How can I prevent my nozzle catching on my print?

Question

I have created a budget 3d printer using parts of old computers, specifically I used the CD drive mechanisms for the x,y and z axis. This printer is similar to the curiosity E-Waste printer, as seen here: Link

After quite a bit of time working on it I have got to the point where my printer should be able to print, but unfortunately, I have encountered an issue. The layers in which the printer prints fluctuate in height, and so when the nozzle travels over the lower layers to do the next layer, it hits a bump, misses some steps and becomes mis-aligned. I have never owned a 3d printer before, but I think that it is likely that the problem I have which causes the prints to not be flat is likely a common 3d printer problem. However, with commercial 3D printers, these bumps would probably only cause a drop in the quality of the print and not a complete fail; it is only due to how weak my motors are that the nozzle will miss a step with even the slightest force against it.

I have thought about why the layers may not be flat and I have come up with a few possibilities that I think are the problem. I do not know if these are in fact the source of the issue, but these are the things that I have considered so far.

1. The nozzle height when starting the print. If I lower it then the layer height will be smaller, and so there is less chance for it to be higher in different places. However upon testing this I found that, due to the reduced height upon the first layer the nozzle would get stuck.
2. When the nozzle changes direction, for example at the edges of the print, there is significant vibration and it is possible that this cause the filament to overlap and not be flat. The vibration is due to the nature of my printer and would be very hard to reduce. A solution could be some kind of software fix, but I do not know enough about this to do so.
3. Maybe the speed at which I am printing is not good. I'm printing currently at an incredibly slow 40mm/s.I have tried different speeds but at low speeds there is over extrusion and at high speeds, the vibration is too much.
4. I have tried experimenting with flow rate (100%,75%,and 50%) and at the moment I am using 50%. This is because my extruder motor is a bit weak and often misses steps, also the filament requires considerable force to push it through. Is this normal?. My idea is that maybe there is too much filament being extruded and so if I lower the flow rate the print will not create bumps.
5. The filament curls slightly when it comes out of the nozzle and I have tried to fix this by cleaning it and printing faster but it is only reduced. I'm printing at 200° currently; Will higher or lower print temperatures cause the filament to curl less and be more easy to push through the hot end?

As you can see there are a lot of factors in which I need to consider if I want my printer to be able to print correctly. And unfortunately, with my printer it is either perfect or a failed print; there is no in between. Due to the weak motors everything has to be exactly right, or the nozzle will get stuck.

I am not sure how to add videos here so I will instead. add some photos of the prints, and three photos detailing how the prints fail.

Below is an image containing the 6 most recent prints in which I played around with the different factors mentioned above. The top middle one is the most recent one. The object i am trying to print is a simple cuboid.

This is what the first layer of my most recent print looked like. There is some kind of gap in the middle for some reason, but I don't think that is the source of the error. The print appears to have adhered well, at this point and it is relatively flat.

This is what the second layer of the print looked like, notice how the lines are wobbly and not very neat. There is also a small area of higher height in the bottom left corner which inevitably causes the nozzle to get stuck.

This is the print after the nozzle hit the now cooled down blob, missed some steps and then was misaligned. It then goes on to print the next layer in the wrong place and gets stuck very badly.

Thank you, for reading this. Any help would be much appreciated

Answer 1

A printer must be working very well to not have the problem with the head hitting against small verticle protuberances and losing control of the X and Y positions.

Some factors I've found that make bigger bumps. If you have any of these, fixing them will make the problem better. From observation, it is ultimately the power of the motors, the ability fo the nozzle to melt through small bumps and the resilience of the mechanism (not something that is otherwise helpful) that let decent prints proceed.

1. The first layer may not be the height you expect. First layers are typically 100% filled. If you are extruding too much plastic for the layer height, it has to go into a bump. To fix this, check your vertical height. Measure with calipers the height of the flat portions of a 1-layer print, and compare that with your slicer expectation. Adjust the vertical offset to make the actual meet the intended.
2. You may be extruding too much plastic. Depending on your slicer, you can adjust this by tweaking. I user slic3r, and can adjust the filament diameter. Overstating the diameter causes under-extrusion. Understating the diameter will cause over extrusion.
3. Sometimes the bumps come mostly at changes of direction. This is possibly caused by several things, but I'd look first for backlash. The mechanism should be tight, and not move under moderate side-to-side or front-to-back force. If it jiggles, it will can cause problems. Wiggle it. Look at what moves. Should it move? If belt driven, the belts should be tight. If driven with a lead screw, the nut should not move and the screw should not move. If they do, fix it somehow.
4. If you are running the motors near the maximum speed and/or acceleration, their torque will be lower than if they are running slower. Try slowing everything down by a factor of two and see how the problem changes.
5. It might help to print at a higher temperature, so the nozzle can melt through the bumps with less force. This could cause other problems, but if you are marginally cool now, warmer might work better.