help with speed and feed carbide end mill

[alex 850]

need help with my bridgeport series one . i am useing a 1/8 th inch carbide end mill running it at 6 inchs a minute at .034 a pass with flood coolant. i just installed a new hybrid nema 42 motor for the y axis, table is running smooth. but the spindle motor is still running rough. i replaced the timen belt and at 3000 rpms it runs good but still breaking tools. i am breaking the head down tomorrow for the 3rd time and going to put some plastic spacers in the varible speed pully.

thanks alex

[9 1/2]

What is the material being cut?

[alex 850]

154 cm stainless steel for makeing knives. it has not been heat treated yet so it is soft. also could you help me with a formula to use on figureing speeds and feeds. thanks alex

[pixburghenat]

...you should be running that endmill at least 6000rpm, on a bp I think max is 5400, with a mist or coolant flood. Try 1 or 2 ipm, depth of cut .030 or so. Once you get things working, then worry about tool efficiency.

6 ipm at 3000 rpm will break carbide endmills, cobalt might be a better choice at that rpm.


enat

[9 1/2]

enat beat me to it. sorry I was out all day. though, alex, all the info you need is in the Machinery's Handbook, or just buy the Machinery's Handbook pocket edition. The Pocket version contains all the info a chipmaker would need.

I'm curious though, are you using the CNC to cut out knife blanks or cut out liners and such like that?
owen

[alex 850]

i cranked it to 3500, i am in the red on rpm spindle speed my dial only goes to 4200. i cut out 12 blades the other night with a 1 inch tin coated 4 flute carbide endmill at feed of 3.9 inches per miniute at 3500 rpmseemed fine. i have a 27 th edition of machinery hand book but idont understand everything on the formula for speeds and feeds. i guess the new stepper motor helped me.

thanks alex

[pixburghenat]

...the red zone is a warning not to engage the quill feed gear.

enat


aka Scott

[keebler303]

Originally Posted by pixburghenat ...the red zone is a warning not to engage the quill feed gear. enat aka Scott

I don't think you are correct as my BOSS has the same spindle speed dial and is CNC on the Z, meaning no quill feed gear anyway. I think machinetek said that the red zone is for "intermittent use" ie. reduced duty cycle.

Matt

[pixburghenat]

Don't know about a BOSS....but on a S1 BP, in the red zone there is warning text about do not engage quill feed at those high rpm's. I do believe there is a warning tag next to the gear lever also offering the same info.


...I wouldn't use the hand brake either at those speeds.


enat

[merl]

As a general rule I start with 200 SFM for speed in SST with carbide. Remember if you can't take the heat away from the tool with the proper size chip you will have to reduce your SFM drasticly (80 SFM or less) because once you heat the tool and breakdown the sharp cutting edge, the tool breaks down and everything gets hotter and fails at an exponential rate ( often befor you can get to the stop button )
I would probably run this at 700 rpm .02 depth of cut and 1 inch per min feed (.00035 per flute w/ a 4 flute end mill)
One methode I use to determin SFM/RPM of the tool is from the old days when we only had a set of step pullies or a fixed gear box to match up to the required SFM
is--- tool dia, X 3.14 X RPM divided by 12 ex. .317 X 3.14 X 2150 / 12 = 178 SFM
to determin chip load simply divide feed by speed and further by number of flutes or cutting teeth Ex. 30 IPM (Inches Per Minuet) divided by 500 RPM = .06/ rev. / 16 flutes = .0037/ flute. That is a 16" dia. cutter running at 500 Rpm at 30 IPM and .380 depth of cut in cast iron with dry air blast for coolant. The chips that come off of that tool are a dull red and the dust is hot enough to burn you but the part remains cool to the touch.
You should consider having these parts cut out on a water jet. You would probably break even on time and tooling saved compared to the additional cost of jetting.