My next prints have largely been additional tuning of the printer, the test print being a roller platform for the PLA spool, with varying degrees of success.
My first issue has been that I have issues with Z height for subsequent layers of a print – I can manage to lay down a beautiful first layer, yet one or two layers later the print is being dragged off the build platform because the print head has not risen enough.
At first I thought that this was because the print was not sticking well enough and tried various different methods of helping the print to stay put, increasing/decreasing the heated bed temperature, Kapton tape, PVA glue, bunny ears, all to no effect, the print fails after about 10-11 layers after being dragged off the bed.
This caused me to look more closely at the Z movement. I double checked the free movement of the axis by moving it up 100mm and back down again.
Initially I was having some results that seemed to imply that my steps/mm were out and I reset these a couple of times until one of the Z screws came loose from the motor and after putting it back in place and re-calibrating, I was back at my original figure of 4000 steps/mm for M5 threaded rod.
The next print was again promptly dragged off the bed again due to the Z axis not having risen enough.
This is when I started reading all sorts of forum posts relating to similar issues, but not really finding anything that would solve my issue, they mainly centre around bed levelling and additional methods of adhesion or bed temperature.
Eventually I stumbled across a posting that related to maximum feed rate and decided to give it a try, changing the MAX_FEEDRATE_Z value from 5 to 3.
This had the effect of slowing down the speed that the Z axis attempts to respond to requests. The result of the change was quite dramatic – I could now see that new layers actually had a noticeable height where previously they had looked more and more squashed.
Looks like on the 5 setting, the acceleration was such that it was causing the stepper to miss steps and slowing it down has stopped this from happening
This new setting combined with a 70C heated bed and I had no corner lifting and no failure of the print due to being dragged off the print surface.
The print still eventually failed, but this was due to insufficient hot end temperature at 180C to cause the new layer to fuse with the existing plastic so the print failed due to de-lamination of the filaments.
I found a table that someone had compiled that showed maximum feed rates against temperature
Considering at this point that I was using 180C and 30mm/s I was probably a little outside what is realistic.
The next print at 200C was much stronger exhibiting none of the previous de-lamination issues.
It still has issues in that the vertical ends are not straight – they wave back and forth, which does not imply an out of true Z axis, as this would be a more consistent and gradual “lean” of the print.
A test print of a 20mm cube shows the issue more clearly.
Not only is the print moving in the X direction, but also in the Y direction, albeit to a lesser extent.
My guess is that it is a combination of an X axis belt that is not taught enough and possibly too much acceleration on the X axis, much like my Z axis issue, so my next steps are to tighten the X belt again and then reduce the MAX_FEEDRATE_X setting down from 200 and possibly do the same for Y, even though I am not currently seeing the issue here, it could well be experiencing the issue but simply not showing due to the nature of the current test print.