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I'm likely to need to print some parts from TPU (Shore 95A or harder) in the near future. I have everything I need to do a direct drive conversion using the original extruder on a bracket above the hot end -- but for most of my printing (PLA and PETG), this setup isn't required or even optimal, because of the extra moving mass on the X carriage.

It looks as if, once I have the bracket installed the first time, I can move the extruder (including adding/removing a wire extension and switching between full length Bowden tube and short coupler tube) in less than an hour -- in addition to the time I'd need to clear one material from the hot end before loading the other, of course. Is it practical at all to swap the extruder back and forth like this, on the assumption that I'll want/need to print TPU parts from time to time (I'll want softer material, too, since some of what I want TPU capability for is gaskets).

Obviously, if I needed to print TPU alongside PLA on a regular basis, I might be ahead to have a second printer, but space considerations, more than money, work against that.

Am I missing something on the effort needed to swap the extruder position back and forth (suggesting I should stick with direct drive and pursue firmware and tuning solutions to correct the accompanying problems with faster printing), or should I plan to do this as needed?

Zeiss Ikon
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  • Have you tried printing the 95A TPU on your machine? With the right settings, you may be able to without modification. 95A is on the stiffer end, people have done it successfully on their Bowden setups. – ChinchillaWafers Aug 04 '21 at 20:53
  • @ChinchillaWafers I had thought about that, it's barely more flexible than PETG -- but longer term, I want/need to be able to print much softer material for gaskets and seals (for daylight color print drums, for instance), and I've understood that for that I'll really need direct drive. – Zeiss Ikon Aug 05 '21 at 17:37

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With some engineering, you could consider creating a tool dock version where you can easily screw off the Bowden driven hotend and screw on the direct driven hotend. You'll only need to have an extension stepper cable to connect the direct drive stepper and pluggable hotend heater and thermistor connections.

E.g. for the Ender printers, there are Voron Afterburner tool heads that are Bowden driven or direct driven (Clockwork or Galileo mods) available. These could be switched very easily, you do need to figure something out to plug the heater cartridge and thermistor.

I'm doing something similar to my Hypercube Evolution where I am creating a Bowden driven 2.85 mm and a 1.75 mm direct driven tool head.

0scar
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  • Putting plugs in a long wire sounds a great deal like a job skill (fourteen years in power tool repair). Just keeping two hot ends mounted, and switching offsets in firmware or slicer might be another option. Already got the stepper extension cable (was preparing to mount the stock extruder on the X carriage). – Zeiss Ikon Aug 04 '21 at 22:35
  • If you use the Voron Afterburner tool head for both Bowden and Direct, there aren't any offsets to consider when you switch heads, only a one time setup offset. You definitely need to set the steps per mm for the extruder if different drive gears are used. Or invest in a board with more stepper drivers, and add a second hotend. – 0scar Aug 05 '21 at 05:15
  • Having two hot ends mounted requires the two to be EXACTLY aligned vertically, or the one which is a bit lower will scratch the plastic printed by the other one. – FarO Aug 05 '21 at 19:44
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It depends on the level of automation you are willing to implement.

The Bowden extruder, including the motor, from the Ender 3 which I think you have (but in general, any Bowden extruder) does not need to be moved at all, since it's not on the printing head. You just need to disconnect the Bowden from the hot end and clip it somewhere safe.

The direct drive extruder, if you have a supporting plate which makes it as a single part, can be disconnected with a couple of screws and hanged somewhere nearby.

Depending on the knowledge of electronics you could set up a very cheap relay array (4 relays) all controlled by a single GPIO pin of your motherboard, so that you can switch the motor with a GCODE command. The relay would have the COM going to the stepper driver, the NO connected to the direct drive motor, the NC to the Bowden motor.

Write GCODE macros to change the current, linear advance, steps/mm settings depending on the activation of the relay board (or, even better, depending on the filament).

However, if money is not an issue, I would consider an Orbiter or a Sherpa mini extruder, which is direct drive but with 120 gram weight (including motor, not including hot end) can be used all the time. You are likely not going to push the X acceleration to the very very maximum you can, so you get direct drive at no performance cost.

FarO
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  • If money were not an issue, I wouldn't object to the suggestions I've had for remote direct drive extruders -- which add even less mass to the X carriage. – Zeiss Ikon Aug 04 '21 at 13:26
  • That said, the Sherpa doesn't seem extravagant (never mind it'll likely take 2-3 months to arrive from China). I'll check for a bracket adapter on Thingiverse. – Zeiss Ikon Aug 04 '21 at 14:47
  • I bought it from US, printed in CF-ABS. ez3dpstore also offers a 8 teeth motor, while China offers 10 teeth (less torque) – FarO Aug 04 '21 at 15:40
  • And they're sold out of the motors. Does the motor include the other gear and the hobs? They don't show on the page... – Zeiss Ikon Aug 04 '21 at 16:01
  • The motor is a custom order from LDO, that's why it's in short supply. They get a custom 8 teeth one. The remaining parts should be bought from E3D or clones. – FarO Aug 05 '21 at 09:39
  • I looked at those extruders in more detail -- with the reduction already present on the Sherpa I don't know that 8 tooth vs. 10 tooth will make a lot of difference. Sure, 20%, but that only matters if you're coming up short by less than 20%. – Zeiss Ikon Aug 05 '21 at 18:04