As described in this thread: http://forum.velleman.eu/viewtopic.php?f=62&t=13772 I have had some issue with Z wobble. After trying out raby’s suggestion and moving the Z rod as far out of the coupler as possible (and the same with the stepper motor rod) the wobble now seems to be gone.
I made a few comparison shots, also changing the temperature just to see what how much improvement (if any) would be visible.
The print is a Ø10 mm cylinder, 50 mm height, 2 shells thick and 0.1 mm layer height. Printed on a 55 deg C heated aluminum bed with Velleman White PLA and close to standard slow settings.
It was difficult to get a good shot, but with a flashlight pointing at the rods the shadows was significantly amplified. This however also makes the good prints look bad; in normal diffuse lighting the middle one is actually extremely nice.
The left most print is prior to coupler change. The bands are clearly visible. Counting the bands actually seems to indicate 1.5 mm cycle; I thought the M8 threaded rod had a 1.25 mm pitch, but anyhow…
After coupler change (well, actually rod position change) the prints is significantly improved. The first 30 mm I printed with the same temperature, but then decided to up it to 215 deg C just to see the effect. As can be seen this is not a good idea.
To test the temperature even further I made the right most print. Interestingly there seems to be some brittle bands where I change the temperature; I wonder why this is so. The brittleness became quite clear when I tried to pull the print off the bed… Also interesting is that the top 10 mm where I use the same temperature as for the middle print, the quality never seems to revert back to quite the same level as for the middle print.
Conclusion: Velleman, why did you write in the assembly instructions to make sure the rods are inserted fully??? It should be quite evident that this is not at all the case. And then there is the temperature: 190 deg C seems to be much better than the higher temperatures; at least for visual appearence. I wonder if the inter-layer bonding is as strong for the lower temperatures.
1.25 is the pitch of a standard plain rod but the Trapezoidal rod has a pitch of 1.5 mm.
After a few tests, everyone noticed that the suggested temperatures are far too high. 190 is enough for PLA and 220 for ABS. It seems that the NTC setting in the firmware is not optimal and instead of the #5 setting the #10 is a far better option.
I didn’t modify the setting to keep some references. Equally the steps/mm of the extruder is too high and I had to lower the flow accordingly (about 75% with some variations depending on the brand of filament).
hi Pm… I have some comments on your post.
I did mount the coupler as it was told , good down over the axis . I noticed that the tread would not go into the iglidur tread ,and filed the rod in one end , it could be seen that it was grinded ,and this always leave sharp metal. when I had done this ,the treaded rod run into the iglidur smooth.
maybe your problem is here, maybe you remember it did not pass throug easy )
then I was intersted in the sound the z would make, as I have seen posts here. But it run without any noise . and later I oiled it a bit. I notice that the free end wobles a bit , maybe 2 mm swinging out , but it makes no problem.
Then I started to print in early january. the vertical sides look very smooth , there are a pattern but not more than maybe 0,05-0,1 mm differences.
until now. now it suddenly began making patterns like your photo. I had the theory that it must drive a bit slower and after half a turn of z rod it would run faster again… because the layers seem to fill more and after 0,75 mm they fill less . I saw that the z coupler is distorted ,and wonder how this happened , but it seems that the layers widt will change with 1,5 mm repetision ,if there are any thing wrong with the spindle… or bearing or If you have mounted the coupler in the outer end of the axis, you are sure to get problems as the screw mount then will flex a bit if it is needed . … I’m sure my surface is much better than yours ,so you will be able to get a better look .
alex
I did the same, separated motor axis and Z rod from each other in coupler and got lot better results, but when I printed out thingiverse.com/thing:635751 I got perfect results so try it, doesn’t take too much time to print and you will notice difference directly, at least I did.
I have to correct myself in last mail.
There is a drawing in another post , its in "Z axis vibration"tread
here you see that the rods goes in until the flexible part begin, I meant the same, but did not express it well.
alex
Also interesting is that the top 10 mm where I use the same temperature as for the middle print, the quality never seems to revert back to quite the same level as for the middle print.