RepStrap: much better software...

As I have said before, the RepRap host software is not fun to use. There are several reasons for this. First, it's a memory hog and crashes if you are not careful. My workaround for this is to first create the GCode through the host software and then read it back in. Thus, I am really only using the host software for converting 3D STL files to machine instructions GCode. Second, the host software writes very poor GCode. I have experienced axis drifting, random noise, bad layers, and bad prints. I have finally had enough. I spent the first part of the day looking for alternatives.

Skeinforge is a model to GCode converter that was written by Enrique Perez. It is used by Nophead and is the suggested converter of the CupCake. I decided to give it a try. It took me a while to get the hang of it. I now plan on using Skeinforge exclusively.

So far I have noticed the following benefits of printing from GCode that was generated by Skeinforge. When it pauses for cooling between layers it keeps the extruder head moving. This eliminates the head from burning and warping and oozing on the object. Its filler strategy uses less plastic and looks to be stronger. It converts objects faster. The end result is a better print.

I hope to post comparison pictures in a bit.

RepStrap: more parts...

I haven't been able to take time to work on my projects for quite a while. Now that I have time I decided to resume where I left off by finishing a set of Darwin parts. Here is a part I have been having difficulty with. This is an Opto Switch Bracket. The first few goes turned out funny because the Y axis drifted. I'm pretty sure it was a software bug because I printed to GCode and read from the file without any problems.



Now that my hardware is working consistently the host software is really the only thing giving me problems. I would rather deal with its shortcomings than take the time to rewrite it, so I am just taking the quick way out for now. Printing to GCode file and loading it back in seems to work pretty well.

Below is a corner bracket I just printed. This print took five hours.



I am getting quite the collection of parts!

RepStrap: a happy Y axis...

I realized on close examination of my first print that the coupling was off a bit in the Y dimension. After a bit of troubleshooting I found that the X belt was too tight, causing too much friction for the Y axis and slippage. I fixed it and printed another coupling. I also went ahead and printed a Darwin PCB clamp. I am very happy with the resolution. The motor coupling took 70 minutes. The PCB clamp took 30 minutes.

RepStrap: my first successful print...

I finally got my shipment of ABS plastic in. I was at my wits end with HDPE! No success at all. To put weeks worth of work simply... HDPE was too soft for me to use a pinch wheel extruder and I just couldn't get the drive screw extruder right. Once I am a pro at printing things I plan on printing nophead's solution. ABS worked the first time with my pinch wheel extruder... or the second time, rather. I spent most of the night trying to figure out why the RepRap host software kept crashing. It turns out that with a system with only 512MB of RAM the visual aid runs out of memory and crashes the host. To get around this I generate the GCode and send it to a file. Then I read in the GCode file instead of the 3D STL model. Tonight I had my first successful print! I printed a Z axis motor coupling since my electrical tape solution keeps failing me. I really like that I am able to better my machine on my first print!

Here are some pictures while printing.




Here is the final product cleaned up a bit.



Here is a screen capture of the 3D object I printed. As you can see, I got what I asked for.



Of course, I had to video such a momentous occasion! Unfortunately, there is no sound. You will have to take my word for it that it is very quiet!


My first successful print... from gavilan on Vimeo.

RepStrap: an unsuccessful print...

This weekend I finally got an opportunity to mount my extruder onto my machine and attept a print. I am using HPDE as my current printing material and photo paper as my bed. I have still been having problems with the accuracy of my Z axis and didn't pay enough attention to the print head during my first few prints. I eventually noticed that the head was being pressed into the printed shape so much (due to a slipping Z axis) that the print head was wiggling its way out of its PTFE holder / thermal barrior, causing irreversible dammage to the holder. I went ahead and ordered two more, in case this happens again, as well as ordering a supply of ABS plastic for extruding. From what I have read, ABS doesn't have the warping / sticking problems that HDPE has, and I should be able to extrude it faster, cutting down on print time.

Here is an image of my last print.



You will notice that the raft is too thick to be practical. This is a configuration issue that should be easy to fix in the future. I was attempting to print a pully from the Darwin STL Library and got past layer 8 before the Z axis slipped.

The next step is for me to get my Z axis more solid so this never happens again. I am seeing that the weakest link of my Z axis is the motor coupling, so that is where I will direct my attention.

RepStrap: building an extruder...

I started building my extruder in the last few days. I am still waiting on a stepper motor driver board, so there is no hurry to get this working. However, I have made quite some progress.

Here is a picture of my heater.



Here is picture of my pinch wheel driven by a Nema 23 stepper motor. Overkill? Maybe.



A pinch wheel extruder is still very cutting edge for RepRap and so the details of how to correctly build one are still being talked about. When I read the builder's blog a few weeks ago Adrian was suggesting knurling the stepper motor drive shaft. I purchased a knurling tool for a lathe from a tool shop for $8 and rigged up a vice, twisting the drive shaft in the vice to complete the knurl. It appears to have worked pretty well. I guess we will just have to see...

The red substance on the above heater is my solution to a problem the RepRap team has been trying to solve for quite some time. How do you hold a barrel, some nichrome heating wire, and a thermistor together at temperatures above 190 degrees Celsius? My solution is some Red High Temp SuperFlex LOCTITE silicone based sealant. How long will it hold up before it starts decomposing like other substances the RepRap team has tried? Again, we will just have to see...

RepStrap: milling PCBs with a Darwin...

I do not enjoy admitting defeat on anything. I find myself checking and rechecking my work until I realize an entire weekend worth of work was wasted by not admitting defeat. At this time, and after an entire weekend of work, I must admit that milling PCBs with a 1.0 Darwin is not possible. The reason for this is quite obvious, in retrospect. Put simply, the force required to etch copper is enough to twist the X axis guide rails. When the guide rails twist, while moving the toolhead in the -Y direction, the milling bit gets pushed into the milling surface. This results in a really bad situation. If the design requires further milling in this direction the bit eventually pushes clear through the 1.5 mm board and into the table.

Here is a picture of one of six goes I had this weekend.



As you can see, when milling just to scratch the surface the resolution was perfect. When attempting to mill through the copper the bit would catch and dig right through. I put a piece of red tape where the bit went through to make it stand out.

I still think it may be possible to pull PCB milling off if you are willing to redesign the x-carriage, but I am against drifting this far away from the original Darwin design. For anyone wanting to go as far as redesigning the x-carriage, I envision mounting the milling head between the guide rails. In this way, if the guide rails twist, the bit should retract from the milling surface in both the -Y and +Y directions. A better long term solution would be to use a design closer to a McWire for milling / subtractive manufacturing and the Darwin for additive.

At this point I have gone ahead and ordered a stepper motor driver board from Zack's new shop. When I regain my motivation I will continue working on my extruder.