Creality Ender 5 Pro modifications

I’m in the process of making an attachment for my wood lathe to turn it into a straight-line engine for ornamental engraving of pen parts. More on that later…

However, in order to make a large portion of the attachment, I needed to produce a bunch of parts on a 3D printer. So, I got a Creality Ender 5 Pro, since lots of reviews seemed to tell me that it was a good choice for the price.

My first test prints on the printer worked out great, and then I started running the print of my parts, and things started to go horribly wrong. The problem was that my filament was clogging at the end of the Bowden tube, right above the nozzle. This would typically happen about 4 – 6 hours into a 14-hour print. I tried many things to fix the problem – and finally fixed it. I’ll go through each of the steps below… However, to begin, here’s a view of the part that I’m making, since it’s part of the issue.

To make things simpler for the rest of this story, here’s a schematic of the important parts of a Creality Ender printer.

The way this system works is that the filament is pulled off the spool by the Feeder Wheel, which is a toothed brass wheel that is fixed on the Extruder Feeder. The filament is pinched between the Feeder Wheel and the Pinch Wheel, which is just a steel bearing with a groove in it to keep the filament centred. The force applied to the pinch wheel is provided by the Spring, whose tension can be adjusted by changing its compressed length using the Spring Tension Adjustment screw.

When the is heated to the desired temperature, the Feeder Wheel pushes the filament through the Bowden tube and the molten plastic is extruded to the part you’re making. When the printer needs to stop the feed (for example, for the nozzle to move to another place on the part without laying down plastic) then the Feeder Wheel pulls the filament backwards a little.

The problem: A clogged Bowden tube

My printer would get a couple of hours into a print, and then the nozzle would start running out of plastic. This would result in a stringy mess like the one you see below. This is a shot of the interior gear, and not the spur gear shown above, but the problem is identical, for the same reason.

In a worst-case, I wouldn’t notice this until a while later, only to check on the printer and see the nozzle a couple of mm off the surface of the print, moving around, not laying down plastic…

By the time this had happened, it was impossible to pull the filament back through the Bowden tube. Trying with a little force resulted in breaking off the filament back at the extruder feeder. The only way to get it out was to remove the entire bowden tube, drill out the end of the filament with a 1.5 mm drill bit, and then pull it back through using pliers and a vice. This technique and the associated cautionary warnings are described here.

Once this was done, the question was how to avoid it from happening again…

Step 1: Different filament

The most obvious problem was to change the filament and try again.

4 hours later: same problem. That didn’t work.

Step 2: Reduce the temperature

The next thought was that maybe the PLA was melting inside the Bowden tube, so I tried printing at 195ºC instead of 200ºC.

4 hours later: same problem. That didn’t work.

Step 3: Increase the temperature

The next thought was that maybe the nozzle wasn’t hot enough for the extruder to push the filment through adequately. So, I tried printing at 205ºC.

4 hours later: same problem. That didn’t work.

Step 4: Check for a gap between the nozzle and the bowden tube.

Some sites that mention clogged Bowden tubes mention that, if there’s a gap between the end of the tube and the top of the nozzle, the plastic will fill that gap and slow down the extrusion. This Youtube video gives a good tutorial on how to eliminate that gap.

I did this, but 4 hours later: same problem. That didn’t work.

Step 5: Change the Bowden tube

By now, I had been removing the Bowden tube each time and pulling a large wad of filament back through it, which was probably tearing up the inside of the tube. So, I forked out some cash and bought a new Capricorn XS Series PTFE Bowden tube to replace the stock one that came with the Creality.

Of course, when I put that one in, I was careful to avoid having a gap between it and the nozzle. While I was at it, I put in a new nozzle this time; not because I though that the original one was the problem, but because it was easier to replace it and clean it later.

4 hours later: same problem. That didn’t work.

Step 6: The Feynman Problem Solving Algorithm

Richard Feynman is credited with an algorithm for problem-solving which goes as follows:

  • Write down the problem
  • Think really hard
  • Write down the solution

By now, I figured I had tried everything… until I stumbled on this page, where Woodpeckercz says

“Upon closer inspection I noticed teeth marks from the feed cog were quite deep and the filament was wavey from the extruder pushing it in too hard.”

This description was awfully familiar… When I pull the filament out of my Bowden tube it looks like this:

and the end at the Extruder Feeder looks like this:

Not only that, but when I look at the rocker arm, just below the Feeder Wheel, I can see PLA dust all over the place.

So, it appears that the Pinch Wheel is applying too much pressure to the filament, causing the teeth in the Feeder Wheel to cut grooves in the filament. This, in turn, makes the cross section of the PLA more than 1.75 mm, which then requires more force to push it through the Bowden tube.

So far so good… now the question is: why does it take 4 to 6 hours for my prints to fail – and why does it always happen around the same point in the print? Time to look back at the part I’m printing…

If you look at that part (in the figure at the very top) you’ll see that I’m making a spur gear (or an internal gear) with 36 teeth. When I watch the printer making this gear it starts by tracing the line around the edge of the gear, and then works its way inwards. At some point, the only thing left to fill on each tooth of the gear is a single dot, so the nozzle moves to the correct spot, lays down the plastic, then moves to the next tooth and repeats this 36 times.

When this is happening, the Extruder Feeder is pushing and pulling the filament (to stop the flow between teeth), rocking back and forth, but staying in almost exactly the same place until all 36 teeth are done. While that’s happening, the filament is getting crushed between the Feeder Wheel and the Pinch Wheel. (In fact, if you look at that last photo, you can see two places where the feeder was rocking on the PLA.)

Step 7: Fixing the problem

By now, it’s been about 2 weeks of trying to fix this problem, and I was getting more than a little frustrated… But I was almost certain that the problem was at the spring in the Extruder Feeder was applying too much force to the Pinch Wheel. The solution that Woodpeckercz described is

There was just no way to loosen the extruder grip on the filament. I tried loosening the mounting screw by 1/2. 1 This caused the extruder arm to drop about 1mm and the filament guide wheel stopped turning and filament finally stopped feeding. I could then use the spring adjustment screw to set correct pressure the extruder puts against the filament. I tightened the screw until the guide wheel turned continuously.

However this didn’t work for me, since it means that the rocker arm is loose, which makes me nervous about just creating a different problem later. However, later in that same thread (s)he says the following:

The problem lies with the spring being too tight even with the tension screw loosened all the way. There are three ways to fix this:
1. Loosen the mounting screw 1/2 turn
2. Cut the original spring shorter
3. Replace the spring with softer spring.

I decided that the second option was the way to go – at least as a start. So, I got out my larger wire cutters, and shortened the spring – the only question was “by how much?” But this wasn’t difficult to decide, since there is a Spring Tension Adjustment Screw on the Extruder Feeder. I just needed to make sure that I didn’t shorten it by more than I could recover with the screw…

In my case, I made two cuts. The first was directly below the end of the spring, but this was only to get the last coil out of the way. The second cut was to shorten the spring, which was done at 90º rotation back from the original end of the spring, as shown below.

I then filed down the burrs on the newly-cut edge so that I wouldn’t injure myself next time… and then re-assembled the Extruder Feeder with the shortened spring, putting the cut end upwards, so that it’s held in place by the collar around the Spring Tension Adjustment.

One last thing…

In searching for the solution to this problem, I found this page, which describes how to calibrate the extruder speed. So, before I started printing again, I followed those steps and found out that my printer was actually under-feeding the nozzle (better that than over-feeding). Now it’s calibrated so that I’m within 1% of the correct extrusion steps (±1 mm for a 100 mm extrusion).

Finally: Success!

Since doing the stuff I just described, I’ve printed 3 parts, each of them running for at least 13 hours…

Of course, there’s a certain satisfaction in having fixed this problem myself, and I’m glad that I didn’t return the printer and spend twice as much on a new / different one. However, it seems to me that Creality has an issue here that can be easily fixed by using a more compliant spring (or just a shorter one) and making use of the Spring Tension Adjustment screw…

As for the parts that I’m making to turn my lathe into a straight-line engine: I’ll talk about that when it’s up and running.

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