Good day everyone
I am new here and beginning to enter the world of CNC, hence my silly newbie question.
What would it take to be able to cut 2mm steel with one the CNC mills?
Does it come down to time or a more professional actively cooled spindle than the Makita? Why could one not set a design to be cut over an 8 hour period -for argument’s sake?
Thanks in advance! 
My thoughts:
Rigidity. Cutting forces are WAY higher on steel. In order to actually ‘cut’, the mill has to be strong enough to take slices off the workpiece. You can’t just reduce the amount of feed because then you get into ‘rubbing’ territory which quickly overheats the cutter and the work piece.
Another way of looking at rigidity - let’s say you take a thin cut/bite off your work piece (you want to reduce the cutting forces so you take thin cuts). If your mill deflects too much, the cutter will no longer ‘cut’ but will ride up onto the surface of the work piece and rub instead of cutting.
The Makita isn’t even rated for CNC wood work - sure, people use it for that but Makita does not rate their router for CNC work. It also doesn’t have enough power. It’s mechanical built (things like bearings and what not) are simply not suitable for anything other than hand guided wood routing and even then it has a rather limited life time. It’s a stop-gap measure to use a Makita router for CNC wood working.
All you guys using Makita routers - don’t get your knickers in a knot. Deep down you know it’s true.
Another aspect is the RPM range of the Makita (or spindle for that matter). You need to remove a certain amount of material with each pass of a flute. If you have a high RPM spindle you have many cuts per second and that determines the amount of power required. You would need massive HP to remove even thin slices of steel because of the high RPM. If you bring the RPM down to practical levels and with the same ‘slice’ of material removed, your removal rate goes way down and your HP requirement goes way down.
Lower HP used directly reflects on cutting forces which directly affects the rigidity you need.
Ever used a drill press to cut a largish hole (let’s say 1/2 inch diameter) without bringing the RPM way down to only a few hundred RPM (don’t quote me on the exact numbers)? You will dull your drill in a matter of seconds for HSS tooling. Carbide tooling can run faster but I am pretty sure you can’t go over 1000 RPM with a 1/2 cutter in steel.
Running a Makita router for 8 continuous hours - LOL - life span will be measured in days even in wood.
Two more often overlooked little issues - cutter runout becomes much more important when you cut steel and a slipping cutter in the Makita collet is a well documented issue even when milling wood.
Many thanks for your elaborate response. To your point on the importance of rigidity, I interestingly found this YouTube vid where an awful lot of thought has gone into this.
My next bits of research will be on the best suited spindles for sub-2mm metal work if one can address rigidity accordingly. I see the challenge of striking the right balance of RPM and speed at which they slice off metal. Lots to learn here! 
@AfriO If your primary work will be in steel, IMHO you will be wasting your time and money on a CNC router/spindle based machine. You should either look to a true metal working mill or at least look at going with a plasma cutter on an otherwise-wood working machine. There are posts on here from members who have done that successfully.
Hi Afrio,
You might be interested in this here topic if it is only cutting through steel you seek to do.
You ain’t kidding. https://pie.yt/?v=https://youtube.com/shorts/pkWk2RlZ1kQ?si=-7UChsuk2BjUO-cr&pieshare=1
More to the point of your question, this is 1/2 in steel plate with the machine set to a very low power and going slow. I could have turned the power way up and gone faster. https://www.youtube.com/watch?v=OWcN6rHlMvo https://www.youtube.com/watch?v=OWcN6rHlMvo
Thank you, it makes sense