Specs and accuracy questions…

[ben]

Hi all,

Our office makerbot replicator just blew up (Mightyboard issues). I think I’ve finally had enough, so its time to start building a new 3d printer (just as soon as I get the replacement board through from MBI support).

I’ve been keeping an eye on Morgan for a while now and am seriously considering it over building a Prusa i3, both for the cost and because it looks damn cool 🙂

However, I haven’t been able to find much by way of specifications for comparison. For instance:

Whats the best layer height you guys have been achieving?

How reproducible is it (as in, how much calibration does it take between prints)?

Whats the horizontal accuracy like, given that this is polar I assume accuracy drifts over the whole print area?

Whats the total usable print area?

This would be my first 3d printer build, though I have just finished my Shapeoko CNC build so I’m not adverse to a bit of DIY. But any advice anyone can offer with regard to the Morgan would be much appreciated.

Thanks!

[RobertKuhlmann]

Hi Ben,

so many questions…

The horizontal accuracy , as I see it on Quentin’s test prints is really good (not measured in mm until now, but looks great). The good horizontal accuracy is caused by the relatively big drive wheels in combination with small pulleys, giving a good ratio between motor-and arm-movement. This might be even improved in future versions by using even bigger drive-wheels or additional gears.

If you mean the vertical accuracy over the platform: The Morgan adjusts the platform vertically during the print of a layer, depending on the actual horizontal printing position.

The usable print area is 200mm x 200mm x ???mm (didn’t measure the height, but should be > 350mm). I think Quentin mentioned it somewhere.

In addition to Quentin’s assembly instructions I’ve done some drawings in the RepRap-Wiki: http://reprap.org/wiki/RepRap_Morgan_extended_BOM
(I recommend to use Quentin’s platform plans though, due to his idea of tensioned PVC-pipes for more stability)

And some notes on my personal Morgan-build: http://reprap.org/wiki/User:RobertKuhlmann/RepRap_Morgan

[Quentin Harley]

Thanks for the help Robert

Morgan has a build size of 200x200x230 nominally, but the height is easily scalable. I typically print using a layer height of 0.2, but printed 0.1 quite a couple times with great results.

The Morgans I built are very stable and travel well. The main feature is that the parts that matter move together and stay together. My Morgans travel a lot, and i do not need to recalibrate regularly.

The best horizontal resolution is in the center of the bed, and the ratio of the wheels give reasonable horizontal resolution even in the corners.

I recommend using Robert’s guides – I use them myself 😉

[ben]

Thanks for the responses guys.

If you can reliably pull off 0.2mm layers then you are doing as well as my MakerBot replicator 1. I haven’t yet finished a 0.1mm print at all!

Interesting that you auto level over the platform. Very cool.

Would expanding the arm length be possible to provide a bigger build plate?

I am thinking that I would quite like to cut most of the 3d printed pieces from hdpe since my MakerBot is so unreliable and my CNC is a lot more fun right now. Do you think it would be possible to modify the design for this? I’m fairly comfortable with cad and openscad.

[Quentin Harley]

Morgan is scalable. Longer arms will give bigger prints, and if you increase the drive pulleys with it, the resolution will remain similar.

It should be relatively easy to convert to a CNC cut version.
projection is your friend…

One issue with scaling up is that is is relatively hard to get the drive wheel round at the size, and any deviation here will cause calibration issues later. The wheels are one of the things I would like to improve on, and traditional tools be be the answer.

Once everything is perfect, your calibrated Morgan should be as well.

Looking forward to your efforts. Feel free to fork Marlin on Git. I would love to give new users more ways to get the parts to build the first Morgan.

PS: The replicator build plate is too small for the wheels…

[ben]

Aha, I had wondered if all the parts would fit on a standard replicator.

Well I guess that solves it then, I’ll have to go CNC 😉

Would the increased mass of cutting from something like HDPE cause any issues with backlash or momentum? I assume that one of the many benefits of the design is that the arms are actually rather light making it easier to control accurately.

With regard to the drive wheels, is there anything specifically about them (other than their size) that is essential to the design? I’m just wondering if there might be an off the shelf alternative that I might be able to source in the USA.

As I understand it, I just need a really large step up ratio between the stepper motors and the drive wheels, the larger the better giving me more accuracy? I assume I can switch to a geared system over a belt driven system too without issue?

[Quentin Harley]

As long as you can sufficiently get rid of backlash, you can use any gearing system you like. I used belt because it is easy to get, and relatively free from backlash.
The bigger the ratio, the better your resolution.

Look at the exploded diagrams Robert made in his extended Morgan BOM on the RepRap wiki. The shaft is self supporting, meaning that the center shaft holds the bottom end, and the outer shaft holds the top end.

The PSI arms should be very sturdy. They form the SCARA arm of the design, and supports the movement of the head. You want limited flexibility here, so when designing make sure that it is so. Theta arm is only used for steering. Lighter is always better.

[ben]

Ok thats great, answered all I need to know for now.

I’m going to look into various power transfer mechanisms as I’m not sure how perfectly round I can cut that drive gear with the CNC. Will have to see what the accuracy is like.

I just need to finish the soundproof enclosure for it first, otherwise the wife won’t stand for that much noise cutting all those parts 🙂

I’ll update with a build log when I get going.

[Author]

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