Question Aluminium Milling

Hi all,

I've been trying to cut aluminium (6061 T6) on my stepcraft 600 (2) with the following settings and have been having serious issues with the machine going into reset mode and only getting (max) 0.1mm depth of cut:

Spindle: HF500 @13000 RPM
Endmill: 6mm HSS-CO 2 Flute
Material: 6mm thick 6061 Aluminium plate
Depth of cut (stepdown): 0.1 to 0.3mm (jamming constantly at 0.3mm)
Stepover/Lateral engagement: 2mm (have tried reducing with little positive results)
Lubricant: Water/detergent or WD40 at times reduces noise but doesn't seem to help with depth of cut

I'm getting a LOT of chatter and feel like the machine is under a lot of stress, to the point I'm worried it might do damage can anyone assist?

It took about 2 hours to get 1mm down on a 200x250mm cut which I understand is a big area but it just seems really slow.

Would an air hose help or would that not make a huge difference? Would a single flute cut better? Would a smaller diameter end mill cut better?

use air to clear the chips 13000rpm is to slow use 20000rpm and feedrate 8 to 10mm/sec

Wrong type of Aluminium. The specs I found say that it is bad to mill/drill.

Thanks, I've tried increasing RPM and slowing feedrate or depth of cut and it seems to actually perform worse.

MagIO2 wrote: Wrong type of Aluminium. The specs I found say that it is bad to mill/drill.

Thanks, but I'm now confused because everything I've read seems to say that 6061 Aluminium is the best and easiest to machine.

Also, the Stepcraft example here shows that they can mill 6061 Aluminium with a depth of cut around 0.020" (0.508mm) at 15,000 RPM and a feed rate of 15mm/Sec, which is very close to what I've been running. The only difference I'd say is that I'm using a two flute, larger bit, however, I've had the same issues and broken smaller bits when I tried running the same speeds and feeds.

are you sure its 6061? I dont have any issues. I dont use large endmills on aluminium.

MagIO2 wrote: Wrong type of Aluminium. The specs I found say that it is bad to mill/drill.

Firstly, this is completely incorrect. 6061 (T6) should machine no problem because it is a harder grade. Look at the Brinell hardness factor.

Secondly, is your 2 flute end mill rotating in the correct direction? This might sound like a very obvious and patronising question to ask but I made this mistake twice recently; once on my first attempt at cutting 1050A grade aluminium sheet with a 2 flute 2 mm diameter solid carbide end mill and again on acrylic sheet with a Trend router bit, both of which were reverse direction cutters!

I successfully cut 1.2 mm thick 5251 H22 grade aluminium sheet this afternoon with the following parameters:

No cooling air supply
7,500 rpm spindle speed
1,000 mm/min XY feed rate
30 mm/min Z plunge rate (10 for drilling holes)
0.1 mm depth of cut per pass
2 flute 2 mm carbide end mill reverse rotating

See attached picture. Video to follow later when I've edited it.

Last point: Stepcraft machines are not rigid systems or milling machines so all parameters must be highly conservative. As jonalm commented about not using large end mills on aluminium, it is likely that a 6 mm cutter is simply generating too much drag for the axes to cope with. Only you can know how well set up your system is. Possibly the smaller footprint machines with a T Slot bed are more rigid and thus will cope better.

Doug

My parameters are:

- water, alcohol (spirit), washing-up liquid
- 10.000 rpm spindle speed
- 600 mm/min XY feed rate
- 0.2 mm depth of cut per pass
- 4 flute 2 mm end mill

Aluminium was a unknown hard type (PROMA alumium case)

I found 2 sources telling that AW-6061 is not the best alloy for milling. Does the AW mean a different material? But maybe bad was a bit too hard, but at least it is not good and definitely not the best alloy.
The problem with metal is, that the range of overall parameters which produce good results is much narrower than with other materials like wood... this means, that for Material wich are told to work worse, it might be more difficult to find the sweet spot.

We all have the same basis, the SC CNC, but this does not mean that all those machines work exactly the same. One was more shy when tightening the screws as someone else ... different spindles ... different fixing of the material ....
So, in the end everybody has to experiment a little with the parameters. And I'd say it is totally possible to have a total setup scenario where milling Aluminium simply does not work.

Found this while doing the research: CNC cookbook

To clear this up with facts and figures, 6061 T6 aluminium machinability is listed as "acceptable" with 95 HB Brinell hardness:

http://www.aalco.co.uk/datasheets/Aluminium-Alloy-6061-T6-Extrusions_145.ashx

So yes, not "the best" grade but certainly not bad.

A common grade with "good" machinability is 6082 T6:

http://www.aalco.co.uk/datasheets/Aluminium-Alloy_6082-T6~T651_148.ashx

Please always try to quote referenceable sources rather than state unqualified opinion.

Doug

I think those kind of statements you find in the specs refere to a professional CNC mill. Reading your parameter proposal seconds this .. 0.1 mm depth per pass ...
You should try the other alloy! There you have 0.5-1mm per pass. This is where acceptable starts for me ;o)

MagIO2 wrote: I think those kind of statements you find in the specs refer to a professional CNC mill. Reading your parameter proposal seconds this .. 0.1 mm depth per pass ...
You should try the other alloy! There you have 0.5-1mm per pass. This is where acceptable starts for me ;o)

No thanks. Machinability is related to the material hardness and not specific to professional CNC mills. Rory recommended 0.1 mm depth of cut per pass on the Stepcraft system. I am comfortable with that from what I have witnessed. Additionally, I do not require to remove more material per pass for my small aluminium sheet parts although I think the Stepcraft would cope. If I needed to mill more aggressively I would have specified and purchased a different machine and spindle.

Anyway, here is my edited video with the screw hole drilling speeded up 8x to avoid boredom setting in too early:





Doug

what happened at the end it just stopped?

jonalm wrote: what happened at the end it just stopped?

It stopped when the cycle finished, as normal. The video is not complete; there is a pocket cut missing because the camera turned itself off.

Doug

Hi,
Had my 600(1) for 2 years & finally cut ali. Must have cut all grades now (T6 , scrapbox stuff,e bay stuff). All cut Ok - now.

Success for me was wet cutting - tried wd40 -that simply accumulates swarf round the bit. My system involves a Morrisons roast tin, and an old central heating pump to supply the suds, some ch valves & tubing & 10% suds. Pictures later.

My set up :- 3mm, or 2.5mm 2 flute carbide cutter,depth of cut 0.5mm, v-plunge 5.0, v-advance 3.0, Dremel tool @ 20,000 rpm. Some finish cuts 0.25 mm.

Works a treat - no chattering, no strain on axes,no heat, dremel runs cool -some jobs take 2 hours, but so what. Well pleased with results. Finish far superior to dry cutting as well.

Also - agree with comment above - a 6mm cutter may be too much for the machine. Suggest 3mm to test, then go up in cutter sizes. Biggest problem with aluminium is cutter gets too hot due to friction & chips stick to the cutter making things worse. Friction and heat is the killer - lubrication an answer, provided the cutter is not too big.