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Thread: Oval Drill holes

  1. #1
    Join Date
    Feb 2007
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    Default Oval Drill holes

    I know there has been some discussion on this topic, and I have read it, but I believe my problem might be a little different.

    I tried 1/8" drill-holes, using the 1/8" cutting bit to various depths. I observed the so-called "Wood-Pecker dance", used by the CW unit when drill depths are greater than some threshold, presumably to clear dust. Between attacks of the cutting bit, the traction belt moves back and forth. I was assuming this was an accuracy-improving maneuver on the off chance that drilling shifts things a bit (I'm only guessing and giving the unit the benefit of the doubt). Common sense says it should have to move, but there you go. So, in the end, my drill-holes were oval shaped, with a major axis at a consistent angle to the y-axis (about 30-45 degrees). Even on the first attack, which sinks to a depth of about 1/8", I'm pretty sure the oval pattern was already established, so I DON'T think the traction-shifting caused the problem (although the fatness of my 1/4" drill holes MIGHT be due to this behavior).

    One explanation for this behavior might simply be that my Quick-Release chuck might be bent relative to the z-truck. Could have happened during an unpleasant discussion I had with the machine over a stuck bit. If the bit itself were bent, you would expect the whole bit to move in a conical motion (they call it "play-out", no?). It would produce oversized holes as opposed to oval ones. But if the whole chuck were at a small angle, the bit would spin straight within the chuck and the z-truck would lower for the drill attack, but the slight angle would produce an oval hole in the direction of the bend as the entire cutting bit hit the wood slightly "sideways". Just one theorey.

    On the minus side for my theorey, a deeper hole would be more oval than a shallow one. I did a 1/4" depth hole and it it wasn't noticably more oval-shaped than a .8" hole. Could just be my eyes.

    So if my "bent-chuck" theorey is correct, is there anything I could do about it? Maybe remove and re-place the chuck? Is there a screw adjustment somewhere to "right" things up between the z-truck and the actual chuck-bit linkage?

    Let's assume my "bent-chuck" theorey is bogus (what are the odds?). Is there a common, well-understood reason for oval drill-holes that I'm overlooking? Will "calibrating" the machine address this issue? I finally have a 3/8" double-flute, straight routing bit with a flat head, 1/2" shaft and 1 1/4" depth (don't think THAT didn't take some hunting down). If I calibrate, what are the measurement characteristics that should improve?

    Any thoughts?
    Cycollins

  2. #2
    Join Date
    Mar 2007
    Location
    Ohio
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    1,109

    Default Oval Holes

    Cycollins,

    I have been in the CNC field for 26 years, doing pretty much everything from A-Z.. including precision machine alignment.

    If your machine chuck is bent, and running out it would simply give an oversized hole. It duplicates a boring bar, and cuts on the flute of the tool that is positioned furthest from center. But it does give you a fairly straight hole.

    If the bearings are loose in the spindle, it is possible it would be a tapered hole that would look slightly like a cone. Fairly round at the top, but bigger, then getting smaller as it gets to the bottom. It does this due to the bit finding center as it gets deeper, and starts guiding itself and centers up.

    If the "Z" axis is out of alignment by the truck guides, it would produce a round hole that looks like an oval at the top, but is truly a round hole that is put in on an angle. You could check this by taking a drill bit that fits the hole and see if it wobbles in one direction or if it fits snug top to bottom of the hole but is on an angle when left in the wood.

    If the spindle is out of alignment but the "Z" guides are straight it would give you a hole that is oval at the top but more round at the bottom. Depending on the direction it is loose at the top, would tell you which way the spindle is out of alignment to the guides.

    Now with all that said, you mentioned that you think the traction belt is moving as it is pecking the bit in. That sounds very abnormal if it is, and it could duplicate the spindle out of alignment condition above. I would watch your traction belts very very closely to see if they are moving, and if not also watch the rubber cog belt inside the machine "Y" axis track to verifiy that it isnt moving either. If they are i would definately contact CW....

    Hope this is helpful... if i can clarify anything let me know !!!


    Ron
    To order the "Made in USA" Rock Chuck, and other custom tools and accessories I make for your CarveWright, see my website by clicking here -> http://www.cw-parts.com
    See a quick video of the new Rock Chuck in action here!
    Read up on QC Removal for stubborn chucks here
    See the Rock install video here
    You can also visit here for discussion content.
    Email me by clicking here

  3. #3
    Join Date
    Jan 2007
    Location
    NE PA USA
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    Default Oval in length or width?

    I have good luck making holes .175 thick for the LED's to light my signs. I was wondering if you get the oval problem every time every hole or just once in a while? If the brass roller is not making contact with every movement of the board then that could cause the oval holes. Is the oval in the length direction or the width direction? Length = brass roller problem, Width = loose drive belt on the left right.

    This is what I use the drill function for. Solar 911 signs.

    AL
    Last edited by Digitalwoodshop; 07-01-2007 at 08:55 PM.

  4. #4

    Default

    Oval holes can also be caused by gear slop in the x axis gears.
    The 50-50-90 rule: Anytime you have a 50-50 chance of getting something right, there's a 90% probability you'll get it wrong.

    Do it on a Mac.
    Vietnam Vet '65-'66

  5. #5
    Join Date
    Feb 2007
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    Palo Alto, CA
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    Default OK, so how to fix?

    I appreciate all your feedback. Starting from first to last, rjustice, my terminology may be lacking, but I think what I was suggesting was your spindle-out-of-alignment case. I was suggesting that the Quick-Release chuck which represents the spindle in the case of the CW, was out of alignment on the z-truck. However, now that you mention the entire z-truck being out of alignment, I actually did the test you suggested. I was drilling the hole to run a dowel through the wood and sure enough, the dowel was not perpendicular to the surface of the wood (by an amount that was obvious to the naked eye). I guess I'm now leaning toward your out-of-alignment-z-truck theorey. So, am I screwed? (No pun intended.) Is righting the z-truck a home-repair adjustment or is it a (gasp) send-it-to-texas kind of thing? Is it the kind of thing that the calibration will address? I'm doing two-sided projects, so having a perpendicular spindle is key to getting the registration right between the front and back.

    DigitalWoodshop, rockin' projects. My ovals are neither width or length-wise ovals. They are literally at something like 30-45 degree angle to the y-axis. Wierd, huh?

    Pkunk, same question to you as to rjustice: which of the maintenance procedures that have been discussed will help with "gear slop in the x-axis gears"? Home repair or back-to-texas?

    cycollins

  6. #6
    Join Date
    Mar 2007
    Location
    Ohio
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    Default Alignment

    Cy,

    I personally havent had to get into alignment on the machine yet. It probably isnt that difficult. As you stated earlier when getting rough with it to get a bit out of your stuck chuck you could have possibly knocked it out. I seriously doubt that it is out anywhere near 30 degrees. I would bet that it looks alot worse than it is.

    I would contact CW and ask them for a PDF on alignment proceedures. If you get it, it would be nice to post on here.

    Also, you asked about calibration. I would consider calibration a different animal than alignment. Calibration would allow you to fix something like in designer you have a carve region that measures 4" square, and when you cut it you actually get a cut that measures 3.9 x 4.1 I believe that you can tweek the machine in to get your true 4 x 4.

    Someone that has run the calibration routine please chime in on that ....

    Ron
    To order the "Made in USA" Rock Chuck, and other custom tools and accessories I make for your CarveWright, see my website by clicking here -> http://www.cw-parts.com
    See a quick video of the new Rock Chuck in action here!
    Read up on QC Removal for stubborn chucks here
    See the Rock install video here
    You can also visit here for discussion content.
    Email me by clicking here

  7. #7

    Default

    Quote Originally Posted by cycollins View Post

    Pkunk, same question to you as to rjustice: which of the maintenance procedures that have been discussed will help with "gear slop in the x-axis gears"? Home repair or back-to-texas?

    cycollins
    It does sound like you have other issues, but gear slop is easy to fix from under the right hand panel.
    The 50-50-90 rule: Anytime you have a 50-50 chance of getting something right, there's a 90% probability you'll get it wrong.

    Do it on a Mac.
    Vietnam Vet '65-'66

  8. #8
    Join Date
    Mar 2007
    Location
    Ohio
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    1,109

    Default

    Quote Originally Posted by cycollins View Post
    My ovals are neither width or length-wise ovals. They are literally at something like 30-45 degree angle to the y-axis. Wierd, huh?

    cycollins
    if you put the dowel through the hole is it snug from the face of the board and the back of the board?

    Also, did you carefully watch to see if either the sandpaper is moving or the "Y" axis belt is moving during the pecking cycle?

    Ron
    Last edited by rjustice; 05-02-2007 at 10:11 AM.
    To order the "Made in USA" Rock Chuck, and other custom tools and accessories I make for your CarveWright, see my website by clicking here -> http://www.cw-parts.com
    See a quick video of the new Rock Chuck in action here!
    Read up on QC Removal for stubborn chucks here
    See the Rock install video here
    You can also visit here for discussion content.
    Email me by clicking here

  9. #9
    Join Date
    Feb 2007
    Location
    Palo Alto, CA
    Posts
    110

    Default Just to be clear

    ...the 30 degrees was in reference to the major axis of the oval with respect to the x-axis when one view the board from on top. Here's a picture to elaborate (the holes highlighted in red are 1/4" deep, the blue lines indicate the approximate orientation). There's also a picture showing a 1/8" brass dowel passing through a completely penetrating hole, taken up against some floor tiles for reference. Finally here are two pictures indicating how far a brass dowel can slop to the left and right in a 1/4" depth hole. All of the holes are nominally 1/8", cut with the 1/8" cutting bit.
    Attached Thumbnails Attached Thumbnails sloppy_holes.jpg   slop_left.jpg   slop_right.jpg   alignment.jpg  


  10. #10
    Join Date
    Mar 2007
    Location
    Ohio
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    1,109

    Default oval shaped holes

    Cy,

    Ok your pictures really helped. But, not necessarily in a good way. The fact that the holes are leaning in random directions like this takes alot of the concern of alignment out of the picture. If it was simply out of alignment in a direction, they would repeat and all be leaning the same way.

    Did you watch the traction belt or the "Y" axis cog belt to see if they are moving yet?... If they are moving while it is pecking the hole in, Pkunk could be on to something with the gear issue. It would allow the workpiece to "float" around.

    If no, i would be interested in trying the same tests on a piece of MDF. This would tell us if perhaps just the hard spots in the grain of the wood is influencing the bit to lead or wander off. It has been mentioned that the cutter diameter to length ratio on the 1/8" bit is a little long, perhaps the bit just doesnt have enough rigidity to stay straight, and starts wandering

    The other thing would be to grab the "Z" truck, and see if it has play in any direction. My thoughts here would be that if it is loose, it is just finding a happy spot once the bit hits the wood, and stays there till the next hole...

    This is an interesting problem to say the least...

    Ron
    To order the "Made in USA" Rock Chuck, and other custom tools and accessories I make for your CarveWright, see my website by clicking here -> http://www.cw-parts.com
    See a quick video of the new Rock Chuck in action here!
    Read up on QC Removal for stubborn chucks here
    See the Rock install video here
    You can also visit here for discussion content.
    Email me by clicking here

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