Determining Maximum Layer Height based on Nozzle size?

[Pattycakes]

How do you determine what you want your max layer height to be when printing with different sized nozzles? What's a good percentage to use?

I'm trying to print using a 0.25 nozzle but have no clue what to set my layer height max at. Any suggestions?

[3dkarma]

Layer height should be no more than 80% of nozzle diameter, according to the reprap calibration guide. Extrusion width should be greater than nozzle diameter.

[meka]

Hi Guys,

I do think you also have to take into consideration the threaded rods and motor angles for your Z-axis.

Not 100% sure how to do it and i'm not even sure the way I do it is correct, so hopefully someone else can help us out here.

[RobH2]

I'm not sure that the threaded rods make any difference in what the theoretical maximum layer height should be for a given nozzle diameter. No threaded rod is going to make a .25 nozzle lay down a .30 height layer. The reason the layer height should not really be more than 80% of the nozzle diameter is that you need to force each layer into each other just a bit so they stick. If you extrude too high above a subsequent layer, then adhesion is severely affected. Since the nozzles extrude straight down, you can't "push" material backwards against itself to make it thicker than the nozzle diameter.

The threaded rods might affect a "minimum" layer height somehow but I don't think a maximum layer height is affected by them.

[KDog]

Your z-axis screw can cause ribbing if it is not straight. We've discussed this at length at printrbottalk and threw lots of numbers and calculations around. In the end it all boiled down to how straight the lead screw is and how it is attached to the stepper. I'd recommend you use 0.2mm as a starting layer height and not worry about your screw pitch and diameter.

[RobH2]

KDog, sure, I understand that and it's good to keep that info in the back of your mind for fine tuning. But I think in answering the initial question, we all generally assume that our machine's hardware is behaving and capable of performing within tolerance. A ribbing induced by a curved rod doesn't affect the theoretical maximum layer height suggestion. It only determines if it is achievable or not.

[KDog]

I was responding to the suggestion that screw pitch and diameter had to be used to calculate the layer heights that you could print at. The reason folks were exploring these calculations was to reduce z-ribbing which, in the end, was determined not to be effected by this and was discounted. A layer height of 0.2mm is the 80% target range for a 0.25mm nozzle and would be, imho, a good place to start with this nozzle. Sorry if I wasn't a bit more clear.

[RobH2]

No KDog, I understand what you are saying and right you are. I was just continuing to contemplate about it all. Your input was good and valid to be sure.

[3dkarma]

The layer height needs to take into account the z-axis motor step angle and threaded rod screw pitch such that the height is a multiple of full steps of the stepper motors. The simplest way to do this is to use the reprap calculator. The calculator can also help you with your X & Y steps per mm and acceleration settings.

[KDog]

I've spent some time trying to figure the z-ribbing out. There are some very good write-ups on printrbottalk about it. However, when folks finally started calculating the real values for the ribbing you can expect for having mis-matched screw pitch and step the values were in the single-digit micron range. This is sub-microscopic. The conclusion is that visible z-ribbing is a result of lead screw wobble, loose screws, etc. The lead screw measurements do not effect visible z-ribbing at all. Please feel free to head on over to their forum and do some reading on this.