Sunday 26 June 2011

Half belt hack

I found that I didn't have enough belt to complete the x-axis of my Prusa, but I did have a couple of offcuts about half the required length. Since less than half the belt actually passes over the motor pulley I simply joined them in the middle. My first idea was to print a two part clamp. Another idea was to use heat shrink sleeving, but in the end I simply tied them with some wire.

I joined them back to back so that the teeth mesh, keying them together. This has the beneficial side effect that the smooth part of the belt goes round the smooth idler pulley.

It might actually be worth doing this to get smoother running, even if you do have a belt long enough. Also if you are on a tight budget the second half does not need to be toothed belt at all. It could be packaging strapping or steel wire, etc.


  1. What about adding two half twists to the belt in the right spots? The twists may move along the belt as needed, too.

  2. Yes I think that would work. Just one half twist along the top and opposite sides facing up at the belt clamps.

    I will try that on my y-axis, thanks.

  3. I dont think half-twists will work, there is not much space between bearing and carriage

  4. You only need one half twist in the long path between the motor and the idler, where my join is in the picture. I can't see how that would cause a problem.

    The second twist is just the fact that you insert it into the belt clip upside down on one side.

  5. Packing strap wouldn't mesh as well as you join has, but definitely cheaper. A good way to make a second Mendel, cutting your first one in half.

  6. Where did you get the X axis design? It is sideways instead of downwards.

    What about that x carriage design?


  7. The X axis is normal for a Prusa. eMaker Huxley has the bars above each other.

    The carriage has a beard attached, it came from here:

  8. Hi Nophead,
    Going slightly off-topic, but of interest (maybe) non-the-less, have you ever looked at using Gas Hob Jets as extruder nozzles? Came across these by chance when I had a new gas hob fitted.

  9. Yes I have some to try, but I haven't got round to trying them.

  10. Hi Mate,
    I´ve being thinking about building myself a reprap.I´ve seeing some amazing prints done on the ultimaker, but as always no one talks about parts accuracy.
    So before take the plunge on building one i would like to know how precise does the printed parts comes out? how much does it deviated from the cad model, So, I think you have being on the road for a loooong time and could give me a answer on what to spect from it.
    the last print I did on powder got around +-0.1mm, but I would prefer to have a reprap with a 0.2mm than the powder sistem I have.What do you say?

  11. It is difficult to state the accuracy TBH. A lot depends on how well the machine is constructed and calibrated.

    SLS prints are pixel based so you can easily state the resolution and the repeatability and accuracy should all be the same.

    With FFF it is a lot more complicated. You have the resolution, repeatability and accuracy of the positioning system that are all different.

    The filament width tolerance also has a small effect on large dimensions and a large effect on small dimensions.

    You also have minimum feature sizes related to the filament width and layer height.

    When filament bends round a corner it has a minimum bend radius. If the model has a sharp corner then you get a discrepancy.

    In summary a simple figure like an accuracy of 0.2mm doesn't mean much. I guess you could get outside dimensions accurate to about that ignoring things like corner radii, etc.