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Hi everybody

I think it is time to start discussing the dual extruder for Rostock Max topic. Although I won't tackle this, before I haven't got a perfectly running machine (onyx leveling, LCD, new nozzle, backlash, platform tipping, ooze), it is well worth to agree on how to do this properly from the beginning.

I am holding the add-a-struder kit in my hands, but don't have more clues on how to mount the hot-end. The only reference I can find, is the CAD rendering on Rostock Max's reprap wiki page:
[img]http://reprap.org/mediawiki/images/thum ... oncept.JPG[/img]

This picture suggests to remove the hot-end mounting plate spacers and screw the plate directly to the delta platform. The two or three hot-ends would all be screwed directly into the mounting plate. I don't like this particular version very much, for several reasons:
- If the delta platform suffers from a slight tipping during movement (which is probably inevitable), the nozzles would be moved quite a bit, increasing displacement of perimeters and infill. Further, the nozzles would change Z distance due to not sitting in the center of the platform.
- With the spacers, I am able to cool the heat barrier of the hot-end with a fan above the delta platform, preventing the airflow from cooling the heating block below the platform. This would be much harder without this separation and would need a specific fan duct.
- I love my LED ring. Due to the hot-end mounts covering the lower side of the platform, it would not be possible to have the LED ring attached.
- From experience with other printers I know, that nozzle alignment in Z is vital. With the suggested version, the only possibility to properly align the nozzles would be to make sure, that all thread fittings are tightened, the nozzle sits on metal inside the heating block and then sand down the nozzles irreversibly until they are aligned. Or am I not seeing the obvious solution for this?

Since my first printer, I imagine a seesaw like construction, to slightly lift the inactive nozzle from the print by a solenoid or servo. Maybe, a construction similar to the Dimension printer heads (http://www.youtube.com/watch?v=I8v11G0WZds) would be possible (only the lifting, not the rest of the construction).

Looking forward to read about your thoughts concerning dual heads for Rostock Max!

Andy

Great topic Andy. I got my Max primarily to add multiple extruders. I should be finished with my build tomorrow. We are expecting 24-30" of snow here in the Boston area tomorrow thru Saturday so I'll have lots of time to wrap it up. Then I plan to design a 2 and/or 3 extruder mount. I have a CNC mill and lathe so I can fabricate whatever I dream up. I have thought about the issue of making sure the nozzles are all at the same Z. I've also thought about a turret style extruder that has a rotating head with 2 or 3 nozzles with only 1 in position. The advantage of this is there is no loss in X or Y because the orifice is in the same location for each nozzle and it eliminates the possibility of a nozzle from hitting the print like in a fixed design. Search lathe tool turret for the idea.

Cheers,
Michael

Hmmm, I was sketching a bit, how such a construction could look like and came up with three possibilities.

The two extruder seesaw:
[img]https://lh4.googleusercontent.com/-qo77 ... seesaw.jpg[/img]

spring loaded, to tip over from one side to the other and lock in position. This could easily be actuated by a two way solenoid, controlled via one single arduino pin (second extruder in use command).


A revolver like construction for more than two tools:
[img]https://lh6.googleusercontent.com/-ztPA ... volver.jpg[/img]

Your tool turret approach led me to something similar to a microscope lens revolver. Since we do have bowden tubes and cables running from the hot-ends, unlike microscope lens revolvers, the tools would have to be arranged in something smaller than a semi circle around the disc, to allow for proper mounting of the revolver as well as routing of the bowden tubes. The hard part here is, to control the tool change and lock in position. I don't think that an electromagnet for each tool could hold the disk in place. Probably, it would have to be a gear driven revolver with at least one sensor (end stop) and some locking mechanism (spring loaded ball or a solenoid driven bolt). This would definitely need some more engineering and is possibly not printable so easily.

The third idea would be to only move the tools up and down by either separate solenoids or a motor turned wobble plate. Here, X/Y poitioning is no problem, but the whole force in Z would have to be absorbed.

I think, one of the main challenges will be to get a sturdy, but still lightweight design, which can take forces in all three dimensions and keep position. However, the movement of what ever construction proves to be best, does not have to be big at all. The lift of about 1 mm in Z would be enough. Of course, positioning the new tool on the same x/y coordinates would be preferable, but a loss of 1-2 cm of the build space should be passable.

Well well, a highly philosophical discussion But so far, I haven't seen any construction like this for hobby printers. Let's be the first to come up with a nice and easy solution.

Here is what I spent my Saturday afternoon with:

[img]https://lh5.googleusercontent.com/-Ai6Z ... SeeSaw.JPG[/img]

Unfortunately, this won't work, as the hot-ends are too close to the platform. If I move the construction further down into the hole, the PEEK parts would be covered by the platform. But as they need to be cooled for PLA, so this is no solution. The only solution I see right now is to move the hotends completely through like shown in the first picture of seemecnc. I definitely fear vibration and instability of the nozzles.

Well, not exactely a success story...however, one experience richer.

This is an old topic, but I wanted to add an idea I am working on. Using nothing but the stock parts, I came up with a way to mount 1-3 extruders, and level them. I would love input on the design.

Basic idea is to mount the plate under the base, using the screws and aluminum barrels as a way to hold a cooling fan on the PEEK. Next, a spring is placed between the mounting plate and the base on each screw, allowing the adjustment of the height of each head independently.
Advantages: Easy to level, no complicated parts, most parts already included in kit.

Disadvantages: May suffer if base is not stable during movement, as heads are not in the center of the motion (someone else mentioned this before). Currently their is not enough room on the top for the spacer and nut. The nut could be used to adjust the height, so this might work out.

This is what I made up to mount two Steves hot-ends on my MAX.
http://www.tricklaser.com/Dual-hotend-a ... RM-DHA.htm
Pretty simple, but should work fine i think.
I have not actually printed with the setup, it was quite awhile back when I did this and at the time the firmware support for dual heads was rather dicey. Maybe it is better now?
The heads could be fine tuned to both be at same level by using shims made of paper.
We have sold quite a few of these, so somebody must be experimenting with dual heads.
If anybody wants the CAD file for this (or any other of our laser cut products) just shoot me a PM or email.

I do not understand why you would need to make the heads index in a turret style? or index at all??
Seems overly complicated.
Am I missing something?

I think the idea of indexing or lifting is to reduce the effect of drooling from the extruder not currently in use. Right before a change from one extruder to the next you could index to the appropriate extruder, wipe on a brush somewhere, then begin using the next extruder. Great idea in theory, but the devil is in the details.