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Thread: Lost drill hole size accuracy in drilling operations

  1. #21
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    Default Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by mactec54 View Post
    It does not matter what the machine is CNC or a manual Drill Press a Spot drill is always needed unless the Drill bit is designed to be used without a Spot Drill, there are some quality Drills that are ground so a Spot Drill is not needed, I would say he got lucky with his hole sizes before, a drill Bit unless you know how to grind it can make any size hole you want, over size or on size

    Using the Drill Chuck that he has is never going to be very accurate, these drills are some of the best there are if he wants a quality drill Wedevag that will drill on size if his spindle and holder runout is very low and he would need to be using a Screw Machine Drill

    North Bay Cutting Tools

    Or Ebay https://www.ebay.com/itm/3906-25-64-...ss!37179!US!-1
    Sorry, forgot to mention that I'm using spot drill always.



  2. #22
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    Default Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by Chris D View Post
    I agree with the comments that something changed between when it was working and now. However, the original process, based on the small amount of details provided, is fundamentally wrong. Drilling a hole for a "slip fit" is not the proper process. Twist drills are not even made to an accurate enough diameter to do this consistently.

    The videos showing the indicating process really show us nothing. You have run-out, apparently more as you get further away from the spindle. Does the tool holder fit tight in the spindle? Have you put a shaft in the chuck that you know is straight and round and measured that to see if there is run out? Who sharpened the drill, factory or by hand on a bench grinder? It is very strange that a 6mm reamer is also cutting "Still too oversized ".

    I believe you are making a lot of assumptions and you are attempting to do precision machining operation yet you have no way to measure what you have with any level of accuracy. Using terms like "Way looser" doesn't mean much in the world of precision machining.

    I would suggest you do the following:

    Find a straight 6 mm shaft that you can chuck up with your various tool holders. Put an indicator on it like you have in the video and rotate the tool by hand so you can actually measure to a value as opposed to watching the indicator's needle wobble back and forth.

    Check to make sure that you can't deflect the tool holder by pushing/pulling on it sideways while you have the indicator on it.

    Assuming everything runs true and your spindle and tools holders are not messed up, review your speeds and feeds, have they been changed since it last worked?

    You mentioned that you have tried a new drill and the old drill both with bad results. You also stated that drilling undersized and reaming resulted in poor results. Did you check the size of the hole before the reamer performed its operation? The drill could have drilled oversize and you would believe that the reamer is the problem.

    Finally, getting back to the proper process.

    In order for a drill to cut on size, it cannot wander when starting the hole. Without a spot drill, the probability of the drill wandering is increased substantially. I would recommend spot drilling to help prevent wandering and the ill effects that will cause.

    The drill must be sharpened properly, if it is not, it will NOT cut on size or close to size. If the drill measures 6.1mm in diameter, do NOT expect it to drill a 6 mm hole. In all likelihood, a drill will cut bigger than it is. MEASURE THE DIAMETER OF YOUR TOOLS WITH A MICROMETER so you know what you are starting with. Common twist drills are NOT designed for making holes so close to size you can count on them to give you a "slip fit" every time. They are a roughing tool which is why Reamers are used!

    Reamers are ground to very tight tolerances and can be purchased for under/over size applications. They are designed to cut: straight, round, and accurately with regard to diameter.

    In my very humble opinion (based on a few decades of doing this) you should:

    Spot drill
    Drill the hole under size by about .3 mm
    Ream the hole with a 6.025 reamer

    Be sure to use tool holders that run true
    Be sure to use proper speeds and feeds for the materials you are cutting
    Be sure to use proper lubricant when cutting
    Don't expect the wrong tool or wrong process to perform magically all the time, sometimes luck happens though.

    Chris D
    Hi Chris, thank you for the reply.
    I'll test what you've suggested.

    Not sure if just got lucky because I've been making these drill holes for a slip fit with a 6mm pin. Actually for pins I'm using broken end mills.
    Figure out that they are perfect for my purpose.
    It is been done on several applications with at least 10 holes on each. That's why not sure if it is just luck.
    Drills are factory sharpened.

    I suspect that the drill chuck has run out or probably moved in the holder. Will try to take it out and to mount it again.
    Something that forgot to mention in the first post is that the spot drill is always used.

    Before using the reamer checked the size of the hole by trying to fit a pin in it and it didn't go.
    I'll check for deflection by pushing/pulling the tool holder.

    Thank you!



  3. #23
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    Default Re: Lost drill hole size accuracy in drilling operations

    Its hard to diagnose a problem when it cant be seen. I hope you post the results that fix the problem, would be helpful to all of us.

    mike sr


  4. #24
    Member Don Clement's Avatar
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    Default Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by kstrauss View Post
    What is the red layer in the middle of your floating reamer holder?
    Turcite X. https://www.boedeker.com/family/turcite

    Don



  5. #25
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    Default Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by Don Clement View Post
    GOOD design!



  6. #26
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    Default Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by popspipes View Post
    Its hard to diagnose a problem when it cant be seen. I hope you post the results that fix the problem, would be helpful to all of us.
    Sure, I'll get into this further and post back.



  7. #27
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    Default Re: Lost drill hole size accuracy in drilling operations

    I suspect the original batch of drill bits were slightly oversize as I wouldn't expect to be able to insert a 6mm pin in a hole produced by a 6mm drill bit and to expect a number of them to match perfectly on the same job is asking for very high standards of accuracy.A few moments with a micrometer and the original drill bits and pins might reveal a few things.Add in the possibility of wear in the drive mechanism and couplings and it gets even more demanding.If i had to do something similar I would expect to use a 6mm drill in a collet and not a chuck and I would follow up with a 6.1mm reamer.If it didn't fit it would be time to check the machine for backlash and wear.Somebody may come along with a sermon about GD&T for the part and they will very likely be correct.



  8. #28
    Member AUSTINMACHINING's Avatar
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    Default Re: Lost drill hole size accuracy in drilling operations

    Have you checked the tram recently ?. If its out, that's a recipe for an oversized hole. Keep the gauge length as short as possible.



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Lost drill hole size accuracy in drilling operations

Lost drill hole size accuracy in drilling operations