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IndustryArena Forum > Tools / Tooling Technology > CNC Tooling > End Mills and Feeds n Speeds
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  1. #1

    End Mills and Feeds n Speeds

    Hey Community,

    Hope someone could help shed some light.
    I am relatively new to CNC and am struggling with the whole feeds and speeds selection as I am a metric user (sorry ) always seems the good information is in imperial, which has to be converted, so I have been relying on various tools such as BobCAD Machinist Toolbox, The Machinist Calculator and a couple of online source, all of which produce varying results.

    I have a Syil X4, controlled via MACH3, with BobCAM integrated to Solidworks.
    The particular tool I am making is using aluminium stock and requires the use of a 2mm diameter end for roughing/finishing.

    Max rpm of the Syil is 5000rpm, so using this, the material and my 2mm, 2 flute carbide end mill data, I have gotten machining data as follows.

    Depth of cut = 0.8367mm auto calculated from total depth and number of steps.
    RPM = 5000
    SMM = 31.4 M/min
    Feed per tooth = 0.012 as supplied for the mill
    Feed rate = 120 mm/min

    Initial feedrate calculate by BobCAM was 990!!
    I then did some recalculations and checked a couple of calculators which came up with the 120, so when I started the job I ran it at 70 and worked for a while before jamming and snapping.

    At the moment, I dont know if my problem is wrong end mill selection or my feeds are way off, so was wondering if anyone could offer some advise.

    Appreciate any response.

    Simon

  2. #2
    Join Date
    Apr 2010
    Posts
    294
    There's a feeds and speeds wizard built into Mach3. It's not the last word in sophistication, but you've already got it, so it's worth a try.

    It comes up with 127 as the answer with your input figures - so agrees with your recalculations.

    Feeding too slow is sometimes as bad as feeding too fast. Your 70 figure will be taking such tiny slices that the tool may be reluctant to "bite" into the material.

    You also need to pay attention to clearance of chips. A small mill like that may easily become overwhelmed. Air if you have it.

    Last thought - you don't specify if you're profile cutting with a part-width stepover, or cutting a slot the full width of the tool. A full width cut of that depth is asking quite a lot of the tool.

  3. #3
    Thanks for your quick reply, its appreciated.

    I am running a pocketing routine, in to out and I was too scared to run at 120, the step over is 50%.
    I have some cutting fluid which can be added to help cool, but I decided not apply any to prevent clogging and instead use a hogs hair brush to clear debris, but could use some air instead.

    Although we have a coolant kit, the system just isn't designed for it, no enclosure or splash covers on motors and electrics, so adding a permanent air blow/cooling is in the pipeline.

    I did read that maybe the cobalt bit could be too brittle too, but tried to take it easy with small plunge.

    Down to my last end mill and wondering if I should go for a different type.

    There's a very fine balance which I need to master here.

    Thanks again, back to playing.

    Simon

  4. #4
    Join Date
    Sep 2010
    Posts
    87
    Chances are the aluminium is welding to the cutting edge(it is quite sticky stuff), give it a shot of WD40 to keep the chips from sticking and either use a vacuum or air to remove the chips.
    job, jobbed

  5. #5
    Join Date
    Apr 2010
    Posts
    294
    You should be able to see if the aluminium welding is an issue for you. I have had this problem with turning in the lathe, untill I changed my inserts for appropriate ones.

    I'm not familiar with the X4, but I'm supposing machine rigidity is not an issue. But you might like to examine your toolholding arrangements, for any lack of concentricity here would contribute to your problem.

    Lets hope we get some more comments.

  6. #6
    Join Date
    Sep 2010
    Posts
    87
    I decided to try and cut in ali with no lubrication and air blast to clear the chips a while back just to see, this is a 3mm HSS cutter it managed about 2 mins of pocketing before....ting...gone
    Tried the same again with a few squirt of WD40 and ran without a hitch.


  7. #7
    Join Date
    Feb 2010
    Posts
    371
    With a bit as small as 3mm, I would try to back off the step over, (although your deptch of cut is pretty conservative). On my 1/8" end mills at 3000RPM, I use 25%. For slotting, I use .08" DOC. I keep a vacuum pointed at the cut to remove as many chips as I can from the cutter, and give it a short blast of WD40 on every pass.

  8. #8
    @Rikk

    My very first attempt using a 10mm end mill caused major clogging and really melted the ali, luckily I was able to clear it from the end mill.

    On this 2mm end mill, it does not appear to have clogged.
    There are no visible signs or material melting and no blocked flutes, see attached.

    @AiR_GuNNeR
    I will take your advise and reduce the step over to around 30% whilst reverting back to the feed of 120 as calculated and confirmed by @UUU.
    I do have some cutting fluid which I normally paint on, so will use that in addition to blowing air to clear chips.

    @UUU
    I am using an ER40 collet system to hold the end mill and have the end mill locked as tight as possible.
    There is 12mm (1/2 inch) of mill out the end to allow for clearance and machining.
    The workpiece is under bolted to a jig, with the jig clamped down to the table, I doubt that thing is moving in a hurry.
    As for rigidity of the mill, this is no pro system, but we are only using it for light work.

    Guys, thanks to you all for your advise and I will update once I run this job today.

    PS: If you interested about how I took the pictures, its simply a 20x watchmakers eyepiece magnifier, mounted to the case holding my HTC desire HD mobile. Auto focus, then move the phone distance to get best the best results.

    Simon
    Attached Thumbnails Attached Thumbnails IMAG0796.jpg   IMAG0797.jpg  

  9. #9
    Join Date
    Jan 2012
    Posts
    0
    Ive used some cheapo 3mm 3 flute end mills and ran perfectly with confirmed 6061 grade Al alloy, conservatively running 1mm DOC, 2500RPM, 70mm/min, 50% stepover. Nice long stranded chips.

    The same config for unknown grade Al (must be some super soft stuff), and I lost 3 cutters attempting the run again, even after modifying DOC each time. The cutter gets clogged up and welded to the cutter I suppose and started to pull end mill out of collet and eventually snapped. The solution was to lower RPM, keep everything the same.

    I guess it depends on your grade of aluminum also. Im looking for a good machining calculator/database also. Mostly I do a much conservative end of what those numbers come up to since those runs are using cheapo end mills. Expensive end mills give recommended chip loads?

  10. #10
    Quote Originally Posted by bebob1 View Post
    Ive used some cheapo 3mm 3 flute end mills and ran perfectly with confirmed 6061 grade Al alloy, conservatively running 1mm DOC, 2500RPM, 70mm/min, 50% stepover. Nice long stranded chips.

    The same config for unknown grade Al (must be some super soft stuff), and I lost 3 cutters attempting the run again, even after modifying DOC each time. The cutter gets clogged up and welded to the cutter I suppose and started to pull end mill out of collet and eventually snapped. The solution was to lower RPM, keep everything the same.

    I guess it depends on your grade of aluminum also. Im looking for a good machining calculator/database also. Mostly I do a much conservative end of what those numbers come up to since those runs are using cheapo end mills. Expensive end mills give recommended chip loads?
    I am using this end mill from MSC and they have advised a chip load of 0.012.
    Chips were small and sharp and there are no signs of melting or jamming.

    I use Machinist Toolbox from BoBCAM, the Machinists Calculator from Machinist's Calculator-machine shop math calculator for trigonometry, speeds feeds, bolt circles and more.

    Simon

  11. #11
    Well, I just ran my job again and broke my last end mill.
    At £13 a pop, and this the third broken one, something is going amiss somewhere.

    This was run at 0.8mm DOC, 5000RPM, 120mm/min, 30% stepover.

    Time to find some cheap end mills, any suggestions in UK?

    Many thanks.

    Simon

  12. #12
    Join Date
    Sep 2010
    Posts
    87
    Here ya go, not used them but bookmarked the page as several people have mentioned them being good.

    http://www.cutweltools.co.uk/files/w...t%20drills.pdf

  13. #13
    Quote Originally Posted by Rikk View Post
    Here ya go, not used them but bookmarked the page as several people have mentioned them being good.

    http://www.cutweltools.co.uk/files/w...t%20drills.pdf
    Cheers Rikk,
    Bookmarked and now researching the mass of links I have.
    MSC is the only place I have bought from so far.

    I have to admit, their service is exceptionally good.

    Simon

  14. #14
    Hi Simon

    Give this company a try Milling Cutters | Milling Cutter | Machine Taps. If you give them a ring and tell them what you are trying to do they will give you some good sound advise and the cutters will be with you tomorrow.

    I have no personal interest in the above company but have used them in the past and found them to be very helpful.

    Andy

  15. #15
    must type faster ; )

  16. #16
    Quote Originally Posted by audioandy1762 View Post
    Hi Simon

    Give this company a try Milling Cutters | Milling Cutter | Machine Taps. If you give them a ring and tell them what you are trying to do they will give you some good sound advise and the cutters will be with you tomorrow.

    I have no personal interest in the above company but have used them in the past and found them to be very helpful.

    Andy
    Thanks Andy,

    Thats the 2nd recommendation for them, so will follow that up.

    Simon

  17. #17
    Join Date
    Sep 2010
    Posts
    87
    Don't suppose your anywhere near east London at all?

  18. #18
    Quote Originally Posted by Rikk View Post
    Don't suppose your anywhere near east London at all?
    Hampshire.

    Just spoke to Cutwel, who have offered a solution and confirmed that my feeds and speeds are correct.

    Spoke to MSC who say my feeds and speeds are incorrect, but they have offered to send some freebies for testing, some cheap £3.50 mills, which they suggest to run at 5000rpm and 250mm/min.
    Apparently, I should be running the original mills at 28000rpm!!!

    I need to get my head around the relationship between rpm and feed.

    Thanks.

    Simon

  19. #19
    Join Date
    Sep 2010
    Posts
    87
    Have a look at this GWizard: A CNC Machinist's Calculator for Feeds and Speeds really good, loads of info and you can lock the different criteria. So say lock the rpm at 1500 and with all the cut info it will tell you your feedrate.
    Well worth the money.

  20. #20
    Join Date
    Jan 2012
    Posts
    0
    Instead of CNCing right away, maybe you can try manual machining first to get a feel for the material.

    What type of aluminum is it? Also get a 3 flute end mill if you do a lot of Al milling. Use cutting oil. Get a shop vac to suck away chips or high pressure air or flood coolant.

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