Belt tension



  • Just finished my BLV mgn cube build and now need to fine tune all the stuff. I'm wondering what the right belt tension is. Are there any rules of thumb?


  • Moderator

    I just set the tension on my corexy after re-stringing the belts. Here's how I did it. I pushed the X axis gantry all the way to the rear against the Y axis hard stop and used a piece of rope to secure it in place. I strung the belts and secured them in place. They were slack at this point. When I released the rope I could see that the gantry would want to skew out of place on one side. I adjusted the belt tension until that skew was removed and it wanted to stay true. I then tightened the X gantry carriages on the gantry to lock it in place. Now that the belts were even and fairly snug I manually moved the carriage around by hand (slowly) to feel for resistance. I tightened both belts equally until I could feel extra resistance and then backed them both off until it was smooth again.

    For far more detail see here: https://drmrehorst.blogspot.com/2018/08/corexy-mechanism-layout-and-belt.html



  • @MartinNYHC said in Belt tension:

    Just finished my BLV mgn cube build and now need to fine tune all the stuff. I'm wondering what the right belt tension is. Are there any rules of thumb?

    There are just two rules of thumb for corexy machine belt tension:

    1. Belts should be tight but not too tight.
    2. When you're finished tensioning the belts, the X and Y axes should be square.

    If the belts are too tight, you'll be putting a lot of force on the pulley and motor mounts, and if they are stacked belt type that stand up like a fence post, they are liable to flex inward. The mechanism may not move smoothly and may bind depending on the type of linear bearings and the design of the pulley mounts. If you see pulleys tilting inward, you're putting too much tension on the belts (or you need to redesign motor or pulley mounts).

    If the belts are too loose they may slip on the drive pulleys - that's MUCH too loose. If they are so tight that the mechanism won't move smoothly, they are too tight. You want them to be somewhere between those extremes, and just about anywhere between those extremes will work fine.

    Before you tension the belts, the X and Y axes should be square. When you tension the first belt, they X and Y axes will usually be pulled out of square an amount that will vary depending on the flexibility of the X axis assembly, the type of bearings and guide rails used, and the absolute tension applied.

    When you tension the second belt, it will also increase tension on the first belt that you already tensioned, so when you tension the first belt, leave it a little looser than you feel is sufficient. Then, when you tension the second belt, the first one will tighten up. You are done adjusting tension when the X and Y axes are square and the belts are tight but not too tight. Usually, the belts will be close to equal tension when you're done, but getting the axes square is the final indicator, not equal belt tension.

    If the belt tension varies as you move the extruder carriage around, the pulleys guiding the belts are not positioned correctly, and a major redesign is in order.


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