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IndustryArena Forum > MetalWorking > MetalWork Discussion > Help...Issues with perpendicularity of 8mm hole.
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houghtont0520 Help...Issues with... 04-05-2015, 02:43 AM
Superman Re: Help...Issues with... 04-05-2015, 03:11 AM
houghtont0520 Re: Help...Issues with... 04-05-2015, 03:37 AM
Superman Re: Help...Issues with... 04-06-2015, 12:17 AM
houghtont0520 Re: Help...Issues with... 04-08-2015, 03:26 AM
mactec54 Re: Help...Issues with... 04-05-2015, 04:10 AM
rcs60 Re: Help...Issues with... 04-05-2015, 05:16 PM
  1. #1
    Join Date
    Dec 2012
    Posts
    10

    Help...Issues with perpendicularity of 8mm hole.

    Among the many issues that I have been having with this particular part another one just popped up. Here are some details, this particular part is cast aluminum. The hole I am now having problems with is a 3 inch long 8mm hole that goes through 1 inch of material, then 1 inch of a cored out area, and back into another inch of material. The hole must be perpendicular to datum A within 0.002in. I am using a solid carbide accupro drll with 150 drill point and going straight through no pecking. I then follow with a spiral flute reamer with 3 inches of flute length. Also, even though the CMM reports that the hole is out of tolerance, about 0.003, I am still able to pass a very tight slip fit pin all the way through. Please provide input...

  2. #2
    Join Date
    Dec 2008
    Posts
    3216

    Re: Help...Issues with perpendicularity of 8mm hole.

    I'd say the A datum face was machined in the same setup as when the hole was machined ??

    Don't assume that the CMM is always right. Many, many times it was a CMM operator error ( either not calibrating correctly, or bad data input to give an erroneous report )
    - many aerospace part that I had made were rejected by the CMM, but all features were either machined in one setup, or tolerances allowed a little leeway when doing the last ( ie facing excess material only )

    - have the CMM prove the part incorrect, by doing a re-calibration of all probes ( at all the used angles ) BEFORE probing the part.
    - have the CMM do circles at the top & bottom to find which is out ( both at the same probe angle. (minimise a probe calibration error ) )....it may also point to "why" & "who" is wrong

    - also by using manual methods to show the part is correct to prove the CMM may be in error. ( It can go the other way, to highlight an error on your part )

    It can be on your side, as a drill normally makes it's own path (yes, a CDB drill would make the hole more true....and a reamer does follow a previous hole ). But this also assumes that Z slide is perpendicular to X & Y slides.

  3. #3
    Join Date
    Dec 2012
    Posts
    10

    Re: Help...Issues with perpendicularity of 8mm hole.

    Yes datum A, which is actually a line between two dowel holes in this case, is done in the same setup as the reamed hole. In fact I have the process such that all critical related features are done after everything else and the part is fixtured in such a way that no clamping pressure can distort it.

    Just a thought since you have done aerospace stuff, would it make seance to drill, bore to size through only one wall, and then ream with the hope that the nice true bore will lead the ream correctly into the next hole.

    How would one go about checking if the Z slide is perpendicular to the X and Y?

    Also, thanks much for your input.

  4. #4
    Join Date
    Dec 2008
    Posts
    3216

    Re: Help...Issues with perpendicularity of 8mm hole.

    Quote Originally Posted by houghtont0520 View Post
    Yes datum A, which is actually a line between two dowel holes in this case, is done in the same setup as the reamed hole. In fact I have the process such that all critical related features are done after everything else and the part is fixtured in such a way that no clamping pressure can distort it.

    Just a thought since you have done aerospace stuff, would it make seance to drill, bore to size through only one wall, and then ream with the hope that the nice true bore will lead the ream correctly into the next hole.

    How would one go about checking if the Z slide is perpendicular to the X and Y?
    What m/c are you using ?

    So if datum A is a line (2D feature), when are the other datums done ? ( you need more datums, as the CMM is giving a report back on a cylinder ( a 3D feature) )

    My suggestion ( everyone else has had a go ),
    seeing that a CBD drill is quite stiff, but the tip angle is very wide (150°...not far off from being a slotdrill), It should be around Ø7.6mm

    - spotdrill
    - drill thru one wall, by pecking ( to try to have the tool NOT make it's own path )
    - long shank c'drill, spot other wall ( yes, you may have to make/modify/whatever ) ( other face is cast, it could deflect )
    - start 2nd wall slow, increase feed when drill is fully engaged
    - interpolate top of hole (1st wall) to Ø7.9/7.8 using 3/16" endmill going to 0.2" deep ( you might get away using a 5/16" slotdrill plunging 0.2 deep ) ( no need to bore full distance)
    This op give a true position for the reamer to start ( the 1" gap is not a problem, it is the start of the hole - if it isn't true here, it'll never be true )
    - ream thru


    I did a helio part, it had been installed, but it didn't work properly and had to be pulled out ( big a$$ kick went down the line ) ( CMM inspected as OK , didn't check that "lower" hole....murphy's law )
    - found that a 5.5mm hole going thru (2x) 3mm walls ( 45mm gap ) was deflected by a large fillet (either side of the 45 gap) , the drill didn't touch the edge of that fillet by much, but it was enough
    - solution was to spot the 2nd wall ( using customised c'drill ( my next batch were (need I say) "perfect" )


    Checking a machine's slides
    - using decent quality square ( or 4"- 6" ground cylinder ) sitting on table
    - indicate up/down the cylinder at the 3 o'clock position ( for X error ), & the 12 o'clock ( Y error)
    - an indicator in the spindle onto the table is "tramming" , but you NEED the Z axis to move to do the check

    X & Y error should be ZERO, ( or that bloody close)

  5. #5
    Join Date
    Dec 2012
    Posts
    10

    Re: Help...Issues with perpendicularity of 8mm hole.

    Thanks, Superman for your suggestions. Anyway, I ended up just drilling the hole and truing it with a 1/4 endmill before reaming it. This did the trick...On to the next problem.

  6. #6
    Join Date
    Jan 2005
    Posts
    15362

    Re: Help...Issues with perpendicularity of 8mm hole.

    houghtont0520

    The reamer will just follow the drilled hole, the Drill will easily wander over 3", if you want it .002 or better true position, you would Drill, Bore, & then Ream
    Mactec54

  7. #7
    Join Date
    Feb 2011
    Posts
    353

    Re: Help...Issues with perpendicularity of 8mm hole.

    one other thing to try is after drilling the 1st half of the hole and to create a flat area on the second half of the hole and spot it, drill and ream

    drilling boring then reaming would be the most accurate

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