Printing


This page contains some information on how I print, or just basic info regarding printing.

I will try to add some useful links to interesting threads on the reprap forum, or any other site that I have come across as I get the time.

I am quite pleased with the quality of the prints I get from this model-T of a printer. It may be slow but the results are quite good. I don’t know too much about printing and how to achieve top results, but I am not afraid of trying and researching for a while on the reprap site.

I strongly recommend though that before you start printing any parts at all you must have the printer calibrated. Get your x,y and z right. Then get the extruding right. When you have this correct it makes the rest so much easier to achieve. It gives you consistency.

 Does my computer need to be powerful?

Well, I have not done any testing as such, but, my laptop I normally use with my printer is a celeron 1.8Ghz with 2Gb mem. It works fine but some times my printer will stutter during a print. It will only happen during a complicated print if I also run some other applications.  This is to me typical of a computer that may be just on the borderline to be able to cope with the load. It basically runs out of memory or cpu power and starts to schuffle data around, hence the small delays. Printing from an SD card should solve this. (Or just leave the computer alone while printing).

I use pronterface to communicate with my printer.
Have used Slic3r for a long time and I like it, but lately I have used Kisslicer as it also works great and is easy to set up and you are up and running pretty well from first go.
I do feel that i have a bit more control over the settings with slic3r, but it requires a lot more tweaking. Skeinforge is another slicer which also is good but this requires a lot of understanding of what to do with all the settings. Not recommended for the beginner. But by all means give them all a go, as that’s the way you find the best one for you.

First layer is squashed a bit onto the table. This gives very good adhesion and is essential for a succesful print. But make sure it is not too close to the table so it rips the kapton tape. If it is so close that it actully scrapes along the table it will also prevent any plastic being extruded and the pressure build up in the nozzle can/will eventually cause the extruder to strip your filament.

Bed MUST be hot for the plastic to stick properly and to avoid warping.

Printing smaller parts a cooling fan makes a big difference on the end result. A fan that cools the part down as you print. Try not to cool your nozzle, but the printed part only 🙂 . It may take a few tries to get it right, but it does work.

Make a small test piece like 10 x 10 x 2mm square to print first. I had all my axis calibrated and they all measured very close to what it should be on the part. I then adjusted the flow of filament by increasing the amount to be extruded in the firmware. Okay, if my E value in the firmware was 650 and when I extruded 10mm it measured 10.5mm then I would decrease the E value to 620 and try again until the plastic that the extruder feeds in measures 10mm exactly. Then it all should be fine. But please do remember that you measure the plastic going in to the extruder, not what comes out of the nozzle. Very important. Measure only the 3mm (or 1.75mm) filament entering the extruder.

Strength of printed part:

To achieve good strong parts I have found that the layer height must be correct (or within a certain range). If the extruded filament size is 0.35 I will use layer height of 0.2 up to 0.28. Most of the time I use 0.2. This makes each layer stick together well and is essential in achieving strong parts. If I just need  to print a part just to see what it will be like I may use 0.28 as this will print faster. In other words the smaller the layer height the better they stick together.

Another very important factor is the design of the part and how you place it on the table. If you will be adding any force to the part you are making, make sure that the force is going along the layers. A part is very strong in the direction of the layers and less strong 90deg on the layers. In other words, it is easier to pull the layers apart than it is to stretch them or rip them in half.

Repairing Broken Parts:

As I was assembling a part on my next printer, I did what I am sure many others have done before me, broke it……Yep, I broke off a piece on a part that takes 7hrs to print. If you have looked on the RepRap website you would have come across that some reprappers have made up a glue, by dissolving plastic (filament) in Acetone! I try to avoid using Acetone as it needs really good ventilation to get rid of fumes. (As you know, very bad for you 😦 ). Anyway, it works just as good as they say. I glued the part together and it looks pretty good. I am happy and if you do have Acetone handy, it is pretty cheap glue. But don’t inhale that stuff as it is very bad for your health.

Read This:
The difference a bed controlled with Bang Bang or PID and a perfect Hobbed bolt compared to an oval hobbed bolt can make:

Cold Bed and uneven Hobbed Bolt

In Photo 1 I printed using a cold bed and a not perfectly round hobbed bolt. You can see the print is pretty even but with a repeating pattern. As I watched the printer very closely I noticed a slight bump on the hobbed bolt and just after it passed I got the defect on my print. Ok, I need to fix that one for sure.

Warm Bed Bang Bang and Uneven Hobbed Bolt

Photo 2
I then printed with the bed hot and wow…uneven print with a new pattern to it apart from the hobbed bolt. Looks like a z-wobble problem, but the bad pattern is due to the bed being turned on and off using Bang Bang. That means when the temperature has been reached the bed switches off and cools down a bit and then turns back on again. What happens during this cycle is that the bed expands and contracts. This makes the bed go up and down a fraction resulting in squashed or stretched layer height.

Warm Bed PID and Perfectly Round Hobbed Bolt

Photo 4
Finally fixed my hobbed bolt and look at it now!
PID on the bed regulates the temp within +/- 0.1 degrees.
And with the good bolt the repeating pattern has gone.
(The difference between Photo 2 and 4 is that in 4 I
have a good hobbed bolt and PID on the bed, quite unreal.)

So the moral of the story is, make sure your bed dont’t move up or down during print.
Make sure your hobbed bolt is perfect.
I see many questions asking what can cause this and what do I do.
Rule number one:
Make sure your printer is perfectly right hardware wise and calibrated perfectly, otherwise your software is not going to be able to give you good prints. And you will be tweaking your brains out not going anywhere.

Links:

CALIBRATION

About Hole Sizes

Nozzle Size

Interesting discussion on belts

Do we need tape on the hot bed?

Regards

Jan

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