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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.

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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

  13. #13
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    Re: Tips for straighter bores

    I still disagree with you...…....end of topic.
    Ian.

  14. #14
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    Re: Tips for straighter bores

    look handlewanker, you are right, is not ok to check with another gauge, is not common behaviour

    also, future perspective, is hard, when it comes to find good workers

    there are still places with a high level of experimented people; some places still have 1:1departments, other are 1:3 or 1:5; such things are pretty high, but i don't know for long

    average is below 1:10, or 1:30, and this is an average from 30 yrs ago

    what i had been talking about is not common, since shops tend to be sporadic, but there are still places that are centralized



    ok, let's say that you have hundreds of gauges at hundreds of people ... how do you check them ?
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  15. #15
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    Re: Tips for straighter bores

    Who cares!! The OP never even mentioned the tolerance of the bore he is working on. He only said that he is using gauge pins to check the hole and could tell the interpolated bore was tapered. A gauge pin may be just fine depending on the tolerance requirements. He simply asked how to take care of the taper.

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    Re: Tips for straighter bores

    This time I disagree with most posts.

    We did not get original posters d/l tolerances .. which are what it is all about.
    And size, depth, speed, qty goals.

    A reamer will deliver a hole about 0.01 mm in size, or a bit better, and mostly follow the bore while improving it a bit in straightness.
    Carbide reamers will make the hole straighter, and double-reaming will make the hole straighter and more uniform.

    Typical holes made with boring heads or modern vmc machines will have 0.01-0.02 mm tir/taper, to 0.04 mm (weak) bore sizes and straightnesses in the normal 1-3-4 d/l ratios.

  17. #17
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    Re: Tips for straighter bores

    LOL....a veritable storm in a tea cup...…...the problem I highlighted arose form the ongoing conversation/post.....whatever...…..and concerned the aspect of a customer supplier relationship when it comes to producing work to a customer's toleranced drawing., so I suppose it doesn't matter if the hole is not to the tolerance as long as it's parallel.

    As long as the gauge pin, no matter what size it is, goes into the hole it will as you say tell you if the hole is tight at the bottom…….I can't imagine what you would make of it if the hole was tight at the top and oversize at the bottom.
    Ian.

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    Re: Tips for straighter bores

    LOL....a veritable storm in a tea cup...…
    hello, yup, i started it i just remembered that a while ago, there was a calibration loss near the limit tolerance ... whatever, like you said, agreing with the client on control method helps

    so I suppose it doesn't matter if the hole is not to the tolerance as long as it's parallel
    i don't understand this

    I can't imagine what you would make of it if the hole was tight at the top and oversize at the bottom
    sometimes this happens ... for example part is controlled inside the machine and is ok, but after it is taken out, sometimes it happens to be oversized at the bottom

    most common cause, is that the fixture puts too much pressure on the part, & the part changes shape

    a quick way to check it, is to leave the gauge inside the part, and take the part out : if the gauge does not slip as easy/hard as when the part was inside, or, if the gauge is blocked, than few adjustemnts are made

    this is "fluaj", i don't know the english word, rigid material that leaks slowly; unpleasant situation is when this phenomen has effect spread across a time period greater than fewhours-1-2 days

    to fix this, it may be enough to program a taper, or to reduce fixture forces, stabilize internal part tension through prior heat-treatments, etc / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

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    Re: Tips for straighter bores

    Lol jesus you guys went off into the weeds. Ok all I'm asking is that say you're milling a .125" hole, or maybe some weird size where you can't just run a reamer through the hole so you have to bore it out with an endmill, or its too small for boring head. And you have a close tolerance to hit, whatever say it's a press fit and it needs to be +- .0002". If, when checking with a gauge pin from a set with .0001 increments, a .1248 only goes maybe halfway into the hole depth its milling to, indicating a taper in said hole, and when you comp the tool on the cnc machine still get an equivalent taper, what are some good tricks to mill straighter holes.

    Sent from my SM-G950U using Tapatalk

  20. #20
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    Re: Tips for straighter bores

    JS......I think you missed the part where I said......You cannot enter a 20mm diam hole with a 20mm diam pin.....that is a press fit or as we commonly say a size for size press fit.

    Go back and read the thread and see where the go-no go gauge application applies.

    LOL....and you want to "bore" a .125" diam hole with an end mill....by helical interpolation....LOL...... to a +- .0002" tolerance????….you will get an odd ball size for sure.

    Your eventual question regarding "good tricks" to make good holes...…...there are no good tricks...….you need skill and experience to make good holes......good machinery also helps.

    A hole that is not a standard size and is relatively small in diam would have to be bored with a boring head or a specially ground undersize reamer....or perhaps an adjustable reamer, but hitting the +- .0002" tolerance would be very tricky to say the least.

    BTW.....if the job volume is not sufficient to cover the cost involved in getting a hole to such a tight limit....give it away and move onto more profitable work.....you have to know when to fold them, know when to hold them and know when to walk away etc etc.
    Ian.

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