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  1. #1
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    Boring head confusion!

    Here's the scenario:
    - Milled out a hole. Want to make it larger, so I thought I'd use the boring head for practice (but also because I don't have a jobber drill bit in the size I need).
    - Removed the end mill & collet.
    - Inserted the boring head arbor, then screwed on the head.
    - Did NOT move the table at any time.
    - Tried to adjust the head so that the bar just starts touching the inside top of the hole, but can't get it to touch all the way around!?!

    It's like the hole or the head is out of round? Or the table moved (but it hasn't because I reinstalled the collet & end mill and they still line up).

    Shouldn't the boring head line up with the hole? Why does it appear that I need to move the table to center the boring head with the hole? What am I missing?

    tom

  2. #2
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    Did you have cutter comp on? "Zero" when a tool touches an edge, isn't zero of the column.

  3. #3
    Monkeywrench Technician
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    It is very easy and common (depending on your drilling practice) for drilled holes to be off center and/or out of round.
    Are you talking .005 or .080 off?
    www.integratedmechanical.ca

  4. #4
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    @MrWild: Forgot to mention that this is manual milling. I'm actually milling the parts to convert it to CNC (X2).

    @DareBee: Closer to .005.

    So do I assume it's my (newbie) technique or end mill and further assume that the boring head is positioned correctly?

    What can cause off-center or out-of-round holes?

    thanks.

    tom

  5. #5
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    how you started your hole. If you just drilled without locating the hole with a center drill, the drilling drill can walk the drill point that far before digging in. Once started, the drill follows the hole path. As I wrote that, two things popped into my head. If the deviance is front to back, the column may have flexed from the stress of the drilling forces. If it's out side to side or a combo of both, it could be you need to tram the head.

    Newbees don't realize they need to tune up the mill before they start cutting. Not a problem though, just a bit of experience will fix that. If I were doing a X2, the first thing I'd add is a back support. Are you doing an X2 Freak? Lots of good info in Hoss's threads, and he has a sale at the moment on all the mods in one CD for Zoners.

  6. #6
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    Are you doing this in a vertical mill like a Bridgebort? If yes - did you move your knee down to get more room for your boring head? If yes- you may want two check the alignment of your head and tram it again.

  7. #7
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    Quote Originally Posted by MrWild View Post
    how you started your hole. If you just drilled without locating the hole with a center drill, the drilling drill can walk the drill point that far before digging in. Once started, the drill follows the hole path. As I wrote that, two things popped into my head. If the deviance is front to back, the column may have flexed from the stress of the drilling forces. If it's out side to side or a combo of both, it could be you need to tram the head.

    Newbees don't realize they need to tune up the mill before they start cutting. Not a problem though, just a bit of experience will fix that. If I were doing a X2, the first thing I'd add is a back support. Are you doing an X2 Freak? Lots of good info in Hoss's threads, and he has a sale at the moment on all the mods in one CD for Zoners.
    I did use a center drill. Checked it again just now and it looks like it's off < .015 in the X axis. Y looks okay.

    I definitely need to tune it up. I thought I'd do that while I was installing Hoss's CNC conversion (which is what I'm milling right now). All his parts are pretty non-critical, so I think I'm okay.

    And back support is on the list. I just gotta figure out which solution I like best.
    Quote Originally Posted by juergenwt View Post
    Are you doing this in a vertical mill like a Bridgebort? If yes - did you move your knee down to get more room for your boring head? If yes- you may want two check the alignment of your head and tram it again.
    It's a table-top mill from Harbor Freight. Got ahead of myself and haven't trammed, shimmed, etc, anything.

    Thanks for the help. Looks like a tune-up is in order.

    tom

  8. #8
    Monkeywrench Technician
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    Back to the drilling thing.
    Correct sharpening of a drill bit is critical to its proper function (oversize, wondering, etc).
    You did use a center drill which typically will get a drill started in the correct location.
    www.integratedmechanical.ca

  9. #9
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    If I can get away with drilling a hole rather than boring a hole I will drill it every time. This is off topic of your question, and practice is always good, but I would go and get a jobber, and forget about the boring head, and drill it if gets you in print.

  10. #10
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    Quote Originally Posted by tooManyHobbies View Post
    I did use a center drill. Checked it again just now and it looks like it's off < .015 in the X axis. Y looks okay...tom
    Being off in X but not in Y is diagnostic for the head out of tram; correct this before boring the hole ecause if you do not your hole will not be perpendicular to the top of the work.
    An open mind is a virtue...so long as all the common sense has not leaked out.

  11. #11
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    Quote Originally Posted by Geof View Post
    Being off in X but not in Y is diagnostic for the head out of tram; correct this before boring the hole ecause if you do not your hole will not be perpendicular to the top of the work.
    What Geof said.

    You mentioned you never trammed the mill. So here's the deal:

    When you're out of tram, the column is not perpendicular to the table travel. As you move the head up and down the column, it's moving on a diagonal, which changes the X.

    So, very likely your boring head is at a different head height than the twist drill. There's your issue. Tram right away!

    The hole, BTW, is not straight down. I'd be tempted to tram, center up on the hole again, redrill, and then get on with boring.

    Cheers,

    BW
    Try G-Wizard Machinist's Calculator for free:
    http://www.cnccookbook.com/CCGWizard.html

  12. #12
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    Okay guys I'm having the exact same problem. Now I am trying to make a pinion gear adapter. 10mm od cylinder 15mm tall with a .1245 center hole.

    Now my machine (x2, manual, solid column) its trammed to no greater than .0003 an ill shoot for .0001 on very percise things. I am very meticulous about checking before every operation and a stickler in getting things dead nuts.

    So this piece started as 1/2 bar stock mild steel. I trammed the upright of this bar to the column. Used a center drill bit 5mm down then a jobber to depth of 20mm. Reamed to .1245.( I did not drill dead center of bar due to using my boring head for od) Machine is locked during all of this. Threw boring head on to cut outside diam. Once I got to about 14mm I noticed my boring head is cutting about 1mm diag. +xy. I'm so lost center of boring head should be center to column right? If nothing ever moved I even checked with center finder once noticed this how is this od off from I'd???

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