How to: Get hardware as accurate as possible?
- Tools you gonna need
- Square tool
- Metal rules (optional)
Using a long metal rule against the z-frame shows quite good if the x-axis is perpendicular to the y-axis as you can move the bed and compare the bed lines with the ruler. Or eye ball it like shown in http://manual.prusa3d.com/Guide/7.+PSU+%26+Heatbed+assembly/297?lang=en#s5058
In case you have a MK2/s or MK25:
The 100 mm are a good start. But i spend lot of time to get the 100mm between the printed parts and the Z-frame, and still got 'severely skewed'...Final solution was to use a 90° square/corner tool on the 155 line (any line) on one side of the heated bed and gently push the y-axis against the x-axis rods, and then without touching the y-axis place the 90° corner tool on the other side of the heated bed against the x-axis rods and eyeball/measure the difference/distance. In my case i had to adjust it to 101.80mm and 100.10mm to get the 'congratulations, you are a master MK2 kit builder' :-) i mean perpendicular.
Conclusion: Try to get the 100mm distance BUT check the heated bed lines up in 90° angle with the x-axis, even if you get different distances (1-2cm not more, then something else can be wrong)
I use also the square tool to verify if the z-frame is perpendicular to y-axis.
By placing it on the bed and against the x-rods the square tool should touch both x-rods. How higher you move the x-axis the more you can see if it touches both rods.
This is bit more difficult to adjust:
- on a MK2/s and MK2.5 you can try to use the PSU as a stiffening/alignment device buy moving it. Or try to adjust the z-frame until both rods have contact with the square tool.
- On a MK3 i expect better. But if it is you may want to try to adjust the y-rod holders.
Example: The top x-rod has no contact while the bottom one has.
Issue is that the Z-frame leans too far back ... or the bed + y-carriage + y-rods are lower at the front than back (hope got it right).
As the MK2/s and MK2.5 have y-corners with threaded rods there is not that much you can do to get front or back up or down. You can try to use the PSU or try to tight down the M10 nuts in a different way on the Z-frame to correct it.
On the other hand the MK3 y-rods holders are screwed to the front and back plate and there should be bit play to get small imperfection corrected.
- Tools you gonna need
- Calipers
If you are in the assembly process take the time to measure the dimensions of the bed spacers:
- MK42 bed which is used on the Prusa i3 MK2/s
- Use the depth measuring part of the calipers and measure the distance of all spacers to the PCB they should be identical. There are several Prusa forum and Facebook groups posts that some weren't that equal. You can try to shim all to the same length. Few users reported that the washers had different dimensions and removed them.
- MK52 bed which is used on Prusa i3 MK2.5 and MK3
- Measure all 6x6x3t spacers with the calipers
You want to get the bed as perpendicular as possible in x,y,z but at the same time you also should try to get the bed as leveled as possible.
After having the printer perpendicular with a low skewed degrees value and xyz calibrated is the time to get the bed hardware wise as leveled as possible.
Before you try to do anything with the bed check the y-rods are leveled
- Measure at all 4 bed corners the distance of the y-rods to the
- threaded rod on MK2/s and MK2.5
- extrusion on MK3
- flat surface the printer stands on on the MK2/s and MK2.5
Now we can start with the bed leveling
- Measure the distance from the y-carriage to PCB at all point where the it is screwed to
- double check that all screws are tightened the same and there no spaces between bed and spacers
- you can shim the spacers if needed (but try to keep all the same)
- if there is a significant difference at some places you can try to put precision shim washers between
- Connect your printer via USB and connect it to Pronterface
- Do a z-calibration
- Use G1 X20 Y0 Z100 to move the x-axis and extruder
- Measure from the top x-rod to the bed, while the depth measure part touches both x-rods, on the left, center, and right
- Move bed with G1 Y95 and measure again like before
- Move bed with G1 Y180 and measure again
| Left | Center | Right | |||
|---|---|---|---|---|---|
| Rear | 131.15 | 131.57 | 131.82 | ||
| Middle | 131.13 | 131.33 | 131.37 | ||
| Front | 131.27 | 131.33 | 131.05 |
We can use these values to find potential spots to investigate by visualize it
Here you can see that the back right corner is quiet high compared to the center. By subtracting the center value from the others you can see how much it differs:
| Left | Center | Right | |||
|---|---|---|---|---|---|
| -0.18 | 0.24 | 0.49 | |||
| Rear | 131.15 | 131.57 | 131.82 | ||
| Middle | -0.20 | 131.13 | 131.33 | 131.37 | 0.04 |
| Front | 131.27 | 131.33 | 131.05 | ||
| -0.06 | 0.00 | -0.28 |
As we should be able to use precision shim washers or shim the spacers to +-0.10 try to fix the spacers/washers/screws at least with an value above/below +-0.20. In this case
- With a MK42 heated bed (Prusa i3 MK2/s) Rear/Right and Front/Right (as it has 6 spacers, 4 in the corners and 2 in the center)
- With a MK52 heated bed (Prusa i3 MK2.5 and MK3) Middle/Left, Rear/Center, Rear/Right and Front/Right (as it has 9 spacers)
Re-measure with calipers and compare your results after every change.