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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...
    Yep that’s why I’m drag engraving. And I’m guessing the machine isn’t up to it from what I’m gathering

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    Thanks guys for your comments and suggestions. So I'm gathering my 3018 isn't up to the job for what I'm trying to achieve. So what would machine would be? Bear in mind I'm a beginner and don't want to spend $1000's. Also I don't have a lot of room in my office so need something smallish, but I am up for considering a better machine. Or alternatively would upgrading some parts be a solution?

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    Maybe start with explaining what your goal is. Is this a decorative process, or are you making a linear Fresnel lens, or? What are the precision requirements, the target width, pitch, and accuracy of the lines, etc.

    More information is always (well, almost always) better. We save a lot of time with guessing or going down the wrong avenue when the poster (you) tells us what the real need is.

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    Quote Originally Posted by Milland View Post
    Maybe start with explaining what your goal is. Is this a decorative process, or are you making a linear Fresnel lens, or? What are the precision requirements, the target width, pitch, and accuracy of the lines, etc.

    More information is always (well, almost always) better. We save a lot of time with guessing or going down the wrong avenue when the poster (you) tells us what the real need is.
    Sorry yes good idea. So there are 40 straight lines I need to engrave onto a piece of clear acrylic. The lines need to be equally spaced 1.5mm apart and 60mm in length. The lines need to be hairline in width and accurate, I'm not sure what the pitch is though. The acrylic is 2mm thick and 100mm square in size. It is not decorative. Is this enough to go on?

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    picture is worth a thousand words... under magnification, to see what the "bad" line looks like next to a good one

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    Quote Originally Posted by jz79 View Post
    picture is worth a thousand words... under magnification, to see what the "bad" line looks like next to a good one
    The bad lines are thinner than the good lines

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    do you want to actually solve this or just talk about it for couple more days wasting peoples time?

    it takes 5min to make a decent pic of the problem, and I'd also suggest posting pic of the drag tool itself, the tip especially - under high magnification so we can see what the shape and condition of the tip is

    else this will drag on for couple more days of guessing what may and may not be, then everyone will get bored and this will end up just another thread with no solution, and there are plenty of such threads here already

    and find at least a loupe to take the picture through, digital zoom may not produce the desired detail

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    Quote Originally Posted by bennyboy75 View Post
    Sorry yes good idea. So there are 40 straight lines I need to engrave onto a piece of clear acrylic. The lines need to be equally spaced 1.5mm apart and 60mm in length. The lines need to be hairline in width and accurate, I'm not sure what the pitch is though. The acrylic is 2mm thick and 100mm square in size. It is not decorative. Is this enough to go on?
    Try using a much thicker piece of acrylic as a test. If it still happens it is likely the machine. If not it is your clamping. Best would be a vacume table hold down to keep the thin piece flat.

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    Quote Originally Posted by jz79 View Post
    do you want to actually solve this or just talk about it for couple more days wasting peoples time?

    it takes 5min to make a decent pic of the problem, and I'd also suggest posting pic of the drag tool itself, the tip especially - under high magnification so we can see what the shape and condition of the tip is

    else this will drag on for couple more days of guessing what may and may not be, then everyone will get bored and this will end up just another thread with no solution, and there are plenty of such threads here already

    and find at least a loupe to take the picture through, digital zoom may not produce the desired detail
    Sorry, see images below. Hope this helps to make it clearer. Unfortunately I can't get any more magnification on these, but hopefully these will show enough.

    img_7266.jpgimg_7277.jpgimg_7277b.jpg

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    Quote Originally Posted by Superbowl View Post
    Try using a much thicker piece of acrylic as a test. If it still happens it is likely the machine. If not it is your clamping. Best would be a vacume table hold down to keep the thin piece flat.
    Thanks, I don't have any thicker acrylic at the moment, but I can get some in and give it a try.

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    it seems that the pictures are telling a story:
    1) the line width on the part seems to correlate with the lighter/darker patches of the part itself, perhaps that is an optical illusion, but I definitely see a pattern with shallow lines, which suggests that it is material related,
    2) the angle of the tip and sharpness may be a factor, perhaps a 60 degree tip might be a better fit, difficult to tell, but the tip doesn't look a 90, more like a 120 degree grind, but the grind also looks a bit suspicious, it might simply not be sharp enough for the job (requiring excessive pressure), since it seems you're trying to use a quite light pressure to get fine lines.

    Regarding the material, you might want to try annealing it, couple pieces perhaps, use the ones where the defect has a noticeable pattern like in the picture you took, from what I'm finding quickly, 80 degrees C is enough for acrylic, but needs a slow ramp up time, so put the pieces in on a flat piece of aluminum (aluminum or copper, so the warming up goes evenly across the part) in an oven and heat them up gradually, perhaps 20C every 20-30min till you get to 80, hold for a bit, 20-30min perhaps and then switch off heat, let it cool slowly for half and hour or more till you can comfortably touch it with a bare hand, heating too quickly or overshooting the temp can cause problems, do a dry run to see if the control on the oven is sensitive enough to do this.

    Then set you X/Y so the new test lines fall right between the already scribed lines, to get a good idea if the annealing had any effect on the material.

    If this doesn't help, use a new narrower angle tip (and remember that narrow angle is more fragile and can chip more easily), it might be possible to lap a dull tip into a useful condition, but to do that reliably you'd need something like a Deckel S0 type tool and cutter grinder, and a possibility to get run the spindle slowly, 50-150rpm slow, but that would be a different topic in its own

    A pic of the work holding setup might also shed some light, I wouldn't use anything soft under it, a hard/flat surface, might start with just taping it down with electricians tape on the perimeter, should be enough for the job

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    The likely reason for the problem is the formation of a built up edge on the tool. To reduce this effect you can do the following:

    1) make the tool sharper and make the point of the tool with a more acute angle

    2) flood the workpiece with water or other coolant

    3) cut slower

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    That would not be my choice for a tool to cut such grooves, as it seems to have a rounded point, and the broad angle itself invites significant width variation with minor changes in downward pressure.

    I would try a sharper tool, ideally something like this: Solid Carbide Single Flute Engraving Bit | Inventables but perhaps find one with a shallower angle (closer to 90 degrees included).

    Set the bit such that it's locked with the flat facing the direction of travel, and in a minor miracle I have found a point of agreement with the troll - a thin film of water or even light mineral oil may improve the uniformity of the cut.

    With this setup you might find your machine works as you need, although how you hold the cutting bit will determine success or not. You need it to be stable, yet free moving vertically such that weight alone influences downward pressure. "Locking" it in the spindle will not allow it to follow the contours of the plastic unless you're willing to machine it flat before doing the scratch cutting.

    BTW, "pitch" in the context I inquired about is the spacing, in your case 1.5mm.

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    Quote Originally Posted by jz79 View Post
    it seems that the pictures are telling a story:
    1) the line width on the part seems to correlate with the lighter/darker patches of the part itself, perhaps that is an optical illusion, but I definitely see a pattern with shallow lines, which suggests that it is material related,
    2) the angle of the tip and sharpness may be a factor, perhaps a 60 degree tip might be a better fit, difficult to tell, but the tip doesn't look a 90, more like a 120 degree grind, but the grind also looks a bit suspicious, it might simply not be sharp enough for the job (requiring excessive pressure), since it seems you're trying to use a quite light pressure to get fine lines.

    Regarding the material, you might want to try annealing it, couple pieces perhaps, use the ones where the defect has a noticeable pattern like in the picture you took, from what I'm finding quickly, 80 degrees C is enough for acrylic, but needs a slow ramp up time, so put the pieces in on a flat piece of aluminum (aluminum or copper, so the warming up goes evenly across the part) in an oven and heat them up gradually, perhaps 20C every 20-30min till you get to 80, hold for a bit, 20-30min perhaps and then switch off heat, let it cool slowly for half and hour or more till you can comfortably touch it with a bare hand, heating too quickly or overshooting the temp can cause problems, do a dry run to see if the control on the oven is sensitive enough to do this.

    Then set you X/Y so the new test lines fall right between the already scribed lines, to get a good idea if the annealing had any effect on the material.

    If this doesn't help, use a new narrower angle tip (and remember that narrow angle is more fragile and can chip more easily), it might be possible to lap a dull tip into a useful condition, but to do that reliably you'd need something like a Deckel S0 type tool and cutter grinder, and a possibility to get run the spindle slowly, 50-150rpm slow, but that would be a different topic in its own

    A pic of the work holding setup might also shed some light, I wouldn't use anything soft under it, a hard/flat surface, might start with just taping it down with electricians tape on the perimeter, should be enough for the job
    Thanks for the info and advice and about annealing, I hadn't come across that process before but I will have a look into it. Interesting about the tip angle. I just measured it using my design software from the photo I took and the angle is actually 104˚. Strange. So are there better diamond tip engravers out there? Just a thought could it be the tip is turning slightly maybe and catching different edges of the tip making the lines wider? Regards the work holding set-up I've tried different options. One, taping to MDF, then 1mm foam on top of the MDF, then 20mm sponge on the MDF. I'd wondered if having pressure from below as well as from the top would keep the tip on the surface better, assuming the tip wasn't staying on the surface properly, hence using the foam. I think it helped a bit but didn't solve the problem completely as I still get the blotchy patches where the lines go thinner.

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    Quote Originally Posted by jscpm View Post
    The likely reason for the problem is the formation of a built up edge on the tool. To reduce this effect you can do the following:

    1) make the tool sharper and make the point of the tool with a more acute angle

    2) flood the workpiece with water or other coolant

    3) cut slower
    Thanks. I'm not sure its build up as the blotchy patches are where the lines go thinner. They start off normal weight, but go thin in these places, if there was debris, wouldn't this make the cut coarser and the line wider? I've also tried cutting slowly too and fast, but get the same results.

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    Quote Originally Posted by Milland View Post
    That would not be my choice for a tool to cut such grooves, as it seems to have a rounded point, and the broad angle itself invites significant width variation with minor changes in downward pressure.

    I would try a sharper tool, ideally something like this: Solid Carbide Single Flute Engraving Bit | Inventables but perhaps find one with a shallower angle (closer to 90 degrees included).

    Set the bit such that it's locked with the flat facing the direction of travel, and in a minor miracle I have found a point of agreement with the troll - a thin film of water or even light mineral oil may improve the uniformity of the cut.

    With this setup you might find your machine works as you need, although how you hold the cutting bit will determine success or not. You need it to be stable, yet free moving vertically such that weight alone influences downward pressure. "Locking" it in the spindle will not allow it to follow the contours of the plastic unless you're willing to machine it flat before doing the scratch cutting.

    BTW, "pitch" in the context I inquired about is the spacing, in your case 1.5mm.
    Thanks, I will try this. Can you clarify what you mean here... "You need it to be stable, yet free moving vertically such that weight alone influences downward pressure. "Locking" it in the spindle will not allow it to follow the contours of the plastic unless you're willing to machine it flat before doing the scratch cutting."... Not sure I understand what you mean.

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    Quote Originally Posted by Milland View Post
    That would not be my choice for a tool to cut such grooves, as it seems to have a rounded point, and the broad angle itself invites significant width variation with minor changes in downward pressure.

    I would try a sharper tool, ideally something like this: Solid Carbide Single Flute Engraving Bit | Inventables but perhaps find one with a shallower angle (closer to 90 degrees included).

    Set the bit such that it's locked with the flat facing the direction of travel, and in a minor miracle I have found a point of agreement with the troll - a thin film of water or even light mineral oil may improve the uniformity of the cut.

    With this setup you might find your machine works as you need, although how you hold the cutting bit will determine success or not. You need it to be stable, yet free moving vertically such that weight alone influences downward pressure. "Locking" it in the spindle will not allow it to follow the contours of the plastic unless you're willing to machine it flat before doing the scratch cutting.

    BTW, "pitch" in the context I inquired about is the spacing, in your case 1.5mm.
    Also there will be some angled lines too coming off the straight ones, same pitch and all the same angle. Will the tool you mention still work ok for this?

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    The defects being in "blotches" tels me the problem is the material. Maybe variable thickness. Maybe varying hardness, maybe even fingerprints changing the way the material "cuts" I also agree sharper tip is likely to help, and a tip geometry that will cut rather then plough

    You can check to see if varying thisckness is a problem by replacing your graver with a dial indicator, and locking the vertical float. Traverse between your existing lines and se if height variation tracks with the "blotches".

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    Quote Originally Posted by bennyboy75 View Post
    Sorry, see images below. Hope this helps to make it clearer. Unfortunately I can't get any more magnification on these, but hopefully these will show enough.

    img_7266.jpgimg_7277.jpgimg_7277b.jpg
    You could try taking the engraver apart and polishing the sliding surfaces. Might be "sticky". Looks like the point is being gradually pushed up and then snapping back down after the spring is compressed enough.

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    Quote Originally Posted by magneticanomaly View Post
    The defects being in "blotches" tels me the problem is the material. Maybe variable thickness. Maybe varying hardness, maybe even fingerprints changing the way the material "cuts" I also agree sharper tip is likely to help, and a tip geometry that will cut rather then plough

    You can check to see if varying thisckness is a problem by replacing your graver with a dial indicator, and locking the vertical float. Traverse between your existing lines and se if height variation tracks with the "blotches".

    I think that the "blotches" are from whatever material the acrylic was on when they took the picture. Looks like fabric.


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