[Lemonmcgee1]

Hi,

Forwarning, I am not a machinist.

I need to mill very small parts in some 3mm thick alu, brass and copper with a 2mm single flute endmill. I have no idea what my feeds and speeds need to be. I am using Fusion 360 for my CAM and I have tried using different CNC speeds and feeds wizards with very poor results and constant tool breakage.

It's very hard to describe exactly what I need help with so I have provided some picture to help illustrate my point.

My cnc machine is a custom 500kg+ epoxy granite mill with a 24k 7kw single.

radius of the cut is 1.9mm

https://imgur.com/nCtqbFM
https://imgur.com/lmDIVGp
https://imgur.com/3OvSWKN

[joeavaerage]

Hi,
as a starting point work out the surface speed to be 250m/min. This would be a conservative middle-of-the-road surface speed for an uncoated carbide tool in those materials.

2mm =0.002m

RPM= 250 /( pi x 0.002)
=39800rpm.

This is faster than your spindle can go, so just max it out.

Small tools are tender and will break if you try to take a too big chip. As a starting point try 1% of diameter per tooth per rev.

distance per rev= 0.01 x 0.002 x1
=0.00002m or 20um per revolution.
At 24000 rpm , the fastest you can spin the tool:
distance per minute= 24000 x 20um
=0.48m/m or 480mm/min.

This should get you started. Increase the feed rate a bit at a time until you break the tool, that is just beyond its limit!! Back off by 50%, and that should give you a bit of margin.

Craig

[joeavaerage]

Hi,
what cooling are you using?. No cooling is a failure. I use flood cooling and recommend you do to.

Craig

[RCaffin]

Soft aluminium, soft brass and copper - a world of pain without an air blast to clear the chips and lubrication to prevent 'Built Up Edge'.

Cheers
Roger

[joeavaerage]

Hi,
damned right. I found flood coolant to be even better. Its not really about lubrication or cooling but more about getting the chips out of the cutzone.

When a chip is made the metal in the vicinity of the cut deforms until the deformation exceeds the materials ductility and it breaks. That requires energy and the chip gets hot.
You can try it yourself. Get a nail or some piece of steel wire and bend it back and forth a few time in rapid succession, and lo, it gets hot. The same thing happens to a chip.
With any sort of luck the chip will carry away most of the heat, but inevitably the parent material and the tool get hot too.

The real trouble occurs if the chip is not flushed away. Its already very hot and then it gets recut again or even a third or fourth time, and by now its hot enough to stick to damn near anything.
Obviously cooling helps, but even better is to ensure that the chip does not get recut and for that flood cooling and air blast are the best. A liquid exerts a lot more force on a chip
than a gas like compressed air, and that is why I prefer flood cooling.

Craig

[metalmayhem]

improper speeds and feeds can cause tool breakage but it's not a cure if the tool paths are poor . Are the lead ins plunge , ramped or helical ? Center cutting tools are great but they are still prone to issues when plunging and a proper ramp in will always be better than plunging . Step over and depth is another thing to consider . A 30-35% step over is generally safe at the right depths . If your running hss then cut at a max depth of 1/2" the diameter , carbide 1x dia max to start with . While there are cutters designed to run at full flute depth at 100% engagement a single flute won't . Personally I'd ditch the single flute .

In regards to " coolant " , it's proper term is water soluble cutting fluid , coolant is quicker to say and more of a slang term . Over the 20 yrs I've followed these forums the use of automotive coolant was brought up many times since it's "only meant " to cool . No one is running it for a multitude of reasons .
If the point of coolant was to only blast away chips and add some cooling then we'd be using pure water with an anti-rust agent . First and foremost it is design with lubrication in mind which is why a single company can manufacture dozens of fluids for a variety of applications . It was designed to replace flooding with cutting oil , and anyone who has run a machine that pumped/pumps oil onto the parts will know it's benefits and it's disadvantages . A poor coolant concentration can easily result in a lot of problems and is especially noticeable during tapping cycles .
A well lubed tool will easily recut chips and the lube will help prevent the chips from welding to the tool . We don't want this to happen but it does and this is why proper lubrication is important

I am not a fan of air blast for numerous reasons and the noise is probably the biggest nuisance . Through spindle coolant is pretty much always better than the other methods of delivering coolant but that isn't an option that we can benefit from with hobby machines , which leaves us with flood coolant or mist . Flood is the best option but mist is also very effective . The key thing with air mist is to up the concentration level to ensure that the cutter is getting enough lube

[Formantjim]

I too am using very small end mills to cut aluminum 2.3mm diameter and I concur with both joeavaerage and metalmayhem coolant lubricant is a must. I use a mist system and it has the best of both worlds clears the chip build up and the coolant/lubricant cools the tool. I'm currently milling 11 mm deep slots with the 2.3mm and taking it very steady. Copper has to be the worst of all at it generates burrs along the edges and without the lubricant in the water the tool will clog up in a fraction of a second.

[joeavaerage]

Hi,
copper is very ductile and thus it takes more deformation...read energy....to create a chip, even more than steel. Its not because its hard, copper is in fact soft, but rather
you have to 'stretch and stretch and stretch' copper to get a chip to break off. Steel on the other hand deforms a few percent, maybe as much as 10% in mild steel, before
the chip breaks free.

The only thing worse than copper is nickel, its about 25%-50% worse again than copper. Try machining monel.....it makes austenitic stainless look like child's play.
I had to make a bunch of monel keel boats for a customer, cutting the steps and cutting threads in the lathe just about drove me up the wall!

I use 0.5mm two flute tools on certain thick copper PCBs that I make. The copper layer is 420um thick, so to a 0.5mm tool is 84% of its diameter. I really struggled to get it
to cut, with tools loading up and breaking in short order. Then I started using flood cooling and that was 'night and day' difference. Where I had been getting 1/4 to 1/2 hour per tool now
I can get 8 hours before the tool becomes too blunt to be carried on with. Initially I used just plain water, and that worked, but soon progressed to water soluble oil to stop my machine
rusting. In this case the water flushed the chips away, and that was the biggest step in the right direction, and it provided cooling, worthwhile but not the main event. Adding water soluble
oil stopped the rust and no doubt provide some lubrication which cant hurt, but the flushing the chips away is the critical feature.

I still use water soluble oil, but only in modest concentrations....UNLESS....I'm cutting steel. Then I make it as oily as possible...it really helps.

Craig