Alignment issues with passes creating gaps!

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This topic contains 28 replies, has 2 voices, and was last updated by  SteamPunkProgrammer 3 weeks, 5 days ago.

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  • #62064

    I had this issue before with my old MPCNC build but it would always go away when I tightened things down this time however everything is really rigid (But still very mobile) and im seeing a similar issue where passes get spaced out maybe I’m losing motor steps? Anyone got any advice?

     

    First image is a test I’ve used to calibrate things in the past and quickly shows the problem.

    Second image is the obligatory crown run from the example 12/mms file which also shows the issue.

    #62070

    Ryan
    Keymaster

    I don;t see it on the crown. Is this with your vacuum hose on? What bit are you using? You sure the wood is not moving?

    #62071

    Wood isnt moving, tried removing everything on the middle assembly but the drill to remove that as a possbility, ran it again on the crown which this time it was much more obvious, birch wood.

    #62074

    Ryan
    Keymaster

    I can;t tell from your builds pics but maybe your belts are loose, and they look like thick zipties which can kinda act as a spring if you aren’t careful? Try making sure they are bent square and don’t spring when it moves. You built a really tall machine which doesn’t help but it should not be this bad.

    It is not the same as building it shorter but try stacking material to get the wood to just under the gantry to reduce the z axis sickout. See if that helps.

    #62076

    Alright, I’ll give those a shot, the belts feel pretty tight and I just checked for squareness again and its pretty dang square, worse case I can drop it an inch shorter, and the gantry can definitely be shorted (lots of wasted space there) but I don’t think that would be causing this kind of issue.

    #62077

    Ryan
    Keymaster

    but I don’t think that would be causing this kind of issue.

    In what direction is the issue, it is not happening in them all. It looks to be one direction only, that makes it much easier to find. Is it a diagonal, or purely x or y?

    As for the super long Z, when driving the bit through the wood it gets pushed opposite the direction of travel. The z stepper motor gets swung in the direction of travel, it s a counter weight that makes it worse. So yup the shorter the better. This is usually a direction change (acceleration issue) not a straight line issue. Rapid constant oscillation can get nasty.

    So half the z stickout makes the machine twice as rigid (Linear), + all the gains from shorter distance the z stepper weight is away, + the rigidity gains for shorter legs (x’s 4). 1″ extra height is significantly less rigid.

    • This reply was modified 3 weeks, 5 days ago by  Ryan.
    #62079
    but I don’t think that would be causing this kind of issue.

    In what direction is the issue, it is not happening in them all. It looks to be one direction only, that makes it much easier to find. Is it a diagonal, or purely x or y?

    As for the super long Z, when driving the bit through the wood it gets pushed opposite the direction of travel. The z stepper motor gets swung in the direction of travel, it s a counter weight that makes it worse. So yup the shorter the better. This is usually a direction change (acceleration issue) not a straight line issue. Rapid constant oscillation can get nasty.

    So half the z stickout makes the machine twice as rigid (Linear), + all the gains from shorter distance the z stepper weight is away, + the rigidity gains for shorter legs (x’s 4). 1″ extra height is significantly less rigid.

     

     

    It seems like its occurring on both axis, but now that you explain the gantry a bit more it sort of makes sense the issue could be caused by that because all of the issues seem to arries from pivoting in the direction that would pull at the bottom against the motor at the top the most, so after this next test, I think its time to cut an inch or two off the gantry!

    #62080

    Ryan
    Keymaster

    Stick out is the key not total length. Making the tip of the cutting tool to the center of the tube crossover point distance shorter.

    #62081

    Stick out is the key not total length. Making the tip of the cutting tool to the center of the tube crossover point distance shorter.

    Trying to understand that, you are saying, shorter legs help not shorter gantry,  because that would put the center of the drills mass in the center of the middle assemblies mass and there for make it more rigid?

     

    Seems it has improved greatly, the belts were tightened (some were actually loose) and I also noticed that one side of the Y axis isnt staying square to the other side (half an inch off or so) so before I started it I gave it a shove on the side that wasn’t lined up right, would this have caused the issue? Also, what is the source of this offset? is it in the middle assembly? My corners are very square compared to this offset.

    #62086

    Ryan
    Keymaster

    Trying to understand that, you are saying, shorter legs help not shorter gantry, because that would put the center of the drills mass in the center of the middle assemblies mass and there for make it more rigid?

    Nope. Nothing to do with mass. Grab a pencil, wrist on the table, sign your name, now move your hand further away from the tip grab the eraser, sign it again.Which one is more accurate, this represents how far the tip of the tool is from the center of the gantry assembly. Now while holding it by the eraser pick you wrist up off the table and only use your elbow, sign it again. This represents long legs. The shorter every single part is on the machine the more rigid the entire machine gets.

    Maybe a better way to think of it is this. Pick a foot, move the spindle as far away from it as possible and set the tip of the tool on the table. From the bottom of the foot (at the table surface) measure from the foot to the center of the corner, from the center of the corner to the center of the gantry, from the center of the gantry to the surface of the table. The smaller this number the more rigid the machine, the more rigid, the more accurate, the more accurate the faster you can move and maintain the desired accuracy.

     

    I also noticed that one side of the Y axis isnt staying square to the other side (half an inch off or so) so before I started it I gave it a shove on the side that wasn’t lined up right, would this have caused the issue?

    This is caused by you not moving both steppers with both hands, dragging it around by the gantry. This is normal. You should be checking before you start a cut to make sure they are even. This could cause your issue 100%. Of it could be any of the other things I mentioned, or other things including what bit you are using, how fast your spindle is, how it is mounted, how sharp.

     

    #62087
    Trying to understand that, you are saying, shorter legs help not shorter gantry, because that would put the center of the drills mass in the center of the middle assemblies mass and there for make it more rigid?

    Nope. Nothing to do with mass. Grab a pencil, wrist on the table, sign your name, now move your hand further away from the tip grab the eraser, sign it again.Which one is more accurate, this represents how far the tip of the tool is from the center of the gantry assembly. Now while holding it by the eraser pick you wrist up off the table and only use your elbow, sign it again. This represents long legs. The shorter every single part is on the machine the more rigid the entire machine gets.

    Maybe a better way to think of it is this. Pick a foot, move the spindle as far away from it as possible and set the tip of the tool on the table. From the bottom of the foot (at the table surface) measure from the foot to the center of the corner, from the center of the corner to the center of the gantry, from the center of the gantry to the surface of the table. The smaller this number the more rigid the machine, the more rigid, the more accurate, the more accurate the faster you can move and maintain the desired accuracy.

    I also noticed that one side of the Y axis isnt staying square to the other side (half an inch off or so) so before I started it I gave it a shove on the side that wasn’t lined up right, would this have caused the issue?

    This is caused by you not moving both steppers with both hands, dragging it around by the gantry. This is normal. You should be checking before you start a cut to make sure they are even. This could cause your issue 100%. Of it could be any of the other things I mentioned, or other things including what bit you are using, how fast your spindle is, how it is mounted, how sharp.

    Ahhhhh I get it, its a pivot point issue with the gantry, I totally get that!

     

    As for the Y axis, Yea I always did grab the gantry and move it around I guess that was my issue whats odd is that the whole time I used my other cnc it never caused a problem, very weird!

    Its very resistant to go into alignment so I feel like something else is wrong like some amount of warp in the middle assembly or something.

    I guess moving the motors around and checking for square is just my life now haha…

    #62088

    Ryan
    Keymaster

    Ahhhhh I get it, its a pivot point issue with the gantry, I totally get that!

    Lever arm..close though. http://hyperphysics.phy-astr.gsu.edu/hbase/torq.html

     

    I guess moving the motors around and checking for square is just my life now haha…

    Yes, it is an issue for every machine. Some more than others. That is why we put so many months worth of work into the dual endstop firmware and hardware. You can watch some other CNC machines and how this only gets realized when they try to do some fine adjustments/cuts/tool changes.

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    #62089

    Ryan
    Keymaster

    Its very resistant to go into alignment so I feel like something else is wrong like some amount of warp in the middle assembly or something.

    Not warp, assembly tension. You should have been checking for square during assembly. I have a few pictures of this in the instructions.

    1 user thanked author for this post.
    #62091

    Ryan
    Keymaster

    And don’t take any of this in the wrong way. I do my best not to critique peoples builds until asked (think cable chains on the Z axis, I stopped warning them). You seem genuinely interested and have asked for solutions, so I am trying to give complete answers. I enjoy helping people have the best experience with CNC. All of this is kinda small stuff but each little bit adds up.

    If it is overwhelming amount of info just ignore it for now, you will eventually figure it out with more test cuts.

    1 user thanked author for this post.
    #62093

    And don’t take any of this in the wrong way. I do my best not to critique peoples builds until asked (think cable chains on the Z axis, I stopped warning them). You seem genuinely interested and have asked for solutions, so I am trying to give complete answers. I enjoy helping people have the best experience with CNC. All of this is kinda small stuff but each little bit adds up.

    If it is overwhelming amount of info just ignore it for now, you will eventually figure it out with more test cuts.

    Definitely not taking it the wrong way! I’d prefer more information then short answers because they help me understand how you arrived at that answer so I can later answer these questions for myself!

    I wouldn’t call it overwhelming in fact…*re-reads the middle assembly instructions* oh…I’m an idiot lol…its all square now!

    #62102

    So, next question;

    I’m noticing a slightly aggressive ‘pop’ as the dril cuts into an already cut into space, this sounds like the kind of thing that is caused by the drill not being more centered with the middle assembly (IE the legs are to long for this kind of rate/feed) does that sound right?

    #62103

    Ryan
    Keymaster

    What kind of endmill are you using (not all are meant for plunge cutting)? Is it dull? Is your tool perpendicular? Are you cutting too fast (plunges should be pecked or spiral) and not making a hole within tolerances? Why are you going back into a hole? Are you using a finishing pass?

    Too broad of a question. You will need to do more test cuts, put on the safety glasses and get your face in there. Watch everything.

    #62104

    What kind of endmill are you using (not all are meant for plunge cutting)? Is it dull? Is your tool perpendicular? Are you cutting too fast (plunges should be pecked or spiral) and not making a hole within tolerances? Why are you going back into a hole? Are you using a finishing pass?

    Too broad of a question. You will need to do more test cuts, put on the safety glasses and get your face in there. Watch everything.

    2 straight flute long; bought it from you so I hope its not dull 😛 (feels like if I applied to much pressure when touching it, it would break the skin, so its pretty sharp) 12/mms feed rate 3mm depth per pass.

    It occurs when going along paths and meeting up with the start of the path (the troopers outline makes it most obvious).

    #62106

    After tightening a few things down (mostly the feet) it seems to have gone away, I guess just about anything can cause that.

    #62107

    Ryan
    Keymaster

    Okay. So 12mm/s 3mm DOC might actually be too much for that bit. A straight flute does not clear the chips very well it’s job is to not mess up either surface, not a fast material remover. The cuts you keep testing are slotting operations, even worse. If you use a slotting operation with say a 0.5mm finishing pass it should be much better. You can try shallower or slower or both. I don’t like the straight flutes. I almost exclusively use the single flute up cut and vbits. In the 1/8 diameter I don’t think it gets any better. A larger straight flute might be okay do to larger flutes but a single flute is going to make a world of difference in the cuts you are doing….don’t believe the hype on those straight flutes.

    I think most would do a majority of the job with an upcut and if the wood has a veneer or a delicate surface they were trying to keep a sharp corner on (rare) you would then do your finishing pass with a straight flute, never use it for slotting.

    Now you know why I repeatedly asked what bit you were using.

    • This reply was modified 3 weeks, 5 days ago by  Ryan.
    #62109

    Okay. So 12mm/s 3mm DOC might actually be too much for that bit. A straight flute does not clear the chips very well it’s job is to not mess up either surface, not a fast material remover. The cuts you keep testing are slotting operations, even worse. If you use a slotting operation with say a 0.5mm finishing pass it should be much better. You can try shallower or slower or both. I don’t like the straight flutes. I almost exclusively use the single flute up cut and vbits. In the 1/8 diameter I don’t think it gets any better. A larger straight flute might be okay do to larger flutes but a single flute is going to make a world of difference in the cuts you are doing….don’t believe the hype on those straight flutes.

    I think most would do a majority of the job with an upcut and if the wood has a veneer or a delicate surface they were trying to keep a sharp corner on (rare) you would then do your finishing pass with a straight flute, never use it for slotting.

    Now you know why I repeatedly asked what bit you were using.

    Okay! I have an upcut actually so I’ll slap that in there!

    #62110

    I switched over to the 2 flute upturn bit (thats the only one that I ordered sounds like I need to order a single flute one as well) and the difference is insane. It just eats the wood up, can hear and feel the difference. What have been doing with my life lol.

    #62111

    Ryan
    Keymaster

    The one you just put in is fine but it wants a really high feed rate because of how fast the stock 660 turns. A single flute cuts that in half and has a more aggressive flute to get the chips out. Re-cutting is the enemy. So if you have the dimmer to slow it down for your current endmill and it can get really really smooth. You need to find the sweet spot (this is where a PID would come into play).

    #62113

    The one you just put in is fine but it wants a really high feed rate because of how fast the stock 660 turns. A single flute cuts that in half and has a more aggressive flute to get the chips out. Re-cutting is the enemy. So if you have the dimmer to slow it down for your current endmill and it can get really really smooth. You need to find the sweet spot (this is where a PID would come into play).

    Yup, got a router dimmer already and was playing with that, its already pretty amazing how much of a difference this made, going to order two single flute upturn bits asap!

    #62114

    Right to left, top to bottom, they progressively get better till the last one which looks great! Thanks for all the help ryan feel like I can actually make some stuff with it now!

    #62116

    Ryan
    Keymaster

    Make sure you use a finishing pass, 0.2-0.4mm or so works for me. It can get better/easier/faster. Fine balance of all kinds of stuff.

     

    Thanks for all the help ryan feel like I can actually make some stuff with it now!

    Your welcome.

    #62117

    Make sure you use a finishing pass, 0.2-0.4mm or so works for me. It can get better/easier/faster. Fine balance of all kinds of stuff.

    Thanks for all the help ryan feel like I can actually make some stuff with it now!

    Your welcome.

    I’m not sure how to use finishing passes in estlcam, but in fusion 360 I know quite a bit of that whole process. I was using the trooper as a test case because it had a lot of different kinds of cuts from my limited perspective anyways. Now I gotta figure out what im going to make, probably a birthday gift for my brother im seeing next month!

    #62118

    Ryan
    Keymaster

    The two yellow boxes. Pick the tool (usually the same one) and the number. Super easy.

    #62119

    The two yellow boxes. Pick the tool (usually the same one) and the number. Super easy.

    oh wow; that is easy… I’ve missed this for so long haha.

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