Small end mills feed speeds for 1mm steel

[paulr4]

I am trying to cut 1mm sheet steel (alloy not known) using a 1/8 2fl end mill. Currently at 20k RPM and 180mm/min (~7in/min) under flood cooling of soapy water.

The endmill will last about 2.5m (98in) worth of cutting before it dulls/smokes. My end mills are all of questionable qaulity and unkown material (HSS??). I have tried taking 2 passes but it seems to make no difference in overall tool life.

Different tables and calculator don't seem to have consistant data on smaller tools. Would it be worth trying to decrease RPM? The spindle is a porter-cable laminate trimmer so I doubt it would sustain torque at lower speeds. Also is it worth looking at higher quality endmills? Carbide seems not be a good idea due to vibration of the trimmer compared to a real spindle.

Any advice would be appreciated!
Thanks!

[sploo]

The attached doc floats around this forum on occasion.

I've never cut metal with a CNC machine, so can't add any personal experience, but 20k rpm does sound pretty high.

[dertsap]

20k sound pretty high, with the feed you are using you will be dulling the tool because it isnt cutting anything , you need some chip load on the tool or you will burn it out

[Kiwi]

I think with 1/8" Dia. 2 flute HSS cutter you should be about 3500 RPM at 3.5in/min (90mm/min). This about .0005" feed per tooth.

[msomerville]

the RPMs sound pretty high especially if you are using HSS for cutting sheet metal. Some of that stuff can be nasty. I dont know about your spindle rigidity, but I dont think an endmill that small is putting any more torque on your spindle compared to a dull smoking tool. Like Kiwi said start with 3500 rpms and maybe even try a little lower rpms and maybe 5in/min.
matt

[sendkeys]

If you can't change the rpm to 3k like others said, get carbide endmills they run at 8k or so.

[tobyaxis]

I feel the same as all the others that have posted. That RPM is way too high. Definately use better quality tooling. Carbide would be the better choice if the machine and setup rigidity are good. If not M42 Cobalt (Putnam End Mills) and an even lower RPM. Low quality end mills from places like china is like cutting carbide with aluminum-foil . The other issue that you have no idea what alloy the steel plate is leads me to believe you should be using a lot of caution when your cutting. That smoke could be toxic , plus the fact that your using soap water? Don't use soap water! Find a spray bottle and get some kind of coolant. Check out Widgitmasters coolant tank configuration and find a way to apply his method to your configuration. Doing what you are, you could get hurt.

Above all don't forget to wear safety glasses . I hate to seem like I'm busting your chops, but on the other hand don't like to see people get hurt either. :frown:

[paulr4]

Thank you all for the advice.

I have lowered the RPM to around 5K, not really sure since it is dimmer style control and I have no tach. Switched to a 4 flute slotted endmill (not by choice since my order of better ones has not yet arrived). So far I have kept the feed rate the same. If the endmill survives I will try lowering RPM.

Safety wise I am not too concerned since I use a face shield and stop it at any sign/sound of trouble. Not letting it run unattended anytime soon

Why would the soap and water be worse than no cooling? I have used it for aluminium and it seems to work quite well. I could also run oil or commercial coolant.

The endmills are only $0.47cdn ea, comparing to any real tools may not be a good idea but I would still like to find their maximum potential

[sendkeys]

Where are you getting your endmills from? That's so cheap. As for the coolant rust would be my biggest problem.

[tobyaxis]

Originally Posted by paulr4 Thank you all for the advice. I have lowered the RPM to around 5K, not really sure since it is dimmer style control and I have no tach. Switched to a 4 flute slotted endmill (not by choice since my order of better ones has not yet arrived). So far I have kept the feed rate the same. If the endmill survives I will try lowering RPM. Safety wise I am not too concerned since I use a face shield and stop it at any sign/sound of trouble. Not letting it run unattended anytime soon Why would the soap and water be worse than no cooling? I have used it for aluminium and it seems to work quite well. I could also run oil or commercial coolant. The endmills are only $0.47cdn ea, comparing to any real tools may not be a good idea but I would still like to find their maximum potential

The Soap water will be fine. I am a machinist by trade and never heard of using soapy water. Sorry about that.

[msomerville]

I haven't used soapy water as a coolant. I would be worried about how well the soap holds up to heat. If you are only paying $0.47 and endmill I would definitely check out better tooling. That sheet metal might be harder than your tool.

[paulr4]

So far I have about 110in on the 4fl at 5k PRM and its still working. The lower part has dulled slightly which is noticeable on entry into the metal.

Temperature of the mills (stop mill, stop coolant and measure wiped surface via IR is about 30C), So running temp is probably 40-50C??. Of course that is when they are fairly new. The soap seems to work better than just water, real coolant is about $20/gal so it was a cost thing to try it. Tray and reservoir contain about 15gal.

The machine is a gantry over a stainless tub which I originally thought of running submersed w/ 1/4in of water over the job. Everything below the working area is either Al, Brass or stainless and no moving parts. The problem with that was keeping the water level right, running plastic occasionally would clog the drain holes. Water would build too high causing excessive spray, it was hard to control the level without frequent cleaning. As it stands it is running as flood only.

Endmills are from Princess Auto, $6.99 for a box which used to contain 15-18pcs, now is down to 12-14. They seem to be used PCB working bits but have no nylon collars.