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Thread: Endmill RPM

  1. #41
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    Feeds on a manual machine are usually vague anyway. Unless it is an all gear driven machine (power feeds), one usually can't determine the feed rate without a clock. I've seen an old K&T horizontal that spelled out the feed rate for you, but every "Servo" brand style power feed always has near useless 0-9 or 1-10 or whatever on the dial. Does everyone who disagrees with 67Cuda calibrate their power feed on their manual machine, or do all you guys have Deckels or K&T's or do you stare at a clock while you crank the handle?

    To the novice: make up a chart showing the recommended SFPM for a material. Then determine RPM for a given cutter. Now you have a starting point. For the novice, don't start at the extremes. Stick with middle of the road values, or err with lower values. For steel, if your chips are blue, and your using HSS you're doing it too fast.
    Last edited by Keith Krome; 04-04-2011 at 08:08 PM. Reason: grammar

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    Quote Originally Posted by Keith Krome View Post
    Feeds on a manual machine is usually vague anyway. Unless it is an all gear driven machine (power feeds), one usually can't determine the feed rate without a clock. I've seen an old K&T horizontal that spelled out the feed rate for you, but every "Servo" brand style power feed always has near useless 0-9 or 1-10 or whatever on the dial. Does everyone who disagrees with 67Cuda calibrate their power feed on their manual machine, or do all you guys have Deckels or K&T's or do you stare at a clock while you crank the handle?
    .
    How true, but amazingly, my Hardinge TM (with the OEM powerfeed) gives the feedrate like those mentioned above. Somehow Hardinge got something of value on that machine. I then have to "translate" that feed rate when running my other mills.

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    Quick handy figure that lets you have a starting point without burning up or breaking tooling instantly... 500rpm for .500" diam in mild steel with HSS cutting tools. This gives you about 68ft/min, which is about low mid range. 1000rpm for 1/4", 2000rpm for 1/8", 4000rpm with 1/16". Conversely 250rpm for 1", 125 for 2", 65 for 4", 45 for 6". This works on drills, lathes, endmills and horizontal mill cutters.

    Triple for aluminum, double for brass and bronze. Double all these figures for carbide.

    Without a geared powerfeed like a K&T, Cincy, Van Norman or early Bridgeport, feeds are just guesswork for the most part. Try to get a steady feed rate and beware of overfeeding and breaking the cutter. For feeds on geared powerfeed machines with geared spindles, you can take your desired chipload, multiply times the number of teeth on the cutter to get feed per rev, then multiply by the spindle rpm and that is your feedrate in "/min.

    Example, .002"chipload on 12tooth cutter at 90rpm.... .024"/rev times 90rpm= 2.19"/rev. Use 2"/min or the closest selection you have available.

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    (cuda post) The OP was asking thoughts on speeds and feeds, I gave my response. Good or bad, I wasn't slamming him in any way, just a different prospective.

    Didn't you mean perspective?
    Last edited by oldbrock; 04-14-2011 at 08:10 PM.

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    here is the bone head calculator....

    1/4" endmill 1,500 RPM, 1/2" endmill 350 RPM. In soft metal speed it up and hard metal slow it it down. it is that simple.

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    Default feed with small end mills

    i find feed with smaller end mills needs to be reduced if they have many flutes.
    .
    for example a 1/4" rotary file with 12 teeth cannot be fed at 6 times the rate of a 2 flute end mill as the flutes will clog with chips. i have added an adjuster to excel calculator but basically
    ...... theoretical feed - (1/diameter x number of teeth x factor (between 1-3)
    so say theoretical feed
    100 ipm - (1/.250 x12x2 = 96%)
    100ipm - 96ipm = 4 ipm
    with 4 flute
    33ipm - (4x4x2 = 32%) = about 22 ipm
    with 2 flute
    16ipm - (4x2x2 = 16%) - 13.44 ipm
    so basically anything with a small diameter and high number of flutes the formula will adjust theoretical feed to the point a 1/8 dia end mill with 10 teeth the feed will be negative or basically formula saying not practical at a certain point too many flutes at too small a diameter. the factor of 1 to 3 is adjustable depending on material being cut. alloys that like to stick to and clog flutes need a 3 or more adjusting or reducing feed on small diameter end mills with too many flutes.
    ......
    only thing that amazes me is why this is not taught to beginner machinist. it does not take 2 minutes with a rotary file on a mill to figure out you can not run at theoretical feeds without clogging flutes and burning up small end mills
    .
    i repeat any factor that a machinist can think of can be made into a formula and a computer can calculate a 1000x or more faster rate. Only problem i had was my math was a little rusty. but i think if kids are shown that algebra and trigonometry can actually solve real world problems they might show more interest in it.

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    I would post a WTB add for one of the old Kennametal/Valenite/Sandvik/Harig feed and speed slide rules. I use one quite a bit, very handy for going from sfm to rpm and feed/tooth to in/min.

    If you write down what sfm and chip load your hobby machine likes (it will be much lower than you can run on a real mill) you can get good rpm values for your particular machine. My second op lathe turns the best around 200sfm with positive rake carbine tooling while my Mazak will run 400-1000 sfm with a negative rake insert.

    I work mostly in steel and use the .500 dia -> 500 rpm ratio on the mill. If you double the diameter halve the speed, Halve the diameter, double the speed. 1in drill at 250rpm, 3/4" -> 375, .25" ->1000 rpm, 5" -> 50 rpm ,etc. You can get close enough with mental math and then adjust from there. This will put you around 60sfm which will make uncoated hss cutters in steel happy.

    It is better to start slow and speed it up rather than dull your cutters by starting too fast. If you have a variable speed drive, get a tachometer! It is very important to know the spindle speed.

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    Quote Originally Posted by oldbrock View Post
    (cuda post) The OP was asking thoughts on speeds and feeds, I gave my response. Good or bad, I wasn't slamming him in any way, just a different prospective.

    Didn't you mean perspective?
    Oh, my bad. Spelling error.

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    When I do manual machining, I calculate the rpm per tool material, workpiece, etc., and go from there. Feed-rate; I pretty much go by the chip coloration and shape but that's how my old man taught me when I first started out machining. He got by as a master toolmaker all his life without much more than a basic rpm calculation. For manual work, I don't think you need much more.

    CNC is another ball-game and that line between acceptable speed/feed and broken tools gets finer as the materials get tougher and/or the tools smaller.

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    I think the newbe needs to learn to calculate feeds and speeds, this will come in time. The easy way to start out is to look at your chip color. In steel, with HHS tooling no color or chatter, your safe. Gold, your pushing it. Blue, your maxed out.

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    Tom must be an english major. He'll admit to a spelling error right away but not to a machining error. Go figure, Peter

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    Angry

    There's always one or two guys that are glaringly insecure and angry and don't realize how obvious it is to everyone else. Someone says they are new and asking for help and you just jump in with insults. It's always the guy that wants you to know that he is a "real" machinist and you are not. Kinda pathetic really.

    The calculators are generally based on the machinist handbook formulas. The machinist handbook was written by people much smarter than you or I. It's pretty well know that the speeds and feeds in there are based on ideal conditions with super rigid machines BUT they give you a quick, ruff starting point. BTW "real" machinists use the machinists handbook. They don't just go by feel. The advancements in cutter material and coatings is something that guys like this hate because not all cutters and coatings "feel" the same or sound the same when they are cutting correctly. You can adjust the speeds so the tool sounds like your hand ground HSS tool from 1972. Good for you, you matched sounds. Unfortunately for the tool, it's designed to be pushed much harder than that and you're just wearing it out twice as fast.

    Sorry for the long post but bitter older machinist that refuse to change with the times / technology but still have the nerve to say they are "real" machinists just irritate me. The truth is that 30 years ago you were a real machinist. Now you're just the manual mill guy that hates all the younger guys on the CNC equipment because they don't know how adjust something by feel. Why would they? They're spending time learning the programming side and learning about new tools that cut parts 30 x faster than the guy out back.





    Quote Originally Posted by 67Cuda View Post
    If you need a calculator to tell you how fast to run a cutter or turn a spindle on a manual machine, then you my friend are not a machinist.

    You are somebody in search of a clue.

    Do those calculators you use tell you how to compensate for tool wear? Machine condition or rigidity of a set-up?

    That's what I though? NO.

    Good luck in your endeavors.

    Tom

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    So very interesting to read a thread where people have such diverse opinions.

    Jim

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    There is no "absolute" answer to your question. As a general rule of thumb I teach my guys to start with these numbers as a base line. Keep in mind however that there are so many variables and the best calculator for the variables is experience. Also, I tend to run things on the conservative side because I run a job shop. We have lots of one off parts and/or prototypes. Basically though
    6061 Alum - HSS 150 SFPM, CARB 300
    A36 OR 1018 - HSS 75, CARB 150
    A572 - HSS 65, CARB 125
    304L SS - HSS 50, CARB 100
    ******BUT***** like I said, these are only a relatively safe STARTING point. Things that experience will teach you that are big factors are......
    1. setup rigidity
    2. tool length
    3. Coolant type
    4. Coolant concentration
    5. Chip gaul
    6. Geometry of the cutting edge
    7. Coatings on cutter
    8. Climb cut or conventional
    9. Lathe or mill
    10. Material condition
    11. Material type
    12. Process being used
    13. Condition of the machine

    I could go on and on. I have been in this game for 24 years and I still have a thirst for knowledge. Now, I specified I run a job shop and that is important because on one off parts there isn't much of a budget for R&D on cutters so we are cautious. On the occasional production run that I will set up that is a whole different critter. I just finished one job where we were maching a 4.6" deep step on the side of 6061T6 flat bar. Material was 1.5" x 8" x varying lengths most around 60" Cutter I bought was a 2" dia., 6 flute cobalt-hss end mill. I had a custom ground "S" shape on the end then I had it TiCN coated. We successfully cut full 4.6" depth in one pass, radial cut was around .06", SFPM 700, feed @ .012 per tooth so 96 inches per minute. We ran the cut on the bottom side so gravity would remove the chips and ran the coolant mix with a higher percentage on the refractometer to reduce any chip weld. We cut the entire 6000 plus feet on one endmill and it is still sharp. Also what experience teaches you is our machine which is new to us is quite used. Somebody took a grinder to the quill and I only get about 60% contact when I check the fit with prussian blue. I also know that my Belleville springs are aging because I am only seeing about 2000lbs/force applied by the draw bar.

    When we initially started cutting we had lots of chatter, mostly because of the spindle condition. My guys wanted to slow it down, not me. I changed the cut direction to conventional cut, then cranked on the feed a bit then played with the coolant mix. Our estimator gave us 1335 hours for this process, we used 500 and that included milling the ends and drilling/counter boring holes on another machine.

    My point........the calculators and apps should be used for REFERENCE only. Your eyes and ears will help you with the rest. One last point and this is not directed solely toward the originator of the question. When you look up to a senior tradesman and you are trying to learn from him/her, listen with your ears and not your mouth. Watch with your eyes and not your tongue. No journeyman will give you time or knowledge if you think you know it already. If you are new and eager, ask, listen and if you don't understand then say so. Not much worse than somebody saying oh ya ya I got it when in reality you don't.



    Sent from my SM-N920V using Tapatalk

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    I work getting young folks into the skilled trades field, machinists, industrial electricians and such. I hope that none of them ever start their first job with Bob the early posted on this thread. Someone asks for help and instant "I am God's gift to...... whatever.
    Also, as a MoPar guy, he should forfit his '67 Barracuda to me. BTW, there was no '67 'Cuda, they were Barracudas then.

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    You can feel whether the removal rate is in the zone, in light of the hp, rigidity etc. You can't feel when speed hits the spot where cutter wear vs removal rate is no longer linear. It doesn't have a feel or sound or any other BS, your cutter just wears faster per cubic inch removed. With manual work, I never use a calculator, ....you do it in your head, approximate style, while setting up the work/walking over to the machine. whatever speed is conveniently close to/less than 4xCS/dia.


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