• Tension so thick....

    Chris • 12/31/2018 at 06:16 • 3 comments

    For those of your just tuning in, hello, and welcome. Where we last left off was at a pretty much functional conveyor belt print ejection system for the Printrbot Simple Metal with heated bed upgrade. You can take another look at that below because I think it is pretty cool.

    Now you may notice my choice of words here, "pretty much." That is mainly because this project still has one glaring issue, and that is belt tension. 

                                                                        Belt Tension: The Odyssey 

    There are two major issues when it come to belt tension, print wobble and print warping. Chances are on a 3d printer you are going to encounter prints that will exhibit both of those issues. To being lets start with the warping.

    This is a pretty mundane topic at this point because print warping has been occurring since the dawn of time and each hacker has their own favorite way of preventing it. The problem with printing on relatively floppy belt of paper is that paper isn't particularly rigid. This means that as the print is cooling, the corners of the print will begin to curl, ever so slighting taking the paper belt with it. For this most part this could be alleviated with a raft, but why use one if you don't have to?

    The issue of print wobble is a bit more exotic, especially in this instance. The jerky motions that the printer normally makes on sharp corners and infil normally don't have all that much of an effect on a rigid piece of plastic. However those rapid movements cause the print to wobble much more than it would if it was anchored to a proper bed. Not to mention I was using flexible filament which meant this wobble would lead to outright failure.

    So what is a hacker to do? Make a better design of course! However there were a few design constraints that I wanted to follow. Mainly I didn't want to really increase the part count of the project; I only wanted to make it out of stuff that I had laying around. I also didn't really want to have any more 3D printed parts. As you can see below the structure really just consists of the 4 corners that hold the bed and then the 2 3D printed rollers. I didn't want to add any sort of separate idler or tensioner for the belt to run through

    Below you can see the design that I came up with.

    You'll notice that it is very similar to the picture I posted in the previous log. However this mount has a wider "jaw."  This design is taking advantage of the fact that the four holes on the corners of the heated bed are threaded. The basic idea of this design is to use long M3 screws almost like threaded rods. With this method, the basic idea is that you mount the heated bed at the bottom of the "jaw" with the screw, and then attach the belt. as tight as you can make it by hand, and then you just turn the screws, thus raising the entire bed up, and tensioning the belt. It's a bit hard to explain.  Check out the animation below.

    Imagine that the nut is one corner of the bed. Also note that the screw isn't actually being screwed into the plastic. It is just seated in a hole to keep it stable.

    With this new design in hand it was just a matter of printing some replacement parts and swapping things out! But of course once you fix one problem another one arises.

                                                                                Moar Powa!!!!

    My first print on the newly tensioned belt went very well, and made the entire assembly much more robust. However there was now a new problem. My tiny little motor couldn't handle the increased load!...

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  • The First(ish) Try

    Chris • 12/24/2018 at 04:40 • 0 comments

    This project (as many projects do) started as a result of another project in which I needed a way to 3D print LOTS of things for the foreseeable future. Each one of things takes 2-3 hours to print so it wasn't really like I could babysit my printer all day. I wanted a little factory

    For a while  I was banking on PrintrBot releasing their PrintrBelt, which Brook Drumm had teased on a number of occasions. This printer used the typical angled printer head and belt system of an "infinite build volume" printer. The main difference from other infinite build volume printers on the market is that I suspect  it would have been of the high quality and the reasonable cost of PrintrBot Products. Little did I know that it would never see the light of day.  

    Now of course there are some other people that are working on exactly what I wanted i.e. a printer that could just keep spitting out little bobbles until it ran out of filament with minimal human interaction. Most notable that included this project on Hackaday.io. Swaleh Owais did serve as a bit of inspiration for this project but I thought that there had to be a better way. His custom made infinite build volume printer was pretty cool, but I already had a perfectly good Printrbot Simple Metal. Why not just modify the one that I have?

                                                                       Why don't we just replace the whole y-axis?

    Initially I thought the best approach was going to be to replace the bed of the Printrbot Simple Metal entirely. That would mean that all the y-axis movements would be handled entirely by this hypothetical belt. For those of you who are not familiar with the Printrbot Simple Metal, please see the expertly illustrated rendering below for a general idea of what I was thinking.

    This seemed like a not so bad idea if you didn't think about it so hard. Of course there were somethings that I had to figure out like how was I going to tension the bed? How was I going to keep this thing as 3D printable as possible without using much after market hardware? What was I going to eat for dinner? Sooo many questions. So the best thing think that I could think of doing was jumping in feet first into some CAD just to get the creative juices flowing and see what I could make. Things were a bit chaotic to say the least.

    I initially started out thinking that I was going to need some sort of external truss structure type thing on the outside of the print to support the rollers and hopefully give me an idea about how to get an adjust about tension system. Below you can see a picture of one of the earliest attempts to make my dream of a PrintrFactory come true.

    Yah. I am honestly not really sure what I was thinking here? I think that the idea was that the scoopy bit in the upper right hand corner would somehow lock y-axis bed assembly and then the two little do-hickeys on the left would be where the roller would slot. Based on the tone of the last few sentences you can probably guess that this didn't get too far. Despite feeling pretty good about this idea initially, I actually did some Googling to see if anyone had attempted  this whole belt-replacement nonsense and sure enough someone had done it before......

    ...and I would love to show you how they went about doing it but for the life of me I cannot find the video.  Seriously I think that the internet just gobbled...

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