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different bits, different speeds

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  • Doozer
    replied
    Bah dumb bum ching ! ! !

    -D

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  • polaraligned
    replied
    Originally posted by Doozer View Post

    You need to get in there, play hard, and get out quick.
    Last time I tried that I ended up married...

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  • Doozer
    replied
    Originally posted by polaraligned View Post

    Just to expand on this for the beginner, going too slow is just as bad as going too fast. If you go too slow the cutter rubs and prematurely wears the cutting edge. You really want to be making chips. After a bit of experience, you get the feel for how fast you should be cutting and what good chips look like. I learned the hard way years ago about stainless steel work hardening. Lost a few brand new 1/2" drill bits because I did not keep on the down feed hard enough. (304 is brutal) But even if the material doesn't work harden, rubbing is bad for the cutting edge. So yes, I agree that slower is fine as long as you are making chips that you can pick up and measure the thickness.
    You are very correct.
    Stainless steel is actually a good learning tool for doing it right.
    You need to get in there, play hard, and get out quick.
    Like the Navy Seals.
    Good practice really and a good feedback exercise,
    if you are observant and adaptive.

    -Doozer

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  • Mcgyver
    replied
    Originally posted by polaraligned View Post

    Just to expand on this for the beginner, going too slow is just as bad as going too fast. If you go too slow the cutter rubs and prematurely wears the cutting edge.
    To clarify, I assume you mean feeding too slowly, in which case I agree. No point in spinning a million miles per hour and making dust.

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  • polaraligned
    replied
    Originally posted by Mcgyver View Post

    For hss anyway there is no issue (except it takes longer) in going slower. Without knowing that, the beginner is sometimes perplexed; e.g. "how can I drill this little hole, my lathe won't go to 20,000 rpm", etc
    Just to expand on this for the beginner, going too slow is just as bad as going too fast. If you go too slow the cutter rubs and prematurely wears the cutting edge. You really want to be making chips. After a bit of experience, you get the feel for how fast you should be cutting and what good chips look like. I learned the hard way years ago about stainless steel work hardening. Lost a few brand new 1/2" drill bits because I did not keep on the down feed hard enough. (304 is brutal) But even if the material doesn't work harden, rubbing is bad for the cutting edge. So yes, I agree that slower is fine as long as you are making chips that you can pick up and measure the thickness.

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  • Doozer
    replied
    Just me talking here,
    but the only material I have trouble finding a good
    speed and feed for is cast iron. Too slow and it seems
    to not leave a good finish. Too fast and the tool chatters.
    I think this tricky dance is because, although Iron is not
    very strong (20 to 30,000 psi), it is very tough and hence
    the expression, it wears like iron. So for cast iron, I might
    look up the numbers.

    --Doozer

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  • Mcgyver
    replied
    Originally posted by Doozer View Post
    That chart is about as attractive as looking at pictures of naked dudes.

    -D
    agreed, zero interest in either.

    Guys, this is not a three decimal exercise. RPM = FPM * 4 / Diameter. that's it. Memorize a few common FPM numbers for the materials (work and tool) you use and you can do the whole speed calc thing in your head while you setting up the machine.

    The other thing for beginners to note, is that the resultant rpm is the theoretical maximum. Its the point where going faster disproportionately increases tool wear, i.e. removal rate vs wear is no longer linear. For hss anyway there is no issue (except it takes longer) in going slower. Without knowing that, the beginner is sometimes perplexed; e.g. "how can I drill this little hole, my lathe won't go to 20,000 rpm", etc
    Last edited by Mcgyver; 01-14-2022, 01:58 PM.

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  • Doozer
    replied
    aaaa
    Click image for larger version

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  • SVS
    replied
    Doozer,
    You can make fun of my chart and my Chippendales calendar but don’t EVEN start on my Starrett tap and drill poster……

    Bob,
    When my buddy showed up with this chart I was probably lukewarm in my thanks. It grew on me, but I’m not evangelical about it.

    Your chart reformats the data to allow machine specific lines. As a fpm chart alone I don’t see an advantage beyond personal preference, and likewise, I don’t see utility in the horizontal lines for my particular machines. (All gear heads with speed change plates.)

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  • polaraligned
    replied
    In the distant past I had looked for blue chips in carbon steel as internet rumor has it that the chips are then taking the heat from the cutter. I found that this killed my carbide life. I now look for straw colored chips. Aluminum is a lot more difficult to find the sweet spot as going too high on the SFM just causes aluminum to weld to the cutter and it becomes a PIA once that happens. I find that about 400 SFM has worked well for me with carbide in aluminum using WD-40 and air blast. Take a good size cut at a lower than "max" SFM seems to work for me.

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  • eKretz
    replied
    Suggested speeds in any chart or table are only starting points. From there you need to dial in speed by watching the chip AND the tool edge. No speed recommendation is going to be accurate unless you have a material (including hardness if it's possible to vary that much) a depth of cut, and a feedrate suggested along with it. All of those things affect the best speed to be used. Watching the chip color can be a decent indicator of appropriate speed. Watching the tool edge (under magnification if necessary) is the most accurate and reliable indicator. When using carbide, whether you get a highly reflective finish can also be a good indicator. The thing you're trying to achieve is proper tip temperature. You don't want too cold (built up edge and chip weld issues, both leading to earlier than ideal edge failure) and you don't want too hot (rapid tool wear/edge failure). All of those factors form a sort of triangle, with your ideal speed being in the middle. Change any of those factors and your ideal speed changes as well.

    And I definitely don't agree that cutting speeds will be the same on manual and CNC machines. Manual machines generally do not have the high pressure coolant that CNC machines do, nor do they have the advantage of the tool never dwelling in one place and rubbing. They also generally take much heavier cuts at higher feeds than most CNC machines (talking big industrial machines here, not home shop). All of which mean they need to run lower speeds for the same workpiece materials.
    Last edited by eKretz; 01-14-2022, 09:08 AM.

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  • Bob Engelhardt
    replied
    Originally posted by SVS View Post
    That’s great Bob. Which is more useful, TODAY, to a novice without a clue?
    Fair enough.

    Here's a much better idea, though:

    Click image for larger version

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    The diagonal lines represent constant FPM for various diameters & speeds. The horizontal lines represent the speeds for all the belt & gear settings (e.g., the line labeled HLB is 140 RPM when the motor pulley is on high (H), the jack low (L), and in back gear (B)). To use, for example, you start with the diameter (1-1/2) & go up (red) to the line for the FPM wanted (125 - green), then the nearest horizontal line (blue) is the belt/gear setting to use (motor on low & jack on medium - 340 RPM). You don't actually use the RPM. You can't set your speed to a specific RPM anyhow, so that level of accuracy is over kill.

    The horizontal RPM lines are, of course, specific to my lathe. But the FPM lines are universal, depending only upon the 4xFPM/Diam formula. The chart can be easily made for any lathe.

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  • polaraligned
    replied
    Originally posted by Doozer View Post

    Just being funny. Come on.

    -D
    And it was funny.

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  • Bented
    replied
    Originally posted by Doozer View Post
    Bented, This is not CNC central.
    Your chart is nice to look up a number and plug it into the computer screen.
    But with manual machine tools, you just look at the chips color.
    For a guy starting out in manual machining, a chart with numbers like that
    is just a source of frustration and a buzz kill. I have never calculated
    speeds and feeds on manual machines. Been using manual machines
    for 30 years (gosh, wow, time flies). Keep it fun, just look at the chips!

    --Doozer
    I always calculated a speed to start a job 25 years before ever touching a CNC machine.
    The same principals apply, cutting speeds remain the same on manual and CNC machines, the same tools and materials.

    Nothing could be more simple than the "suggested" speeds in that chart.

    Low carbon steel with HSS tooling, 120-170 SFM.
    Uncoated carbide, 400-450 SFM.

    Exactly what is confusing about this?
    Last edited by Bented; 01-13-2022, 07:55 PM.

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  • Doozer
    replied
    Originally posted by SVS View Post
    Sorry it doesn’t meet your high standards……you don’t use’em any how though right?
    Just being funny. Come on.

    -D

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