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IndustryArena Forum > MetalWorking Machines > Tormach Personal CNC Mill > Lost drill hole size accuracy in drilling operations
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  1. #13
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    1349

    Re: Lost drill hole size accuracy in drilling operations

    BUMP the main point was that for precision holes I don't rely on drilling but use the boring head and single point bore the hole.

    Don

  2. #14
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    1653

    Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by popspipes View Post
    If the surface is dead flat, and using a web thinned drill, or preferably a screw machine drill no need to spot drill.
    Correct and its only 6mm hole size and he has done it for months without issues! This is a production line thing, not one off. Something has changed.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router

  3. #15
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    Re: Lost drill hole size accuracy in drilling operations

    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

  4. #16
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    Re: Lost drill hole size accuracy in drilling operations

    One more thing, have you verified that the material you are cutting today is the same as the material you were cutting last time? A lot of alloys look the same but behave very differently when it comes to machining.

    Chris D.

  5. #17
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    1458

    Re: Lost drill hole size accuracy in drilling operations

    What is the red layer in the middle of your floating reamer holder?

  6. #18
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    Re: Lost drill hole size accuracy in drilling operations

    Red layer in the middle of the holder? Sorry don't understand what do you mean by that.
    EDIT: I see now, interesting build.

  7. #19
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    Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by Chris D View Post
    One more thing, have you verified that the material you are cutting today is the same as the material you were cutting last time? A lot of alloys look the same but behave very differently when it comes to machining.

    Chris D.
    Hi Chris,
    I've tried after that drilling on the same aluminum material that I have perfect holes with the same speeds and feeds but couldn't repeat that result.

  8. #20
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    Re: Lost drill hole size accuracy in drilling operations

    Quote Originally Posted by Steve Seebold View Post
    What material are you drilling? What are your feeds and speeds? What is your peck depth? Did you change the brand of drill you are using?
    The material is S235JR (calibrated steel sheet), Feeds and speeds (for the drilling operation): 760 RPM, surface speed 14.3 m/min, plunge feed rate 20 mm/min, pecking depth 1.5mm.
    I've also tried without pecking since the depth of the hole is 6mm. It was no difference though.
    Haven't change the brand of the drill bit.

  9. #21
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    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.

  10. #22
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    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!

  11. #23
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    Jun 2014
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    1488

    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

  12. #24
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    1349

    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

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