Planning to build a bigger Prusa i3, need help.

Hello guys, I currently have the 8" Makerfarm (Rev 1) and I am planning to build a bigger i3, salvaging parts from the Makerfarm. I really like how the gMax 1.5XT+ and the Folgertech 2020 i3 frame looks with the aluminum extrusions. Here are some of my questions:

1. Where can I buy the aluminum extrusions locally (in MA) or online for a good price?
2. What size the aluminum parts would have to be to fit the big heat beds (affordable) already available in the market?
3. Is it a good idea to build a prusa i3 of that size? What I mean is, is it feasible (price, electricity, heat needed etc.)?

Thanks!

[us.misumi-ec.com] Misumi will cut them to the length you need.

Openbeam on Amazon in fixed lengths

[openbuildspartstore.com] in fixed lengths

Having designed and built two printers with a 12" square bed moving in the Y axis I would not recommend doing it. If you want larger size, look at one of the designs where the bed moves in the Z axis.

There are multiple problems with moving a large bed in the Y axis:

Too much moving mass requires that you reduce acceleration which slows down printing, or spend a lot more on power supplies, external motor driver, and a big motor, or maybe all three.

If you care about print quality, throwing all that extra mass around requires a VERY rigid frame. 20 mm t-slot isn't going to cut it.

As parts get taller on such a design, they start to wobble when the Y axis reverses direction. That means the taller the part gets, the worse the print quality gets. That's especially true if the tall part has a small footprint on the bed plate.

There isn't much point in building a machine with a big bed if you can only print over the central 30% of it because it isn't flat, or you can't keep it level, or it doesn't heat up evenly. 1/4" cast aluminum tooling plate can be used on a 3 point leveling system, but it costs a few dollars more than a thin piece of aluminum plus a glass plate. It also weighs more which takes us back to the previous problem. I use a 450W heater (0.5 W/cm^2) to heat my bed plate and it gets to 105C in about 5 minutes. Lower powered heaters will take longer to heat up the bed.

A larger bed requires longer Y axis guide rails. The extra bed and undercarriage mass requires that you use larger diameter rails to reduce sagging, or spend more money and go to fully supported linear guides. I started with 1/2" diameter rails in the Y axis and decided that they were sagging too much so I went to linear guides supported by a 1" thick aluminum plate.

If you're going to go tall, you need a better frame design that the machine you linked. That "tower" is going to wobble and reduce print quality. It needs to be braced.

If you intend to print ABS, you'll need to enclose the machine and keep the enclosure warm (45-50C) to prevent delamination. Plan on putting the electronics outside the enclosure so they don't overheat.

If you want to see how to make a machine with a largish bend plate moving in the Y axis the (a) right way, click the link in my sig, below, then decide if that's the architecture you want to use.

Edited 1 time(s). Last edit at 05/07/2016 12:00PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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stephenrc
[us.misumi-ec.com] Misumi will cut them to the length you need.

Openbeam on Amazon in fixed lengths

[openbuildspartstore.com] in fixed lengths

Thanks a lot for the links. I tried Misumi's website but I was really confused since there are way too many options, the Openbuildspartstore looks much easier for me to handle. That being said, can you please tell me the length and quantity I would need for building something like the gMax? The gMax only states the print area but not the frame. Thanks.

Quote
the_digital_dentist
Having designed and built two printers with a 12" square bed moving in the Y axis I would not recommend doing it. If you want larger size, look at one of the designs where the bed moves in the Z axis.

There are multiple problems with moving a large bed in the Y axis:

Too much moving mass requires that you reduce acceleration which slows down printing, or spend a lot more on power supplies, external motor driver, and a big motor, or maybe all three.

If you care about print quality, throwing all that extra mass around requires a VERY rigid frame. 20 mm t-slot isn't going to cut it.

As parts get taller on such a design, they start to wobble when the Y axis reverses direction. That means the taller the part gets, the worse the print quality gets. That's especially true if the tall part has a small footprint on the bed plate....

Thanks for the suggestion, I was almost considering a delta style or cartesian printer but the only reason I wanted to stick with a Prusa i3 frame is because I know how it works. However, my main priority is quality over build volume. I will definitely put some more thought into it. Thanks!

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scarecrow2k6
Thanks for the suggestion, I was almost considering a delta style or cartesian printer but the only reason I wanted to stick with a Prusa i3 frame is because I know how it works. However, my main priority is quality over build volume. I will definitely put some more thought into it. Thanks!

A delta printer with a 300mm build diameter isn't difficult to build, see my blog for details. If you really want a 12" square build area, you would need to scale it up to a 425mm diameter bed - not impossible, but certainly more challenging.

Whatever design you choose, it doesn't pay to skimp on the mechanical build or the electronics when building larger printers.

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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].