This long blog page describes the process I went through to upgrade my SuperRacer with the Bondtech LGX-Lite extruder. I did this because I wanted to find out if eliminating the Bowden tube setup that is common to all delta style printers was a good thing to do. My sense was that it is since there is widespread belief that the Bowden tube design causes increased stringing and other problems with filament retraction and de-retraction. You can read all about the LGX-Lite extruder here: https://www.bondtech.se/2021/10/27/ultra-compact-bondtech-large-gears-extruder/

Here are the important parts that come with the extruder:

The extruder has 2 parts: the squarish extruder itself (right) and the cylindrical pancake stepper motor (left). It has attached it’s own stepper motor cable which is long enough for the SuperRacer. The plastic bag contains 8 M3 square nuts (more about these later) and a short piece of PTFE tube.

Getting things ready

The upgrade process starts with completely disassembling the standard hotend and end effector plate. Here’s how mine looked at this stage:

The 2 blue parts are the replacement for the FLSun metal cage that holds the fans. I opted to use the stock fans because I had no problem with them after almost a year of printing, but there is also a cage design that accommodates the 5150 fans. Here is the link to get the STL files for either set of fans: https://www.thingiverse.com/thing:5138588

Attaching the extruder to the housing

Actually the extruder attaches to the locking piece of the housing. To do this you need 2 size 12 M3 screws. You can see them in locking piece attached to the extruder in this photo:

The tricky part to this process is installing the M3 nuts that hold the screws. There are slots on the inside of the extruder to hold the nuts. Standard M3 nuts are hexagonal, which is why Bondtech sends you square ones. DO NOT LOSE THESE NUTS! To install them you disassemble the extruder by removing it’s screws and push the nuts into their slots like this:

Be careful not to do like I did and drop parts out of the extruder when you have taken it apart. The black gear at bottom left belongs on the extruder’s silver pin so it meshes with the internal gear whose teeth are jus showing.

After reassembling the extruder it is time to put everything back together.

But wait…

What about that little piece of PTFE tube? What is it for? Is it needed for something?

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Edit 09 Jan 2022

The little piece of PTFE is not useless! It is supposed to be poked into the opening at the top of the extruder to help guide the filament into the gear drive. I thought it was supposed to connect the extruder to the hotend, but this was incorrect. SUch is life with no directions!

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The answer is that particular piece of tubing is useless, but it’s function is critical. So you’ll have to make your own piece of tubing. What that tube does is provide a connecting path for the filament as it moves out of the bottom of the extruder and down to the top of the hotend’s heatbreak. It is important that there be no gaps in this connection because gaps can cause all sorts of obscure problems (like leaking filament or jammed nozzles). Because of the geometry of the SR’s hotend parts you’ll need a piece of tubing that is 52 mm long. I recommend using Capricorn tubing, but PTFE should also work OK.

Here’s a little trick I developed about these connecting tubes: Spin an Exacto knife blade around the top opening of the tube to increase it’s diameter a little bit. This makes it much easier for the filament to gwt a good start while going in to the tube:

Now it’s time to put it all back together

Here’s the hotend and heat exchanger connected to the extruder:

And here is the front and back views of the the above after assembling it together with the cage:

Motherboard Connection

Connecting the extruder to the motherboard is quite easy. You simple replace the existing extruder’s connector with the one from the LGX-Lite. To do this you have to cut the black tie-wraps around the wires coming from the motherboard. Here are before and after photos of the motherboard connection:

But wait…

Before you make the connection you have to reverse the extruder’s direction. If you don’t do this the extruder will retract when it should feed, and feed when it should retract. Reversing the extruder direction is easy if you compile your own version of Marlin, but if you are using a pre-compiled version like I am you have to reverse 2 wires in the extruder’s connector. The 2 wires to reverse are either the red/green pair OR the yellow/blue pair – but NOT BOTH.

Here’s how I did that:

The stepper motor’s connector is wired like this:

I decided to switch the red/green pair. D0ing this required extracting both wires from the connector, rearranging them, and then putting them back into the connector. This is actually easy to do if you know the trick. The trick is related to how the metal gizmo on the end of each wire is made. This gizmo looks like this:

The little prong in the top is a small metal finger that sticks up and stops the wire from being removed from the plastic connector. If you simply pull the wire out of the connector you’ll break this prong off and have to install a new one. The way to get the wire out successfully is to push the prong down and then pull the wire out. Most web pages say to use a pin or tip of an Exacto blade to do this, but here is a much better/faster/easier way:

Yup – that’s one of my most favorite and useful tools – an unbent paperclip. Using it like this does 2 things – it compresses the prong and also lets the wire slide out of the connector quite easily. Using this method I was able to switch the 2 wires in less than a minute. Here’s the re-wired connector back in the motherboard.:

Is this a thing of beauty or what? And it actually works – the extruder now moves filament in the correct direction.

Setting Extruder’s Parameters

Before the extruder can be tested it has to have 2 values in the printer firmware set properly: the E-steps and the extruder motor power. The motor power tells the motherboard how much power to send to the extruder. Too much and the extruder will overheat. Too little and it won’t have enough power to push the filament properly. Either case will result in a ruined print.

E-Steps tells the motor how much filament to feed each time the motor turns by one step. (It’s not called a stepper motor for nothing!) An incorrect E-Steps value will result in either over or under extruding, either of whichcauses a ruined print.

To make sure I got the correct values for both I emailed Bondtech support and got a reply with these values: E-Steps = 562 and Power = 600 milliamps. So how to get these values into the firmware?

The answer is by sending the firmware the correct GCode. The codes are M92 E562 for the E-Steps and M906 E600. These are Marlin commands that the firmware recognizes and makes the indicated adjustments. After doing this the firmware needs the command M500 to save the values in the motherboard’s EEPROM (Electrically Erasable Programmable Read Only Memory) so they will be there when the printer reboots. So the GCode script looks like this:

M92 E562

M906 E600

M500

How to send these codes to the printer? The simplest way is to make a text file containing the 3 lines of code and give it some name like setextruder.gcode. Save this file and print it. Nothing will print of course, but the motherboard will run the commands like a normal print job and make the required adjustments to it’s internal values. Once this is done everything is ready for an actual test

Testing the Extruder

To test the extruder you have to heat the hotend up to 200C, otherwise the printer firmware will not let the extruder move. Here’s my setup for doing the testing:

The extruder has it’s cable replacing the stock extruder cable, the end effector has the hotend connected, and the stock metal cage has the 3 fans still attached to it. This lets the printer turn on, heat up, and respond to the LCD Extrude In/Out buttons.

The test completed successfully and took about 20 seconds after the hotend got up to 200C. I put the 3 GCode commands into a text file, named it extruder.gcode, copied the file onto the SD card I use for the printer, and printed it. Naturally the “print” completed in 0 seconds. Then I put an 8″ piece of filament into the extruder, lined it up with the extruder’s bottom edge (the small hole under the Bondtech nameplate, and used the Extrude menu to push 50 mm (10 mm 5 times) out of the extruder. Here is the results:

I’m happy with that result. Now I just have to reassemble everything which will require removing the fans from the metal housing, installing them onto the new 3D printed one, and installing the housing, hotend, and heat exchanger on the end effector base plate. I’ll also have to think of some way to route the new extruder’s cable alongside the other cables feeding the hotend. Maybe some tie wraps will work.

Calibration

Before starting any actual printing I did the standard Set Z-Min procedure since I had messed around with the entire hotend physical configuration. (I’ve crashed the hotend into the print bed enough times to be wary of that happening again.)

I used this website to calibrate the extruder and printer:

https://teachingtechyt.github.io/calibration.html

The first step is the First Layer test, and here are my results:

The first square printed is the one at the 9 o’clock position, and they continue in an anti-clockwise rotation ending with the center square. Notice that the first square printed is only half there. That’s because, even though I did the Z-Min adjustment the extruder was clicking when it started printing the square. This happens when the hotend is too close to the print bed and there’s no room for filament to be extruded. SO I used the Z-Adjust option to raise the hotend enough to stop the clicking.

But when square #2 was printing I noticed that it didn’t look quite right, so I increased Z a bit more so it evened out. The rest of the squares looked pretty good, so I ran the next test.

Stringing is a standard problem for delta printers, at least partially because of the Bowden tube configuration – which is why I wanted to try a direct drive extruder. Several years ago I made several test parts for checking stringing, so I picked one to try and here is the result:

Not great results, but this was printed with my first guess of a retraction length of 0.5 mm. (I had been using 6 mm for the Bowden configuration.) The print also looks like it is a bit under extruded, so I increased the Extrusion Multiplier from 1.05 (my old value with the BMG extruder) to 1.10 and changed retraction to 3.0 mm. This is the result:

No strings – so it looks like the extruder is working fine and I just need to make a few more adjustments to my slicer settings. That’s a different issue which I won’t address here.

Summary

The LGX-Lite is a first rate extruder and works well on the SuperRacer. Making the switch from the stock extruder – or a plug-and-play clone, which is the extruder I had – is not a simple procedure and I would not recommend it for people who are unfamiliar with mechanical and electrical assembly and disassembly. But if you proceed slowly and carefully the switch is quite straightforward.

Other notes

The extruder is silent, even during retraction operations. The BMG extruder did make some noise when it did retractions.

The BMG extruder was easy to open and clean if there were bits of filament stuck inside. It’s not clear how easy or difficult it will be doing that with this extruder.

The white tie wraps I used to hold the extruder wires next to the other ones are annoying. I need to get black ones.

The LGX-Lite extruder has a flat metal tab that adjusts the tension between the internal gears and the filament. It has 3 positions: off, middle, and maximum. Off lets you manually push filament in and out of the extruder. Middle is an intermediate amount of gear pressure and seems to work fine with PLA. Max seems to be for special filaments that I don’t use. The metal tab is difficult to switch between positions and I’ve seen some photos of the extruder with a red plastic cover over the tab that should make it more comfortable to use. I’m thinking about designing a cover like that for mine. It won’t be red.

After removing the BMG extruder the arm that holds it and the End of filament sensor looks fairly grotesque. Someone posted a photo of a 3D printed arm that is shorter and holds only the sensor – but there was no STL file for it. So I may design and print my own. Or maybe I’ll get out the Dremel tool and cut off the bottom 2/3 of the stock arm.

30 Dec 2021