GilesBathgate

I have completed the Y and Z axes now of my OverlapStrap. I was originally planning to only use one Z axis motor and use one of the syncroflex belts that I bought for the Mendel to drive the two lead screws. But when I saw the price of the cheapest aluminium timing pulleys that I could find, I decided it was cheaper and simpler just to use two stepper motors for the Z axis instead

At this stage I also intend to drive the Y and X axis using lead screws. This required some modifications to the reprap firmware. Annoyingly there are preferences in the reprap software for features that don’t exist. I am a strong believer of YAGNI and also think that Green Code is a violation of this principle, so I was a bit annoyed to find both of these practices employed in the reprap code. Anyway, once I got over it and realised that the software preference for steps/mm had no effect on the hardcoded steps/mm defined in the configuration.h of the reprap firmware I was able to change it and upload the new firmware.

I have a feeling that such a low steps/mm setting will lead to printing problems when overlapstrap is complete, however I have a plan to mitigate these problems. I intend to bootstrap some basic parts using the leadscrews and then upgrade overlapstrap to a belt drive version using these parts. I will need to print a belt splitter jig, and some drive pulleys.

Green code is code that has been commented out. Its usually green because the popular development environments I use syntax highlight the comments in green. In my personal opinion having large chunks of commented out code is a violation of YAGNI. A much better approach than commenting out the code is just to remove it, if you are using  source control, which surely you must be? a record of it will be stored in version control. Doing this has two advantages, firstly the current source code has less clutter, and secondly the source code is kept historically in version control along side the code that it was meant to work with. Keeping the code commented out along side the current code is daft, unless you think that un-commenting out the code six months later it will still work, which in most cases it probably won’t.

Today my colleague Ciaran showed me how I could create a category feed, so that I could keep posts related to OverlapStrap seperate from my other posts, and save having to post to two blogs, whilst still having the reprap related posts appear in the Reprap aggregation pipe. So with any luck this post won’t appear in the pipe, and actually serves as a test.

I wanted to try the bleeding edge software that Adrian is working on. First I got the latest source

svn co http://reprap.svn.sourceforge.net/svnroot/reprap/trunk/reprap/host reprap

There is a setup-reprap-host-dev-environment.sh script that probably works but it downloads an installs versions of stuff, that i didn’t want cluttering up my system.

Also it seems that the intention is to distribute the files that get downloaded with the reprap source anyway, and indeed I already had them by now since they are in the svn repository.

In short I didn’t see the point of setup-reprap-host-dev-environment.sh and took it apon myself to “fix it” so that it uses the jar files included in reprap/lib

Firstly I modified the build-user.xml file so that the classpath was as specified in the manifest section as follows:

<manifest>
    <attribute name="Main-Class" value="${main-class}"/>
    <attribute name="Class-Path" value="./lib/j3dcore.jar ./lib/vecmath.jar ./lib/j3dutils.jar ./lib/RXTXcomm.jar ./lib/swing-layout-1.0.3.jar ./lib/j3d-org-java3d-all.jar ./lib/"/>
</manifest>

The next step was to set the CLASSPATH enviroment variable so that I could compile the source

export CLASSPATH="./lib/j3dcore.jar;./lib/vecmath.jar;./lib/j3dutils.jar;./lib/RXTXcomm.jar;./lib/swing-layout-1.0.3.jar;./lib/j3d-org-java3d-all.jar"

Then I compiled it and moved the resulting reprap.jar file into the current dir …

cd reprap
ant jar
mv jar/reprap.jar .

… so that it could be run by using

./reprap-host.sh

I have finished building the Z axis roller that is mounted on the other Z axis rail. I really liked the axes design that Ed has used for mendel. I can imagine that if the Z Axis rails were not exactly parallel, and I had used two identical skates, then there would be the possibility that the skates would jam either at the top or bottom of the axes.
My design includes a 1/2″ x 1/8″ aluminium bar that is made by cutting an edge off a length of aluminium angle that I have used before.

Here are a few extra drawings of the parts shown in the photo from the post I did a few weeks ago.
The chassis is made from 12mm thick mdf. I chose 12mm thick mdf so that it would be the same width as the original parts that I made from 12mm thick timber, as such someone wanting to make both those parts and the chassis on a cnc router machine could make it from one sheet. I am not really sure why I chose 12mm thick for corner parts, it just seemed like a good thickness at the time.
I think its important to give as much detail as possible so that anyone else wanting to make one could do so, and so that people can make improvements. Well, I suppose that’s the whole point of open source.

As usual the drawings are here

I have built the first of the Z skates for OverlapStrap.They can be tightened using the 4 M4×40 bolts, and when tightened just right they run very smoothly. I haven’t had a chance to upload any drawings of the parts that make it up yet.

This image gives you an idea of angles at which the bearings are arranged.

I have tried to make the chassis constrained the same way as it is in the original mendel, however I am relying on gravity to hold the chassis down so I only need 6 bearings in total for the chassis. Below is a picture of the chassis mounted to the OverlapStrap frame.

The main reason my plans for this repstrap deviate from the work being done by bodgeit was because he uses 606 bearings. I wanted to use the M4 bearings that are part of the Mendel Bill of materials. Instead I have made these skates inspired by those used in the build your cnc project.

The M4 bearings are mounted on 1/2″ x 1/2″ x 1/8″ Aluminium Equal Angle which I picked up from eBay

As usual the dxf files can be found here

A couple more drawings for the Z-Rail Mounts.
The upper mount

The lower mount

All Files can be downloaded here