Complications with scaling?

[erak]

I was thinking about scaling up an ORD Bot by replacing the makerslides with longer versions. Say at least 400x400mm.

Which issues can occur except stability?
Are there heatbeds in this size? Can I combine two or more?
What about material shrinkage when cooling, will these defects become more prominent on larger builds?

Thanks!

[cozmicray]

One Big problem
A good flat bed
The larger the bed the harder it is to get it extremely flat.
Getting the ABS/PLA to stick over the large area

You also must consider the mass your system will move around?
Perhaps as you get bigger it may be better to fix the bed
and just move the extruder around.

Heating the bed?
My bed is aluminum/glass
Set at 90deg it may get to 60 on surface and stay there.

Good Luck

[cvoinescu]

You can make your own hotbed in a custom size using several methods. The simplest is to get a sheet of aluminum of the size you want, and glue a number of power resistors on its back. You still need a glass surface, because the aluminum plate is never going to be flat enough. You can also run nichrome wire on the back of a sheet of glass, or aluminum insulated with kapton tape. It would probably be a bad idea to rely on the tape alone to hold the heated wire in place, though, so you'd need to find a method to fix it in place. You could make your own PCB heater, and it doesn't even have to be one piece; in fact, four PCB heaters of the usual size should be the size you want.

@cozmicray is correct about the flatness of the bed likely being a problem, though. Rafts alleviate this problem somewhat, but it may still be tricky to get it flat enough to print. If you want to go for a static bed, maybe look at the ShapeOko as a starting point for your hacking, rather than the ORD Bot (just an idea!).

[erak]

Thanks for your answers!

Getting the ABS/PLA to stick over the large area

Does it need even heating for the plastic to stick well?

You also must consider the mass your system will move around?

How will this affect the printing? I guess too fast acceleration will require a quite stable environment. But stronger motors and slow movement will maybe help?

My bed is aluminum/glass

Did you make it yourself?

The simplest is to get a sheet of aluminum of the size you want, and glue a number of power resistors on its back.

You can also run nichrome wire on the back of a sheet of glass, or aluminum insulated with kapton tape.

Are there any further instructions somewhere for these?

in fact, four PCB heaters of the usual size should be the size you want.

So I could buy four PCB heaters and stick a sheet of glass on top?

If you want to go for a static bed, maybe look at the ShapeOko as a starting point for your hacking, rather than the ORD Bot (just an idea!).

Interesting. Are there any factors that would limit my ability to get high quality prints if I go with ShapeOko for example? I chose ORD Bot mainly because it seemed like the most stable and easy one to scale because of the the makerslides.

[cvoinescu]

The simplest is to get a sheet of aluminum of the size you want, and glue a number of power resistors on its back.

You can also run nichrome wire on the back of a sheet of glass, or aluminum insulated with kapton tape.

Are there any further instructions somewhere for these?

Yes, the RepRap heated bed wiki page describes these and several other heated bed designs, with some links.

So I could buy four PCB heaters and stick a sheet of glass on top?

That occurred to me while I was typing the post; I've read somewhere about someone using two 200mm x 100mm strips of PCB to get a 200mm x 200mm heated bed, and I don't see why you could not use four 214mm x 214mm to get the surface you want. They'll be more difficult to mount, but I haven't really given it any thought.

Interesting. Are there any factors that would limit my ability to get high quality prints if I go with ShapeOko for example? I chose ORD Bot mainly because it seemed like the most stable and easy one to scale because of the the makerslides.

The ShapeOko (and its European cousin, the eShapeOko) are also based on MakerSlide. The standard ShapeOko has a limited Z build size (about 100mm) but it's cheap and very easy to extend in the Y and Z direction; extending the X direction requires a different set of end plates and some standard extrusion (available from Edward Ford and/or Inventables), but it's also fairly easy. Check out the ShapeOko forum, where there's a section on 3D printing on the ShapeOko. It's been done with good results.

I'm in the process of dialling in my eShapeOko 3D printer (J-Head Mk V-B hot end, Greg's Wade Reloaded extruder, no heated bed yet (printing PLA)). I'll report results when it's done (not sure when, very busy now).

[cvoinescu]

Earlier than expected, I was able to build an object with my eShapeOko 3D printer. As promised, here's the write-up.

I have a J-Head Mk V-B hot end, 3 mm filament and 0.35 mm nozzle, with a 25 ohm resistor instead of the stock 6.8 or 5.6 ohm. This gives me the same power at 24 V as the original resistor at 12 V. The extruder is Greg's Wade Reloaded (it's identical as far as I can tell). I bought it as a kit on eBay; the printed parts are black ABS, extruded with what looks like a 0.5 mm nozzle. It is attached temporarily, through only one hole, to the Z axis of my eShapeOko using a stiff angle bracket from the hardware store.

The eShapeOko is driven by a breadboard RAMPS-like "shield" (four Pololu driver carrier boards and a MOSFET) and powered from a bench power supply set to 3 A at 22 V. I started with 16x microstepping on X, Y and E, and 2x on Z, but later changed the Z to 16x, too. The firmware is Marlin 1.0.0 RC2 on an Arduino Mega 2560. There are no homing switches; I start with the machine in the front-left corner and Z all the way down (I lower it gradually until I can barely insert a sheet of paper between the nozzle and the bed). I calculated the steps-per-mm for X, Y and Z; also for E, but then I adjusted that empirically. I enabled PID temperature control, ran a self-tune cycle, and used those values. The filament is 3 mm clear PLA from Faberdashery.co.uk (actual diameter about 2.84 mm), and the bed is an (unheated) IKEA wardrobe shelf (new, so fairly flat) with Kapton tape. The hot end temperature is set to 185°C. I used OpenSCAD, Skeinforge and Pronterface (and the Arduino IDE to build and upload Marlin) in Windows XP. Without any further adjustment (except the necessary Skeinforge settings for filament size, 0.25 mm layer height, no raft, one perimeter loop), I printed a 12 mm cube. I had to abort it halfway because the 2x stepping on Z was way too noisy and woke up the baby, but it was a very good print, no wobble at all, straight and smooth.

I turned the stepper current down to reduce noise and changed Z to 16x microstepping, and printed a more complex object (a cat I had drawn in OpenSCAD with the "help" of my four-year-old). There were no mechanical problems at all: the platform is stable and precise. The slicing settings need some more work, though. There is some melting in the smaller top layers, so a fan is needed. The "slow down" method of increasing layer time simply doesn't work for me for very small layers (the tips of the cat's head and ears): PLA just accumulates on and around the nozzle tip instead of extruding. The fan will help, and I'll try "orbit" too. The print also suffers from a little excess material in the solid layers and some tiny hanging loops of filament in the overhung areas. I'll try to reduce the "packing factor" somewhat, and change the design to avoid some unnecessary bridges. I need to convince Skeinforge not to turn the whole layer into a solid layer if it has a tiny bridge... The first layer of this print was squished in too much and quite difficult to unstick from the kapton, but limit switches will get me more accurate and repeatable homing, so I can tweak the "base" settings then. I can probably increase the speed from the default 16 mm/sec (both the extruder and the eShapeOko are capable of much more).

My print volume is 210 mm x 335 mm x 100 mm, but I see no problems with scaling it to, say, 400 mm x 400 mm x 200 mm. As I said, it should be a fairly inexpensive upgrade.

So, in brief, I am very happy with the eShapeOko as a 3D printer. For a first and second print with hardly any tweaking, the results are excellent. The J-Head was a great choice.

In the interest of full disclosure, the eShapeOko is my set of tweaks on Edward Ford's ShapeOko design. I sell eShapeOko kits in my online store. I believe the ShapeOko will get you the same results (with the possible exception of Z wobble, as the allthread supplied by Inventables isn't always perfectly straight).

[erak]

Thanks cvoinescu for the incredible extensive write-up! It sounds really promising, I'll get back to you soon with some more inquiries.

I live in Sweden so a "European cousin" sounds good. Do you have any tips on where to hopefully find most of the other equipment, like hot end and electronics?

I'd love some photo samples of the build quality. I've heard that Ultimaker offers the best build quality, any info on how they managed that?

[cvoinescu]

I can confirm that adding a small fan and changing from "slow down" to "orbit" fixes the molten mess problem on small layers. I'll take some photos in a few days.

I don't know much about the Ultimaker, sorry.

I bought the hot end from the US (while there), from hotends.com. I don't know whether they ship to Europe. The extruder I bought on eBay from gcolbourn. The Pololu.com A4988 driver carrier boards are available in Europe from a number of distributors. I built the rest of the electronics myself (not much to it...). In fact, I just finished moving the drivers from breadboards to a more permanent prototype PCB, with proper connectors instead of twisted wires insulated with ordinary adhesive tape. Still working on adding limit switches and cleaning up the extruder connections (heater, thermistor).