Z-axis positioning precision

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hardbc
Posts: 38
Joined: Tue May 17, 2016 1:44 pm

Z-axis positioning precision

Postby hardbc » Sat Jul 02, 2016 12:42 pm

When I got my N2 printer I started to do some testing and I noticed how poor the Z-axis positioning is. Raise3D wants to do something great - Z-axis adjustment at each print. In theory is nice, in practice depends on the implementation.

I've noticed that many of you tried to adjust the Z-axis screw with great precision. Guys, it really does not matter how you adjust the screw, in practice the repetability of Z-axis positioning is based on the *precision of the switch*. The switch used in the printer is a chinesse obscure one, I was not able to get its specs, but the best one on the market in the same format has a movement differential of 0.25mm. Most are around 1.25mm and I suspect that the switch is around 1mm.

The mechanics of the switch are outside the scope of this post, but you can check:
https://www.omron.com/ecb/products/pdf/ ... switch.pdf

Anyway - remember the idea. If you calibrate the printer to 0.15mm distance between the nozzle and the printing bed, on the next print the actual distance can be 0.5mm or it can even touch the bed. This is because the switch closing position is not designed to be precise. In particular the switch with the lever is a very poor choice. Raise3D tries to optimize in firmware - the printer will first close the switch, then moves several mm lower and starts microstep moving. This is not a solution, the switch will still be unprecise in its closing position. This is a common issue in CNC world. For X and Y axis does not matter, since that position is a reference only.

How to solve the problem?

I solved the problem quite well by changing the switch. New switch has MD=0.025mm, it's most likely 30 times more precise.

See below the old switch vs the new one. Impressive difference, right? :) Stock switch has lever removed in the picture.

test34.JPG


You will notice a big difference only on difficult prints, for example a cube will print quite similar.

If anyone is interested, I can provide further details.

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jmp
Posts: 215
Joined: Mon Mar 21, 2016 12:20 pm

Re: Z-axis positioning precision

Postby jmp » Sat Jul 02, 2016 6:34 pm

I'm sure people will want to know more details.
RL Name: Jason Preuss Thingiverse: JMP Youtube:http://youtube.com/c/patterntoprint Website: http://www.patterntoprint.com

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dhylands
Posts: 119
Joined: Mon Mar 21, 2016 9:11 pm

Re: Z-axis positioning precision

Postby dhylands » Sat Jul 02, 2016 6:40 pm

I'd be interested to get a manufacturer/part number for your switch.

Evan
Posts: 136
Joined: Mon Mar 21, 2016 3:07 pm

Re: Z-axis positioning precision

Postby Evan » Sat Jul 02, 2016 8:08 pm

This switch has been working fine for me on the raise3d as well as all the other printers that I have. Not to say that your new switch isn't better, but if your z height varies from print to print then it might be something other than the precision of the switch itself. Again, I've set the Z height once on the n2+ and have not had to change it since.

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rhines44
Posts: 71
Joined: Mon Jun 13, 2016 5:14 pm
Location: Illinois

Re: Z-axis positioning precision

Postby rhines44 » Tue Jul 12, 2016 6:32 pm

I wouldn't mind getting further details as well. I'll pm.

theRenegade
Posts: 60
Joined: Tue May 03, 2016 11:58 am

Re: Z-axis positioning precision

Postby theRenegade » Tue Jul 12, 2016 7:08 pm

Are (most of) you guys serious about that!?
The topic of this thread is Z-Axis positioning precision, this switch has nothing to do with it!

Z-Axis positioning occurs between every layer and there is no issue with the precision of this positioning, the switch is not related to it in any way.

What the switch does is setting the initial bed to nozzle distance before a print starts (the home position for the Z axis) and if this is not accurate your print could be welded to the bed or the bed damaged (if bed is too narrow) or the print could lift of the bed (bed too far from the nozzle).

In case someone experiences issues with a not accurate or repeatable initial Z-Height between prints there is a mod that uses a spring to fix the screw that actuates the switch. I did not have to adjust the switch ever except when switching plates with different heights.


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