Y drive belt arrangement

Y drive belt arrangement

The timing belt mechanism for the Y-axis drive was constructed in such a way that there was a loop over an idler roller to ensure maximum engagement of the teeth of the stepper motor pulley with the belt. This arrangement was adopted so that I can make full use of the available space within the Z-axis holder.

However, during the testing of the movable gantry cnc machine, I noticed that the Y-axis belts were sometimes touching, especially when there was a change in direction of travel of the axis. This was particularly pronounced when the tension on the belt was not too tight. As with any drive belt, the timing belt had a certain amount of sag at the optimum tension and the top belt would touch the bottom belt.

Sometimes, this contributed to lost steps in the Y-axis drive because of the extra resistance to movement.

Belt separator made of thin steel plate prevent the teeth of the top belt from engaging with the teeth of the bottom belt

Belt separator made of thin steel plate prevent the teeth of the top belt from engaging with the teeth of the bottom belt

As a countermeasure, I installed a thin strip of steel plate in between the top belt and the bottom idler roller so that the belt could slide smoothly on the face of the plate. This was the belt separator and it seemed to work.

Holes for Y axis belt idler

Holes for Y axis belt idler

During the time I had removed the belt idler, I noticed that the hole that the belt idler shaft was installed was somewhat enlarged. This was no surprise. The material in which the shaft was installed was MDF which was rather soft. Because the belt idler was subjected to tension in the belt, the lateral force on the belt would be transmitted to the shaft to deform the hole.

Steel plate for Y belt idler

Steel plate for Y belt idler

To counter this phenomenon, I fixed a steel plate against the belt idler shaft as reinforcement. The steel was able to resist the lateral moment of the shaft.

The belt idler reinforcement and the belt separator were installed for the Y-axis belt drive and they worked at the time of writing.

Y belt idler installation

Y belt idler installation

However, I managed to get hold of some plywood later on. I decided that plywood would be better than MDF because some of the MDF parts were found fracturing at the screw holes. I found out that it was very easy to over-tighten screws in MDF. This would lead to fractures because the wax or binder in MDF was not very strong.

And also during the course of the improvement, I decided that belt driven Y-axis was having too much uncertainties. I thought that a lead-screw driven arrangement would be more reliable.

These modifications will be described in later articles.