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  1. #1
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    Tips for straighter bores

    What do you guys do when you are milling a tight tolerance hole with an endmill and can feel a taper towards the bottom. Assume it's a new endmill that's interpolating (ramping down) down the hole. I've heard everything from speed up rpm, to slow down rpm to slow the feed down.
    On a cnc machine, using gauge pins to check the hole.

  2. #2

    Re: Tips for straighter bores

    Second finish pass?
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Re: Tips for straighter bores

    Use a boring head set to size for the final pass.
    Ian.

  4. #4
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    Re: Tips for straighter bores

    hi john rough until depth=h using a tool with normal chamfer, then finish until depth=h-0.03eq using a tool with smaller chamfer; for this to work, you need to measure both tools at same moment, because tool measuring senzor results values changes during a day, mostly because of termics

    depending on setup, you may consider prefinishing with another tool, so to be sure that the finish tool is always cutting in constant ae; like this, using a 3 tools combo, you may push the roughing tool for longer

    kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  5. #5
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    Re: Tips for straighter bores

    Using gauge pin to check the hole????…..did you know that a 20.00 mm diam pin.....whatever...... is a press fit in a 20.00 mm hole?

    I assume the gauge pin is not a regular plug gauge with "go" and "no go" end sizes.
    Ian.

  6. #6
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    Re: Tips for straighter bores

    hello handlewanker

    did you know that a 20.00 mm diam pin.....whatever...... is a press fit in a 20.00 mm hole?
    reading this, i remembered the dimensions translations, caused by the measuring method : for example, if a part has to be delivered with a bore dia20+0.03, then the actual size of the "good" part will be different, depending if it is measured with :
    ... an into or cmm ( this measuring method may deliver the smallest bore )
    ... an internal micrometer
    ... gauges ( this measuring method may deliver the biggest bore )

    in other words, if inside a shop is aplied a measuring method which is different then the method which is apllied at the client, there is a big chance that the client will reject "good parts", or accept "bad parts"

    this dimension shift problem is very accentuated when tolerances get smaller, and measuring method is not discused

    each measuring method, in order to validate a part as being "good", requires a different range for the bore tolerance and cilindricity

    a few years ago, i was in the situation to explain why 15um got shifted; lucky for me, the client understood, and the discussion was short, otherwise it could end in a messy situation

    I assume the gauge pin is not a regular plug gauge with "go" and "no go" end sizes
    you mean those sets, for example, if you have to deliver 20+0.03, then is ok to have gauges 19.95 19.96 19.97 19.98 19.99 20.00 20.01 20.02 20.03 20.04 20.05 ? each one ±3um kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  7. #7
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    Re: Tips for straighter bores

    No....you need to have a plug gauge that has been made and calibrated by a company that makes gauges to be such a size that it will indicate the hole size required by the go and no go method......the customer MUST also use the same plug gauge to check the hole and it will be the same size as the one you are using.....there are no ifs and buts for that.

    You can gauge a hole with a telescopic gauge or an inside micrometer etc and it is the fit of those gauges and the skill of the person using them that determines the hole size.

    It can be said that no two people can measure a part with a micrometer and get the same results mainly due to one or the other using more or less pressure when applying the micrometer….whatever.

    A go and no go plug gauge MUST enter the bore with the go side and MUST NOT enter the bore with the no go side.....that is the only way to give a customer the results that his drawing tolerance states.

    It is also a fact that the plug gauge is made specifically for the size indicated by the customer's drawing tolerance.

    You cannot just stick a gauge pin in a hole and think it's OK......gauge pins are also made to a tolerance which is a one size only.

    You cannot make a plug gauge to check your work for a customer unless you have accreditation as a gauge maker.

    The fact that plug gauges are expensive and must be made to measure means many people forgo their use and rely on measuring their work piece with conventional measuring equipment.

    With batch work the cost of a plug gauge is ALWAYS costed to the customer and it is your guarantee of integrity.

    For example, where would you get a plug gauge to measure a 20mm bore that had a tolerance of plus .02mm and minus .04 mm.....those sizes are pretty slack and you could easily supply a part by measuring with an inside mike or a telescopic gauge alone......if your parts are on top limit they may be over size if you measure wrong......a plug gauge does not lie.

    If you are making many parts to a drawing then a plug gauge is a must have item.
    Ian.

  8. #8
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    Re: Tips for straighter bores

    hi handlewanker, nice infos there / in some cases, i craft gauges, or even simple measuring fixtures

    however, so far, i had encountered setups that required extra-length of the go-gauge : in some situations, i have used go gauges 3d - 10d, and even combined go-gauges, like one that is 6d+6d, designed to check if 2 holes are cilindrical and coaxial

    there are parts that a cmm can not even touch, or, even if it does, it requires too much time to run the inspection, and results are questionable; i am not saying that a cmm is not ok, but in most situations, i preffer to have the measuring instruments near the machine ... this requires a few things, like clean hands, clean machine cabinet, no temperatue fluctuation, etc

    the customer MUST also use the same plug gauge to check the hole and it will be the same size as the one you are using.....there are no ifs and buts for that
    to eliminate doubts, a go nogo gauge, depending on dimensions, should have some friends :
    ... go nogo, for the go side ( go go, and nogo go )
    ... go nogo, for the nogo side ( go nogo, and nogo nogo )
    ... and, of course, these :
    ...... go go go + nogo go go , go nogo go + nogo nogo go
    ...... go go nogo + nogo go nogo , go nogo nogo + nogo nogo nogo

    is not common to use so many gauges, unless there is mass-production
    ... "main gauge" is crafted within tolerance T
    ... "calibration gauges", to verify the "main gauge", are T/3
    ... "factory gauges", to verify the "calibration gauge", are T/4 .. T/5, depends

    and, there is the frequency of usage :
    ... "main gauge" : every part, every 10parts, or daily
    ... "calibration gauges" : once at 4 hours, daily, weekly
    ... "factory gauges" : weekly, montly, yearly

    and there are the documents :
    ... "main gauge" results are not recorded, or maybe is used an "inspection template"
    ... "calibration gauge" results are not recorded, or maybe is used an "passport"
    ... "factory gauge" results are always written insisde the "passport"

    and the real location :
    ... main gauge - i preffer as near the machine as possible
    ... calibration & factory - a bit far away, in a less hazard place, like a peripheral room, under the sink, etc

    in other words :
    ... in most cases, is enough to buy a go nogo gauge + calibration certificate
    ... for long term setups, is ok to buy/have also the "calibration, and maybe the factory gauge" + passport

    is not a must to buy the "calibration/factory gauges", as long as there is a method implemented in order to check the dimensions of the "normal gauge"; but, if this method does not exist, and someone forces a gauge, thus uses too much force on it ( or gauge life is near end ), then :
    ... acceptable tolerance field gets reduced ( this is the nice case, as long as the process is still stable within the new-reduced tolerance )
    ... tolerance gets shifted, or even out of initial specs ( at this point, derogation documents kick in, tring to save as many parts as possible; if a part is out of the derogation, is trashed; derogation, depending, may allow the tolerances to shift with 5-20% )

    again, depends ... kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  9. #9
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    Re: Tips for straighter bores

    No matter what you are using, a new gauge or a well used one, as long as the calibration certificate is current then the part is what the gauge says it is.....that is beyond question...….if your customer's gauges are not currently calibrated they have no valid reason to fail or reject your production...…..a current calibration certificate is holy writ.
    Ian.

  10. #10
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    Re: Tips for straighter bores

    yup ... on some setups, is easier when the client gives you the crafting steps + control; something like : "here, take this, just replicate" - i love those ones

    about certificates, papers, etc ... some persons always check a gauge the 1st time they put their hand on it, regardless of that gauge being new or old; is a minihabit, like checking the caliper, micrometer, etc / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  11. #11
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    Re: Tips for straighter bores

    Well, I can't agree with you on that......a gauge is a set piece and it only checks the dimension that it is made for during the calibrated period of time.

    Gauges are calibrated periodically by a gauge maker who is accredited to do such work.....an ordinary person at the machine CANNOT check a gauge...…..and for that matter a micrometer or a vernier caliper or even a digital caliper.

    Plug gauges CANNOT and SHOULD NOT be checked against a set of slip gauges as the slip gauges need to be calibrated too.

    Did you know that a micrometer normally comes with a setting piece, but that only checks the maximum size range of that micrometer size and cannot check it's screw thread from zero to the big size end......they do wear and must be calibrated periodically etc etc

    BTW....if a customer doesn't give you specific sizes to make a part for with the tolerances clearly marked you may as well use a tape measure.....LOL.
    Ian.

  12. #12
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    Re: Tips for straighter bores

    Plug gauges CANNOT and SHOULD NOT be checked against a set of slip gauges as the slip gauges need to be calibrated too.
    "plug gauges" are checked with "caliber gauges"

    "caliber gauges" are checked with "factory gauges"

    an ordinary person at the machine CANNOT check a gauge
    not everybody, but few can ...

    most operators have normal gauges

    few of them, the shift master and the control room has acces to calibration gauges

    control room has also factory gauges

    and also, there are other things, in other points; is not everything in one place, at one person; kind of a cross-reference

    maybe there are ( 10+ 20+ ... 50+ ) plug gauges, and 5 calibration + factory gauges

    maybe few persons are empoyed only for managing gauges & passports

    BTW....if a customer doesn't give you specific sizes to make a part for with the tolerances clearly marked you may as well use a tape measure.....LOL
    that is reverse enginering just saying / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

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