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Thread: Need advice milling aluminum, broke endmill after 2 hours of milling

  1. #13
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    Default Re: Need advice milling aluminum, broke endmill after 2 hours of milling

    Well guys, I found the problem. It is tool deflection, but it was hard to notice it initially
    Today I started cutting and broke the mill on the 8th minute. Changed it, continued cutting for another hour and a half and broke another one.
    While the first breakage occurred in the shallow circular parts, those next two happened in the deep triangular cuts in the same place of the cut. I guess the first time the endmill lickily survived this part and broke just after that on the easy place. Anyways I blew away all chips and coolant and started examining, what I found was both obvious and very strange.
    On the base two corners of the "triangle" the mill engages with its full diameter for a short time, I was worried about this at the start but all seemed fine.
    After I examined the cut thoroughly I found out that the cut is fine on one side (the one that is farther from me) and like a stairway on the other (The one closer to me). In the places where the triangle's base was less or more than 90 degrees to the X axis there was a very slight stairway pattern. It was only the places where the tool was moving entirely by the Y axis that this occurred. Here are some pics.

    First this is the toolpath:
    Need advice milling aluminum, broke endmill after 2 hours of milling-path-jpg
    The problematic part is on the bottom left and right. However when viewed from the front I usually only see the farther corners, and here is what I see:
    Need advice milling aluminum, broke endmill after 2 hours of milling-cut-clean-jpg
    Looks like a clean cut no different than the rest. Actually part of the stairway pattern is seen in the opposite corner, but that is due to the cameras angle and closeup, and the fact that I cleaned everything. From my normal position this is invisible. Anyways, now looking at the opposite sides, where the pattern shows:
    Need advice milling aluminum, broke endmill after 2 hours of milling-patt1-jpg Need advice milling aluminum, broke endmill after 2 hours of milling-patt2-jpg

    This I believe is a sign of severe tool deflection, but I can not understand why it occurs on just one side, given the fact that the toolpath is symetrical. If you look closely, it seems that the tool has gone a bit further than in the opposite corner. The two corners are not the same, but they should be.
    And the pattern is more visible when this corner is pointed towards me (the tool moves on the (-)Y direction).
    I should first examine the G-Code and see if the problem is not within it, before I blame this on the machine, but the fact that this occurs mostly in one particular direction, makes me think that the machine indeed has something to do with this problem.

    Anyways, in order to be able to finish this thing I will alter the toolpath to avoid working in those corners with the 6mm endmill.
    Something like this
    Need advice milling aluminum, broke endmill after 2 hours of milling-patt3-jpg

    Or maybe try it even safer (and slower) like this
    Need advice milling aluminum, broke endmill after 2 hours of milling-patt4-jpg

    Edit: Just thought of something. The direction towards me is the direction from which the mist cooling is blowing on the mill. Could it be that it is not able to blow away the chips in this direction, and this leads to the deflection?

    Attached Thumbnails Attached Thumbnails Need advice milling aluminum, broke endmill after 2 hours of milling-path-jpg   Need advice milling aluminum, broke endmill after 2 hours of milling-cut-clean-jpg   Need advice milling aluminum, broke endmill after 2 hours of milling-patt1-jpg   Need advice milling aluminum, broke endmill after 2 hours of milling-patt2-jpg  

    Need advice milling aluminum, broke endmill after 2 hours of milling-patt3-jpg   Need advice milling aluminum, broke endmill after 2 hours of milling-patt4-jpg  
    Last edited by zeox; 06-17-2017 at 10:00 PM.


  2. #14
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    Default Re: Need advice milling aluminum, broke endmill after 2 hours of milling

    Just little update.
    Need advice milling aluminum, broke endmill after 2 hours of milling-12-jpgNeed advice milling aluminum, broke endmill after 2 hours of milling-13-jpg

    After a few more tool breakages, I not only altered the tool path, but lowered the rpm/feed and depth/stepover. You can see that the cut looks much better on those newly cut "triangles".

    I am now working at 1mm increments (both depth and stepover) 375mm/min feedrate and 8540rpm. So far I've been cutting for 6 hours without a breakage.
    It is taking forever, but I have no other option.

    I am also now using an emulsion for cooling, works great. After 4 hours of non-stop cutting and the workpiece is still cold.

    I am seriously considering an upgrade now. Been looking at some chinese routers.

    This one
    Mini woodworking cnc router 1212 for advertise sign making,DSP controller - Woodworking cnc router_wood cnc _Acctek Machinery - CNC MACHINES MANUFACTURER FROM CHINA-AccTek Machinery-

    Looks nice, I can order it with an upgraded 3kW spindle. And I can also add a second low rpm spindle (1200-9000rpm) so I can work with larger diameter tools at low rpm.
    All in all with all the extras it will cost about 5500$. Has a built in cooling system, stainless steel tray for coolant collection. It will be a significant upgrade from my current rig.



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    Registered dharmic's Avatar
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    Default Re: Need advice milling aluminum, broke endmill after 2 hours of milling

    Don't forget that, when comparing one side with the other, on one the torque on the tool will be pushing it into the corner and the other will be trying to spit it out.

    Glad you got it sorted though.



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    Default Re: Need advice milling aluminum, broke endmill after 2 hours of milling

    As I need to repeat almost the same cut on the other side, I'll try to speed things up by using an 8mm endmill for the triangle shapes.
    Also The crabide 6mm mills that I have ordered should arrive soon, which should allow me to further speed things up.

    I have a lot of cutting to do with a 3mm endmill, but after I'm finished with those prototypes I'm thinking about simplifying the shape, so they can be cut mostly with a 6mm end mill.
    I'll get one of those 14 prototype pieces and use a dremel to cut the fins, and see if it affects its cooling capabilities. If all goes ok, I'll scrap the fins, and it will be much easier to cut those shapes.



  5. #17
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    Default Re: Need advice milling aluminum, broke endmill after 2 hours of milling

    I was probably a bit too quick to celebrate
    Today after 3 more hours of cutting, the endmill broke again. This time however there was a visible wear on the tool. I guess that is the most that these mills can do. About 9 hours of cutting.
    This was the last of my batch of chinese 6mm HSS endmills.

    I obtained locally two more 6mm 2 flute HSS endmills, made in Russia. They have shorter flute length, but also a lower helix angle.
    Here is a picture of the broken chinese end mill next to the new russian one:
    Need advice milling aluminum, broke endmill after 2 hours of milling-wp_20170627_22_15_51_pro-jpg

    Since these russian mills have shorter flutes, I was able to reduce the stickout. It was 33mm on the chinese mills (that was their flute length), with the russian mills the stickout is 26mm (I can make it even less, but I don't want to block the coolant mist, the deepest cut is 20.2 mm).
    With the lower helix angle and the reduced stickout, everything sounded much better. Especially when doing a helix ramp. I figured those end mills could take some more abuse.

    So I overided the feed rate to 450 mm/min (+20%) and increased the rpm just a bit to 8700 rpm, and so far everything looks and sounds better.
    If this endmill takes more than 9 hours of milling, it will be my new favourite, as they are really cheap (about 3.5$ a piece)

    Attached Thumbnails Attached Thumbnails Need advice milling aluminum, broke endmill after 2 hours of milling-wp_20170627_22_15_51_pro-jpg  


  6. #18
    Registered Jim Dawson's Avatar
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    Default Re: Need advice milling aluminum, broke endmill after 2 hours of milling

    The Russian cutting tools I have purchased have been pretty good quality.



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    Default Re: Need advice milling aluminum, broke endmill after 2 hours of milling

    Like Jim, I use kero for misting, but I mix (cheap) olive oil in at 3 parts kero to 1 part olive oil. I use pulsed misting, down to 1/2 sec pulse every 20 seconds. The oil seems to 'wet' the cutter much better imho and prevents the dreaded Built Up Edge which snaps cutters. And olive oil is skin-compatible!

    Cheers
    Roger



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Need advice milling aluminum, broke endmill after 2 hours of milling
Need advice milling aluminum, broke endmill after 2 hours of milling