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Thread: Problem with Pocket and Profile cutting

  1. #1
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    Problem with Pocket and Profile cutting

    For my tap handles, I was wanting to make them so that there would be a pocket on the front that would hold a printed piece of card stock, and then have a piece of plexiglass that would fit in the pocket to protect it.

    My thinking was I would use 1 vector and create a pocket toolpath for, well, the pocket, and an outside profile tool path to cut the plexi.

    I used a 1/4" bit for the pocket and a 1/8" bit to cut out the plexi and all tool paths were calculated using the correct bit.

    The problem I have is that the plexi has been cut out just about 1/16" to tall and wide, or perhaps a better way to think about it is 1/32" diameter too bit too big all the way around. It won't fit into the slot. Now I can resize the vector for cutting the plexi, but I'm wondering what I might be missing?

    I would have thought that it would have been either a perfect fit or a little too tight, but this seems excessive.

    Note: The pocket is exactly the size as designed, 3" tall. It's just the plexi that is off.



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    Programmer - An organism that turns coffee into software.
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  2. #2
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    from what i've seen in the tutorials, it is always best to use the same bit for the pocket and the inlay.
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  3. #3
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    The thing is, it's CNC, right?

    I understand if there are tight curves that the 1/8" bit would be able to make sharper curvers than the 1/4, which could cause issues, but here the size of the piece it is cutting is plain off.

    That's what's not making sense to me.

    I was wondering if there were any issues with how profile cuts or tools were setup that could cause this to happen.
    Programmer - An organism that turns coffee into software.
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  4. #4
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    I'd probably check the actual pieces with calipers against the dimensions in your drawing to see which of the two are off. Also, I typically allow about .003" to .005" of gap on pieces that go together, usually setting a new boundary on one of the two pieces to cut to.

    Also you may verify that your bits are actually the size they are entered as.
    Last edited by Darren Wright; 01-22-2016 at 01:29 AM.
    Darren

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  5. #5
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    I did check the size of the pieces. I mean if I have a vector that is 3" tall, it should cut to 3" tall. Not a lot of room on the 1/8" bit to allow for that kind of error.

    I think the best thing to do would be to rig up a test with a couple of circles and verify this is really an issue and not just operator error.
    Programmer - An organism that turns coffee into software.
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  6. #6
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    Yep, the way those cuts should work is to cut the pocket with whatever size bit, then cut the inset piece using a right(outside) cut using the same path. I've done that and it worked, but I used a 1/8" bit for both.

    Darren has a good point about checking that the actual dimensions of the bits are correct.
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  7. #7
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    Just ran a quick test doing 2 circles the same size, one a pocket, one the outside profile, with the same 1/8" bit.

    The pocket, best as I can measure seems about ~1/64" shy of 2.5 inches. The circle I cut out is about 1/64" bigger than 2.5".

    I didn't measure the bit, but that certainly seems to be the suspect now.

    Guess I just need to compensate by changing the size of the infill piece a bit in order to make it work or get better bits.

    Thanks!
    Programmer - An organism that turns coffee into software.
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  8. #8
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    I have done that a few times.

    What I have found is that the same vector for the pocket AND the piece being insert just don't work

    I have ended up "fitting" one thing inside the other. I generally make one (maybe the insert) and fit it into the pocket by offsetting the vector for the pocket then running a profile toolpath to cut the perimeter then check the "fit". Maybe to offset and try again.

    If I remember right - I was offsetting toolpath by about .040 or so.

    I played around a little with G41 / G43 but I think Mach3 was not giving me what I wanted. I never really came to a conclusion there. This would be the easiest way, but sometimes I don't want to spend the time in development, and just do what I know I can make work. Sometimes I have time constraints and I just need to get it done. Like I have said before, I do sell stuff and the customer wants it for Christmas, Birthdays, or something like that. These are all things I have sold.

    It's been a while. I made a few things with embedded, sports embroidered patches, pictures. I also made tiny frames to fit into the pockets to look like a border around the inserted plastic cover and inside thingy.

    If there is a better way, I didn't get there. I just made what I set out to make and moved on. I do a lot of that.

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    For this, I made the deep pocket to the shape and depth of the emblem. Total depth of emblem pocket was the thickness of the emblem + thickness of the plastic + some depth to insert the frame.

    I made the frame about 1/8 wide if I remember correctly. So there was another pocket for the frame & plastic insert - like a shelf. The depth of the shelf pocket was thickness of plastic + some depth to inset the frame. I fitted the frame and plastic into the pockets by rerunning the pockets as I said above.

    I did a few of these.

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    I did the same here. The robe border is inset into a pocket. The cardinal is also inset into a pocket. I made the rope and the cardinal, then fitted them into the pockets.

    I did 3 of these. One sold - two not finished yet, one for sale, one for me.

    I have a few more samples, but they are all the same process.

  9. #9
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    Guess what, the bit I was using measured .120 for a 1/8" bit. Mystery solved!
    Programmer - An organism that turns coffee into software.
    If all your friends are exactly like you, What an un-interesting life it must be.
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  10. #10
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    Nice looking pieces Leo.

    I think this might also be a good answer.

    Quote Originally Posted by Leo Voisine View Post
    I have ended up "fitting" one thing inside the other. I generally make one (maybe the insert) and fit it into the pocket by offsetting the vector for the pocket then running a profile toolpath to cut the perimeter then check the "fit". Maybe to offset and try again.

    If I remember right - I was offsetting toolpath by about .040 or so.
    Programmer - An organism that turns coffee into software.
    If all your friends are exactly like you, What an un-interesting life it must be.
    "A door is what a dog is perpetually on the wrong side of" Ogden Nash


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