Accuracy / calibration question

Rob Keeble

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GTA Ontario Canada
So I found errors on my parts decided to change software from Cura to Simplyfy3D and then ran a 20mm calibration block I found on thingiverse.

IMG_0139.jpg

One on right was first one and it had issues with the z axis.

So I played around with the manual control on Z at the height of the trouble and sure enough stepper seemed to be slipping on the lift drive screw.
Took an Allen key tightened up the coupling and ran it again watching the stepper and the head from an angle all the way through where problem previously occurred and no problem got a nice clean print.

So I measured with my callipers and now would like to know what sort of tolerance is realistic for this tech and these cheap machines.

Across my X I am getting 20.17 mm

Across my Y 19.83 mm

And z 20 mm

I would think this is bang on perfect for the machine.

Any alternative thoughts ??
 
I would live with that for my environment. Nothing that I am gonna build is gonna be any the worse for that sort of error. (About the width of two human hairs)

You might somewhere find a "steps/mm" setting that you could change to lose the 0.17mm - or a backlash setting that will take it out of the equation but the chances of that change not causing a different "error" would be small.
 
That's pretty darned good. I've not looked into if there are any backlash settings that can be adjusted in my firmware or S3d. One thing I've heard is that the tightness of the belts can affect the accuracy, so making sure they aren't too tight or too loose is one thing to verify. I also tend to lube the rails with WD-40 PTFE dry lube from time to time to make sure the bearings aren't sticking. I've gone to the drylin bearings now, and though they aren't supposed to require the lube, I find there is a noticeable difference in them lubed and unlubed with it.
 
Darren my bed and x axis run on rubber tyres between the aluminum extrusion. So no lube but I think they can be overtightened and that’s something I am going to address in my big upgrade I am getting prepared to do.


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I ran these at my normal print speeds (4800mm/min) so the sides aren't as smooth as the spacer I showed yesterday. But here is the example cube.
2018-01-15 16.42.14.jpg 2018-01-15 16.42.07.jpg

These are on my old printer, which I just finished the upgrade to the AM8 on.
2018-01-15 16.47.45.jpg 2018-01-15 16.48.14.jpg 2018-01-15 16.48.32.jpg

These are the new printer. Looks like I have some settings to check for the Z axis, which may be a firmware setting, but otherwise look pretty good.
2018-01-15 16.49.47.jpg 2018-01-15 16.49.22.jpg 2018-01-15 16.50.09.jpg
 
What do you think though about the difference on these between the new and the old?

Not sure, they are the exact same gcode file, so may be some setting with the firmware that I've changed at some point on the old. I will see if there's something different with the rods, maybe they are dragging a little causing a missed step or two. The other is the amount of extrusion per layer, which would add up (or just the opposite). The measurement is consistent on all sides of the cube, so leaning towards the extrusion/height theory.
 
Now that’s cool and amazing.

What about jerk and vibration or even belt stretch.

I still think it’s uncanny how precise these things are. In my view for what I want it’s not worth hunting for that tiny difference.



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