Chipping endmills

[lSherlockl]

Hello,

Hoping someone could help shed some light or give some suggestions as to proper usuage or what I may be doing wrong.

I recently chipped 3 endmills playing around with working on steel

For reference mill is PM932V (RF45 clone) VFD controlled max rpm 3200

Endmills i was using were Precision Matthews HSS 4 flute. (yes garbo cheap stuff but i got them to learn on and not be shook up for killing as I leaned)

Pictures are from 3/8" in endmill 3/8 in shank held via collet

material is unfortunately "unknown steel of a mild variety" definitely not tool steel definitely not hardened.

I learned the hard way on squaring up some aluminum how to use a speed/feed calculator, and that is where I was getting this info from and generically it seemed to work well aside of the odd chipping issue.
spindle speed 924 RPM
Feedrate 6 IPM
depth of cut: .04"
coolant: NO (but was brushing chips out of way)
milling technique: standard (finishin cuts i was climb milling at .005 depth of cut)


the chipped endmill

another view seem to be good at making 3 flute endmills

the chip of endmill that broke off


the chips that were being produced some slight discoloration but not excess bluing.




So a few other notes; first I know endmill quality is bad its china cheap stuff so if that's my problem I'm fine with it I got these sets so I could learn without burning up a a pricier bit of tooling.

The first two endmills I chipped chipped or broke in a similar way, one of the others I attributed from taking too deep of a cut about .07" in the endmill I could see was heating up and discoloring when it happened I know I don't have a coolant or mist setup so I took it as take shallower cuts to keep heat down. The other one chipped in a slotting operation. and this one above more or less a facing operation under power feed no discoloration or smoke and it was like on pass 5 or 6 about halfway thru the pass. None of the cuts was I getting like over the top vibration there is some when cutting but just enough to feel. Also as another note these seemed fine to continue cutting and still produced a pretty nice surface finish still even after the chip.

Just confuses me a little of what I am doing wrong (aside of potentially needing coolant) unless I need to be taking deeper cuts mentally a bit counter intuitive but maybe? Or the feed calculator I am using isn't very good.

Thanks for any input!

 

[Bob Korves]

Were all the axes that were not in use for travel tightened down? Any signs of chattering or shaking before the tool started failing? Is there any play in the spindle or the machine setup when you wiggle the tool?

 

[lSherlockl]

Were all the axes that were not in use for travel tightened down? Any signs of chattering or shaking before the tool started failing? Is there any play in the spindle or the machine setup when you wiggle the tool?

all axis locked aside of x the one that was moving.

just checking spindle so on the outside of spindle rotationally .00025 or about half of half a thou is what i was seeing. stationary spindle locked just pulling on the tool/spindle i did see just over half a thou of play so that could be something ill have to see if the manual states the play in the spindle is that what it would be or indication of how tight the spindle bearings are right?

no real chatter or shaking, just some noise and vibration that i think would be expected. as in placing a hand on the bed you could feel some vibration not like visible shaking.

also when cutting the spindle was not heating up or anything like that either so I wasn't thinking I was overloading or feeding too fast

 

[woodchucker]

I would be practicing with HSS or cobalt.
Carbide chips yes. Even good ones.
I learned from a member that using a radiused end mill cutter prevented chipping to a larger degree.
Unless you have a rigid machine, chipping is normal... make sure the gibs are tight, loose ones will transmit.
tighten locks so you can move with friction if climb cutting, but I would avoid climb unless absolutely necessary finishing cut. if it's a small mill less than you think, you'll have to find out for yourself where that sweet spot is.

Higher RPM, slower feed, let the cutter do the work, often chipping is from pushing the feed rate IMHO. Carbide likes speed.
Stick out on the end mill is also a factor... the quill should be retracted as much as possible.

 

[markba633csi]

I always use some cutting fluid/oil when using HSS bits on steel. With carbide endmills you can sometimes make light dry cuts, but fluid is a good idea, and clearing the chips frequently is a must (I stop the machine and use a brush)
Breaking endmills is often a result of chatter which can be caused by lack of rigidity and loose gibs in the machine, and feeding too fast. Gotta get a feel for what the machine is telling you by the sound and vibrations transmitted thru the crank handles. When it starts complaining you are in the danger zone
-M

 

[lSherlockl]

still have the endmill in the collet so i had the thought of indicate the bit concentricity?

so arm on the table to the bit spin in reverse zero to the peak of the cutting edge i get a spread of about a thou some of the cutting edges about 1 thou

Flute number (and measured just above the chip location)
1.) 0.0 (broken)
2.) 0.005
3.) 0.0
4.) -0.005

So im wondering more so too if its just the cheap endmills at least a reasonable factor in it. I'm not sure if they are all supposed to be concentric or equal but if they are essentially my cut or depth of cut is going to be loading certain teeth or flutes rather more and not really being a a truly even 4 tooth cut. So slower feeds or bit higher speed in theory would lessen the impact?

here is the surface finish i was getting on my cuts i think it would be worse if I was getting chatter.



and yes I know its a odd bit of scrap with the half round but it was securely held

and yes the quill kept as retracted as I can, head bought down till it just about touches usually less then .1 from the workpiece so I have reasonable ability to increase my cut depth with with maybe extending the quill less than a quarter inch in at least these cases of getting to know the machine.

just given that I broke or chipped more than one I felt like there is something I was doing particularly wrong. really only dove into steel this quick so I could work on a gear repair that I need to mill a slot for the replacement tooth.

would a brushed on coating of like a thread cutting fluid help or be sufficient for light cuts?

 

[benmychree]

A cutting fluid is essential with steel, period!

 

[benmychree]

I use TapMagic for nearly everything, brushed on.

 

[rabler]

and yes the quill kept as retracted as I can, head bought down till it just about touches usually less then .1 from the workpiece so I have reasonable ability to increase my cut depth with with maybe extending the quill less than a quarter inch in at least these cases of getting to know the machine.

I'd suggest you try leaving the quill fully retracted and locked, and using the head Z travel for all milling operations.

 

[woodchucker]

A cutting fluid is essential with steel, period!

I thought carbide could be used w/out cutting fluid? Especially the coated end mills, and inserts? I do use cutting fluid, but that's because I have a little mill and lathe and want to make sure the cutter is not inducing any more friction than necessary, not necessarily for cooling the carbide.

For HSS for cooling.