As with all things at E3D, we came up with some design objectives before we started getting bogged down in the engineering. In no particular order this is what we wanted from our extruder:
Have the filament pushing performance of a geared Greg-Wades extruder. We love these things, and have used them for years, the performance they give has always been more than capable of dealing with adverse situations and viscous filaments. They might be big, heavy, and a bit unwieldy to use and maintain, but they get the job done.
Achieve the size and weight of small, direct-drive type extruders that just use a hobbed gear directly on the shaft of a motor. They might be a bit weak on performance, but their compact size and simplicity is undeniably convenient.
Be easily mounted and compatible with as many machines as possible.
Be able to run at high peak speeds for snappy retractions and fast printing with Volcano systems. A downside with heavily geared extruders like a Wades or those that use a 5:1 planetary gearbox is they struggle to achieve really high speeds needed for Volcano, as well as the high accelerations needed for effective, rapid retraction.
It has to not be a total pain to use. I’m sick of having to laboriously strip down an extruder and carriage, with lots of awkwardly placed screws of different sizes. I’m bored of having to tweak my idler tension manually until it probably-maybe is set correctly for this new filament I want to use. It’s annoying to not have a way to manually drive filament by hand on direct-drive extruders. It’s a pain when you don’t have a useable lever to release idler tension on geared extruders. Having to clean out debris packed into hobbed bolts is a chore. These problems must be resolved.
It has to run every type of material out there. Brittle, abrasive carbon fibre reinforced materials, slippery Nylon, floppy flexibles. We need to run all of these, easily.
It has to be priced reasonably. There are plenty of ‘premium’ manufactured extruders out there, some good, some terrible, but paying upwards of £100 for a simple thing like this isn’t going to work for most people out there.
What we did to address these objectives:
Compact, machined gearing system.
We did a bit of maths, testing and reasoning, which led us to deciding on a gearing ratio of 3:1. Why? There are lots of factors to balance here.
There is no point in the torque of your hobbed bolt being able turn with more force than the grip of the drive gear is able apply to the filament, this just results in slipping and grinding. Ratios of around 5:1 are common on motors that use planetary geared motors and Greg-Wades type extruders, but having this higher than useful torque is wasted and results in lower achievable speeds and accelerations. A ratio of 3:1 achieves all the required torque and gets you significantly higher maximum speeds. This is useful for Volcano printing and generally being able to retract very snappily.
Another aspect is the resolution of the system. Direct-drive extruders can have issues with ‘pulsing’ of flow, because the lower resolution of filament motion results in filament being extruded in pulses. This results in a slight wavy surface finish, and is particularly prevalent when printing at low layer heights. Using 3:1 gearing triples the resolution of the system and allows for smooth printing at the lowest of layer heights, using the smallest of nozzles.
We looked at a bunch of ways to make the the exact gears we wanted. Sintered powder-metal gears, injection moulded plastic, and off-the shelf gears. Ultimately the best results for this application were going to come from custom machined gears made for the job.
We use a combination of steel and delrin which gives a very low sliding contact friction and low wear on the teeth. Steel on the smaller gear which experiences more wear, and delrin for larger gear which reduces weight. Lower weight not only reduces the overall weight of the extruder, but also means higher acceleration retractions as there is less mass to spin-up.
Because machined gears have much tighter tolerances than printed gears the amount of backlash is almost zero. This eliminates the classic click-clack noise that often comes with printed gears, and further increases the efficacy of retraction as well as the repeatability when resuming extrusion. The low wear properties of steel on delrin mean that these should never wear out, unlike printed gears which do wear out over time.
The gears run on miniature ball bearings which makes everything extremely smooth. We did consider certain bushing and plain bearing options which would have been cheaper and perhaps simpler but you just can’t beat proper bearings.
The classic way to cut teeth on a hobbed bolt is to re-purpose a thread cutting tap as a hobbing tool by spinning it against the thing you want to put teeth on, this cuts a screw-thread type tooth profile around the circumference of the hobbed bolt or drive gear. This is a neat little hack and is easy for an individual to do with minimal tools.
The reality however is that screw threads are designed to be screw threads, not filament drive teeth. The triangular tooth profile means there is a triangular groove into which debris likes to get wedged into and build up in. Because of the helical nature of a thread the teeth are cut at a slight angle, which doesn’t optimally locate and drive the filament. Good grip can be achieved from a conventionally hobbed bolt, but it’s not totally optimal in terms of grip, and the sharp thin tips of the teeth often made of softer material can be easily bent, and are prone to abrasive wear from abrasive materials. Both of these factors change the effective steps/mm over time.
Instead of using a tap we’re CNC cutting each tooth of the Titan drive gear individually with a custom made cutter. This gives us a great deal of design freedom in order to create a tooth profile that is exactly what we want for driving filament.
Titan drive gears are cut with a round bottomed root, and a tooth that curves upwards to a robust tip. The rounded bottom of the profile strongly resists filament debris wedging into the drive gear and in almost all cases it’s basically self cleaning as any debris simply falls off the teeth.
We spent a lot of time playing around with different shapes and sizes of tooth, the number and spacing of the teeth, depth of cut etc to really perfect the degree to which the gear grips the filament. It’s surprising how much of a difference seemingly tiny 0.05mm changes to these parameters makes. What this all results in is a drive gear that grips like an absolute beast, making the most out of the available torque from the gear set.
The toothed drive portion is located on a splined shaft that is press-fit into the delrin gear. This makes for an extremely compact gear and hobbed drive shaft assembly.
Lightweight moulded parts in engineering plastics.
The main body of Titan is moulded in Delrin, which is a very strong and tough engineering plastic. It’s a heat resistant polymer and can easily deal with the heat generated by the stepper motor, and will run in a heated chamber with ease.
The lid at the front is clear polycarbonate, which is again exceptionally tough, strong and temperature resistant. It’s also clear which looks great, but more importantly, it allows you to see what’s going on inside which can be handy should something go wrong. The lid when screwed down retains the HotEnd into it’s groovemount, PC is a pretty grippy high friction polymer and this ensures it secures the HotEnd end against rotation and wiggle effectively.
The idler lever is delrin which has been specially modified to be self-lubricating, low friction, and low wear. This is important because the idler lever uses the motor shaft as it’s pivot pin, and the motor shaft must be able to rotate freely without resistance or wearing the idler. The idler bearing is secured within the idler lever part using a press-fit steel pin.
The filament guide, which ensures filament is constrained and guided right from the drive gear to the hotend, is also Delrin which means it slides into place easily and means even rubbery filaments slide into the HotEnd easily. (In case you haven’t guessed yet we kind of like Delrin!)
These moulded engineering plastics have a much better strength to weight ratio, and the ability to resolve more precise, fine and compact features than printed parts. We trimmed and cored out weight wherever we could. This results in a superbly lightweight package at a mere 90g for the extruder system. Furthermore, because of the gearing you can get away with surprisingly small NEMA17 motors, significantly cutting weight.
NEMA17 Compatible Mounting
At this point some of you might be wondering why we went with a NEMA17, why not a more compact and lighter NEMA14?
The simplest answer is that NEMA17 motors have vastly better power to weight ratios than NEMA14 or lower motors. When you compare the datasheets on a short stack NEMA17 to a NEMA14 of the same weight the NEMA17 produces more torque. This means that using a short stack NEMA17 will get you an extruder with better performance to weight than designing around a smaller motor. Extremely compact short stack NEMA17 motors are available, and we’re experimenting with a range of sizes to establish how compact we can go.
Another large factor is that the vast majority of printers out there are already using NEMA17 motors, and often the motor is mounted to the printer by sandwiching the motor and extruder around a mounting plate. By adopting this mounting style for Titan we’re going to be able to achieve compatibility with the largest number of printers.
We’ve already designed, tested, and documented a mounting for the popular Prusa i3, and we’ve got many more mounting solutions on the way. We also expect and encourage people to design mounting solutions for many of the popular printers out there, and we will be supporting this by offering bounties for well designed and documented mounting solutions in the near future.
An extruder that is actually pleasant to work with
Being the extrusion enthusiasts we are we do a lot of work with extruders, stripping them down, changing hotends and materials often. We have always found this a bit painful in one way or another across the many different designs out there.
We have always liked the ability to manually extrude with a geared extruder by rotating the gear by hand. We’ve carried this over into Titan in a more compact fashion where the large gear partially excroaches the body and can be used as a convenient thumbwheel. Great for loading, unloading, purging filament, etc.
Another handy feature is being able to pull back on a lever to release the idler tension so you can quickly pull out and push in filament by hand. We could perhaps have done with a little more finger-space between the lever and the filament, but it’s still pretty nice.
In almost all cases the drive gear is self-cleaning and sheds debris, but if some particularly gummy material does get stuck onto the teeth then the gear is easily accessible to clean with no disassembly.
Should you need to take Titan apart, it’s very simple. The lid comes off with a single supplied allen key and 4 screws. Once the lid is off every part of the extruder is accessible and simply slides out forward, including the HotEnd. The body will remain secured to the printer which means putting it all back together just means slotting everything back in and re-attaching the lid. Completely stripping and re-assembling a Titan can be done easily within 1 minute.
Titan works for all configurations of bowden, direct extrusion, 1.75mm and 3mm. To switch filament diameters only the filament guide needs to be swapped out, and both 3mm and 1.75mm versions are supplied with every Titan. To use Titan as a bowden extruder you just insert a bowden adaptor into the body instead of a hotend. Bowden adaptors for 3mm or 1.75mm are available as a low cost optional extra.
No calibration, no tweaking, just works.
The CNC cut teeth of the drive gear means that extruder steps/mm is entirely consistent between every extruder. No need to manually measure and calibrate the steps, Titan is consistent enough to just work out of the box.
Calibration of idler tension force has always been guesswork, whereby one has to tweak up the tension and feel for the grip, look at the filament to see if the teeth have bitten enough or too much, it’s generally an imprecise process. It’s also a time consuming process that has to be done for each new filament type to get the ideal settings.
To remedy this we’ve implemented an idler force scale in Titan. Turning the tension adjustment screw causes a nut to travel along a channel thus adjusting the tension of the spring. A window is cutaway into this channel and we’ve added a scale below the window. The position of the nut in the channel can be read off the scale. To ensure this feature is useful and consistent across all extruders we sourced highly consistent springs with a known Hookes constant. This means you can always set Titan back to a known idler force for each of your filament types, and settings for filaments can be shared between Titan users or even provided by filament manufacturers.
With reference to our previously established design objectives:
Titans gearing ratio and exceptionally high grip tooth profile results in more than enough force to deal with every material we know of, and the ability to push through adverse situations like kinked filament.
By using moulded engineering plastics throughout, and a compact machined gear-set we’ve packed all of titan into the form factor of a direct-drive extruder, and kept the weight exceptionally low.
Industry standard NEMA17 mounting gives the widest range of compatible machines, and makes it simple to design mounting systems. The Prusa i3 mounting is ready to go, with many more to come from us and the community.
A balanced gearing ratio of 3:1 means that you can cope with fast extrusion situations like Volcano, and the lightweight gear-set gives snappy retractions. However you still have plenty of resolution for even the lowest of layer heights and small nozzle sizes.
We’ve taken great pains to design Titan to be pleasant to work with. Low maintenance, easily cleaned. Strips down with 1 hex key in 1 minute. Painless loading and unloading with manual extrusion. No calibration of extruder steps/mm. No guesswork idler tensioning.
Enough force for even the most viscous materials. Carefully designed tooth profile grips the slipperiest of filaments. Fully constrained filament profile manages flexible filaments with ease.
Using injection moulding, and a lot of careful design for manufacture Titan is priced at £45, around half of the cost of comparable products on the market.
We’re exceptionally happy with Titan, we’ve run the product for thousands of hours on the BigBox print farm. It’s probably the most optimised and tweaked product we’ve ever designed.
In summary, we’re quite sure that Titan gives you the best performance to weight ratio, performance to size ratio, performance to cost ratio, and ease of use of any commercial extruder out there.