Modular Arco Extruder Core body

Modified ARCO extruder core body with improved filament path 

Edit 3 - Detailed print settings

• It is highly recommended to print the 'Filament path parts' (orange parts in the drawings) with a 0.2 or 0.25 nozzle!

• For both versions, 0.2 first layer, the rest 0.08 layer height for the smoothest surface possible with an FDM printer

• 4 walls and 30 top and bottom layers, to get all solid parts
  
  

• You can use a 0.4 nozzle for the Core part (black), PCB attachment (Grey) and the cable clips

• 0.1 layer height

• 4 walls and 1 wall on all top surfaces

• 30 top and bottom layers to make is all solid parts. 

• The black core part needs to be printed with regular supports. Set Z-distance to 0.15mm for easier support removal. 

Edit 2 -  I have heard of 2 cases where the spring loaded gear arm of the extruder hit a tab of the lower                                filament path. The easiest solution is to file of 0.5mm to 1mm of material from the end of the spring                      loaded gear bracket (red arrow in the picture below) This won't have any adverse effects on the                                working of the spring loaded gear and will not cause problems if you ever want to revert back to the                      stock extruder setup. 

Edit 1 -  I've added "filament path upper V5 - M3 thread" to the uploaded parts, which has been optimised for                   RESIN printing. This version does not require a brass heat insert, because the M3 thread has been                         incorporated into the model. Keep in mind that printed threads are not as strong as brass inserts,                           so tighten the screw for the run out PCB with care!

Before you start this modification, make sure you have the following materials on hand!

• 5x brass heat inserts m3 x 4mm L x 4.5mm D

• 1x m2 x 8mm button head hex 

• (Optionally you can use 6 pieces of m2 x 8mm and 2 pieces of m2 x 10mm hex screws, if you want to replace the original screws for the filament path and hot end PCB)

• m3 washer, max diameter 6.8mm and max 0.5mm thick (serves as a spacer for the gear tension spring)
  
  

I have been working with Phrozen for a while now, to see what can be improved on the Phrozen Arco. 
One of the issues the developer team encountered was with fast TPU printing. Their recommended TPU settings are very conservative, because they had problems with the TPU getting jammed between the gears, causing extrusion failures and print fails. 50mm/s is really slow for a printer capable of reaching speeds of 600mm/s. I tried to find and create a solution for this and this mod is the result of that.

The purpose of this modification is to increase the speed at which soft materials like TPU can be printed, without the TPU getting jammed between the gears inside the extruder body during filament loading and in prints with lots of successive retractions. An extra benefit from this mod is that you can easily swap out worn out parts without having to replace the whole core unit.   

I have been testing this mod for a few weeks now, making small changes and improvements in the design and it works really well. It is still a work in progress, but the print results thus far have already improved by so much, that I feel confident I can already release this version.

With my latest tests I have been able to reach speeds of 250mm/s with TPU 95A. I set the max volumetric flow to 25mm³/s and used a standard 0.4 nozzle, with 0.42 wall width, 0.2 layer thickness and a nozzle temp of 235°C. I turned off the auxiliary part cooling fan and turned the normal cooling fan down to 70%.
During the prints, the TPU was fed through the whole length of the bowden tube without causing any friction issues. I think I can print even faster with a high flow nozzle and if I would directly feed the TPU into the extruder, bypassing the bowden tube and removing the friction the bowden tube causes. This is still something that needs to be tested though.

I have ordered a spool of PEBA air and a spool of TPU 85A, but unfortunately delivery will take a few more weeks, so I haven't tested anything softer than 95A yet. 

I also have no Chroma kit yet, so I have no idea if that would work, but I will test this once I have the Chroma AMS, latest shipping update says it would be at least another 2 months. My guess at this moment is that the loading and unloading sequences from the Chroma AMS will be the problem with TPU. 

For removal of the original extruder body and to detach all the different components from the core body check the Phrozen help center pages here, here and here. When you take apart the original extruder, be careful not to lose any of the many small parts. 

      New extruder core parts: 

• Orange - Filament path guide

• Black - Extruder core body

• Red - Bits of filament

• Grey - PCB holder

• Green - Hot end cable clips

I printed the filament path parts with a 0.25mm nozzle om my Prusa XL with a layer height of 0.08m to get the smoothest result possible. Using a 0.2 nozzle will also work really well!  I have integrated solid supports in the design and it is recommended to use this with a multi material set up, so the support structures can be easily removed.

It is possible to print it with regular supports, but this will require a lot of cleanup of the surfaces to get it as smooth as possible. If you decide to print with regular supports a diamond needle file and some fine grit sandpaper is recommended for the surface cleanup.

The 4 red pieces in the drawing above are bits of filament and serve as connecting dowels, they do not need to be printed. Use the same material you used for printing the extruder core and PCB holder part. I printed all the test files in PETG and used PLA as a support material, but will print the final parts in either ASA or PCCF.

The main extruder core needs to be printed with regular supports. I printed the core and the PCB holder with a 0.4 nozzle, 4 walls, 1 wall on all top surfaces at 0.1mm layer height. I printed it fully solid by setting top and bottom layer count to 30. Support Z-distance between interface and core was set to 0.15 for easier support removal. The surface will need some cleanup so the hot/cold end can be attached flush with the main body. After printing you will need to insert 4 m3 brass heat inserts so the hot/cold end can be attached. 
It is advisable to use a small needle file or some sandpaper to make the channel where the filament moves through as smooth as possible! 

This design also eliminates the need for the small filament cutter spacer (small L shaped piece in the lower right corner of your original extruder body), since I integrated this into the design of the core body.

I used cyanoacrylate adhesive to bond the PCB holder to the extruder core body. Please make sure the filament dowels are cut flush with both the PCB holder and the core body! When the PCB part is securely fixed and the dowels cut flush, you can glue on the cable clips (green pieces) There is a slight difference between the upper and lower clip, so pay attention to which part goes where. 

You will need to add one m3 x 4 x 4.5 brass insert to the upper filament path part. This is to attach the filament run out sensor. 

The upper filament path (long orange part) can be attached to the core body with the original screws. Alternatively you can use m2 hex screws if you have those on hand. You will need to source at least 1 m2x8mm screw though, to fasten the lower filament path piece to the core body. It might be necessary to use a 2mm drill bit to clean up the holes in the filament path parts, when you use the m2 screws instead of the original screws. The m2 screws can be screwed into to the core body with minimal effort without the need for drilling! Once fastened you can insert the original black plastic collet, which secures the bowden tube, into the neck.  

When all the parts have been transferred to the new extruder core body you can attach the run out sensor. Make sure you have the small magnet in the correct orientation, as shown in the photo below. I used an Allen key to insert the magnet with spring and used a wooden tooth pick to keep everything in place when I removed the Allen key. Now you can attach the small run out PCB with the original screw and lead the cable with the larger PCB to the front of the extruder body. 

Attach the PCB to the core body with the original screws. Alternatively you can use 2x m2 x 8mm hex screws here too.

You will have to remove a small bearing from the original core body and add it to the modified body. 

Before you can attach everything back onto the printer you need to add a washer, m3 with max diameter of 6.8mm and max 0.5mm thickness. This serves as a spacer for the gear tension arm, so the gap between the gears is slightly increased. This seems counter intuitive, but this made a big difference with loading of filaments and TPU especially. There is still plenty of tension on any filament I have tested, so there are no downsides to it as far as I have noticed. In the photo below you can see it needs to be placed between the metal extruder body and the gear tension arm. I have included a file, "Gear tension arm spacer", for this part too, so you can print one, but it is recommended to use something metal!

Now you can attach the hot/cold end to the core body. Make sure you do not pinch the cable to the run out sensor between the 25mm fan and the neck of the core body. Make sure the 4 bolts are tight, but do not over tighten them, since this might distort the plastic of the core body through to much tension. Same goes for the original body btw!

Once the fan and and hot end plugs are attached to the PCB the core body is ready to be mounted onto the  printer extruder carriage. You can follow this Phrozen guide to attach everything back to the printer.
Reattach the fan plug from the extruder cover and snap the cover back on the extruder. 

Since you have replaced many of the original parts, it is recommended to do a fresh auto bed mesh calibration and the resonance calibration. Once this has finished your printer is ready to start printing TPU at high speeds. 

Disclamer:

Although this mod works really well on my printer, it is still a work in progress and new iterations will most likely be added here.

I also only tested the high speed TPU capabilities with models I use in my own designs and the products I make, so the range of test models was limited. If you do encounter problems, please send me a message and I will see if I can replicate the issue and then solve it. It would be very helpful if you could share the file with me. I will use the files for troubleshooting purposes only and they will be deleted afterwards.



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