The Standard MK8 extruder on the CR-10 is fundamentally a pretty simple design. There’s an arm, tension spring, toothed drive gear and Idler wheel all bolted onto a base which in turn is then mounted onto a bracket and a Nema stepper drive motor.
In almost all cases this will function perfectly fine for printing the most common of filament types such as PLA and ABS as the material itself is rigid enough to be pushed and pulled by the drive gear during extrusion and retraction without any bending or flexing. If there is enough spring tension acting on the filament from the arm and idler the extruder will perform happily all day long and not really have any issues. So as there’s not a great deal of complexity to this design how can it be improved upon?
Improvements can be made in the reliability of the part/s. The standard plastic, like anything made from plastic, can and does break after continued and constant use. By changing this to a more durable material, i.e. aluminium, it will greatly improve on the reliability of the component. The other area of enhancement is for when it comes to printing in flexible filaments. As the standard design has many ‘open’ areas which can be an issue when printing a softer material, such as flexible PLA, on the Bowden setup on a CR-10.
Macewen3D offer an upgrade for the stock plastic extruder drive feed mechanism which is a vast improvement and is superior in almost every way. The kit includes all the parts required to do the swap from plastic-fantastic to sexy anodized gold aluminium and stainless steel. This upgrade also resolves the issues of printing in flexible filament by having Teflon tubing in places where ‘open’ voids would have otherwise been on the standard feed mechanism.
On the Macewen3D website, there are two options available for the kit: ‘flexiPLUS’ or the creatively named ‘FlexiPLUS with stainless steel gear’. Both these kits are exactly the same except for (you guessed it) the stainless steel drive gear which seems to be the only difference between the two when comparing apples with apples. To be honest, I don’t know why they (Macewen3D) bother offer such an option, for such a minimal price difference (about $4 AUD) it doesn’t seem to warrant the need for a variation of the nature. Obviously, there must be specific reasons for why this option exists which I am overlooking at the time of writing this review.
As you probably would have guessed, I opted for the stainless steel drive gear as I figured if I was going to be spending money on such upgrade and the shipping I might as well get the best version of it and for the pissy few dollars more it really wasn’t worth keeping the standard carbon steel gear.
The kit comes in pieces so there is some assembly required but as long as the easy to follow instructions are adhered to then it is a straightforward installation process and comes together easily in a hand full of minutes. Everything just bolts together in place of the stock extruder drive. Macewen3D provide all screws and miscellaneous pieces required for mounting in the kit which is really useful as the last thing I was wanting to do was to stuff around trying to find the appropriate length screw to recycle from the standard setup. I even ended up with a few left-over screws than I actually needed, maybe I forgot to put a screw or two in somewhere but to this day the extruder hasn’t fallen off the mounting…. Yet…..
One of the features of this setup is how the Capricorn teflon PTFE tube comes right up to the drive gear, only a millimeter or so from it, making it a perfect option for when printing in flexible filament. The standard setup will act fine for rigid material such as PLA or ABS but becomes a problem when printing these types of flexible filaments which bend too much. The PTFE tube being so close to the drive gear means whatever potential flex from the drive and retraction of the filament is very minimal which should, in theory, lend itself to better and more consistent extrusion of this style of material.
There is small length of teflon tubing on the ‘feed’ side of the drive and has been intentionally made this length to act as mechanical protection for the filament from the Z axis lead screw. This feature in itself is so well thought out for addressing a design oversight on the standard machine of having the filament feed way too close to the thread of the lead screw. Macewen3D have incorporated a simple yet effect way to manage this into their design.
The pressure which this Macewen3D drive can apply to the material is significant and a definite improvement over the stock plastic equivalent. The stainless steel drive gear bites into PLA like a fat kid biting into a cupcake, really sinking its teeth into it the material. Caution must be taken though for if the tensioner spring it too tight it is very easy to strip the filament, leaving deep gouges in the plastic. A common occurrence of this happening to me was when the hotend was not up quite up to temperature, even 5 degrees away from setpoint, and filament is trying to be feed into down the Bowden no doubt the filament would get chewed up.
My only criticism about this upgrade is with the adjustment for tension on the spring. While it’s great to have the ability to adjust the idler wheel tension (which wasn’t possible on the standard drive mech.) the way it has been executed is pretty average. The spring itself is kind of wedged in between two 4mm screws, with a third screw just casually slid in at one end of the spring to act as a lever point.
This 4mm screw which is sitting in the end of the spring isn’t actually secured by anything either, relying on spring tension alone to be held into place. Acting on the head of this ‘spring’ screw is the adjustment screw, this would be fine but the 4mm thread of the adjustment screw is too big to slot into the hex head of the spring screw. As a result, the bottom of the adjustment screw pushes just on top off the spring screw rather than slotting into the hex head to make a male/female, plug and socket arrangement.
I have had a few occasions where I’ve gone to adjust the tension only to have the spring screw slide out from the base of the adjustment screw because it’s not being held in with anything at all. I’m sure most, if not all, upgraded drive mechs are like this, but at twice the price of a cheap eBay kit I’d expect something better thought out than this set up. I ended up machining an insert to replace the spring screw which was a) the correct size for the spring internal diameter, meaning it was being held in place and b) had a large enough ‘socket’ on it for the adjustment screw to slot into instead of just sitting on top.
Does it improve print quality? I honestly don’t think there is much difference at all when printing in rigid materials such as PLA and ABS, but would say there would be huge benefit to printing in flexible materials, which I have yet to venture into at the time of publishing this post. Even if this upgrade doesn’t improve printing quality a huge amount, if at all, the overall quality of the part will give better reliability and durability to the machine in the long run. A good example of this is on the drive wheel itself. The teeth on the stock carbon steel will wear down after printing for a period, this is due to the cheap and soft material the gear is made from. With the replacement stainless steel gearing this will not happen as soon and should prolong the teeth for a greater length of time given that stainless steel is so much more durable than mild steel.
So is this kit from Macewen3D worth the money? I’d say definitely yes. While this is a seeming more expensive interpretation of a cheaper Chinese versions which is normally found on eBay or AliExpress, there is an improved sense of quality to everything that is provided. As I mentioned before there are some features which I do not like, mainly the tensioner spring and screw setup, but this is the only fly in a jar of otherwise fine ointment. And let’s be honest, this is not the most expensive upgrade to be had for a CR-10, ender3, Tevo Tornado or whatever other machine this is intended to be put onto. The total ‘investment’ into this part really makes it a low risk option. Does it improve print quality? Probably not; Does it make the printer worse? Definitely not, it makes it just a little bit better and after all, making a printer a little better one small piece at a time will add up to having something greater than the sum of all its parts.