Another first drawing, and another pen holder

Due to a mishap with the extruder (internal shorting due to careless assembly), I got the urge to do some drawing to "test" the cartesian bot. So I made a pen holder (I know one already exists, but the more the merrier). Materials for the pen holder include a 25mm wide, 3mm thick aluminum strip, and some 5mm thick acrylic scrap generated during the construction of the extruder (bits from bytes).

Nice work. I agree with the more-the-merrier-pen-holder philosophy!

Demented

Well done, puts my almost circle to shame . Any chance you can provide a video? Id love to see it in action.

I

Dan the biggest problem with print speed is the extruder itself and how quickly you can get the plastic out the end as the faster you go the higher the pressure you need, this seems to be the limit at the moment.

But don't stop working on better control/ movement systems it's all part of the puzzle.

I see that on another forum it is the bot speed that is limiting people, interesting, I get a bot speed of 60mm/s with some ramping and 45mm/s without needing to ramp.

Edited 1 time(s). Last edit at 10/05/2008 03:03AM by Ian Adkins.

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Ian
[www.bitsfrombytes.com]

Hi Ian,

Thanks for you great work BTW, I

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t was my understanding that bot speed was the issue 2, not extrusion speed

I'm pretty certain it is the extruder limiting the system, though I don't have many useful references to back that one up. Take a look at [builders.reprap.org] though.

The current darwin steppers/stepper drives are far more powerful than the system really needs, so there's plenty of headroom there. Designing a faster extruder is going to require bigegr motors and a more substantial heating system and a bigger, heaveier frame to hold it all together. All that extra inertia is going to make the cartesian bot's accuracy at speed worse.

I stumbled upon some hotmelt glue guns (nordson) recently those were used to glue cigarette boxes and such, they are pretty fast have a needle valve inside and weigh about 700g so not too heavy (but surely too expensive) especially because it's not done with the gun alone ($400) you'll need a heated hose ($250) and the meltpot with pump ($3000)
But we should take a close look at how they work, maybe we can get some ideas from those.
they are pretty fast and can drop alot of glue (and as stated other thermoplasts)
per hour (about 1kg/h)

At least we can use the nozzle for sure (pretty much every diameter we need)

'sid

Edited 1 time(s). Last edit at 10/05/2008 11:27AM by sid.

Ru, yes the current stepper/darwin setup is plenty powerful but most of us don't have darwins afaik. Straps are pretty prevelant, if not most common, and are not nearly as well designed as a darwin for the most part. But, yes, the extruder still needs a lot of work. The accuracy has been addressed by the encoder and valve recently put on them but I think some other method of driving the filament is also needed because the screw is often so finicky and--as you point out--not the ultimate speed bottleneck of the system.

Demented

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most of us don't have darwins afaik. Straps are pretty prevelant

Well, I'm not sure what can be said to that, aside from 'better build a darwin then' or 'build a better repstrap'. We don't have a common repstrap design, so discussions on the widely varying capabilities of people's unique cartesian bots seems a little futile. When answering general queries, talking about the Darwin seems to be the only really sensible thing to do, no? Especially given that 'repstrap' implies production of a reprap, which at this point is the darwin design.

True. Best bet then would be to build your strap, print a set of parts for yourself, build your darwin, then print a set of parts using both your darwin and your strap so that print time is dramatically reduced. Yes?

Demented

Except that the extruder gets moved over to the darwin. It's the most complicated bit to build, and requires the most variety in materials. I was planning on moving the extruder, steppers, and electronics over to the darwin once I have all the pieces printed out.

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I'm building it with Baling Wire

If you have one extruder, you can build another, no?
that's why it's a reprap *gg*

'sid

One should try to have two extruders mounted onto ONE darwin,
most parts are multiple items, so one could print two indentical items in exactly the same time (if both extruders are identical)
that'd be a good thing

Ah, that's a nice idea. As long as the part size was under the offset distance of the two extruders you could do it. Nice way to speed things up. Course, your extruders would have to extrude at exactly the same rate too...feh.

Demented

The extuder isn't too wide to mount them close together so especially for the smaller parts that may work very good (that is if the software can handle multi-item-layouts for multi-head-printing )
but I guess if two parts fit on one bed next to each other one can print two parts with two heads (a matter of positioning the heads manually to do it right i guess)

But yes it's hard to make sure that both extruders are fully synchronized,
it'd become a mess if one of the printouts warp too much and gets loose, and there are many other issues...

but it'd be nice to have two heads.

Not only because of printing duplicates faster, but also because of having the possibility to use the second extruder with another material (talking about support here) or the same material at a different temperature (Adrian said something about ABS at false temp to be well for that purpose afair)

'sid

If an extruder deposits some filament and then turns off and moves back over it without changing its Z position, does the filament get smeared? Given that the filament expands slightly after deposition and that the head has to be pretty close to the build surface, I'm assuming yes, and it would be bad.

In the case of a two-head system where both heads are effectively stuck together and moving over the same piece, you have to take extra precautions to ensure that the other head doesn't cause smearing. Or you could add an extra half-axis to raise or lower each head independantly by a small amount, but that's extra work too.

Anyone who actually has a working extruder care to comment on this one? I can't quite tell from the videoed builds available!, andou know what they say about assumptions...

I removed the head lifting from HydraRaptor recently and didn't notice any ill effects.

The nozzle is wider than the filament so it passes over the previous track anyway.

If you had two heads working on the same object then the nozzles would have to be exactly at the same height. That would require the PTFE expansion problem to be fixed, as the BfB design would appear to achieve.

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[www.hydraraptor.blogspot.com]