Diamond hotend switching usage

Hi!

I'm thinking to buy a Diamond hotend and use it as a switching color hotend, not mixing (I read that passive mixing is not ideal, because of the toothpaste effect).

In theory, switching only needs 1 motor, as only one filament is used at a time. But in the case of the Diamond, all filaments have to be engaged, to avoid back extruding in unused heads.

My first question is: do unused filaments need to be maintained by their respective motors? My first idea was to use only one motor, and a servo to move a gear to choose which filament to drive... But this means that unused filament won't be maintained.

My second question is about Bowden tubes: what is the maximum length I can use? What happens if using too long tubes? I would like to put the extruder on the (coreXY) frame, not above with a swinging stuff.

Thanks for your help.

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Frédéric

Maybe the long(er) Bowden tube is an advantage in this case. The higher friction might be enough to avoid filament being pushed backwards?

But I thought, switching extruders work with two filaments ( not three) ?

The servo to change gears is a good idea, but will it withstand the tension of filament and idler? It could potentially add backlash if it isn't strong enough, and be too heavy if it is. As far as I understand it only needs to have filament loaded in each end to stop plastic creeping up unused ends.

As for bowden tube, the shorter the better. The shorter you can get it, the more precise and short you can make retractions. Some people have massive bowden tubes, but I personally wouldn't want one much longer then say 400mm. Hence the flying extruder mod to get an almost direct drive extruder. If you are considering a servo to change gears, I don't see why a motor driven hanging extruder should be too much of a problem for you to design.

If you only want to change filaments, have you considered alternate methods? eg, IDEX or tool changers. The diamond is very limiting for material switching as they must have similar melting points so you can't experiment with removable support or complex multi materials.

o_lampe, why switching could not work with more than 2 filaments? Ok, it is a little bit more complicated, but possible.

About servo, my idea is to use some sort of cam shaft to disengage the unused filament, by pushing back their respective springs. Using a cam can give string effort without much torque on the servo. Close to what it is done with the Dondolo.

I don't know about the tool changer your are mentioning; do you have links?

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Frédéric

Tool changer

There have been plenty others posted. I've seen one for ultimakers as well. Basically use magnets to 'grab' an extruder and off you go! Has the advantage of multi-materials, multi temperatures, multi nozzle sizes and different heat blocks.

Edited 1 time(s). Last edit at 03/04/2017 01:11PM by Origamib.

I see. This requires a lot of tuning to perfectly find the relative positions of the nozzles... And each time you disassemble a head, you have to do it again.

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Frédéric

Use a piezo sensor for each head to determine Z offset.

Yes, but what about X/Y? If one could find an easy way to calibrate...

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Frédéric

Quote
fma
Yes, but what about X/Y? If one could find an easy way to calibrate...

With a decent mechanism I don't see why XY should be a problem, as long as it's made to a tight tolerance. The example I gave isn't the best designed.

You can't expect having all nozles at the exact same coordinates. Even if the tool changer is perfect, all heads won't be mounted in the same exact position on each tool. You need to calibrate X/Y, as you need to calibrate Z. And each time you unscrew something for maintenance, you need to re-calibrate again.

That's why I'm looking at a single nozzle head as the Diamond...

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Frédéric

Quote
fma
Hi!

I'm thinking to buy a Diamond hotend and use it as a switching color hotend, not mixing (I read that passive mixing is not ideal, because of the toothpaste effect).

In theory, switching only needs 1 motor, as only one filament is used at a time. But in the case of the Diamond, all filaments have to be engaged, to avoid back extruding in unused heads.

My first question is: do unused filaments need to be maintained by their respective motors? My first idea was to use only one motor, and a servo to move a gear to choose which filament to drive... But this means that unused filament won't be maintained.

My second question is about Bowden tubes: what is the maximum length I can use? What happens if using too long tubes? I would like to put the extruder on the (coreXY) frame, not above with a swinging stuff.

Thanks for your help.

Not only do you need to keep the unused filaments in place, it seems that you need to retract them at the same time as you retract the active filament. See section "Extruder retraction" at [blog.think3dprint3d.com].

My delta printer has a Bowden tube more than 600mm long, and although this is much longer than ideal, I get good prints from it. I had to tune the retraction very carefully. 7mm turned out to be optimum, enough to prevent blobs but not enough to cause the E3Dv6 to jam. Using pressure advance helps with print quality.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks for the info! So, the idea of using only 1 motor is not possible...

Good to know about Bowden length.

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Frédéric

Quote
Origamib
Use a piezo sensor for each head to determine Z offset.

I was thinking this would be a very good use of the sensor.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions