Odd Z Movement – Carvings Messed Up – Help!

New Home Forum Mostly Printed CNC – MPCNC Troubleshooting – MPCNC Odd Z Movement – Carvings Messed Up – Help!

This topic contains 17 replies, has 5 voices, and was last updated by  Ryan 2 months, 3 weeks ago.

Viewing 18 posts - 1 through 18 (of 18 total)
  • Author
    Posts
  • #34126

    Kris
    Participant

    So my carvings that I have been doing today are messed up a bit… not sure why and wondering if this odd Z movement has anything to do with it?

    Looking for advice – suggestions – troubleshooting help.

    #34127

    Barry
    Participant

    1 Bring that dust pipe down to maybe the length of the spindle, shorter if you can.
    2 Maybe see if you can tighten up the Z carriage a little. Almost sounds like the lower bearings aren’t making contact.

    #34128

    Kris
    Participant

    Barry – how do you tighten up the z ?

    I should know this but I don’t want to crack any of the printed parts.

    I can hear clicking when I move it so yes, I think there are times were the bearings are not touching.

    #34129

    Kris
    Participant

    Upon closer inspection I can feel two or three bearing just spin freely when moving the x and y axis.

    Not sure how I tighten those up.

    #34137

    Barry
    Participant

    Depending on which wheels you feel spin it will be a couple different bolts. If it’s the up/down part of the Z assembly then it’s the long bolts running at a 45deg angle at the top of this picture. https://www.vicious1.com/wp-content/uploads/2015/07/IMG_20160527_130356-e1464383481346.jpg See how they’ll squeeze the outer bearing in when tightened? Doesn’t need to be tightened too much.
    If it’s the big pieces on the X Y rails, you would tighten the bolts on the bottom of this picture. https://www.vicious1.com/wp-content/uploads/2015/07/IMG_20160527_122518-e1471797921568.jpg Same thing, it squeezes the bearings in. Not much pressure, it will effect squareness if too tight.

    #34139

    Ryan
    Keymaster

    Try the same exact cut without the pvc tube.

    The center seems a bit wobbly but I think 90% is the pvc. Just try one with holding the vac by hand.

    I have a few other suggestions but I think that will fix a majority of it. The Harley sign looks as if your table was unlevel at first glance then I realized I think the cruddy side was just further away from your vac hose and was getting pulled around.

    #34144

    Jeffeb3
    Participant

    I think you’re fighting a couple issues here.

    First, with the Harley sign, you’re cutting that entirely with a 90 degree V-Bit, right? It looks to me like the bit is just going deeper on the right than the left (right and left when reading the logo). If you look at the box around “Harley Davidson”, it gets thinner and thinner from left to right. I think that means the right side was cutting deeper, which made the width of those cuts wider (v-bit).

    With the first route 66 sign, That looks like tearout, which is going to be a problem with pine, or if you have duller bits, or you’re pushing the bit through too fast. I don’t know enough to suggest a way to fix that. I was getting a bunch of tear out with my straight cut bit in plywood, and I changed to a downcut, but that won’t work with a v bit. Maybe there’s a way to make a rough cut, and then a finishing pass, maybe the finishing pass won’t be as aggressive?

    With the second route 66 sign, it looks like maybe the machine moved during the tool change. Or else maybe it skipped a few steps. The motor skipping steps sounds like gears skipping teeth (even though it’s not damaging anything). You should be able to hear it. The reason I think it’s skipped, or misregistered is that it’s still really consistent. If it was something that was loose, it would be bouncing back and forth between the two extremes, and you’d end up with a bunch of spaghetti. This is a perfect cut, just 2mm away from the right location.

    w.r.t. the X axis rocking like that, I don’t think that it is your issue for these pieces. The bit moving through the work should be like a knife through butter, and it won’t have the strength to lift that whole assembly. If your vac hose or a cord tugs on it, then that could cause that assembly to lift, but I think the affect isn’t going to be as regular. I would remove the vac hose, as Ryan suggested, at least until you have a better understanding of where these problems are coming from. I would be careful about tightening it too much.

    #34145

    Jeffeb3
    Participant

    Also, those signs are looking awesome. You’re getting there, stick with it.

    Are you just staining them before cutting them with regular wood stain?

    #34148

    Kris
    Participant

    Barry / Jeff – I did another video below… I tend to ramble so sorry for the length. I agree on the pine tear out and speeds. The Harley sign really shows there is something off. When these are loaded onto the machine they lay horizontally as my Y axis is only about 11.5″ where the X is almost 30″ and the boards are 15.5″ long. I have a strong suspicion that the X tube that goes through the middle assembly is warped and I have a replacement tube but have been too lazy to change it. However, I don’t think that is the cause of the deep cut on the Y axis movement… I could be that the board I have is warped too. I may have to try a better board to see …. however, in this video I show a couple of areas where the bearings are not touching the tubes and i am not sure what first action I should take to help resolve that – or should I not be overly concerned…. given I have a warped tube and a warped board and the route 66 issue is most likely tear out and speed issues. I may be just over thinking this too much.

    Jeff – yes prestained the boards with Rustolem Kona stain.. really like how they turn out.

    I have migrated away from using Estlcam and Repetitier and I am using Vcarve Pro and Cut2d Desktop.

    #34169

    Jeffeb3
    Participant

    w.r.t. tightening, the red pieces form sort of a ‘U’. The bolt that goes through the bottom of the ‘U’ will pull close the ‘U’ a little bit, so that should pull those bearings a little closer. I don’t think tightening or loosening those bolts to get that small amount of slop out is going to matter though.

    I think the Harley sign is because the xy plane isn’t perfectly parallel with the top of the Harley board. The side with the thicker lines was just a tad higher. The wood might have been slightly twisted, or the wood is not a consistent thickness, or there was some sawdust under the workpiece, or the spoil board is so wrecked that part of the board is sinking under clamping pressure, or the spoil board just isn’t flat, or just isn’t parallel to the xy plane.

    I think you can easily confirm this with a good set of calipers. In this image, I think the left part was lower and the right part was higher. Measure the width of the box where I’ve drawn the parallel red lines, and measure the depth where I’ve drawn the red ‘x’s. The depth of cut will tell us the most, but as an added bonus, the difference in width should be 2x the difference in depth. So if it was 1mm deeper then the width of the box would be 2mm smaller. If that’s the case, then you don’t have to go looking at any slop in the x,y, you just have to find out why the top of the work wasn’t “level” (in the same way a 3D printer needs to be “level”).

    depth_test

    If you find out it’s a depth problem, you can make a faster test for that. Just make a gcode file with several holes drilled to a small depth, like 2mm. Make them in several places, like each corner and in the center, or a 3×3 grid of holes. You can measure the depth of those holes to tell you if the top of the workpiece is level to the tool.

    If you actually want to fix it, you’ll have to find the problem first. I should also mention that getting it perfectly flat is pretty much impossible, there will always be some amount of difference. But I think you can do better.

    Attachments:
    #34174

    Kris
    Participant

    So I am still trying to wrap my head around this issue.

    I just did this carve with a 45 degree scrimshaw going to a depth of .04 inches.

    This indeed confirms that the right side is cutting deeper or in correct terms the Y axis.

    This board is totally level and the spoil board although tore up is level too.

    I measured the Harley sign from before and the left bar in your image measures 3.30mm whereas the right side is 2.30mm.

    #34177

    Kris
    Participant

    I bought one of the dial things to help troubleshoot and determine how level the tip would be across the entire work surface.

    So is it possible that the issue is not the center assembly but more so the entire Y is not level and it goes deeper as the Y axis increases?

    #34179

    Barry
    Participant

    Easy way to test how parallel your gantry is to the surface is to drop your bit down to about a mm off the spoil board. Best to use a spot that’s not too torn up for the width of the board. Then jog the bot over to the other side of your board about 10mm at a time. It should stay pretty close to 1mm above the board the whole time. If it starts dragging, you’re not parallel. Looking at your cuts, I’d say your spoil board is higher on the right side of your table.

    #34180

    Jeffeb3
    Participant
    So is it possible that the issue is not the center assembly but more so the entire Y is not level and it goes deeper as the Y axis increases?

    That is one possibility. It would be useful to narrow down whether it’s the spoil board, the work piece, or the gantry.

    Did you measure the depth on the original Harley cut?

    #34185

    Kris
    Participant

    So the depth of the Harley cut per your photo…. Left is .70mm and the right is 1.12mm

    I flipped the mdf spoil board over and sanded the bumps of from drilling through and then I homed the x/y and dropped it down on my thickest feeler gauge.

    When I move the Y axis away from the home position it indeed drops lower and at the max Y I cannot place the feeler underneath it.

    I am also finding this true on the full length of X at the max Y.

    So with the spindle not level in all x/y position and a warped board that explains the deep right sided cuts.

    Question is how do I fix… is this merely adjusting the legs to proper levelness across the work surface or is this also something to do with the center assembly.

    My gut is telling me that I need to re-level the entire machine??

    #34186

    Jeffeb3
    Participant

    That’s good news. A slope is easier to fix than a bow. As for fixing, it’s pretty hard to tell what part is out of whack remotely. Here are some things to check:

    Is the thing the spoil board is sitting on flat and we’ll supported?

    Are the legs all the same length? Are they registered to the same flat surface? You could use a block as a big feeler gauge to make them all the same height.

    If you look along the x axis are the y pipes all parallel? Same for y, x.

    I don’t think the center assembly could be causing it, especially not that little wiggle from the bearings. I bet the pipes have a slope, and it’s in the feet or something. If the Harley design is 1/4 of your total y axis, and you measured about 0.5mm, then the +y is off by 2mm, just to give you an idea of what you’re looking for.

    #34188

    I think the easiest way to do this is to purchase a flattening bit and run it all the way across your spoil board to make it flat.
    First, use a pencil to draw all over your spoil board, then take a few light passes until you cannot see any trace of the pencil marks anymore. Your board should be perfectly leveled by then.

    Also, if you suspect your X axis tube to be bent, just turn it 180 degree and see if it makes any difference. Way easier to do than removing it.

    Your gantry assembly seems quite loose. You can try to tighten the bolts to make all the bearing touch, but in most cases it won’t be enough, because you cannot adjust much the bearing tension of this machine, unfortunately. An other solution I used was to heat the plastic parts with a heat gun and manually force the bearing to be closer to each other. This worked for me, until I switched to an other bearing system.

    #34206

    Ryan
    Keymaster

    I agree with all of the above.

    Don’t worry so much about the bearing thing now. The bow in the tube would have to be pretty severe to the cut to be that far off. Just make sure all the corners are the same height to the best of your abilities and then check that your table hasn’t developed a hump or major warp. Start with the easiest to check.

    I know it is probably frustrating, but the carve is kind of an advanced cut, and a 90 degree bit it ever harder to control. The sharper the point the less severe a depth error shows in the work. If you were carving this with a regular end mill you wouldn’t even notice a 1 mm depth difference.

Viewing 18 posts - 1 through 18 (of 18 total)

You must be logged in to reply to this topic.