Dual extruders on a larger Mendel90?

Hi all,

I have a working (Sells) Mendel (with plastics from nophead) which I keeping firing up and then leaving for a while when work takes over. I'm happy with its operation, but find that when I have time to play I don't get enough done/printed.

I'm therefore in the market to start thinking about a second printer. Having great respect for nophead's work, a Mendel90 is a must, but then I figured I have to add additional value with a second printer, so I am thinking of making it larger (yes I know there are various issues with this, thinking of 300x300), more importantly I want to support 2 extruders for future proofing.

Has anyone done the above with Mendel90? What do you think I should consider? Obviously I can print my own plastics, but would like to avoid obvious pitfalls.

Regards,
Craig

Edited 1 time(s). Last edit at 03/15/2013 03:42PM by CraigRK.

2 extruder on a M90? I'm still a noob, but I think you would want to switch to the 1.75 filament. Which requires less force for extruding. So you can use a smaller gears. Which in turn makes room for a second motor. From there, I would see what other users comment. As I don't know what designs work or could be modified for the M90.

Thanks, appreciate the comments. I agree that it will probably mean a move to 1.75mm filament to keep things lighter.

I have been searching the net, but most Mendel90 builds I can find are form Nophead's kits, so pretty much standard, and others are from before the kit days, but still pretty much standard.

I like to read up on other people's builds to try and avoid the same pitfalls.

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[blogger.kritzinger.net]

i modified the x carriage to fit two makerbot mk8 style extruders on it. so far im still just getting it set up and havent started printing with it yet
the file is on thingiverse.

[www.thingiverse.com]

Hi RBisping

Would love to see any photos/vids you have of the heads attached? I'd really like to get dual-head printing going on my Mendel90, chiefly for a soluble support material, rather than a second colour.

Marcos

I've been searching the forums for a 300x300 printer. Is this a reasonable size or is it too large for the a Mendel90?

I'd like to print some gears at 300mm diameter so it would be nice to have something like maybe 300x300x200.

I've been looking around for ideas for a bigger model too. It looks to me as if the Mendel90 could just be built with a larger frame and work ok without major design changes. But I'm rather noobish too. I was thinking of
[www.robotdigg.com]
for the z axis,
[www.robotdigg.com] for the other 3 motors.
It looks as if 12mm rods are no more expensive than 10mm - does anyone have a reason why 12mm would not be good?

I can't see any fundamental reason why 300x300 would not work but the mass of the Y carriage and the power required for the heated bed are square laws. So for the same performance you need a Y motor with twice the torque, which would be NEMA23 and so require more current than the traditional reprap electronics can supply. Similarly the bed would need about 20A at 12V so a mains one become more practical.

Does anybody make a 300mm PCB or Kapton on glass? If not the alternatives involving an aluminium plate tend to be even heavier.

Once the Y build size gets above about 200mm moving table becomes less suitable and a head that moves in both directions gives a smaller machine and less moving mass.

The main issues of printing something that big would be the problems with thermal contraction leading to warping and the time and cost of filament. Warping gets worse as you scale up because objects want to contract by a percentage of their length but they are attached to a bed that doesn't.

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[www.hydraraptor.blogspot.com]

I was wondering about the suitability of carbon fibre for the bed and how thick it would need to be.
[www.easycomposites.co.uk]

here [users.skynet.be] is a motordriver which you can use to run the nema23 instead of the polulu driver. it costs little more than 20€.

if you only want to print pla i guess the warping problem is reduced?

did anybody actually made a bigger mendel90 and would share his stl files?

thanks, michael

I had some more thoughts - a 300 x 300 Y carriage could be made that is lighter than the existing one. The PCB would be replaced with a nichrome wire heater. The top build surface would be carbon fibre. The bottom section of dibond seems to have a lot of unnecessary mass and could be cut leaving only the needed parts or, a bit more expensively, replaced with carbon fibre. I'm not sure of the weight of peltier units but have ordered one for experiments as a possible alternative which would give a fast cool option as a bonus. I'm still noobish at this so please say if my ideas seem crazy.

I am not familiar with carbon fibre.

Is carbon fibre epoxy laminate perfectly flat like glass is? Glass fibre epoxy laminate certainly isn't.

You can print ABS directly onto PCB epoxy finish but eventually it stops sticking. I have never tried PLA.

I you use nichrome you need something conductive to spread the heat. Is carbon fibre laminate conductive enough? Carbon fibre reinforced epoxy only has a conductivity of 24 compared to 250 for aluminium.

Peltier elements are ceramic so they are moderately heavy, particularly as you would need a lot to tile the bed, or you would need something conductive over them.

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[www.hydraraptor.blogspot.com]

It appears to be perfectly flat and reprapsource include in their kits as a preferred base. [www.reprapsource.com]

From the data at [dragonplate.com] it appears to have high thermal conductivity. The sheets at [www.easycomposites.co.uk] are advertised as perfectly flat.

Carbon fiber may be perfectly flat, but it is a shitty heat conductor. As for the peltier coolers - forget about it. They are a heat pump, and a very inefficient one at that. Regardless of the weight, your not going to get significant heating (or cooling) as a result.

Actually they might be efficient at heating because all the electrical energy that is "wasted" by their inefficiency as a heat pump becomes heat.

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[www.hydraraptor.blogspot.com]

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Is carbon fibre epoxy laminate perfectly flat like glass is?

For both, glass and carbon fibres, this entirely depends on the surface you laminate onto. Flat surface and even fiber distribution -> flat surface.

With a combination of glas and carbon fibres you can even create a compount which doesn't swell or shrink on temperature changes. Because carbon fibres are one of the few materials which shrink on temperature elevation instead of the usual swelling. Properly combined, swelling and shrinking fibres compensate their temperature effects, then.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

[dx.com] seems like a possibly - 23 grams each. Does anyone know or can easily check the weight of the current pcb - I don't want to take mine apart to weigh it?
From theoretical calculation a 200 x 200 carbon sheet should be about 60g compared to 260 for glass.

Only 23g each but you need 25 to tile the bed which is 575g.

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[www.hydraraptor.blogspot.com]

Assuming that carbon fibre is flat and stays flat when heated from one side and is stiff enough to resist the warping force of the plastic then the lightest bed would be that plus a kapton heater.

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[www.hydraraptor.blogspot.com]

Kapton with nichrome was what I was thinking. Is that what you mean?

This is something I probably won't have funds for before xmas. All it seems I need for my main anticipated project is A4 with 2 extruders. My printer has been running most of my waking hours since I finished it. I had looked at the possibility of a delta printer as my second but really don't want to put the time into figuring it all out. The ideal would be if some nice person made a kit with A4 or bigger build size and 2 extruders which I guess would use 1.75mm filament. Theoretically 1.75 filament seems a good way to go with a lighter motor.

I'll order a 20x20 carbon fibre sheet in a few days and see how that goes.

In terms of a dual extruder design, I really like this concept to prevent the inactive extruder from oozing:

[www.thingiverse.com]

(It's a little like nophead's unattended ooze-free start)

I'm sure something along those lines could be worked onto the Mendel90 (You could even use bowdens if you really wanted to keep the mass down)

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Kapton with nichrome was what I was thinking. Is that what you mean?

Too fiddly for me. I mean something like this [www.omega.co.uk] but it is hard to get them the right size and voltage.

People that use them with glass find it heats so fast it causes the glass to warp and move up and down in time with the power switching on and off. I don't know if CF would do the same.

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[www.hydraraptor.blogspot.com]