Fighting with computers

Computers are not always friendly.

Sunday, October 14, 2012

The credit card trick

I have just finished a ShapeOko but because I did some mods: I've got some leftovers: some MXL belting and two 5mm MXL pulleys. What best thing to do than to start a project so they get some use. So I planned on building a new Prusa i3 3D printer. Not that I need yet another printer but a new model to try it out.

I built a Printrbot earlier this year to get a smaller model than the Prusa for home use. At the time the printer dimensions were not very clear and much guess work was done on my side. Besides, I used a direct drive that worked but I was never happy with.

This time I am, again, doing some guess work for Prusa i3, like figuring out that z-axis rods are M5 threaded rods or taking the overall dimensions out of the DXF of the aluminium frame off the Prusa i3 github, while learning that some changes have been done and are not yet into the master branch.

As I was planning on using MXL belts instead of what apparently it is used in Prusa i3, which my guess work suggest is HTD 3M belts, I needed to adapt a couple of parts to this belt. I have used 2.035mm for the pitch and 0.89mm for the inter-teeth retainer. But I have not changed the size of the belt slot.

I have also found tha 413MXL belts used for RC helicopters can be had quite cheaply on eBay, are 3mm wide, and are long enough for X and Y axis (they may be too thin but seem to work ok).

But MXL belts are quite thin, so the belt slot on the parts will be way too big and while the indents in the part will grab the belt, they will not hold it as it will slide easily. A simple way to get a tight fit while making it easy to remove the belt is to use a piece of credit card to fill in the space. This way the belt can no longer slide out of the grip of the little teeth in the part. Removal of the belt is very easy by removing the piece of credit card anytime.