Double Belting - Thoughts?

[LiamN (Liam Newcombe)]

@Caffein8ted

I was attributing backlash on belt driven cnc’s to the length of belts on the x and y axis. For example if the gantry is located at the center of the Y-axis there would be an equal length of belt on either side of the Y-stepper so backlash Y+ or Y- would be the same, however if the gantry would be at the front or back end of the machine the backlash would be different due to different lengths of belt on either side of the stepper. (EDIT: tension would be the same it the machine was not actively cutting in Y or X direction, however tension would change while cutting in a certain direction… if that makes sense). This is why I always try to center my projects in the center of my CNC bed.

Funny you should mention that, I did put together a simple physics model of the belt deflection under load

Backlash, Deflection and Vibration

Chapter 3 Deflection Measurements and Model First Suspect – Baseboard Our first suspect for deflection is the notorious baseboard of the XXL machine. [Shapeoko_Model_2020-Oct-31_05-24-51PM-000_CustomizedView34389806454] Starting with the frame, who main purpose is to hold the Y rails square to each other and level above the baseboard. The front and rear metal frames are linked by 3 steel cross-straps. This is then topped and held square by two 18mm MDF sheets. [Shapeoko_Model_2020-Oct-31_05…

The simple outcome is that belt deflection is minimised towards the end of an axis with a short belt section. I was not able to measure any impact on backlash with varying position on the axis.

As for the interlocked belt, yes, absolutely that’s the magic, there’s only about 80mm of effective belt length at any one time working from solid reference where the lower belt is stuck to the axis.