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Thread: Collet stop

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  1. #1
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    Collet stop

    I am making a 316 tubular part with a thread in the middle,

    I am having a problem with the drill on the sub spindle wanting to push the part when 8t gets just the slightest bit dull, the owner complains he gets 3000 pcs out of a drill on his okuma and i only get around 1000 before it starts pushing parts.

    The part is too long to bore a step in the collet, but i had an idea to press a stop into the back journal and lock it into the relief holes of the collet with set screws, then the part would have a hard stop to push against when drilling, the only other thing I can see is to flip the part around and do more of the drill and tapping on the main, but that throws the cycle out of balance and im drilling into a hole where there could be a tap( currently all tapping is on sub)

    I tried tightening the toggles, but all that accomplished was squeezing the part down more and making the hole barreled

    Am I way off the deep end on this one or is there some merit to the idea.

    Part is 3/8 diameter 3" long with a m6 thread in the center 1/2" and an m8 thread on one side , and 7mm clearance on the other

    Sent from my SM-A515U1 using Tapatalk

  2. #2
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    Re: Collet stop

    hy hacker-de-luxe seems to be a grip-issue on the 2nd chuck ... seems promising that same operation performs nice on the okuma, but comparing an identical setup that runs on 2 different machines involves a few things, and, for that, i need to 'see' the machines

    considering that you compare a swisstype with a turrettype, i would 1st look into clamping travel of the swiss, being sure that all parts are being clamped somewhere in the middle of the travel :
    ... let's say that part dia is 10
    ... check what diameter can enter inside the collet when it is:
    ...... fully opened ( no part inside it )
    ...... fully clossed ( again, no part insid it )
    * you will need a set of rods, like 9 9.1 9.2 9.3 .... 10.5 10.6 10.7, thus it requires an incremental rods set, with the increment equal to an accuracy that suits your setup

    for example, if the collet chuck clamp range can handle:
    ... 9 - 11, and all your parts are between 9.98 and 10.02 ( 0.04 variations is huge for a swiss, but whatever ), then the only issue may be contact area and/or clamping force
    ... 9.9 - 10.3, and all your parts are between 9.95 and 10.1, then you are too close to the limit ( = grip instability ); should i explain more ?

    is all about tolerances ... swiss machines have a small clamping travel, and that travel may shift depending on a few things, like how much you tighten the spindle nut, and others

    i would 1st check that part-clamping range is fully contained within real-collet-clamping range, considering machining tolerance, etc

    on bigger swiss machines, available range increases, thus there are lower chances for a missgrip ... on smaller swiss machines, chances for a missgrip are higher

    so, check how far are you from the available range limits / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  3. #3
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    Re: Collet stop

    I order my pickoff collets ground to size, in that case it is a .365 diameter in a. 365 collet

    I also adjust the closers on every job, the problem is when you drill out the material the part crushes, i can put a finished part in and never get closing pressure, but if i put a raw part in and try to close it i can't by hand, and the machine alarms out if it trys.

    Usually I only run into this problem broaching, and usually I bore a step collet to fix that problem, but this part is a little too long. This guy also buys cheap drills, I dont run into this in my shop where we have almost exclusively Mitsubishi drills, i can see the diference in the geometry that would make it a lot higher force.

    Oh and this is a 38/32mm machine

    Sent from my SM-A515U1 using Tapatalk

  4. #4
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    Re: Collet stop

    before it starts pushing parts
    when you drill out the material the part crushes
    i am sorry, i don't understand, does the part slide inside the 2nd spindle, and/or does it crash/break because of drilling ?

    I order my pickoff collets ground to size, in that case it is a .365 diameter in a. 365 collet
    i don't know your machine, so take this only as wild-info : if play between collet and part is small, then machine may not have enough clearance to deliver full grip force

    also, the collet may be a bit pre-tightened inside the spindle, and this lowers the play ( between collet & part ) even more

    i can put a finished part in and never get closing pressure, but if i put a raw part in and try to close it i can't by hand, and the machine alarms out if it trys.
    this method of checking clamping range for screw machines is common, but is subjective, thus it is not precise

    if you don't know the numbers, then is only a guess

    if a vice is fully opened, it won't deliver same clamping force as when it is only 1/2 open, simply because the master screw can not turn in reverse

    if clamping travel is too short, then full grip is not achieved .... just saying

    for long series, on swiss-type, i recomand considering analyzing grip range as critical point ( high priority ), for machine setup; when i prepare such long setups, after collets are installed, crafting rods and adjusmtents may take from a few hours to an entire day, and periodically grip range is inspected; i inspect available and clamping range with 0.1mm accuracy, being sure that clamping range is not towards the upper ( or the lower ) limit of the available range

    if done, then, you know, just one less thing to worry about

    usually I bore a step collet to fix that problem, but this part is a little too long
    is there a part extractor/knock-out on 2nd spindle ? can you modify it to behave like a stopper, and also to knock-out ? kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  5. #5
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    Re: Collet stop

    just another thoughts, in order to increase grip:
    ... shorten the active length of the collet, in order to decrease the contact area between collet and part
    ... increase feed when machining, in order to achieve a more 'aggresive' contact between collet and part; in time, this may damage the collet, but it may still last long enough to deliver

    i am sorry, i really don't know what is hapening on your machine ... there may be something ' small ' ?!
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  6. #6
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    Re: Collet stop

    It sound like you have subcontracted your services to another machine shop
    "This guy also buys cheap drills ,I don't run into this in my shop" if you are programming and setting up his machine and he won't purchase the better drill you will have to program and use what he supplies
    This not that you shouldn't advise him on tooling because you should be
    It sounds as if you are doing this for a first time in the shop swiss machine and the owner doesn't know much about swiss production machines
    cheep drills are not for production. He may have gotten 3000 holes with that drill but the question would be cycle time ?
    This would be the reason to move it off the okuma to a swiss

    problems i see are
    if the part hits the stop when it goes in to pick it off you would get a servo alarm
    if you keep the part from bottoming out you will get push back (how much can be lived with and will it be the same each time ?)
    how will you eject the part (a traditional swiss uses a knock out which you won't be able to use)
    you will have to put some sort of spring to knock the part out (all this has to rotate with the spindle as you will be against it while machining)
    if you have high pressure coolant thru the sub you might be able to eject the part with a small hole in your stop ?

    if you have high pressure coolant i would suggest a coolant fed carbide drill and drill on the main spindle and leave the tapping on the sub side

    Cheep drills are for low volume
    the expensive drills are for production

  7. #7
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    Re: Collet stop

    It sound like you have subcontracted your services to another machine shop--- Guilty work is slow with the "rona" going on, do what you have to do to pay the bills.

    I do make tooling recommendations, but I also respect that lots of people are often set in their ways, so unless I'm sure it absolutely wont work I tend to stick with what they want to use. I tend to be going in after other people, so I don't usually get first dibs on tooling recommendations.

    This machine does have torque skip so i can push up on the stock to a given servo load and then clamp, I'm not a huge fan as i have seen it cause alot of part length variations on previous jobs, but it does save a lot of cutoff blades.

    my plan was to drill a hole through the stop, this machine has a 4" stroke on the ejector to i can knock it out and still be clear of the stop. I never really trusted using hp to eject the part, one wad of chips and you have a crash.

    Machine does have hp on eject and drill block, drills are yg1 inox drills, and while they seem to have a strong cutting edge, they also take quite a bit of thrust compared to other drills i use, his okuma gets away with it because he is running against a collet stop(and hydraulic chucking doesn't hurt either)

    Any way end of the day, i have his machine producing 10x more parts than he was making slugging them through, and drills can be resharpened.

  8. #8
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    Re: Collet stop

    tooling recommendations
    hello on swiss is harder to compare od tools, since there is not as much machining ( mrr/hour, etc ) comparing to a bigger lathe; on long series, on okumas, i was changing tools once/shift or once/2..3 days, and when i moved to gangs, knowing what carbide is hq, i was changing some tools between a few days to a week

    fewer tool changes help a lot, especially when all turret, or almost all gang-turret posts are being used ...

    so, because gangs are machining much less material, then tools have a relative longer life, but conclusions can be gathered faster on bigger lathes, with increased mrr

    on the other side, on gangs can be compared, without worries, id tools, since those would be the same also on a bigger lathe

    i have my list for turning tools; for milling, i use recomandations from someone that is in contact with a shop that does heavy milling

    This machine does have torque skip so i can push up on the stock to a given servo load and then clamp, I'm not a huge fan as i have seen it cause alot of part length variations on previous jobs, but it does save a lot of cutoff blades.
    please, i did not understood, how do you save blades ?

    about length variations, i only used it on okuma with consistency < 0.05 ( or even lower ), but i never used it on gangs ...

    my plan was to drill a hole through the stop
    yes, why not ... in many cases i have modified the knock-out, in order to ' suit ' the part shape

    if possible, program the part transfer so to have 0.1 .. 0.15mm clearance between knock-out and part ( so to limit the ' slip ' ); may involve a knock-out extension, etc

    they also take quite a bit of thrust compared to other drills
    when it comes to tool life, i don't collect only tool-change-data, but also load data ... yes, there are load variations between drills from different vendors; it may be possible that the part slides inside the gang, because there is a drill with bigger core, and/or frontal attack/cutting-edge demanding more cutting force

    a good load monitor functions will imediatly highlight such differences

    Any way end of the day, i have his machine producing 10x more parts than he was making
    i don't know exactly what you are reffering to, i did not follow who is subcontracting who, but i guess you are comparing an okuma with a gang, and, for small parts, the gang should beat the okuma; if you are intersted into reducing okuma times, then you need to reduce the number of turret indexing ( combi toolholders - craft your own for turning, buy for live tools etc ), ctr, small clearances ( smaller than the gang's ), bar feeding without stoping the spindle, a smaller chuck ( to shorten acc/decc time ), and smaller chucking travel; with all these, time difference between machines should reduce, and the main advantage of the gang should be it's higher rpms, and the 2nd should be it's faster acc/decc; tica-taca times related to bar feeders are not included / kindly

    ps : please, what means ' slugging them through ' ?
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

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