[berin]

Hello, I finished building my new cnc machine. I also finished building my WET jig box for this cnc machine. As of the time of this post there are no pictures of the box but will be soon in the links I post showing photos. My spindle is one of those chines 1.5kw 24k rpm capable spindles. I just finished and as of the time of this post milling my first WET (flood) project on my machine in marble. I would like to mill stainless 316, in fact I have side work offers if I am able. My goal is to do shallow cut signs in stainless, (back story I work on luxury yachts in south florida) for large ships along with other cnc jobs that I normally do. Marble is a huge deal for me, but if I can pull off light duty ss 316 well cheers$!$!
I believe my spindle will go down to around 8krpm, its a water cooled version, I have a new water/water-oil flood system I have built for this machine. I have done a few simple tests with some 3/64th cobalt 2 flute end mills and the cuts were flawless (pre completion of the wet jig box). So really I'm trying to solve what kind of bits, rpm, feeds, speeds, flood fluid type, will work for what I have for a machine. below is a google photo linke showing the machine and some of the work I have done with it so far.
https://photos.app.goo.gl/ggAPhV6uwbvr4jLs8

[berin]

ok after a full weekend of testing my machine rather then dealing with things I really need to be deailing with, I have decided my machine will NOT handle stainless in any way. not with a high quality finish. Even if it is super shallow its just out of its range. wrong spindle and rigid range is to low.

[joeavaerage]

Hi,
milling stainless is hard work.

The target surface speed for carbide tools in stainless is about 75m/min. So for a 3/64th tool (1.19mm) that equates to 19898rpm. Your spindle should handle that.

Next issue is rigidity. Steels and stainless are tough and the cutting forces are high and thus the machine MUST be super rigid. Most people, and I include myself, underestimate this.
If it takes rigidity R to do wood and plastics, then it will take 5R to do aluminum but 25R to do steel. The dramatic increase is required rigidity is such that a steel milling machine is a completely
different animal to a CNC router with the CNC router almost inevitably flexing too much to do steel.

The last issue is tool life. You need to keep the surface speeds down in order to get any decent tool life, but with a high speed low torque spindle that means small diameter tools, say 1/8th and smaller.
The problem with such small tools is that they are just not strong enough.....so you have to take exceedingly slow and gentle tool paths or break the tool.
Four flute tools are better for steel, they have a thicker core and are therefore stronger....downside is that especially in small sizes are more expensive.

I use Destiny Tools 1/8th Raptors ideally with a small end radius, just a well made, well coated four flute tool in steel. For mild steel I run them at a surface speed of 100m/min or 10187rpm. In mild steel
I get four to maybe five hours with flood coolant. Note your coolant must be continuous, consistent and well directed or you will wreck the tool within thirty seconds!

I have bought a new spindle, its been in service for nearly six months now. It is 3.5kW (S1), 3.4Nm (S1), 10krpm (rated), 40krpm (max) with an HSK32 tool interface. The pneumatic tool change is a major MAJOR step up in
my CNCing, but equally the 3.4Nm torque is sufficient to run 6mm (5.3krpm) and 8mm (4krpm) tools in steel with good authority and 10mm (3.2krpm), 12mm (2.6krpm) and 16mm (2krpm) with decreasing authority. 2000 rpm is the lowest
I am prepared to run my spindle. I even bought a Valenite 1.5 inch four tip face mill. Surprisingly it works really well even on mild steel although with really small 'babying' cuts of 10thou or so at 2000rpm.

The extra torque of this new spindle means now that I can take on steel and stainless jobs using 6mm and 8mm tools at reasonable metal removal rates to the extent I can make money doing so. My little 24krpm 800W spindle
was just too slow to be used (for a customer at least) for steel.

What I used for steel jobs prior to this new spindle is a second spindle that I made. It is a 1.8kW (S1), 6.1Nm(S1), 18Nm (overload0, 3500rpm Allen Bradley servo direct coupled to an ER25 tool holder running in P4 angular contact bearings.
It takes about 10 min to swap with my little 800W spindle. I made it about eight years ago and estimate I've had about 1000 hours use from it in steel and stainless. It has more torque than my new spindle (6.1Nm vs 3.4Nm), but my new
spindle cannot be swapped out easily so the old servo spindle has not been used for a while.

Both the servo spindle and my new spindle exert enough cutting forces to cause my machine to flex some.......I have to choose tool paths carefully to retain accuracy. Fact of life. As rigid as my machine is, and even as rigid
as I might like it to be, it will always flex some....its just a matter of how much can be tolerated and still be accurate and with a good finish.

Craig