Where do the SFM values come from
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    Default Where do the SFM values come from

    Amazingly after being a machinist for a long, long time I've never wondered about this. Probably because I never needed to know. I still dont need to know but now I'm curious. How are the SFM values, either generic or provided by a tooling manufacturer, calculated for a particular material? Since carbide is usually some multiple of HSS tooling its not just the material being cut but also the material the tool is made from.

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    Depending on the manufacture that data may be pulled out of destructive testing of their tools.

    Or their ass.

    Ideally the manufacturers speeds and feeds are good for 15 minutes in the cut. Remember for tool life DoC is free, FPR is cheap and speed kills.

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    Quote Originally Posted by Bill Clark View Post
    Amazingly after being a machinist for a long, long time I've never wondered about this. Probably because I never needed to know. I still dont need to know but now I'm curious. How are the SFM values, either generic or provided by a tooling manufacturer, calculated for a particular material? Since carbide is usually some multiple of HSS tooling its not just the material being cut but also the material the tool is made from.
    We got it from Aliens. They beamed (not Jim) down here and told us; "too fast, and the tool wears out", too slow, and you don't make money". They said if we don't do it that way, Space Zombies are going to beam down and eat our brains.

    R

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    Quote Originally Posted by litlerob1 View Post
    . They said if we don't do it that way, Space Zombies are going to beam down and eat our brains.

    R
    So that's what happened

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    Quote Originally Posted by litlerob1 View Post
    We got it from Aliens. They beamed (not Jim) down here and told us; "too fast, and the tool wears out", too slow, and you don't make money". They said if we don't do it that way, Space Zombies are going to beam down and eat our brains.

    R
    I'll by that haha. Glad to see our sense of humor is alive and well on this Sunday morning. So the value is derived from an equation only the Greys or the Reptoids from Zeta Reticuli can understand?

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    Lol. It's a silly morning apparently. I'm sure most of these data are given by manufacturers after a ridiculous amount of destructive testing. Keep in mind that these recommendations are only that, and not intended to be set in stone. There are a cubic shit-ton of variables involved, so they often won't even give a set value but a wide range. I've used plenty of tooling WAY outside the suggested ranges successfully. Mostly exceeding the high end when finishing.

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    Quote Originally Posted by Bill Clark View Post
    Amazingly after being a machinist for a long, long time I've never wondered about this. Probably because I never needed to know. I still dont need to know but now I'm curious. How are the SFM values, either generic or provided by a tooling manufacturer, calculated for a particular material? Since carbide is usually some multiple of HSS tooling its not just the material being cut but also the material the tool is made from.
    .
    they take cuts at different sfpm and ipt and see when sudden tool failure occur. usually they give a range like 400 - 800 sfpm and as depth and width of cut increases you normally use the slower sfpm due to increased heat and vibration. and of course you adjust sfpm til you get acceptable tool life.
    .
    and if depth of cut is very low you can actually use higher than recommended like 900 sfpm. obviously the user with tool in his particular tool holder can do his own testing and get values far more accurate than the generic values from the cutting tool manufacturer who has no ideal what tool holder you are using and no ideal whether you have rigid or flimsy part setup
    .
    same tool can easily run 700 sfpm at .014 ipt on a rigid part and on a flimsy part that vibrates might have trouble at 300 sfpm and .007 ipt
    .
    when you can hear load noises from over 100 feet away and tool life is short usually its cause cutting parameters need adjustment
    .
    its like using a 20" long drill bit thats .25 dia, obviously length to dia ratio has a effect on what tool can take. often vibration and tool deflection determines sfpm and feed ipt more than anything like a cutting edge getting too hot limit.
    .
    i use tool database using standard tool setups with recorded cutting tool parameters tried and all sudden tool failures recorded. and all part machining times are recorded with all above average times recorded with reason why which is often a tooling problem cause of time delays. by working on cause of sudden tool failures the actual average machining times go down per year and per 100's and 1000's of parts

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    obviously if throwing sparks when machining and cutting edge goes red to white hot and melts you need to back off on the cutting parameters
    .
    obviously if you got a large part (10 tons) where same tool is cutting for 3 hours continuously you often need to adjust cutting parameters so tool will last that long. if tool is making 500 lbs of chips again cutting parameters may need adjustment so it lasts that long.

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    Quote Originally Posted by eKretz View Post
    Lol. It's a silly morning apparently...
    Oh no, Rob is dead serious. He left his tinfoil hat in his toolbox on Friday.



    Normally I will double the SFM for a finish pass if I am taking 5 or 10 thou, radial chip thinning and low heat environment etc.

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    Quote Originally Posted by Larry Dickman View Post
    So that's what happened
    They took Fred Taylor.....

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    Quote Originally Posted by Bill Clark View Post
    Amazingly after being a machinist for a long, long time I've never wondered about this. Probably because I never needed to know. I still dont need to know but now I'm curious. How are the SFM values, either generic or provided by a tooling manufacturer, calculated for a particular material? Since carbide is usually some multiple of HSS tooling its not just the material being cut but also the material the tool is made from.

    Not sure how serious your question is...

    SFM is based on the tool material, the work material, and any coatings on the tool (for the very basics). I'm guessing the comparison to HSS is still used because that is what 'they' had in the beginning. As an aside, I am starting to see numbers based on carbide then reducing them for HSS, so a shift in the times I suppose...

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    Quote Originally Posted by camscan View Post
    That may be true but it is not the only option,I get my info from the fairies at the bottom of my garden.
    If you don't believe in fairies that is not my problem,go to an amateur machining forum,see if they can help.
    I believe you're a Fairie. This is serious stuff genitelmen.

    After Ninetyleven years of Machinering, and rework. I discovered too fast, is too fast. Big dog Tool makers, are about 3/4 full of shit.

    The real knowledge only comes after catastrophe.

    R

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    " I'm guessing the comparison to HSS is still used because that is what 'they' had in the beginning."

    Actually, "they" had carbon steel to start with. My Fosdick radial drill has a drill chart with suggested speeds for diameter and has a note at the bottom "double for high speed steel". Also had a big pile of carbon steel drills one time. Never thought of them being carbon and fired up the radial. Burned it up instantly.

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    Most of what gets published was done by users & fed back to the makers & industry at large. Data is collected by US arsenals, GM, GE, Ford, Cat, etc. etc. At the simplest you track 7 variables → material, machine tool, coolant/dry, SFPM, FR, DOC and WL.

    Surface speed is a velocity value, DOC and FR are force values. The wear land (WL) on cutting tools is your boundary. Working with all that you can manipulate your machining for economy up to max production (in any case you try to be in charge of things).

    Generic tests will increase the base point for each one of those values 50% run for a specific time, stop & the measure the wear land & continue that to failure. Reset & bump the next variable value, rinse & repeat.

    General use for the job shop is limited because of cost, but that’s where the generic numbers came from. The makers will test the tools against other proved tools they make for wear & impact using the same things they use for internal quality.

    Will attach graphed stuff from GE & hopefully If I can find it from HSS double hump wear (from SFPM) published in Machinerys Handbook #1.

    Good luck,
    Matt
    Attached Thumbnails Attached Thumbnails increasespeed.jpg   increasefeed.jpg   increasedepth.jpg   hsswear.jpg  

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    IIRC in the late 1800's / early 1900's there was a lot scientific work done on tool wear, quite famous names but I can't remember them …….... think it could have been in France.

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    One of my co-op jobs 50 years back in college was running tool life tests using various coatings and insert cooling methods. Back then, maybe still, Cincinnati Milacron and Metcut were among those doing study after study.

    As Matt says, large manufacturers ran their own tests; especially in the automotive industry. Make 500,000 of something and getting the best possible combination of cutting speed and tool life meant significant savings. Makers like Kennametal also run their own tests (or in combination with a customer); to better sell their various grades of inserts, coatings, and insert geometries.

    Most jobs shops run tools somewhat conservatively. They're more concerned about losing a cutting edge in the middle of a job than getting the last 10% reduction in cycle time.

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    Quote Originally Posted by Limy Sami View Post
    IIRC in the late 1800's / early 1900's there was a lot scientific work done on tool wear, quite famous names but I can't remember them …….... think it could have been in France.
    That doesn’t surprise me Limy, the stuff I’ve collected was done from WW2 up in to the 90’s here in the states.

    The down & dirty is “if you go to the trouble of rigorous testing and build useful ratios for others to test, refine & use for their purpose” → IT IS SCIENTIFIC! And it’s not cheap if peoples time is of any value.

    I don’t care if you’re a garbage collector, if I can use your tools & concepts to make my motorboat go better → it’s like finding free money in the back yard.

    OT, Glad to see you're getting well. My dad had his first by-pass @ 59, had a 2nd about 10 years later & had lost some heart function. Long story short, 5 years later his heart function had improved at LOT, but brain cancer popped up & took him...

    Good luck,
    Matt

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    Quote Originally Posted by Bill Clark View Post
    Amazingly after being a machinist for a long, long time I've never wondered about this. Probably because I never needed to know. I still dont need to know but now I'm curious. How are the SFM values, either generic or provided by a tooling manufacturer, calculated for a particular material? Since carbide is usually some multiple of HSS tooling its not just the material being cut but also the material the tool is made from.
    The most basic answer to your question is that speeds are calculated based on the material's toughness and shear strength. The area of material being sheared, tool geometry, friction against the tool and surface speed of the cut will give you a horse power requirement to make that particular cut. This was relatively straight forward in the olden days using simple geometry of hss tool bits. It was covered in second year of engineering.

    Even with today's complex mix of tools, materials and lubricants I'm sure the tools themselves are developed using the same basic parameters. It still boils down to doing a certain amount of work done over a certain time period. Simply put, physics. Of course today they will be using sophisticated computer modeling of the chip formation that would be capable of including many if not all of the factors. It then goes out into the real world to see how well the engineer did choosing the parameters for the calculation.

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    But required Hp doesn't have anything to do with assigning the correct SFM. The Hp requirement will change with DOC and Chipload.

    R

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    Quote Originally Posted by Rickyb View Post
    ....... The area of material being sheared, tool geometry, friction against the tool and surface speed of the cut will give you a horse power requirement to make that particular cut.....
    .....It still boils down to doing a certain amount of work done over a certain time period. Simply put, physics.......
    If only it was that simple, then the computer models would actually work over a wide range of uses.
    By necessity the SFM numbers given for carbide are very, very generic. Based on testing but not your testing as the number of variables is almost endless.
    So you end up with grades that in say 4140 run best at 200-1000 SFM depending on use. That kind of information is just this side of useless if you don't know why the high and low.
    Bob

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