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Thread: Flipping material - GUY!

  1. #1
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    Flipping material - GUY!

    There's something simple that I'm missing here, but I just cannot see it.

    I have this part I'm cutting (see picture) which is two sided. I have two projects. The material is 10"x4.5" and the part is dead center in the material. The reverse side has the same part, dead center but flipped upside down. On my table I've got two reference edges with XY0 set to the very corner. I am stuffing the material into the corner and flipping the part end over end to cut the opposite side.

    Problem is, I'm ending up with a difference of about .180" from end to end, which scraps the part.

    There's something in the geometry of this part I'm missing, because to my eyes I should be able to simply flip the material and have a perfect cut.

    So, what am I missing? Why is there such a big offset? Help!
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  2. #2
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    Do you rezero your table before cutting each side?


    GC
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    Bob, Is there excess material on the piece that will be removed?

    When I do items that flip over, I drill a through hole at the start point.
    Then when flipping it over, I use the same hole for the starting point for the back side. This is not 100% perfect but for the job that I do it is sufficient.

    Another idea is that if it is off by the same amount, why not compensate for that when setting the starting position on the second side?
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  4. #4
    side to side it isn't aligned, or long wise? either way, you could try programming in a couple or 3 drilled holes that go through the part and into the spoilboard some ways. Then use a metal pin, wood dowel, drill bit shaft, etc to simply confirm or hold the part in the correct position when flipped.

  5. #5
    Any alignment error will be doubled when flipping it end-to-end.


  6. #6
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    Quote Originally Posted by Gene Crain View Post
    Do you rezero your table before cutting each side?
    I do not, because the 0 is in the same place for each side. The part is flipped and centered for side 2.


    Quote Originally Posted by Jim Beachler View Post
    Bob, Is there excess material on the piece that will be removed?

    When I do items that flip over, I drill a through hole at the start point.
    Then when flipping it over, I use the same hole for the starting point for the back side. This is not 100% perfect but for the job that I do it is sufficient.

    Another idea is that if it is off by the same amount, why not compensate for that when setting the starting position on the second side?
    There's a little excess, however, I can add more if necessary. I've done the hole drilling thing, using those tapped inserts (forget the name) in my spoilboard and a template to drill the holes in the material. The two-stop method I'm using seems to be the same method with a different approach, except I have to ensure the part is exactly the correct length. I did have some luck with the drilled method, so perhaps I should go back to it since it's also a good hold down method.


    Quote Originally Posted by Eric Mims View Post
    side to side it isn't aligned, or long wise? either way, you could try programming in a couple or 3 drilled holes that go through the part and into the spoilboard some ways. Then use a metal pin, wood dowel, drill bit shaft, etc to simply confirm or hold the part in the correct position when flipped.
    Long-wise. I've done something similar to this, and *thought* this method was just another way of doing the same thing, but it looks like I need to whip out some cheap wood and do more experimenting. Man, when I did Aerospace/Aircraft years ago, I was excellent at building jigs and templates... I must be getting senile.


    Quote Originally Posted by Harry Hagan View Post
    Any alignment error will be doubled when flipping it end-to-end.
    At first glance that made sense, but thinking about it, I'm not sure why. Wouldn't it double the error flipping it either way?
    CAMaster CR-408 Cobra X3

  7. #7
    Yes. Flipping it either way doubles alignment error. I just thought that would emphasize the necessity to be very precise on your setup and clue you in on why the error was so great.


  8. #8
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    Quote Originally Posted by Harry Hagan View Post
    Yes. Flipping it either way doubles alignment error. I just thought that would emphasize the necessity to be very precise on your setup and clue you in on why the error was so great.
    I've got a small pile of scrap wood that's emphasized this. I've done this before with better results, but was using the two screw method. I think I'll go back to this methodology, although it generates more wasted material per part. Then again, I should be aligned very closely with the method I'm using, as long as the length of the material is accurate and matches my setup in Aspire, so I'm at a loss for this one. But, what works, works, so I may change...
    CAMaster CR-408 Cobra X3

  9. #9
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    Bob,

    How are you measuring the length of the wood? Are you taking your tape measure and using that little hook and making a mark, or are you measuring starting at 1 inch and going out to 11 for a total of ten?

    The little hooks are never reliable for accurate work.

    Guy
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  10. #10
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    Quote Originally Posted by Guy Mathews View Post
    Bob,

    How are you measuring the length of the wood? Are you taking your tape measure and using that little hook and making a mark, or are you measuring starting at 1 inch and going out to 11 for a total of ten?

    The little hooks are never reliable for accurate work.

    Guy
    I was initially going from 1" to 11" but then switched to using a square that has a scale on it. I cut one piece at 10.125" by accident, adjusted the material size in the project, recentered, retoolpathed, and same results.

    Last night I thought my job xy0 may have been off but after moving my dust boot and taking another look, it was right on.

    This should be working, right?
    CAMaster CR-408 Cobra X3

  11. #11
    Quote Originally Posted by Bob Savage View Post
    I was initially going from 1" to 11" but then switched to using a square that has a scale on it. I cut one piece at 10.125" by accident, adjusted the material size in the project, recentered, retoolpathed, and same results.

    Last night I thought my job xy0 may have been off but after moving my dust boot and taking another look, it was right on.

    This should be working, right?
    I work from the center when setting up a project. The center of a file is always the center, regardless of the shape or size of the of the material.
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  12. #12
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    Quote Originally Posted by James Jaragosky View Post
    I work from the center when setting up a project. The center of a file is always the center, regardless of the shape or size of the of the material.
    Jim J.
    Hi Jim,

    How do you maintain your point of reference when flipping the material, without moving the part off-center? I'm not understanding how using the center would maintain positioning over using the corner.
    CAMaster CR-408 Cobra X3

  13. #13
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    Bob,

    Since I do not know how you are setting up your projects and whether or not you are making a sacrificial spoilboard for this project I can only guess at what you are doing. I am going to step by step this the way I do it starting with CAD, then CAM then actual machine.

    In CAD starting at X,Y,Z 0 in the positive quadrant draw a rectangle that is just a little bit bigger then the the piece of stock you are going to be working with. This rectangle is your Area Clear for your sacrificial spoil board. You will use this to create a surfacing program and establish the X,Y,Z home position.

    Next, with in this rectangle, draw your stock rectangle or bounding box. This represents the material you will be cutting. The stock material you are cutting has to match this measurement for this to work. You must also start from the X,Y,Z, home position. Do not guess that you are there. Make sure it is there. Use grid snap to ensure that you are at X,Y,Z home.

    At this point, you are ready to add your vector artwork of the project you want to run. This will be centered in the bounding box. You must ensure that you are centered both horizontally and vertically. No if, ands or buts about it.

    You are now ready for CAM. Generate a tool pathfor the area clear rectangle. Make sure the bit size in the computer coincides with the actual bit you are using.

    Generate your toolpaths for your vector art. Your tool path stock must be the same size as your bounding box. If your stock is not, when you create the flip in your CAM program, you can be off.

    Lets move to the machine now.

    Start your machine and reference return or G28 or C3 or do whatever it takes to make your particular machine orient itself to the manufacturers reference position.

    With that being done, slap a piece of sacrificial board on the table anywhere you want. Yes ANYWHERE! Make sure the piece is bigger then the area clear rectangle that you drew in the beginning.

    Move the machine to the plywood and set a new work position by using the G92 commands for X and Y or the G92 radio buttons (X,Y Zero) on your UI.

    Now that this is done, move the spindle over to the approximate center of the board and lower the cutting bit that you are going to area clear with to the plywood. I find a piece of paper works best for setting Z height when working with wood. Sorry to all you CNC purist who read this, but I work with WOOD, not NASA. No I do not use those stupid aluminum plates that come with the machines for zeroing Z. They are a waste of my time.

    G92 your Z. You are now ready to area clear your sacrificial spoilboard. The depth I prefer when doing this is .125 inches. This gives me a good level board, and it also gives me a clean right angle to position stock against.
    What is very important here is that the bit size is correct with what is programmed. For example if you program for area clear using a half inch end mill and you actually use a sharpened end mill that is now .47 in diameter, you are screwed.

    Anyhow, run your area clear program and when the program is done return the bit to the X,Y 0 and with the spindle running, drop the Z until it bores a hole in the corner. You have now cleared the radius and your stock will fit tight against the X and the Y. At this time, you can also lower your bit .125 and reset Z zero if you are going to use this bit. In my case I have an ATC so after I have measured all my tool offsets, I just have to re-zero Z and I am good to go on all five bits.

    You are now ready to run your program.

    Run side one, flip the piece over, run side two. Voilà. Works for me every time unless, the stock is screwed up, or area clear with the wrong bit, or I do not center my models in the bounding box.

    I am sure there 500 other steps that I left out of this explanation but they are not important. The basic jist is up above.

    Now the downside, unless you know how far you moved the machine from the G28 position to the sacrificial spoil board (write it down) you may not be able to go back to that location if the machine loses power or you reposition for another job. (Yes I am aware of WINCNC returning to last known job orientation on startup so please save the replies, that is why I made the statement may not)

    I suspect, that this may be part of the issue with you. Are you absolutely certain that your work position is truly X,Y 0 from the first time you cut it?

    This is the reason I use sacrificial boards. Plus, if I have to go into another project I can always setup a new spot somewhere else on the table and come back to the other one at a later date.

    Well Bob, I hope that my long fingered (instead of long winded) ...response clears up the mystery for you.

    If I get some time, I will blog this with photos and everything.

    Guy
    Thinking outside the box is one thing, being able to accomplish what you think of, is another.

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  14. #14
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    Question

    Quote Originally Posted by Bob Savage View Post
    Hi Jim,

    How do you maintain your point of reference when flipping the material, without moving the part off-center? I'm not understanding how using the center would maintain positioning over using the corner.
    Maybe Joey or Jim can help here, have you posted this on Vectric as well?


    GC
    Creative Woodwork and Design
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  15. #15
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    Angry

    ...this may be why...

    GC
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