Diamond drag thin lines on acryic, blotchy uneven patches
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    Default Diamond drag thin lines on acryic, blotchy uneven patches

    I am engraving some fine lines onto acrylic with a spring loaded diamond drag bit using my CNC 3018. The problem I have is that the line weights are inconsistent and I don't know how to solve this. I have tried every setting known to man but it still ends up with the same blotchy patches where the lines are engraved heavier in some parts than others. I am wondering if this is due to the surface of the acrylic not being completely flat but I thought it being a spring loaded engraver, the spring would compensate for this. My only other idea is whether a better CNC machine would do a better job. Anyway I'm scratching my head on this one. Hoping someone can offer some advice. Thanks.

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    What brand machine, how are you holding the acrylic down, what size?

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    Quote Originally Posted by bennyboy75 View Post
    Anyway I'm scratching my head on this one. Hoping someone can offer some advice. Thanks.
    Stop scratching your head with the diamond!! I hope you're not sticking your head in the machine to do so...

    Try to set up a weight-based drag system rather than a spring. A stem (for mounting in the spindle) and robust (but free-moving) fork and pin pivot, and with a trailing diamond holder that has a smaller vertical post for adding and removing control weights may work better, as it will not be as load-sensitive as a spring (yes, cast acrylic can be rather variable in thickness).

    Include a stop so the actual travel of the diamond holder is ~3mm or so, when you raise and reposition the engraver you won't lose time by having to lift the spindle higher.

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    Quote Originally Posted by Milland View Post
    Stop scratching your head with the diamond!! I hope you're not sticking your head in the machine to do so...

    Try to set up a weight-based drag system rather than a spring. A stem (for mounting in the spindle) and robust (but free-moving) fork and pin pivot, and with a trailing diamond holder that has a smaller vertical post for adding and removing control weights may work better, as it will not be as load-sensitive as a spring (yes, cast acrylic can be rather variable in thickness).

    Include a stop so the actual travel of the diamond holder is ~3mm or so, when you raise and reposition the engraver you won't lose time by having to lift the spindle higher.
    Thanks, but I don't know what any of that means, do you have a photo or link to what you are describing? I just have a CNC 3018, its very basic.

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    Quote Originally Posted by plastikdreams View Post
    What brand machine, how are you holding the acrylic down, what size?

    Its a generic CNC 3018, one of those Chinese ones I think. So the acrylic is currently taped to a thick piece of foam which is taped onto the CNC bed. I've tried taping the acrylic on to MDF but get same results with that too. What size? What the CNC? Its a 3018. Or do you mean the size of acrylic?

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    Size of acrylic...what size are the lines for shits n grins?

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    Just a wild guess, but I'd look at the engraver sliding parts, assuming it has a low enough spring-rate where minor variations in the height wouldn't theoretically make a difference, perhaps the moving tip is not sliding properly or there is friction when radial force is applied. Also maybe tip sharpness/angle is not ideal. A sharp conical carbide tip might work better also.

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    Quote Originally Posted by car2 View Post
    Just a wild guess, but I'd look at the engraver sliding parts, assuming it has a low enough spring-rate where minor variations in the height wouldn't theoretically make a difference, perhaps the moving tip is not sliding properly or there is friction when radial force is applied. Also maybe tip sharpness/angle is not ideal. A sharp conical carbide tip might work better also.
    I'll have a look at that, maybe it needs some lubrication.

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    So I take it the problem I have isn't normal then? ie. there shouldn't be any variation in the line weight?

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    it is normal for the equipment would the fair thing to say, machines like that are forbidden to be discussed on this forum btw

    if the spring action is smooth with no sticking and the diamond shape is right for the job, then the rest can only be attributed to the machine, you could try reducing the pressure by reducing the Z- height of the toolpath, see if narrower line has the same problem, if it doesn't, then the problem is in the machine, which can't be discussed as I said before

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    You might check closely (as with a magnifier or microscope) that what you're seeing is indeed related to "line weight" (or penetration depth), it might actually be some type of microscopic burr, or change in profile or asymmetry of the scribed geometry..the human eye is really good at picking up variations in reflectivity, shades and such. Also any oils or films would affect the appearance, or if something is stuck to the back that changes the reflective/transmitted light.

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    Quote Originally Posted by plastikdreams View Post
    What brand machine, how are you holding the acrylic down, what size?
    Genmitsu Industries
    – Genmitsu Industries LLC


    They make the 3018

    Sent from my SAMSUNG-SM-G891A using Tapatalk

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    Quote Originally Posted by bennyboy75 View Post
    I am engraving some fine lines onto acrylic with a spring loaded diamond drag bit using my CNC 3018. The problem I have is that the line weights are inconsistent and I don't know how to solve this. I have tried every setting known to man but it still ends up with the same blotchy patches where the lines are engraved heavier in some parts than others. I am wondering if this is due to the surface of the acrylic not being completely flat but I thought it being a spring loaded engraver, the spring would compensate for this. My only other idea is whether a better CNC machine would do a better job. Anyway I'm scratching my head on this one. Hoping someone can offer some advice. Thanks.
    Depending on how much pressure you're applying, it could be the spindle twisting upward on the gantry. The X axis guide rails are 10mm. Wouldnt take much to get noticable deflection.

    Why drag engrave? On that machine, engraving acrylic, I'd be machining the lines in using D bit.

    Then again, I don't know what size lines you're making. If they're really fine, pressure causing deflection in the spindle wouldn't be an issue - I'd be looking at the engraver, itself.

    Sent from my SAMSUNG-SM-G891A using Tapatalk

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    If he wants really narrow lines on a fine pitch, he's better off drag cutting them. Basically using the CNC as a ruling engine.

    But maybe not on that machine - it's super-light duty...

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    Quote Originally Posted by Milland View Post
    If he wants really narrow lines on a fine pitch, he's better off drag cutting them. Basically using the CNC as a ruling engine.

    But maybe not on that machine - it's super-light duty...
    I agree. I definitely see the advantages of drag engraving - just not on this machine. Not in stock form, anyway. Too much deflection.

    Sent from my SAMSUNG-SM-G891A using Tapatalk

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    Like has already been said, your spring pressure is way too high for the material and or not smooth stroking action. The mechanical New Hermes engravers used a hand controlled “feather touch” spindle for drag engraving very soft materials and literally i’m talking ounces or a fraction thereof on pressure.

    Murf


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    Quote Originally Posted by Murf View Post
    Like has already been said, your spring pressure is way too high for the material and or not smooth stroking action. The mechanical New Hermes engravers used a hand controlled “feather touch” spindle for drag engraving very soft materials and literally i’m talking ounces or a fraction thereof on pressure.

    Murf


    Sent from my iPhone using Tapatalk
    Your description says your a call maker What kinda calls you make? Says you hunt.

    Sent from my SAMSUNG-SM-G891A using Tapatalk

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    Quote Originally Posted by car2 View Post
    You might check closely (as with a magnifier or microscope) that what you're seeing is indeed related to "line weight" (or penetration depth), it might actually be some type of microscopic burr, or change in profile or asymmetry of the scribed geometry..the human eye is really good at picking up variations in reflectivity, shades and such. Also any oils or films would affect the appearance, or if something is stuck to the back that changes the reflective/transmitted light.
    Thanks. I don't have a microscope but I've looked through a high powered magnifying glass. it appears the lines get thinner in the blotchy patches.

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    Quote Originally Posted by jz79 View Post
    it is normal for the equipment would the fair thing to say, machines like that are forbidden to be discussed on this forum btw

    if the spring action is smooth with no sticking and the diamond shape is right for the job, then the rest can only be attributed to the machine, you could try reducing the pressure by reducing the Z- height of the toolpath, see if narrower line has the same problem, if it doesn't, then the problem is in the machine, which can't be discussed as I said before

    So I’ve tried different pressures, from the lightest to the strongest, and they all produce the same effect, so I guess its the machine.

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    Quote Originally Posted by 52 Ford View Post
    Depending on how much pressure you're applying, it could be the spindle twisting upward on the gantry. The X axis guide rails are 10mm. Wouldnt take much to get noticable deflection.

    Why drag engrave? On that machine, engraving acrylic, I'd be machining the lines in using D bit.

    Then again, I don't know what size lines you're making. If they're really fine, pressure causing deflection in the spindle wouldn't be an issue - I'd be looking at the engraver, itself.

    Sent from my SAMSUNG-SM-G891A using Tapatalk

    So the reason I’m drag engraving is I’m trying to create very fine straight lines.


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