I’m looking at an intriguing upgrade for Bowden 3D printers to increase quality and print speed.
Bowden systems are common in the desktop 3D printer market due to their low manufacturing cost. The idea is to put the extruder motor away from the toolhead to reduce the toolhead’s weight. This allows the toolhead to move around and change directions more easily: less momentum.
However, a Bowden system also requires the filament to be pushed through a long PTFE tube towards the toolhead. This can cause plenty of issues.
One that I hadn’t heard of was identified by Printables contributor Kiolia, who explains the problem:
“Did you know 20-30% of a Bowden setup’s Pressure Advance (PA) value is just compensating for stretch in the PTFE itself? And did you know that PTFE has annoying stretch properties (fast stretch, slow contract) that make tuning PA for really crisp corners hard to impossible?”
PA is one of the methods used to achieve today’s high-speed 3D print rates, and it must be carefully tuned to ensure proper extrusions at speed.
During print operations, it is common to see the filament retract, typically when making a travel move. This means that the filament will be going up and down in the Bowden tube as the print proceeds, although there’s a lot more down than up, as you might guess. Nevertheless, the printer must deal with all these retractions, while maintaining speed and accuracy.
Kiolia’s proposal is to wrap the entire Bowden tube in an anchored Kevlar sheath. Kevlar is an extremely strong and rigid material that does not stretch significantly. By wrapping the PTFE tube, it constrains the tube’s ability to stretch during filament movements. Kiolia explains further:
“This anchored sheathing system uses the magic of Kevlar to nearly eliminate PTFE stretch, instantly improving print quality on any compatible Bowden printer. It allows a lower PA value to be tuned, increasing acceleration headroom, and also stops PTFE wear within the fittings so they don’t develop quality-wrecking play over time. It’s easy to set up and surprisingly affordable.”
Kiolia has posted an entry on Printables with the necessary parts and instructions. To implement the sheath on your Bowden 3D printer, you need only print the adapters for the ends of the tube and cut a length of standard Kevlar braided cable sleeve. Installation seems straightforward, but apparently cutting the Kevlar is not. Kiolia provides very detailed instructions for doing so.
After installation, the pressure advance settings must be retuned, as you might expect. Better quality results then occur when printing.
This is quite an interesting finding, and an inexpensive solution as well. It seems so straightforward that I can easily imagine some Bowden 3D printer manufacturers simply adopting this approach with their own machine designs.
There are always ways to make your 3D prints better quality, and this is yet another way to do so.
Via Printables
