Need some help, Machine not carving straight lines


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Thread: Need some help, Machine not carving straight lines

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    Default Need some help, Machine not carving straight lines

    I will upload some pictures to give you a better idea of the problem. I thought maybe the angle of the cutter was wrong but when I tried this test it looks like each triangle has something wrong with it. Most of the lines are bowed in and some of the corners don't look right also there was some dog bones while carving a sign earlier.

    I am tramming the spindle now and I see that it is .050 off on one side. Could this be the reason for it not carving straight lines or is it something else?

    I am hoping you guys can help.

    I don't think its a program issue this is definitely a hardware problem. I just changed the spindle out to a smaller one and also made a new and stronger bracket to hold the spindle in place. So as soon as the spindle and bracket was changed I noticed issues.

    If this isn't that right section to post in please let me know.

    Ryan

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    Attached Thumbnails Attached Thumbnails Need some help, Machine not carving straight lines-vcarve-1-jpg   Need some help, Machine not carving straight lines-vcarve-2-jpg  


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    Default Re: Need some help, Machine not carving straight lines

    It looks like flex in your machine is causing the slight curve in those lines. I'd make sure that new spindle bracket was rigid, and that your whole machine wasn't susceptible to motion when the spindle is stressed. With the machine turned on and the motors locked, try putting a pen in the spindle, touching it down to a piece of paper on the bed, and then pushing on the spindle in various directions. Does the mark on the paper remain a dot, or is it turning into a dash, or a comma?

    Andrew Werby
    https://computersculpture.com/


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    Default Re: Need some help, Machine not carving straight lines

    So with the machine turned on and motors locked I can move the entire assembly up like around a 1/16". When I press a board into the cutter the entire assembly moves up. Is it not supposed to do that? Is that what you mean by flex? If I put a pen in the spindle I would be able to move it around on the paper to make more than a dot.

    I would be willing to pay someone to come check out the machine or maybe call me to trouble shoot. I am in NJ.

    Need some help, Machine not carving straight lines-20200101_174244-jpg

    I was setting up a touch plate and I forgot to hook up the ground wire and the spindle crashed and pressed against a piece of metal I was using as a touch plate. I think this might be the cause for the bad carving.

    Attached Thumbnails Attached Thumbnails Need some help, Machine not carving straight lines-20200101_174244-jpg  


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    Default Re: Need some help, Machine not carving straight lines

    Hi R83 - I don't think there is anything wrong with the machine (unless there is something wrong). The V carve function means the depth of cut is varied so the diameter of your tool varies so a straight line ends up curved. To check this use a straight cutter and cut a triangular pocket, my guess is the edges will be straight. Cheers Peter S



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    Default Re: Need some help, Machine not carving straight lines

    I think you have a tool problem and the engraving tool isn't correctly ground for the job.It seems to be leaving a small radius at the tip where it ought to be absolutely sharp.The other question is what depth of cut you are using.It might be best to leave a little material there for a final cut as the reaction of the machine to the forces from a deeper cut will cause more flex than the light finishing cut.The other thing you might usefully check is the exact angle that the V tool is ground to.If the factory was a degree or two out on the precise angle,the program that calculated the toolpath will have generated it for the angle you inserted into the box for V angle and as has been stated,the centre of the spindle will move in directions that you might not expect in order to achieve the desired shape.



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    Default Re: Need some help, Machine not carving straight lines

    Quote Originally Posted by peteeng View Post
    Hi R83 - I don't think there is anything wrong with the machine (unless there is something wrong). The V carve function means the depth of cut is varied so the diameter of your tool varies so a straight line ends up curved. To check this use a straight cutter and cut a triangular pocket, my guess is the edges will be straight. Cheers Peter S

    Hello Peter,

    I did the triangle pocket and the left and bottom sides of the triangle seem to be straight but the top right corner looks as if the cutter went up a little bit. You can see in the picture that there is a small bump in the cut. What would cause the cutter to move up slightly. Do different routers need a different post processor? I was thinking about trying a different post processor.

    Attached Thumbnails Attached Thumbnails Need some help, Machine not carving straight lines-vcarve-3-jpg   Need some help, Machine not carving straight lines-vcarve-4-jpg  


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    Default Re: Need some help, Machine not carving straight lines

    I did the pen test and there is a lot of play.

    I took some video of the ball screw moving. Can anyone let me know if this is normal for it to move this much?





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    Default Re: Need some help, Machine not carving straight lines

    After watching your video I would definitely take a look at your bearing block at the motor end. You should find a jam nut that is used to preload the ball screw to the bearing.
    Usually there are two small set screws. Loosen up the set screws and turn the nut in to get rid of the backlash. Tighten the set screws.



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    Default Re: Need some help, Machine not carving straight lines

    Quote Originally Posted by johnd View Post
    After watching your video I would definitely take a look at your bearing block at the motor end. You should find a jam nut that is used to preload the ball screw to the bearing.


    Usually there are two small set screws. Loosen up the set screws and turn the nut in to get rid of the backlash. Tighten the set screws.
    Thanks John, I think you might be right. I am going to try this later.

    I think I found the jam nut near the motor, let me know if the picture is showing the jam nut.

    So basically I am going to pull the gantry towards the front of the machine to take up the slack and then loosen and move the jam nut towards the back of the machine and then tighten it back up. Does that sound right?

    Need some help, Machine not carving straight lines-jam-nut-jpgNeed some help, Machine not carving straight lines-20200102_143206-jpg

    Attached Thumbnails Attached Thumbnails Need some help, Machine not carving straight lines-jam-nut-jpg   Need some help, Machine not carving straight lines-20200102_143206-jpg  


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    Default Re: Need some help, Machine not carving straight lines

    There are usually two set screw on the black nut you show with the red arrow. Wrap some friction tape of with a piece of aluminum on the ball screw and clamp with vise grips or channel locks to prevent
    turning ( right side of the black bearing ).Turn the nut counterclockwise to remove the backlash. Once it is tight turn the set screws into the nut . Also remove the friction tape or aluminum . There should be no lateral movement now.



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    Default

    Quote Originally Posted by johnd View Post
    There are usually two set screw on the black nut you show with the red arrow. Wrap some friction tape of with a piece of aluminum on the ball screw and clamp with vise grips or channel locks to prevent
    turning ( right side of the black bearing ).Turn the nut counterclockwise to remove the backlash. Once it is tight turn the set screws into the nut . Also remove the friction tape or aluminum . There should be no lateral movement now.

    We tightened the jam nut as much as we could but there was still backlash. We are going to make a special washer to put between the jam nut and the black box.

    Does anyone know if there is supposed to be any backlash at all? We were debating on whether or not it should be moving slightly.



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    Default Re: Need some help, Machine not carving straight lines

    Is the whole bearing assembly moving inside the bearing block? There are two bearings inside. When you move the ball screw back and forth can you see the bearing race moving with the ball screw as one unit ?
    Is the outside of the bearing moving back and forth with regards to the bearing holder ( outside black square block )?
    If so the bearings have probably spun enough to wash out the holder.



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    Default Re: Need some help, Machine not carving straight lines

    Quote Originally Posted by Rschaeffer83 View Post
    We tightened the jam nut as much as we could but there was still backlash. We are going to make a special washer to put between the jam nut and the black box.

    Does anyone know if there is supposed to be any backlash at all? We were debating on whether or not it should be moving slightly.
    Special washer ? If these are the type of blocks I'm thinking of there should be a part #4 as shown in the included jpeg.
    The chinesium version of these blocks can have a small amount of backlash. On one sloppy block I resorted to a thin shim in-between the outer races. Not remotely as sloppy as shown in your video.Need some help, Machine not carving straight lines-bk-ballscrew-support-jpg

    edit/ Where the thin shim mentioned is place depends on the reason for the slop.

    Anyone who says "It only goes together one way" has no imagination.


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    Default Re: Need some help, Machine not carving straight lines

    Quote Originally Posted by johnd View Post
    Is the whole bearing assembly moving inside the bearing block? There are two bearings inside. When you move the ball screw back and forth can you see the bearing race moving with the ball screw as one unit ?
    Is the outside of the bearing moving back and forth with regards to the bearing holder ( outside black square block )?
    If so the bearings have probably spun enough to wash out the holder.
    I don't think the bearing assembly is moving inside the bearing block, the only thing that is moving is the ball screw through the bearing block.

    Here is what the ball screw looks like when we took off the jam nut. We are just waiting for the right size washer to come in to take up some space between the bearing block and the jam nut. I will let you guys know what happens when we try the washer.

    Need some help, Machine not carving straight lines-20200103_105218-jpgNeed some help, Machine not carving straight lines-20200103_105218-jpg

    Attached Thumbnails Attached Thumbnails Need some help, Machine not carving straight lines-20200103_105218-jpg  


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    Default Re: Need some help, Machine not carving straight lines

    Actually it probably is the bearing block. We tried the washer and there is still some movement. Anyone know where to buy this model bearing block?



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    Default Re: Need some help, Machine not carving straight lines

    If you look at the drawing I posted earlier there is a spacer labelled #4. There is also a spacer pushing on the inner bearing races from the other side, and I believe that's the most common arrangement. The second spacer is probably not labelled because a screw can be machined to serve the same purpose as the second spacer but I believe this is less common..

    Disassemble so your just left with screw, bearings and spacer(s). Now when the nut is tightened the bearings shouldn't slide side-to-side. If they do slide the reason is most likely a damaged or missing spacer.
    If it passes that test place just the bearings in the housing and check if the retainer is preventing the bearings from sliding.

    As far as replacing it, google "BK ball screw support" and find what matches in dimensions. If it's better quality the housing may have an identifying stamp. If you find the bearings inside are regular deep-groove it's probably generic China. If the bearings are angular contact it could be name brand or at least better quality generic China.

    Anyone who says "It only goes together one way" has no imagination.


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    Default Re: Need some help, Machine not carving straight lines

    We tried a different router and the engraving looked much better. The router was the problem. No need for a new BK 15 bearing block. Thank you guys for all your help though.



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    Default Re: Need some help, Machine not carving straight lines

    Well we thought the problem was the router but both routers had the same problem. The only difference was the problem is less noticeable on the larger router. We replaced the bearing blocks on the X axis and the problem was still there. So I just tried slowing down the speed at which the machine was carving and it completely fixed the problem. I slowed the machine down about half of what it was. When you look at the picture of the two "e"s the first "e" was done at a higher speed and the second "e" was done at a slower speed. So my question is what the hell would cause this? We replaced the bearing blocks on the X axis do we need to replace them on the Y axis too?

    Need some help, Machine not carving straight lines-20200115_173935-jpg

    Need some help, Machine not carving straight lines-20200115_173945-jpg

    Attached Thumbnails Attached Thumbnails Need some help, Machine not carving straight lines-20200115_173935-jpg   Need some help, Machine not carving straight lines-20200115_173945-jpg  


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