I think it’s #2, and I think it’s some goofiness in the carriages.
I measured the squareness of the pipes to the z carriage part, and they are very square, but the carriages themselves aren’t doing so well. All these pictures were taken without rotating the camera.
You can see that the back wheel mounts are to the right, and the front ones are to the left.
I am also sure the table (under the spoil board) is square, and before turning on the motors, I’m making sure that each carriage is flush to the front of that table.
I think I just need to nudge them a little in the right direction. I’m not sure why they are tracking differently front to back, but my guess is that this is just happening over a lot of movements (and probably exaggerated with some missed steps, or mistakes I made earlier). Maybe I should make some kind of bracket to adjust the square before I start the machine…
It looks like I’m arguing, because of the order of the posts, but I saw this after I responded. I agree with you. I think the goofy tracking is what caused them to me misaligned.
I was able to nudge them back to aligned. The bottom wheels touch the bottom of the table, but I can still turn them. I’m not sure if that’s a good or a bad thing. Maybe they should be tighter?
I also have been driving “off” the front, where the thing is only supported by the top wheels. That might be a problem. I can fill that area out with more material, but I was hoping it wasn’t necessary.
As soon as it moved, it tracked back to offset (in the same direction).
Don’t really understand it, but I think it’s the pipe joint. When I move the carts back to straight, the pipes are no longer square… Makes some sense, sort of… I can’t think of square in 3D…
I’ll see if I can force the carts to be square, then adjust the pipes until they are also square. Didn’t you suggest it was // or \ like a week ago ?
Crashed it…never even left the ground had to remap the motors, gunna try again.
Cali is great, but we pay for it in rent (cuz we can’t afford houses here), and it isn’t perfect there was a mud puddle and I’m wearing flip flops, could have been horrible.
Well, I am circling the drain, and I have a workaround that is working for my simple test.
The Z rails (the 11" pipes) are square to the table top as long as the wheels are in line. After moving forward and backward, it gets misaligned. I thought I could fix that by loosening the connection on the long pipes, but duh, I can only make them shorter, longer, or trapezoidal by moving those. But they are a parallelogram. I think I need to reprint the little pieces in the middle of that joint, at least, maybe those entire joints.
But, I do have a neat workaround. Like I said, the root problem (I think) is that as the wheels turn, it’s getting off track. So I ripped some 3/4" plywood into some strips, and installed them 1" from the edge of the table. Then I loosened the long pipes, and pulled it together so the wheels were touching those strips. I could do it on the bottom too, but since there aren’t pipes pulling the bottom together, I’m not sure how much it will help.
( It’s the middle one, it’s a little blurry, but it’s smooth IRL )
Something is not square. I have a suspicion that it’s either the printed joint, or one of the screws that holds the wheels on is bent.
I can tell from where the hack/track is touching the wheels that the front left and rear right want to move past the track. There is a small gap in the other two wheels. The original cut edge was pretty sharp, so I rounded it over with some sand paper before installing it to try to reduce the wear on the wheels.
I don’t think the hack/track is the right final solution, but I have something I want to cut today and I think this will get me moving until those parts are reprinted.
Once you get it working, make sure your plywood you are cutting is flat! So far I’ve been able to make big pieces of plywood into smaller pieces of scrap plywood. Haven’t cut a good part yet… I have it set to cut 20mm deep to cut 3/4" plywood, but it’s going almost 30mm, not sure what’s happening there, then I have it set to have a 10mm clearance for rapid moves, but it’s dragging the bit. Buying flat plywood at Lowe’s is impossible, all they have is boat plywood. I tried to use a screw in the middle of the plywood to hold it flat, but after 10 minutes of cutting it pulled out of the hardboard I have my table made out of. Because of the height difference, my holding tabs aren’t being cut, so I just had a part pop up and the router bound up on it pulling everything out of zero.
@Barry, OUCH. You think it’s just due to the incoming plywood? Is your table flat enough? You could take the plywood off, and manually move around to see what Z value it is at a few locations. I have a 3/4" Red Oak spoil board, so the screws are holding well for me, but I haven’t cut anything huge yet.
The hack/tracks are working well. I’m working on a new fence based on John Heisz’s plans (ibuildit.ca).
I cut a the CAM handle, but didn’t take a pic before I glued it together. Then I cut the words “HEISZMEYER” into the top piece (Biesemeyer is a popular aftermarket fence).
I don’t know why I don’t use foam more often, especially for prototypes. It’s cheap, fast, and you can just push it into place to see where it’s failing.
The thing that seems very strange to me is that my vertical pipes seem to be very similar to yours, but mine seems to pocket just fine using 3mm steps. Granted I’ve only cut about 7mm deep so far and all in mdf.
But multiple parts from different areas of the table all line up perfectly when I stack them. Turns out yesterday’s cut didn’t even have the bottom wheels on the near side touching the rail.
The vertical pipes aren’t the root problem. As the gantry went in +Y (Y is on the wheels on my machine), it would move in the +X, because the carriages weren’t tracking straight. So as it would travel back and forth, it would slip and that was causing the steps.
I think because it was doing that and probably different underneath, I think that was causing the z pipes to end up crooked. They look straight now.
I also think it was consistent because I kept going back to the front of the table before each test, which was pulling the gantry to one side, then I would move it to the work area, and cut. Then it would move back to the other side.
I don’t think the parts were square in X/Y, but the smoking gun was that the steps were about the same size with 2.5mm depth and 1mm depth. If it was the z pipe angle, then they would be proportionally smaller.
If your z axis has that angle, and it was affecting the cut, I would think you’d see small steps, and one side of a pocket would be perpendicular, but the other side would be sloped. It would be tough to measure, unless you cut deep, and measured the width at the top and bottom of the pocket. It’s only what? 1/2" over 11"? That’s going to be 0.0125" over 7mm, so not very noticeable.
I have a 4th driver that I can make mirror one of the other drivers. Which axis would need it the most? I’m thinking the wheeled axis (my Y, designed as X). The Z would make sense because it’s carrying more load, with the weight of the gantry, but it has the screws for mechanical advantage… Ryan, I’m hoping you have some math that would help me.
The axis that is pulling the wheels. Now that we are wired in series, I can easily max out my steppers before the drivers. I don’t think this will gain you any advantage, but you never know till you try.
I should probably try wiring in series. It should take me all of ten minutes to do it since I have everything wired up with removable connectors. I’m really just looking for things to change. I’ll do this instead of the mirrored driver, because then I won’t have to take the pi out of it’s box.
The only skipped steps or stepper problems I’ve had in a long time are due to my connectors coming partially disconnected. It happened once with the Y motor and it happened yesterday with one of the X motors.
I upgraded the pi’s OS, and I updated to the latest CNC.js (1.9.7). I want to get a webcam timelapse recording of my gcode, but that will have to wait until I get a solid block of time to work on it.
Yesterday I started trying to push my lowrider, 2 hours of cutting and I was getting board. I found the belts stretching if I went to fast. I looked at thicker belt. It is way more expensive, and the pulleys and idlers are as well. The 6mm gt2 is dirt cheap from printers in mass production, the bigger setup is at least 3x’s as much if not more. As soon as I get the sand table part on the printer I am going to try and double up the belt, if that doesn’t work I am going to stack them face to face. Two 6mm belts should be stronger than a 8mm or at least as strong as a 10mm right? Two belts will also always be in slightly different tensions so that could be a good thing as well.
Seems like twice as many zip ties for folks to complain about. IDK. I thought these belts were supposed to be pretty tough to stretch. I’m guessing it works pretty much like a spring, so the deflection is proportional to the distance and the force. It will probably just change that stretch by 1/2 with twice the belt (if they are both configured the same). If the belts are really an issue, then 2x might not be enough of an improvement. Maybe there’s a better way to reinforce them? Are there belts with steel inside them, or made from a serpentine belt?
At some point, the answer is just, c’mon! It’s an 8 foot long machine! Is 1/8" going to kill you?
What do you set your accelerations to? I know they are detrimental to printing fast, and to lasers, but for CNC’ing, reducing them gives a perception of quality, and will reduce the force on the belts. I was just messing with mine, and the defaults for grbl are set to 10mm/sec^2. I set mine to 100mm/sec^2 for xy and 10 for z. I have no idea where I got them from, but I was hopefully smarter then.
The belts we use are reinforced, and one side of mine is worse than the other. It is the side we walk by, and it always gets hit and stretched and plucked like a guitar. I might have broken some of the fibers in it. Maybe I should just replace it and see if that helps. Lower accelerations would really help.
The ones I have are as fast as I am comfortable with that still give half decent 3D printing quality…for the MPCNC. So maybe I should lower them an make a separate Lowrider firmware again.
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