Big Aluminum Printer

[3D_Kudu]

I just wanted to share the project I've been working on. I'm building a large format delta printer for school that looks similar to some of the things I've seen here on the forum. It's not up and running just yet, but I'm getting close. I've been having a few issues with my joint solution, and I was wondering if anyone here knows of a tool for calculating the forces in the linkage system? Most of the people I've spoken with just spec their rod ends/joint systems based on physical size, but I'd like to take it a step further and do a dynamic analysis. I don't mind building one from scratch if there isn't already something out there, but I'd rather not reinvent the wheel if I can help it.

3D_Kudu

[geolupulus]

Sorry, I know nothing of robotics aside from what it takes to assemble a Rostock. As such, I don't understand your question. I hope I'm not out of line by just saying I am really wowed by your machine! That's one big ass delta! Looks awesome!

[Generic Default]

Awesome printer. You probably won't be able to print single parts the size of the bed because of warping and thermal contraction though. Unless you put in a heated build chamber......

The forces on the arms are proportional to the acceleration of the effector and the mass of the effector. You might want to check the forces from the arm inertia too, although it will be negligible because of the low mass of CF arms.

The more rigid your arm setup, the less you will see ripples in your print. Ripples are caused by momentum; when there is a change in direction on the print path, the acceleration of the effector will not follow the path perfectly. It will overshoot. I'll try to get the link to a thread that discussed this a while ago.

[Tinyhead]

Holy crap. That didn't look so big till I saw the stepper on the effector (zoomed in), then I noticed the chair in the room, then everything else! That thing is MASSIVE! How big is the final build area going to be?

[3D_Kudu]

The bed is 24" in diameter and the print height is roughly 30". I'm still playing with the arm lengths, but I think the final printable area will be somewhere between 18" and 24" in diameter. Obviously, anything that large would have to be printed hollow or it would take an age, so I'm working on some ways to do that effectively. Overcoming thermal contraction is also a significant barrier to large printing that needs to be overcome, but I wanted to develop a platform that we could use to start tackling some of these issues instead of running from them.

[JohnStack]

Nice work!!!

Doing projects like this really push the envelope!

(Also, I believe someone will develop a material - soon - that will get past thermal contraction issues.)

[3D_Kudu]

I agree. Once the right chemical company or appropriately skilled group of open source proponents recognize the need/demand, it will only be a matter of time. Thermal contraction was actually a feature purposefully designed into ABS when it was formulated with injection molding in mind. This contraction allows parts to pull away from their molds as they cool, eliminating the need for messy, complicated, or time consuming removal processes. Eventually we will see more plastic compounds purposely formulated for FFF which will do a much better job at meeting the demands of this unique process.

[Generic Default]

There are currently only a few thermoplastics with low thermal expansion coefficients, but when you add glass fiber or carbon fiber, the thermal expansion drops rapidly.

For a reference, here are some thermal expansion coefficients;

Glasses : 4-10
Steel : 13
Aluminum: 22

ABS :74
Nylon :72
Polycarbonate: 70

Glass filled polycarbonate: 21
Glass filled ABS : 30

So the general trend is that putting fibers in plastic greatly reduces their thermal expansion. It also increases strength and stiffness by an enormous amount.
These plastics already exist and are in common use, you can buy a bunch on ebay or from suppliers and extrude it through a filament extruder if you have one.

Which makes me wonder why nobody has jumped on this yet.....I would pay a premium for a kilogram of glass filled anything. The first thing I do when I get a filament extruder is make a bunch of 60% glass filled polyphlalamide, which is almost as stiff as concrete and as strong as mild steel or nice aluminum.

[Mimo]

What about t-glase (PET), from my experience it has no warp issues.
Anybody knows what is its thermale expansion coeeficent?

[Polygonhell]

So the general trend is that putting fibers in plastic greatly reduces their thermal expansion. It also increases strength and stiffness by an enormous amount.
These plastics already exist and are in common use, you can buy a bunch on ebay or from suppliers and extrude it through a filament extruder if you have one.

These guys to carbon fiber filled PLA - http://www.proto-pasta.com/shop/cfpla
But in general I think it's largely tooling costs that stop people trying to do runs of esoteric filaments. I looked into having filament manufactured at one point and for ABS/PLA it was reasonably cost effective (although all the samples I got from multiple manufacturers had horrible tolerances), anything esoteric required "large" runs with no guarantee you get something useable/saleable at the end. You'd also need to find a manufacturer willing to try mixing fibers into their extrusion machine which is probably not something they typically do since most of the manufacturers make the bulk of there income from plastic welding rod.

[Mimo]

I think it more likely that most people are still struggling with PLA and ABS and most printers are not capable of printing other materials. unfortunately there are more Rep2 then Rostock and Orion out there...