Printed ORD Bot

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Re: Printed ORD Bot

Postby TLHarrell » Sat Jun 09, 2012 7:57 pm

We need a parts recycler that will grind up the flawed prints and extrude new spools for the printer.

Those parts are looking really nice.
40w Full Spectrum Engineering 5th Gen Hobby 20"x12" w/ Rotary Engraver
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Re: Printed ORD Bot

Postby tylerv » Sat Jun 09, 2012 8:19 pm

+1. So many failed prints and things I don't need anymore, it would be nice to recycle the plastic. That way, you'll never worry about screwing up a print because you can always reclaim the spent plastic.

I'm waiting for this project to become available.
http://www.kickstarter.com/projects/rocknail/filabot-plastic-filament-maker?ref=live
http://filabot.com/
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Re: Plastic Recycler

Postby crispyfry » Sat Jun 09, 2012 10:15 pm

TLHarrell wrote:We need a parts recycler that will grind up the flawed prints and extrude new spools for the printer.


*facepalm*

Grinding up plastic to re-use it is a bad idea.

Why? Every time you heat up and cool down a thermoplastic, its chemical and physical properties change. There is a limit to how many times you can do this before the plastic becomes not very plastic-like. If you've ever printed with PLA and had some get stuck to your hotend, it eventually turns into this brown caramel-like substance, and this is basically what happens when you heat cycle a plastic too many times: All the volatile compounds bake out of it.

It is possible to recycle plastic, but you need to re-polymerize it in order for it to have the correct properties. This is NOT what regrinding plastic does. Regrind literally means you grind up scrap into small bits and mix them in with virgin plastic pellets.

Regrind plastic is not re-polymerized and has inferior physical properties.

There is a ton of literature out there about why regrind is bad, because this is a topic that is pertinent to the plastic injection molding industry. To get you started, here's 1 link from UL: http://www.ul.com/asiaonthemark/as-en/2 ... /page5.htm

Our printers are if anything more sensitive to plastic quality than injection molding, so using regrind is going to have a large impact on print quality. I don't know about you, but I have enough issues with getting good prints without worrying about whether my plastic is any good or not.
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Re: Printed ORD Bot

Postby crispyfry » Mon Jun 11, 2012 1:14 am

I assembled most of the frame today, and did temporary assemblies of all the moving parts to check for issues. Didn't find any show stoppers, so I started tearing down my Prusa to transfer the parts over. No pictures right now because it's not much to look at.

I had to cut a slot in the rib on the bottom of the Y plate for the return path of the belt. I completely forgot to account for this when I did the design.

Motion on all axes is smooth, no play, and the printed parts look like they will be stiff enough to avoid any issues. The biggest area of concern are the Z endplates: they are under a fairly high bending load from the X axis belt tension. If belt tension is too high the plates will start to bend. I may design a small brace that ties into the end of the X axis extrusion if this turns out to be a problem.

I decided not to reprint the X carriage in PLA because a) it takes a lot of plastic and is a long print; b) I have concerns about having PLA parts that close to the hotend when I print ABS. I installed the wheels on the carriage and even though the back is not perfectly straight it moves along the axis ok.

I test fit the extruder onto the carriage and I have about 2mm of clearance between the gear and the vertical plane of the carriage :-) The extruder will have to mount motor out, which is not ideal from a weight distribution perspective. I plan to design a better extruder body in the future, and will probably redesign the X carriage to be a flat plate at the same time.
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Re: Printed ORD Bot

Postby Enraged » Mon Jun 11, 2012 5:18 am

For bracing the X, could you add a bracket to put the X pulley into double shear? It might help resist the bending, depending on the design. Example: http://images.asme.org/MEMagazine/Articles/2010/March/22162.jpg
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Re: Printed ORD Bot

Postby crispyfry » Sat Jun 16, 2012 3:05 am

Finished assembling the frame, installed new motors for X, Y, and E. Got the electronics back together well enough to do some primitive axes testing. All axes move, movement is smooth - much smoother than LM8UU bearings which were a bit rumbly. Need to update the FW, install the end stops, then we're ready for the first print.
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Re: Printed ORD Bot (first print)

Postby crispyfry » Sun Jun 17, 2012 12:50 am

Some more progress...

I've got all the wiring run so that everything can move and power on. Not pretty yet. I have 2 of the endstops mounted.
I ended up re-hobbing my extruder drive bolt in order to bring the gears closer to the extruder body. I did this because in order to clear the belt clamp bolts the extruder had to be moved as far away from the vertical piece of the X carriage as possible. This increased the cantilever effect and I didn't like it.

Along those same lines, I can tell already I'm going to have oscillation problems on the X carriage because of the weight of the motor being suspended so far out. When I jog the axis I can see the extruder body wiggle around. I think it'll work, but the part quality is going to suck until I can design a better X carriage with an integrated extruder body.

I'm also seeing issues on the Y axis. There seems to be a lot of play between the v-wheels and the extrusion. As best as I could tell I had the eccentric spacer adjusted correctly, when I was working on that. I can see a little bit of "splay" on the eccentric spacer, so it looks like there's enough lateral force to push it off the vertical. I may also not have the bolts torqued down enough, but I am leery of over-torquing things because the PLA will just crush. Adjusting the bolts on the Y is a bit of a pain because I have a piece of plate steel mounted on top of the printed carriage to carry the HPB, and this covers up the bolt heads.

Anyway... Despite all these issues, it does print!

2012-06-16_20-16-47_803.jpg
Printed ORDbot Printing!

Amidst the chaos, a new printer is born. You can see I'm still missing the crossbrace on top of the verticals, but at low speeds any impact that has is lost in the noise of the X carriage/extruder assy vibrating.

2012-06-16_20-40-57_144.jpg
First Print Results

Here's the results of my first test print. The surface finish is, as expected, a bit rough. Other than that it came out fine. Sorry about the rotation, not sure how to fix that.

In the coming days I need to print some brackets to mount the endstops more professionally, mount the head fan, clean up the wiring, and work on a better X carriage.

I do intend to release the files after one more round of revisions once I work out any bugs that crop up. No timeline.
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Re: Printed ORD Bot Update

Postby crispyfry » Wed Sep 05, 2012 5:02 pm

(I had a 5 paragraph reply typed out, then lost it because my login timed out. So here's the abridged version...)

Printed ORD bot is still going strong. Print quality has significantly improved following the upgrades to the extruder/x carriage, and replacing the first printed Y carriage with an aluminum plate.

My experimentation has shown the Y carriage is exposed to too much heat from the printbed PCB, and thus will soften and develop slop in the wheels. Insulation will slow but not eliminate this problem.

I intend to release the files for the project, possibly by the end of the week. There are a couple remaining changes I'd like to make but as it stands the printer works pretty darn well.

ETA: Picture of test print with improvements.

2012_09_03__21_29_35.jpg
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Re: Printed ORD Bot

Postby Enraged » Wed Sep 05, 2012 7:52 pm

a random thought, but what about forced airflow for the Y printed plate? would some fans combined with insulating the heated bed help?
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Re: Printed ORD Bot

Postby crispyfry » Wed Sep 05, 2012 8:51 pm

Enraged wrote:a random thought, but what about forced airflow for the Y printed plate? would some fans combined with insulating the heated bed help?


I suspect it would make a small but noticeable difference, but ultimately you'd still have issues.

Part of the giant post I lost was my experiments in thermally isolating the PLA from the PCB. My gut feeling is that most of the heat transfer was taking place via radiation, not convection. So in order to improve the situation you would actually move enough airflow to pull the radiated heat out of the PLA - you couldn't just disrupt the convection currents. I think trying to move this much airflow underneath the print bed would either cause the bed temperature to drop undesirably, or you'd generate stray air currents in the print volume and cause print quality issues.

My PCB is mounted on bolt standoffs on a heavy gauge piece of sheet steel (~1cm clearance between the two). The sheet steel was mounted on plastic standoffs to the PLA carriage. So already there's a fairly significant amount of insulation. But I found that when printing ABS the sheet steel could get upwards of 70C after a while.

I tried making some insulation out of corrugated cardboard and aluminum foil, and putting this on top of the sheet steel underneath the PCB, and another layer between the sheet steel and the PLA. My thinking was that the foil would reflect most of the radiated energy, and the cardboard would help insulate the foil from conducting its heat down. This made a noticeable impact in the time it took for the sheet steel to reach damaging temperatures, but ultimately I still had the same problem of slop developing in the wheels.
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