End mill Accuracy
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    Default End mill Accuracy

    If I pilot drill a hole and slow (low RPM)plunge cut with a .750 four flute new end mill on a tight Bridgeport, what diameter can I expect?

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    Hard to say as mounted runout turns one tooth into a "proud" boring bar tip.
    As ground diameter will most always be below nominal. But you then chuck it with some off center, maybe microns, maybe many thous.

    Would be interesting to see what others have gotten and if any surprises or maybe changes between hole number one and hole number 10.
    Bib

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    Likely .7502 to .751 with a very good running/best spindle and holder to perhaps .770 with having .010 run out in the holding device or spindle error of the end mill.
    End mills are sharp at the OD and so cut to the sides..Having a corner bevel or radius can help size, also a little wear land at the corner can help size.
    A drill or/and reamer have an OD circle land and so cut much closer.

    A two flute drill with a pre-drill hole will often cut + .0002 to + .0003 to micrometer size much like a reamer.

    Reamers often cut + .0002 so that is figured in when making them. They can get a little tighter with a small wear land and the then start to get looser.

    Drills and reamers can be shortened to make them cut smaller ..end mills are straight sided so shortening them does not change their size.

    Reamers can some times size about 25 millionths closer if back ground.. that is finishing the OD grinding with the flute heal hitting first.

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    Other then saying it will likely be oversize, this question is not really answerable without testing on the OP's setup. Part of that is because of manufacturing tolerances on HSS end mills, which can get pretty broad. Honestly without testing and then testing again should a new end mill be needed during a run, all answers are guesses. Runout or not. I suppose I could answer the question with... you can expect a broad range of sizes, so testing is in order if you're after a certain number. If you're not after a particular number then just do it and don't worry about it.

    Dave

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    Quote Originally Posted by GZ3S36 View Post
    If I pilot drill a hole and slow (low RPM)plunge cut with a .750 four flute new end mill on a tight Bridgeport, what diameter can I expect?
    .
    normally wouldnt plunge deep with no pilot hole. bridgeport tends to shake and or vibrates easily. as hole gets deeper the hole will steady end mill shaking so its often bellmouthed 1st 0.1" depth with steel. with aluminum maybe 0.2" depth cause its softer
    .
    collet holder normally runout .001 or less so should be .752 or less. end mills often .7495 to .7500 they are not made like reamers often and often get tapered wear or smaller dia at the end. occasional might get .7495 hole where .7500 plug gage wont get in all the way
    .
    if you make 11/16" pilot hole and then use .750 end mill it normally gives a better and tighter hole

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    Quote Originally Posted by GZ3S36 View Post
    If I pilot drill a hole and slow (low RPM)plunge cut with a .750 four flute new end mill on a tight Bridgeport, what diameter can I expect?
    Depends how far out of tram the head is, how deep the hole is and the length of cut of the end mill.

    Bill

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    Would head tram matter?
    If you wanted the hole or other plunge cut on 41 by 33.2 degrees and the head was tilted and nodded would it influence size of the hole?
    For sure in such case if you move the knee at all you are a dead man and exit location cares a whole bunch about this alignment or tram.
    Seems to me that the quill becomes the boring tool axis.
    Puzzled by this and perhaps not getting the picture straight in my head. (Freely admit that I am easily confused and often proven wrong in thinking on this stuff)

    If done with the quill how does tram or off angle change size or form with this operation?
    I see controlling runout at the tip and the full depth as the real killers here. Most do not indicate such tools in two places on the length even in very big dollar machines and all those fancy ass presetters.

    IMO, here it is a boring bar with a very long cutting edge. He who stands proud wins.
    That maybe the front, the tail or somewhere in between.

    One thing for sure it is not reliable or repeatable. It works and I think many of us have done it. It is one one of these get lucky things.
    Hell yes I've done it and would not dish anyone else for trying.
    Sometimes it goes to poop but that is the deal in this world, sometimes you get shit on for trying things, other times are simply like gold.

    In the world of mega buck gauges this process makes very decent hole/cylinder but you have no control over size dia.
    There is a whole another deal if you should stop the spindle at depth and pull out or bring it back up at a slow feed speed or rapid. Many disagreements lie there.

    Welcome to the world of making holes.... It should be so easy and simple.
    WTF. I just want to punch a simple round hole in a piece of whatever....and then all this added bullshit comes along to worry you.
    Bob

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    Being stupid. I should not have replied to the thread.

    Bill

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    C'mon Bob!

    Would it effect the diameter? Theoretically, No, but aren't you just being difficult?

    Plus the answer is theoretically, No. Really, I think the weight of the out of tram head would cause major problems with the Diameter, especially using a 3/4" Endmill.

    R

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    Quote Originally Posted by Bill in PA View Post
    Being stupid. I should not have replied to the thread.
    Bill
    There is no stupid or any disrespect here as we all think things others may think elsewhere.
    I just asked. Do not take this as any sort of insult and I hope you do not view it as such.
    Sorry if I came off harsh in a response, I do that sometimes but often wish I had not.
    Do not let me or another any other such pissy ass know it all posts limit any of your input.
    Speak free and as you see it, that is the whole deal here.
    The more input we have the more we learn and I do have so much to learn.

    I did not mean to step on you in any shape or form and do publicly apologize if I crossed you in not a nice way.
    I am an ass, poking so much and others. Do not respect me if I have insulted you.
    Bob

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    Yeah it's easy to make a quick response without thinking that doesn't make sense when you read it later, especially in the morning. I've done it more than a few times, we all have.

    Use a rough drilled hole as close to the size of the endmill as you've got and keep the feed pressure with the endmill light too, that will help prevent the "lead" tooth (the one on the high side of the runout) from pulling further off center and making the hole larger. It is absolitely a good idea to slap an indicator on the endmill and check that run out isn't excessive before even trying this.

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    Another thing to consider likely is if the holder has .0003 run out, the spindle bore or taper another .0003 so depending or the 180* you place it in you will have zero at one 180, and at the other 180 likely .0006 to.001 because of the stick out increase...That on a near perfect machine and holder.

    Still if you indicate the end mill to zero run-out it might cut .7502 to ,7053.

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    on size in balsa wood. possibly slightly larger in Inconel. or smaller when you get to the bottom of the Inconel and the mill is mostly gone. use of coolant will affect both situations. good luck.

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    Thank you all for the responses. Guess I'll bore it. It just seemed like I might have got lucky. The sized hole called out is .751 +0.001/-0.000. I would have probably jig bored or jig ground if I was at my old shop. I'll be lucky if I can bore it to that spec.

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    Quote Originally Posted by GZ3S36 View Post
    Thank you all for the responses. Guess I'll bore it. It just seemed like I might have got lucky. The sized hole called out is .751 +0.001/-0.000. I would have probably jig bored or jig ground if I was at my old shop. I'll be lucky if I can bore it to that spec.
    You're welcome... but a little FYI for future reference. You've really wasted a lot of people's time and efforts in this post by stating here well after the fact that you had a plus one tolerance on your hole. For all practical purposes that tolerance makes your initial or original post irrelevant. Meaning something like you were after wouldn't even be considered in this situation so why ask?

    Get smart. State you case precisely form the beginning. This is a precise business we're all in. Generalities spoken around one thou tolerances are practically meaningless.

    Dave

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    Quote Originally Posted by 13engines View Post
    You're welcome... but a little FYI for future reference. You've really wasted a lot of people's time and efforts in this post by stating here well after the fact that you had a plus one tolerance on your hole. For all practical purposes that tolerance makes your initial or original post irrelevant. Meaning something like you were after wouldn't even be considered in this situation so why ask?

    Get smart. State you case precisely form the beginning. This is a precise business we're all in. Generalities spoken around one thou tolerances are practically meaningless.

    Dave
    Sorry you feel that way Dave. I don't think I wasted anyone's time. I got a lot of valuable information from this post that I can use in the future. The tolerance of the hole was irrelevant. My original question was "If I pilot drill a hole and slow (low RPM)plunge cut with a .750 four flute new end mill on a tight Bridgeport, what diameter can I expect? ". I was wanting that knowledge to use in the future not just for a single job. Thanks everyone. I learned some things.

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    Quote Originally Posted by GZ3S36 View Post
    Sorry you feel that way Dave. I don't think I wasted anyone's time. I got a lot of valuable information from this post that I can use in the future. The tolerance of the hole was irrelevant. My original question was "If I pilot drill a hole and slow (low RPM)plunge cut with a .750 four flute new end mill on a tight Bridgeport, what diameter can I expect? ". I was wanting that knowledge to use in the future not just for a single job. Thanks everyone. I learned some things.


    Well all that said... you could have done the "job" and figured it out for yourself in the same time as posting the question here... If fit was production or such and you wanted to know, different story I suppose...

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    Quote Originally Posted by GZ3S36 View Post
    Sorry you feel that way Dave. I don't think I wasted anyone's time. I got a lot of valuable information from this post that I can use in the future. The tolerance of the hole was irrelevant. My original question was "If I pilot drill a hole and slow (low RPM)plunge cut with a .750 four flute new end mill on a tight Bridgeport, what diameter can I expect? ". I was wanting that knowledge to use in the future not just for a single job. Thanks everyone. I learned some things.
    .
    reliability is the problem. sometimes you get a big or small hole randomly that cause big problems.
    .
    new or resharpened endmills sometimes have a taper that is the dia on end or bottom of hole might be smaller than beginning of hole. this in addition to runout and vibration giving a bellmouth hole that is hole bigger when end mill first starts and after in hole deeper the hole itself steady's it a bit. thats why reamers often are chucked sticking out alot to allow more easy flexing of tool so when deeper in hole it will ream a tighter hole. its the first 0.1" in depth where hole often the biggest. i have often seen beginning of hole .001" to .003" oversize


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