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aviphysics

Designing a quick change hotend system.

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It seems like there isn't any one hotend design that is best for all tasks, so it would seem like it would be nice to have a quick change hot end system. I am looking for thoughts on designing one.

To me, it seems like the system has 3 main design challenges.

1) A mounting system that allows hot ends to be exchanged without dissembling the X/Y axis. I think this would look like a two piece system, where one piece mounts to the bearing to which a cartridge holding the hot end can be attached.

2) Interchangeable electronics interfaces for heater and temperature probe. I think this would be a matter of having electronics and a common header on the hot end cartridge.

3) Easy switching (preferable automatically) of PID setting and other software settings. To me, the main issue of this seems like it would be writing the software modification where it wouldn't make updating Merlin a PITA. For auto recognition, I believe the Arduino has an ADC, so recognition could be done through a resistor on the cartridge head linked to a voltage divider that is read by the Arduino.

Any thoughts?

 

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My first thought:

Never again a permanently installed print head, it needs to go in the direction of fast clip. At least the nozzles shall be easily replaceable, good things do not need a redesign.

A compact printing head including heating, temp sensor, nozzle, as easily removable module, that would be good. Easy to install, for example, by a twist lock.

Markus

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I think that for challenge #1, a more compact version of Jelle's cassette system would work (http://www.thingiverse.com/thing:25836). Rather than lasercut wood, I'd go with a minimal printed central crosspiece to preserve as much print area as possible. I like the idea of having up to four locations for attachments.

I'd like to keep the amount of fussing to add and remove cartridges to a minimum, so you could quickly pop them off and on. I'd prefer the option to use clips or magnets to hold them in place when forces are not too great (like for fans), but use screws when needed (like for heavy paste extruders). Perhaps print a coarse knurl on the mating surfaces on the crosspiece and print a complementary knurling on the cartridges to keep them from slipping and to help align multiple heads.

We'd need to make endstop triggering idiotproof when a cartridge protrudes into previously free space. The current solution of triggering with the slider blocks hitting mechanical switches won't work as-is, but I wouldn't want to give up the maximum margin of cartridges in all four corners all the time. So, in addition to the current stops, we may need a proximity sensor on the outer edges of each cartridge to detect when it is about to hit a slider block. Perhaps if blocks have magnets, we could use a cheap reed switch on the far corner of each cartridge.

 

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On second thought, reed switches probably won't work. There's way too much motion. It's probably better to KISS and move the endstop function to the printhead. Mount the mechanical switches on each arm of the crosspiece, and then cartridges would need to include extensions on their mating sides to press the switch.

 

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I change whole printheads very often for various experiments. That's why I designed THIS.

Not exactly what you proposed, but a step in that direction. :) I'm working on an easily replaceable hotend mount since I have the E3D and UBIS now and plan to get a Merlin hotend too.

 

As an alternative to your design, you could do pretty much the same thing at the printhead and cut the number of screws in half, The downside being that all your print heads would need to be custom.

 

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