Topics created by Peter120

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After lots of testing I am finally ok with this version.
Turns out the seesaw concept is amazingly accurate for measuring the nozzle tip to probe height offset. The resulting measurement produces single digit micron errors. While this level of accuracy is overkill; all elephant foot is gone.

I used a ¼”-28tpi hex bolt and with a hack saw converted it into a T-bolt. The friction (rotation brake) results from ball bearing preload. Two belleville washers (cupped spring washers) axially squeeze the inner bearing races together as the nut is tightened which increases the braking force. The nut also secures the T-bolt to the 2040 extrusion. An aluminum pipe is used as a spacer between the 2040 extrusion and the belleville washer.

The seesaw "board" is bent to lower the T-bolt mounting position on the 2040 extrusion.

A paper clip was formed into a ramp that resets the seesaw height for the next offset probing cycle whenever the Y axis is homed.

For cleaning plastic from the nozzle tip, I used a 614 foil from an old Braun shaver (it didn’t have any big holes when I started). This is effective for cleaning plastic from a HOT nozzle tip over a few mm of Z height but it is not fully finished.

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Some parts for a previous design that were not used.
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Cheers -Peter

It is not a problem but an observation which I have been pondering. Typically, I slice thin layers with a wide paving width using cooler filament temperatures. Recently I Increased the layer thickness to reduce the print time which resulted in a failed print. The surprising and odd bit was the first several layers went down just fine. The thermal mass of the heater block provided lots of extrusion capability at the start but the PID servo loop was not able to keep up. Well it did catch up after the filament was ground free in the extruder and the print failed. I have done PID extruder tuning and the thermal control loop is responsive and seems critically damped but with a slow time constant. Adding the filament E steps would be and instantaneous prediction of a future pending extruder temperature change. Fuzzy logic is a very simple form of artificial intelligence that learns on the job and it is good for controlling nonlinear systems.

Thanks for the welcome and sharing your thoughts.
My underlying interest is just how accurate can a PLA object be printed or better perhaps is what is limiting print accuracy. Is SLA required for better print accuracy or can FDM be improved.

dc42 Point 1 is valid and it was not on my radar. I have a Cetus with a Z axis belt which I can coax it into showing micro stepping errors on selected printing tests. You picked a good printer geometry example. I thought about a springy leadscrew to motor shaft coupler supporting the build platform weight.

Point 2 I did consider but figured that internally the stepper is periodic every 4 steps or in my case 0.8mm and that one could choose a winding and polarity that resulted in some step position margin; however, I was thinking of belts and not screws. Your point 1 using a leadscrew might be hit and miss for Z, but probably not for the X and Y belts.
I found this link where they measured the stepper accuracy and it is obvious why thin Z layers have a problem with belts.
https://www.applied-motion.com/news/2015/10/stepper-motor-accuracy
Between two adjacent bad steps the difference error is 1/10 of a step which is 0.02mm for my belts. This is small until you think about the error as a percentage of a 0.05mm layer. Micro stepping errors would also subtlety vary the extruder nozzle flow rate.

deckingman. The interference fringe is sensitive to several printer errors but the trick would be separating out the individual variables and adjusting the printer. I posted an extrusion calibration test that you might like. It is based loosely on a micrometer. You print a nut and bolt and the snug final angular position measures the axial thread clearance which is known for the STL model printed. Flip the nut over and remeasure the angle and you get the overhanging thread sag.
https://www.thingiverse.com/thing:3390910