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Newbie question on milling speed

Discussion in 'A BEGINNER'S FORUM (Learn How To Machine Here!)' started by Aris, Apr 6, 2017.

  1. Aris

    Aris Greece Iron Registered Member

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    Hi all, with my limited experience on my lathe, I now want to expand into milling where I know nothing. After ruining a HSS end mill cutter, I just bought a 50mm Face End Mill Cutter with 4 carbide inserts and tried milling the bottom face of my AXA holder that sits too high on my toolpost. My initial results are no good, so after some googling I realize there are RPM, feeding and other parameters that need to be correct. I also found some 'formulas' but I cant can't make anything from them
    Can someone please suggest the correct RPM and other parameters?
    Thanks ahead for any help!
     
  2. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    What size and type of mill do you have, and what is holding the work? What do you mean by "My initial results are no good"? What spindle speed were you using, and what depth of cut?
     
  3. Ed ke6bnl

    Ed ke6bnl Active Member Active Member

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    Tool holder could be pretty hard material
     
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  4. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Yes, test it with a file for hardness. If you can't file it, you will have real problems cutting it.
     
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  5. markba633csi

    markba633csi United States Active Member Active Member

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    Do you have a milling machine or are you doing this operation on your lathe?
    MS
     
  6. Aris

    Aris Greece Iron Registered Member

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    Hi Bob, thanks so much for your immediate reply!
    I will try to answer, even though being Greek, I'm not familiar with the terminology of the lathe and mill components, please excuse and correct any mistakes.
    I have the Austrian classic Maximat Standard MQ3100 made by EMCO that I bought and have used the lathe for restoring classic cars. It is a combination lathe/mill (sorry I'm not allowed to attach pics yet) and both the lathe the mill take an MT2 shank and it can use a Draw Bar to hold the tools.
    To mill the toolpost holder, I initially tried an End Mill, made of HSS, that has an MT2 sahnk, so I put it straight into the mill, and tried RPM's up to 520. It was jumping all over and I did manage to shave off about 1 millimeter after 3-4 passes, but the End Mill was very worn round at the edges. As to the Depth of cut I was trying each time to lower the mill by about 1/2 millimeter or maybe less, and as far as 'horizontal speed movement' I went very slow (here I have no idea of how to measure this....)
    I guessed that the HSS end mill was too soft for the hard metal the holder ids made off, so I went ahead and bought the 50 mm Face Mill Cutter with the carbide inserts that I tried again up to 520 RPM and about the same 'Depth of Cut' and Horizontal movement. Even though I have the draw bar tight, all available tightening screws set to very tight, there is still jumping around.
    Frankly I'm so newbie in milling that I cant describe how bad the results are, I only know that I'm WAY far from all the wonderful youtube milling videos I see!
    Hope all this is not Greek to you!
     
  7. Reeltor

    Reeltor United States Active User Active Member

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    Last edited: Apr 6, 2017
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  8. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    If the mill is jumping around, then it is not rigid enough for the cuts you are trying to make. Try shallower cuts, and it might help to take two of the inserts out of the face mill. Aris, your English is excellent, Greek is all Greek to me... ;)
     
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  9. Reeltor

    Reeltor United States Active User Active Member

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    I think you are running the spindle at too high a speed. On my mill, the lowest speed is 50 RPM and then it jumps up to 90 RPM. When I first read your post I thought that 520 rpm was too fast. I would first see how the mill cuts at 50 or 60 RPM and then go up to 90-100 RPM.
    I agree with Bob, your combination Lathe/Mill is not rigid enough to run the mill cutter at the speed selected.
    There are speed and feed calculators available on-line that are setup in metric.
     
  10. Aris

    Aris Greece Iron Registered Member

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    Thank you all! Daft me I thought the higher the speed the better but it is the other way around ...... thanks also for the on-line calculator, the only thing I dont get is the SFM, surface speed per minute. How can this be applied on my lathe
     
  11. just old al

    just old al United States Chaos Merchant Registered Member

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    SFM is one of those weird and wonderful things that makes endless sense with a bit of explanation.

    Imagine a lathe tool bit cutting a round bar 4 inches in diameter. That lathe tool bit is going to be happiest cutting that kind of metal at a certain rate of speed - call it 100 SFM just for argument's sake.

    The piece is 4" in diameter - so a bit of maths tells us its circumference is 12.5" or a teeny bit over 1 foot (Pi x diameter). So for 100 SFM you need to spin the piece at a little under 100 RPM so that the speed the part is moving presents the material to the tool at the rate the tool is happy cutting it.

    All of this can be done in the metric system - it just happens I'm most comfortable in Imperial and explained it that way - apologies.

    With your milling example we're spinning the cutter instead - so it's the cutter circumference we're working with here. That kind of metal is going to be happiest cut at a speed that presents one cutter tooth at the proper SFM.

    Let's say you're using a 1" diameter cutter made of high-speed steel on brass. Brass likes 300-350 SFM. So, cutter circumference (3.1 inches, or about 1/4 foot) to cut brass should be spun at about 1200 RPM or so (300 SFM X 1/4 foot) to get the cutter speed about right.

    None of this is cast in stone, and minor variations on speed are not an issue - slower is better than too fast, though.

    Carbide allows for much higher SFM, but most hobby sized machines aren't suited to take full advantage of it.

    Al
     
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  12. Reeltor

    Reeltor United States Active User Active Member

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    Aris,

    The on-line calculator that I posted has a list of different materials and what the SFM is recommended for each material. That calculator is setup for HSS endmills, but will get you close to a feed/speed that will work.
    I am not in any way an expert and am just passing on what has worked for me; it may or may not work for you.

    Here is a link to a calculator that must be downloaded. It has many more advanced features. In this calculator you can choose if you are using a HSS or Carbide twist drill, HSS or Carbide end mills, Face Mills. It is more versatile but can be a little confusing. Many times I reduce the recommended RPM and feed setting. It also has a setting for Turning.

    http://download.cnet.com/ME-Consultant-Professional/3000-2064_4-10522439.html

    good luck

    Mike
     
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  13. Aris

    Aris Greece Iron Registered Member

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    OK guys, I spent many happy hours working on the mill the last three days, and following your advice I can proudly say I'm just a tiny little bit wiser about milling :)
    First I checked for loose parts and discovered that some could be tightened so I now have a more rigid setup, which helped. Next, I went down to 100rpm (the lowest I have) and removed three of the four inserts. Initially the results were poor, with many 'jamms' and two broken carbide inserts, but I kept trying this and that and at the end of the day I found out that I needed much 'deeper' cuts, very low-low speeds and a continuous supply of liquid. I learned along the way that my lathe experience is not applied to milling !
    Today I tried with two inserts and achieved fewer jamms and a much better finish. I also realized that jamming is also due to my somehow 'weak' belt-driven power transfer, which seems like a drawback, but also a blessing for beginners like me that would otherwise damage the equipment!
    Like you wrote, it took ages to mill five tool holders, but so be it, I'm sure it will be different with softer metals.

    Here is the job in progress
    WP_20170408_15_38_09_Rich.jpg WP_20170408_15_50_54_Rich.jpg

    I realize expertise comes with time and experience so I don't pretend to become an expert overnight, just to learn slowly while enjoying this hobby when I have time, so would appreciate more advice, such as a link to a good youtube tutorial. Also some brief answers to my following questions will help me at this point!

    1. SFM, I learned it means Feet Per Minute, but how do I implement this value on my machine? Here is a pick of what I have, are any of those numbers SFM's?
    WP_20170408_18_46_22_Rich.jpg
    2 On the carbide inserts, here is what came on the 50mm face plate, they look quite 'oval' to me, like if they might be specific to finishing work on soft metals. I wonder, would it help with 'jamming' if the inserts were more 'pointed' like the regular triangular carbide ones? If so, could I find 'pointed' inserts to go on the face mill I bought?
    WP_20170408_18_48_22_Rich.jpg
    3. Should I mill always with the 'moving table' going always 'one way', or go back then forth? Or should I use a last backwards swipe for finishing?
    4. Should I try to mount the work so that the carbide insert 'comes on' to the metal at an angle, to avoid bouncing or this makes no difference?

    I'm done milling my AXA tool holders and now plan for my next projects whenever I find the time. I'm contemplating a Steady Rest and have already the material for it, it's steel and I trust it will prove easier to work with ! Here is what I'm aiming for, a bit complicated, but a challenge! http://www.toolsandmods.com/lathe/lathe-steady-rest

    THANKS to all for your support and advise and HAVE a NICE EASTER !!!!!
    Aris
     
  14. Reeltor

    Reeltor United States Active User Active Member

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    3. Should I mill always with the 'moving table' going always 'one way', or go back then forth? Or should I use a last backwards swipe for finishing?
    4. Should I try to mount the work so that the carbide insert 'comes on' to the metal at an angle, to avoid bouncing or this makes no difference?



    THANKS to all for your support and advise and HAVE a NICE EASTER !!!!!
    Aris[/QUOTE]

    The quick answer is No, always go "one way" and that way should have the cutter entering with work for conventional milling not climb milling. I have some diagrams but they are on another computer that I cannot access. I'm sure some of the real experienced experts will chime in and explain it better, in the mean time; please look up Climb Milling, you do NOT want to climb mill on your combination machine, or any mill that is not 100% rigid and setup for it.
     
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  15. dalvorius

    dalvorius Australia Swarf Registered Member

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    Hello Aris,

    I am also very new to machining, but I have found some good information here and also on the web.

    Surface Feet per Minute (SFM) is dependant on RPM (revolutions per minute) and the diameter (size) of your work.

    It is the speed of the surface of your work, as it revolves around the diameter at the RPM your machine runs at.

    I use this table: http://www.tapdie.com/html/sfm_to_rpm-_surface_feet_per_minute_to_revolutions_per_minute.html

    You probably know how to convert inches to mm but just in case - for reference with this table in relation to the diameter of your work : 1" (1 inch) = 25.4mm, and 1/4" = 6.35mm (approx.)

    I hope this helps.

    Cheers...
    Dalvorius
     
  16. TORQUIN

    TORQUIN United States Active Member Active Member

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    I very neat trick I learned from an old machinist is to take note of the RPM speed for various SFM's for 1 inch diameter cutter/work piece (in case of a lathe). Then when you need to calculate your RPM you just look at your note and divide the RPM speed for the 1 inch piece by the diameter you are actually cutting/cutter you are using.
    For example: 70 SFM is 267 RPM for a 1" work piece (lathe) or 1" cutter (mill). If you are actually using a .5" end mill, you would divide 267 by .5 and get 534 as your RPM for that cutter. Works the same for a lathe. You just use the work piece diameter instead. If your SFM was 100 then you'd divide 382 by your cutter diameter.
    SFM Spindle Speed
    40 153
    50 191
    60 229
    70 267
    80 306
    90 344
    100 382
    110 420
    120 458
    130 497
    140 535

    Sorry, I don't know of a way to do this trick in Metric.

    And when you do not have the speed it requires on your machine, go slower. It will keep you from burning up your cutter.

    Chris
     
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  17. jlsmithseven

    jlsmithseven United States Active Member Active Member

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    Here is what I was taught:

    To Find RPM - Take cutting speed (1018 steel) which is 70 X 4 (inserts of carbide) / by size of cutter. So if you're cutting steel it would be 280 / 50mm which is 280 / 1.9685. Your RPM for this would end up being 142.2 RPM. Pretty slow because you're using a 2 inch cutter almost. But then you times this number by 3.5 because you're using carbide which likes a faster speed. Your RPM would be about 500, but you can go 600 if you'd like.

    To Find IPM- Inches per minute feed rate. Take RPM (500) X .0015 (chip rate) X number of cutters. End up with about 3 inches per minute feed rate.

    This example is cutting plain steel with a 2 inch carbide cutter with 4 blades on it. Just an example.
     
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  18. aliva

    aliva Active User H-M Supporter-Premium

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  19. scwhite

    scwhite United States Active Member Active Member

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    Here is a good rule of thumb
    Run your end mills or cutters at the speed that you can see the flutes - just before they start to blend together.
    To fast you can't see them . To slow you see them to good .
    Regardless of the size end mill
    This rule of thumb will put you in the working
    Envelope Of the SFM
    You can go up or down from there
    No math needed just watch your flutes
    Six flutes run slower than Four flutes two flutes
    Run faster than Four flutes .
    Feed rate is based on the depth of cut .
    Rule of thumb
    Steel or cast iron
     
  20. benmychree

    benmychree United States Active User H-M Supporter-Premium

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    Just to qualify things, I tested my Aloris holders for hardness with my Rockwell hardness tester, and came away with a Rockwell "C" hardness of between 37 and 40. At this hardness they should be machinable with carbide, with some difficulty at cutting speeds below 100 sfm, or about 200 RPM or less.
    My cutting speed calculator, taught in my machine shop class in high school and JC takes the allowable cutting speed (say 100 for steel) times four, divided by the diameter of the moving part. Going to the internet aside, the easiest way is to get a slide rule type cutting speed and feed calculator; these were given away by all the carbide companies in the past, and it should be easy to find one on E Bay.
     
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  21. kd4gij

    kd4gij United States Active User Active Member

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    One thing I was told many years ago and found to be true is Face mills with odd number inserts will cut much nicer then ones with even number inserts. My 2" face mill has 5 inserts and cuts much better finish than the one I have and don't use anymore that has 4.
     
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