Z-Axis Compressed

Hello everyone,

I recently acquired my first 3D printer about 3 months ago (a 7 year dream finally coming true). I love the thing and am printing all the time. I have already completed my first pair of props a little while back and moving onto my next.

As I have become more comfortable with the printer I have started to mess around a little with the settings in Cura, using the base Colorfabb nGen (High Detail) template as a basis. Most of the changes have been to get around the elephant foot it likes to create, as well as to prevent items from sticking to the bed so much. So z-offset, lowering the percent of the first layer (by default 125), as well as the fill of the first layer and tweaking temps.

Anyway, the other day I had an issue with my prints curling off the bed, which I have mostly resolved, but that’s not the real concern. What’s bugging me is my z-axis of prints is being compressed. I noticed this with a barrel I was printing (prop gun for a friend), as well as another piece that had a hole in it. The later piece I went to connect with another part that was meant to slide in to hear a crack. The hole after I looked at I realized wasn’t symmetrical. It was wider then taller. I thought I was seeing things when the barrel did it, but now it’s this part as well. This model was built to be re-assembled, so I doubt it’s a flaw with the model, especially when I look at it in Cura, and it looks perfectly round.

Sure I can print the item 90 degrees upright to get around that, but I would rather fix the issue. I am running 30% infill, 0.14mm layers, and I think 230 print speed (pretty sure, don’t have my settings on me at the office).

Does anyone have any idea what might be causing this? I will admit I have replaced the heatbed after cracking my first trying to get an ABS piece off the bed (hint, why I am tweaking settings with other filaments as well to prevent that).

UPDATE: After looking over a piece I brought into the office to talk with a co-worker about, I am starting to thing my replacement bed isn’t level. I remember installing it thinking the ends sat a little lower, but thought it was me. Now I am starting to think my bed is sitting high in the center

If you suspect an accuracy issue with one (or more) axes, the best way to troubleshoot would be to print a simple 20x20x20mm cube. That will give you a better idea of where any inaccuracies are.

If this is a mini, I doubt the problem is the bed. In particular, being “high in the middle” would be very unlikely since it is a piece of glass and can’t flex any appreciable amount.

Try printing a 20x20x20mm cube, then measure with calipers. That should tell you if there is an accuracy issue in any axis.

I will give this a try tonight.

I ran a test the other night with the same piece but on the suggested configuration from Cura (except I raised my z-axis offset 0.21 mm), and got similar results with the circle. So I tried again, but this time I rotated it 90 degrees to go straight up. If I get a similar result, I am going to assume the model actually is faulty. I’ll know later today on those results

I did have to ask. Can the screws on the side be fascinated too tight to where they angle up? I didn’t try to over torque them, but wanted them to where the wrench stopped moving (when tightening)

It’s possible that one screw is higher than the other. But i have my doubts that is your issue.

What it sounds like on first glance is that your x and y belts need tightening, but hard to say until you do more investigation. There is also a calibration pyramid you can print on thingiverse and one lulzbot provides.

http://devel.lulzbot.com/mini/novelties/make_test_parts/dimensional_accuracy_test.stl

Are you referring to the four screws at the corners of the bed, in the middle of the washers? There SHOULD be a tubular spacer under each washer which stops the washer at the proper height. If you’re seeing a washer that is “tilted” then it is possible you dropped/lost one of the spacers when replacing the bed. Check under each washer to make sure there is a spacer under each one.

I was reading about this, but when I was it was related to circles being printed flat (so in otherwords if I look from above I see the circle). I am printing the circle on the side (think a cylinder on its side).

Would those still relate then? (I’ll try the pyramid soon, hopefully it’s not too large)

All the spacers are in tact. It might have been my eyes messing with me. You’d be surprised how you “think” it’s not straight, when in fact it actually is

I don’t think any of my horizontal holes (like a screw hole) are perfectly round unless they are really small (like M3 sized holes and smaller). The larger the hole, the more it sags and becomes oval. I’m pretty sure (newbie here) it’s just due to the filament sagging as it’s printed over nothing (overhang), unless supports are used. Anything above a 45 degree angle won’t print very well, which the top 25% portion of a horizontal circle would be.

In Cura, try looking at it in the “overhang” view mode and see about those areas. The overhangs will highlight red. View from the lower portions of the part looking upwards. You’re basically looking at the “ceilings” of these areas.