my experience).

Going back a long way to my student days and yes feeds and speeds could well be a contributing factor..
Aluminium has characteristics which are problematic . Built Up edge was always a problem with aluminium where a ball of plasticised aluminium builds up on the cutter, interfering with free cutting. A decent cutting oil will help but if all else fails some WD40 will improve matters a little.

It is also significant that a 1mm cutter is part of the process. I suspect that it came from the far east and the quality may be questionable to say the least .
Are your spindle revs adequate to give decent cutting speeds at this diameter ?

To my mind known science with regard to cutting speeds is hard enough to achieve with cutters at 3 --6 mm cutters .

More interesting advice!

The comment about thin ali sheets being soft makes a l;ot of sense, and I shall try to get some 6061
You are correct that the 1mm cutter is Chinese - I got them because a set of 10 was cheap, and I assumed that in trying to find out what cutting speed/feeds were needed I would be snapping a lot of them. The spindle is a cheap 775 motor, which seems good for speeds up to around 16.500 rpm and has lots of torque at 36V.

If the calculators recommend 100mm/min at 10,000 for a 1mm mill, would it be reasonable to lower the revs and lower the feed speed, or is 100 a figure I should stick with? it seems rather fast to me.....

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I shall try to get some 6061

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6082-T6 if fine as well the stuff you have is awful to cut

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Originally Posted by Clive S

6082-T6 if fine as well the stuff you have is awful to cut

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Agreed. Also I’ve generally seen thin sheet as 1050 and thick sheet as 5000,6000,7000 series. I have not seen thin sheet at 5,6,7000 series but I might not be looking in the right places. There could be a technical reason for the alloys produced like that or just that thin stuff is often bent and fabricated.

I've ordered some 6061 - let us see what that is like to cut when it arrives....

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Originally Posted by routercnc

Agreed. Also I’ve generally seen thin sheet as 1050 and thick sheet as 5000,6000,7000 series. I have not seen thin sheet at 5,6,7000 series but I might not be looking in the right places. There could be a technical reason for the alloys produced like that or just that thin stuff is often bent and fabricated.

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I've got a few sheets of 6082T6 in 1mm/2mm/3mm thicknesses - not common as thin sheet, but it's out there. As ever, the problem is buying in small quantities - I bought a few sheets in each thickness to make it worth the suppliers while - Metalweb on that occasion. I use Smiths nowadays.

2014 and 7075 also machine well - bit pricier, though...

5 grade works, but I'd choose 6082 over it any day.

Wal.

I had not considered brass, which is a more expensive material, but I wonder if that would be a better metal for an inexperienced operator to start with?

C360 Brass (Free Cutting/Machining) is the benchmark for ease of machining...

https://www.metalsupermarkets.co.uk/...ass/brass-360/

It's a joy to use - CZ120, CZ121 etc. readily available, but like you say, not cheap...

If I were you, I'd stick with getting the right parameter sussed out for ali - you may as well. I've still got my beginner melty bits in a box of scrap somewhere, you need to break a few eggs to make that omelette. Get crackin'.

Wal.

also what type of cutters are you using? are they polished flutes or are they coated? uncoated polished flutes are best for aluminium. Also with a 1mm cutter i would be looking to spin it as fast as possible, on my machine i would run that flat out at 24000rpm and about 100mm/min with 0.5 depth of cut.

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Originally Posted by johngoodrich

also what type of cutters are you using? are they polished flutes or are they coated? uncoated polished flutes are best for aluminium. Also with a 1mm cutter i would be looking to spin it as fast as possible, on my machine i would run that flat out at 24000rpm and about 100mm/min with 0.5 depth of cut.

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I'm using cheap Chinese two-flutes. Advertised as carbide, but who knows...?
The calculators say run at about 10,000, and the earlier suggestions that I was melting the Ali make me think that this may be too fast. I can run up to about 18,000 on my system.

I have not tried running much above 20mm/min, since I am concerned about breaking the cutter (which is why they are cheap!). I have been cutting at about 0.5mm - perhaps if I cut at 0.2mm I can try running a faster feed....