MegaMendel

From RepRap
Revision as of 09:53, 8 July 2010 by Gert Joergensen (talk | contribs) (MegaMendel documentation)
Jump to: navigation, search
Crystal Clear action run.png
MegaMendel

Release status: Experimental

[[image:|center|190px]]

Description
Giant version of Mendel
License
GPL
Author
Contributors
Based-on
Categories
CAD Models
External Link

The idea for the MegaMendel came in the early 2010. The project was spurred by an idea of printing part for a small wind turbine.

It is a mighty machine with a build area of 766mm x 453mm x 497mm. The X and Y dimensions are the freedom on the axes the 497mm on the Z-axis is actually the height of the tallest object printed on it so far, please refer to the image below (the ruler is 600mm).

Record.JPG

It is possible to tweak it to print at least 55mm in height, but that will have to wait as I don't see the point in doing that right now :-)

The machine's the dimensions are 1160mm x 880mm x 830mm and my guess is that it has a weight of some 30 to 35 kg's.

The whole project made me rethink parts of the construction. I had two reasons for that:

1 - I made the "plastic" parts in MDF - So there was a need for a design that would compensate for the weaknesses in MDF.

2 - I don't agree with some of the solutions in the standard Mendel, so I changed lots of details to what I consider simpler and better solutions.

So the MegaMendel is more of a RepStrap.

This page is meant to document the build process, and most important design decisions for others to adopt or comment.

What I really like about the Mendel concept is the frame and the idea of extruding material instead of removing material.

The frame

The first practical decision was the size and dimensions. My first thought was to simply double the size of the frame, but the I learned that threaded rod come in 1 meter pieces. That decided the length of the X-axis. The triangles are size so the whole thing fits on a 80cm wide table. The rod themselves are 12mm instead of 8mm, that seems to be a good decision as the machine is fairly stable without to much weight.

The frame vertices were a bit of a challenge as I was working with a 9mm MDF sheet - I made a lot of small pieces and glued together to a larger piece that cut into shape so go the thing in the image below.

Frame start.jpg

After some more cutting and drilling I had a frame that's just a big copy of the standard Mendel frame.

The Z-axis

After the frame the turn came to the by far most complicated part - the Z-axis.

I made a few changes to the design here: The 60 degree angle between invites to tension, thus causing more friction than necessary, so I changed the angle to 90 degrees.

I also decided to mount the angled bearings on the Z-carriage itself, this is due to the fact that the angled bearings are the most important constraint, so I don't like having them on a part that has been weakened for adjustment purposes (I applied a similar philosophy to the other axes - more about that later).

I decided to keep the lead screw in the 8mm dimension, but I added bearings to the top.

The belts, I got, are 10mm wide so I had trouble finding space for them at the bottom of the machine. The solution was to put the whole Z-drive on top of the machine, so the lead screws are actually hanging in the top bearing rather than "standing" on the bottom bearings.

This proved to be a good solution as I get a lot smoother run this way.