My measurements for the distance the motors are offset up is actually different, I get about 544mm rather than the 534.6mm but I don’t think that really matters.
How good do you feel about the positioning of mounting points where the linkages attach to the sled? I’m not sure if we’ve seen a calculation for how precisely those need to be placed, but it could be a factor we haven’t looked into
that matters quite a bit, but IIRC the instructions have you position those
using the links themselves, so if that is done it shouldn’t matter.
check how solid the mounts are (make sure they don’t move if you yank on the top
of them), and check that if you put the center hold of the link on the router
bit the end holes match up with the mounts.
David Lang
you mentioned earlier that the motor distance was pretty consistant. what did
the rotation radius end up as?
you are close to correct, so small errors in these measurements can account for
this.
a difference of 1cm in yoffset is quite a bit, can you try to measure it and see
which measurement is closer to correct?
David Lang
I feel pretty confident about the linkage holes. I spent a lot of time measuring and laying out my original sled and drilled all the holes on a drill press.
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Are you saying that when you move the sled, it goes to precisely the right spot but when you cut something, your shapes are coming out oblong?
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So I am using the links initially for the motor offset but when I measure from cut 5 to the top of the sheet it adjusts that parameter down that ~1 cm dimension.
The mounts on the frame are quite solid I can take a quick picture but I have a stud wall type frame and I bolted unistrut extensions out to gain some extra width. I did attempt to make the frame mimic the original Maslow frame and the motors are mounted at 45 degree angles.
EDIT: I am going to whip up some new flat mounts. If I really go and pull on the very top of the motor I can get a small amount of deflection. This might be enough to be causing the increase in error when the two motors are pulling against each other.
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It sure seems like that. Which is why when you or someone else pointed out that my gcode was showing up oblong I thought you had it figured out.
It certainly looked that way when I loaded it in one viewer, but another looked ok.
A reverse .nc to .dxf confirms that it’s not in the gcode.
- vertical hight
- rotation radius
- motor distance
I tried in the past with +25% and -25% tweaking settings and got a picture what fine adjustment knob to turn.
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I am convinced it’s an issue with the vertical height, I know there is a mismatch in the number it is calculating versus what I am measuring. It is off by nearly 1 cm.
@dlang got me thinking more about my motor mounts and their overall stiffness. I think after playing around hanging some heavy things from them, they may be causing at least part of the issue. I rebuilt the top side of my frame to be a true top beam with the motors flat instead of at 45.
I would have test results now but in the process of switching over I dropped my top beam and cracked a piece of my linkage kit, it is currently being glued back together. So, tomorrow…
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Okay, just went through the calibration process again with my new top beam. After calibration the vertical height to the motors matches what I measure and the distance between the motors is also matching with what I am measuring. However, I am still off by approximately the same amount in my circles. There is only one variable left for me to play with; the rotation radius.
Playing with the simulator, as @bar and @blurfl were likely alluding to, my rotation radius is where I need to tweak. If I am confident in my linkage hole positioning I should expect to be closer to 260mm vs the 272.5mm I am seeing.
Should I zero out my chain sag number before I start playing with the rotation radius?
I would make a copy of my ground control.any file and save it somewhere, then just change the rotation radius and see what difference that made in cutting. No need to rerun the calibration, just change the value and try the cut.
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I just did that and both perturbations made it significantly worse.
The best I can get even with this top beam seems to be a loss of 1/16" vertically across a 10" circle dead center. Then near 1/4" loss across 6" at the top edge of the sheet.
I am too frustrated to continue down this path for the time being.
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Do you have pictures posted somewhere of your setup (frame, sled, mounts, etc.)? maybe something there we can spot that is leading to this.
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Alright guys I am almost back up and running, I built a new sled and that’s taken a bit to get it all set and ready to go. By tomorrow I should be ready to do some testing. I will also post some pictures of my setup.
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Pictures of the new sled.
I had originally been trying to cut a new sled on the Maslow, I had 2 main goals.
- I wanted to make sure the sled did not warp, the current sled I have has warped and I think is causing the issues with circles that I am having.
- Dust collection capabilities even while the z axis hung down in the bottom center.
My idea for the Maslow cut sled was stacked rings of 3/4" plywood and screw glue them on the sled. While I do have a router compass, I wasn’t confident I could locate the “datum” holes accurately without the assistance of a CNC machine so I used some really nice peices of plywood I picked up at IKEA standing on edge, arranged in straight lines, with interference fit box joints.
So the proof, as they say, is in the pudding. I will test it this afternoon.
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Nice! That looks rock solid. Waiting for the new circles
I haven’t seen the height on the linkage kit set that way before and I like it a lot! I had some issues with my linkage mounting points flexing. I don’t think you will have that issue at all!
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@bar, I was having the same issues with the linkage flexing and I wanted to fix that too.
So…I just ran my calibration and tried the good old 10" circle, dead center in the workspace again. I am exactly the same dimension out of round as I was before. The new top beam and fixing rocking sled made 0 difference.
I am totally stuck. I don’t understand how completely changing large parts of the machine are bringing me back to almost identical results unless the nc file is wrong or the machine is losing exactly the same number of mm each and every time. It is simply too consistent to be coincidence. Would someone be willing to cut just that center circle from the gcode I provided in an earlier post?
Pictures of my machine.
You might notice I have cut many circles.