Hi all,
I designed a filament pressure sensor some time back for our large printers and it seems to be reliable.
I thought it might be useful and can share more information if people are interested.

I have found that this sensor has replaced the need for a filament rotating monitor (this is good because I have had lots of issues with these) and even the need for a filament out switch (for a basic setup) if you use it with a feeder motor.
(we use orbiters as our feeder) We need a filament feeder because our machine is big, although it would be great on a smaller machine also to take the load off the extruder.

It works like this:
We have orbiter feeders in our reel chamber, when you put filament in the feeder it is driven through this sensor up to the print head. Once it hits the print head the shuttle moves back and makes a connection that stops the feeder motor. if the print head starts extruding and taking filament the shuttle drops back and the feeder motor starts again, so it starts and stops over and over supplying the extruder with a slight positive pressure. when the feeder motor is driven we send a division of the stepper pulses to the duet, emulating a rotating filament sensor input (#7 pulse generation sensor). if the nozzle gets gammed then there won't be enough pluses from the feeder dive then the print will pause, if the filament runs out or a PTFE tube breaks then there will be too many pluses and the print will pause also.
I have designed it so you can put more filament in truck-and-trailer style, so the new roll of filament is pushing the old up to the head and it won't get jammed through this sensor setup.

This is a duet wifi controlled machine.

A ground up design, you can see more on our Instagram. (But still not showing much due to IP)

The ABS print pictured below is 500mm wide, printed at 0.25mm layer height with a 0.4mm nozzle. (See nozzle top left of picture) Parts come out very flat, much better than our current off-the-shelf heated chamber machines.

It seemed a bit crazy at the time to design and make our own machines but, this machine produces parts a level up on what we currently do and a lot faster.

Have found Duet Wifi a great platform to work with, we are using external drives via the extension header.

Here is a short video.
Key principle is:
1: The PTFE tube held by the shuttle wants to move away from the pressure of the fed filament when there is a blockage at the other end (i.e. there is no filament extruding)
2: When there is no blockage at the other end (i.e. filament is being extruded) pressure is released.

Use a fine capillary tube (2.5mm OD - 2mm ID) and drill out the end of the PTFE tube so that it slides easily. Using this method Filament will not get jammed when a new roll of filament is fed behind the old (as there is no way for it to get around the outside of the pushed filament)

A few pictures of our V2 machine. the printer is about 6.5ft tall.

It has heated filament chamber and auto filament change over.
Heated bed is 1kw, chamber is 5kw

100% polycarbonate black is very hard to make look good as it's shinny and refracts on every imperfection. very strong layer bonding, good enough to not break on layer lines. this print was 0.25 layer height.

Video: https://www.instagram.com/p/CRFmC_NFnSw/
Image:

@jay_s_uk Yes I can share the files. I will make a little video of it working and how it goes together first

A short video showing this machine running.

https://youtu.be/iDEyjMv7538

@john-meacham
Just measure the resistance at the board, that covers everything (disconnect from daughterboard first)
if it's high, then check, the sensor directly. If there is a difference then its a bad connection between the board and sensor. If the sensor is reading a higher resistance than it should and wiggling the wires makes no difference then the sensor is stuffed.

@chrishamm thanks, is there a way to drop a youtube video in here or can it only be a link?

Below is a picture of a nylon 6 print, works as well as a Multi-jet fusion part, maybe better. I think FDM has a lot of future, it was on the back-foot for a while but it still has a long way to go. (plenty of good refinements coming along) our latest print heads are making a big difference.

A few pictures of some big prints we did last year on this machine, these are ABS:

Here is a short video.
Key principle is:
1: The PTFE tube held by the shuttle wants to move away from the pressure of the fed filament when there is a blockage at the other end (i.e. there is no filament extruding)
2: When there is no blockage at the other end (i.e. filament is being extruded) pressure is released.

Use a fine capillary tube (2.5mm OD - 2mm ID) and drill out the end of the PTFE tube so that it slides easily. Using this method Filament will not get jammed when a new roll of filament is fed behind the old (as there is no way for it to get around the outside of the pushed filament)

@oliof Hi, no I don't but it that could work also, or a distance measurement using a hall sensor and the spring rate. Ether way would give interesting opportunities, but I like the idea of the strain gauge.
With force feedback we could set different pressure setting depending on the material, for example TPU, very low. Also if you want big retraction the feeder motor could then reverse to reduce the pressure.

Right now it is just set and forget and it works fine for over 1,000 hours.

@jay_s_uk Yes I can share the files. I will make a little video of it working and how it goes together first

@generisi It does not work due to drag or resistance. It works like this: if you try to push filament up a tube without holding onto the tube, the tube will simply move away and you will not be able to push filament up that tube. If you hold onto the tube then filament can be pushed through it, the more force at the other end restricting the filament the more you need to hold onto that tube.

With this sensor the tube is held buy a shuttle that is able to side, as the pressure increases it pushes against that spring you see until makes contact. you can adjust the pressure by moving the contacts in and out.

Hi all,
I designed a filament pressure sensor some time back for our large printers and it seems to be reliable.
I thought it might be useful and can share more information if people are interested.

I have found that this sensor has replaced the need for a filament rotating monitor (this is good because I have had lots of issues with these) and even the need for a filament out switch (for a basic setup) if you use it with a feeder motor.
(we use orbiters as our feeder) We need a filament feeder because our machine is big, although it would be great on a smaller machine also to take the load off the extruder.

It works like this:
We have orbiter feeders in our reel chamber, when you put filament in the feeder it is driven through this sensor up to the print head. Once it hits the print head the shuttle moves back and makes a connection that stops the feeder motor. if the print head starts extruding and taking filament the shuttle drops back and the feeder motor starts again, so it starts and stops over and over supplying the extruder with a slight positive pressure. when the feeder motor is driven we send a division of the stepper pulses to the duet, emulating a rotating filament sensor input (#7 pulse generation sensor). if the nozzle gets gammed then there won't be enough pluses from the feeder dive then the print will pause, if the filament runs out or a PTFE tube breaks then there will be too many pluses and the print will pause also.
I have designed it so you can put more filament in truck-and-trailer style, so the new roll of filament is pushing the old up to the head and it won't get jammed through this sensor setup.

@chrishamm thanks, is there a way to drop a youtube video in here or can it only be a link?

Below is a picture of a nylon 6 print, works as well as a Multi-jet fusion part, maybe better. I think FDM has a lot of future, it was on the back-foot for a while but it still has a long way to go. (plenty of good refinements coming along) our latest print heads are making a big difference.

@sputnikoc3d I have to laugh at that comment, we are a 3D printing business and that was an Instagram post to promote us. This is how we pay our rent. (I don't think i'll get business from this forum) but people can see what we can do with Duet3D. Thanks for the comment.

@3dpmicro Sorry for the late replay....
Actually the pattern you can see was a result of a bad bearing on one end of the leadscrews. It's good having more than one of the same machine, this allows me to see if the other machines have the same issue. (they did not). The bearing had no brand name and was bad from the start, I replaced it with a brand name bearing and it's all good now.

https://youtu.be/-0LE2Qhkd-k

We are on the lookout for a 3D printing enthusiast to join our team to help run and improve our machines.
Would you like to make a career out of 3D printing with a team that is building advances 3D printers?
Or if you know of someone you can contact me: andrew@palmerdesign.co.nz

@3dpmicro
The lead screws are American made, supper nice, they alone are $1500 but worth every cent in this machine.