Belt tensioning tip

[Derek the Admin]

The "Tips" thread was a great idea, and I am going to link this in a reply to that one. I felt like belt tension was important enough to have its own thread. Adequate belt tension is very important. I'll admit that sometimes it can help to have three arms when routing the belts and trying to get them tight. If your belts are really floppy then your work results won't be good at all,

Let's use the X axis as an example. The assembly instructions describe one way to do it (start with right side, route around motor pulley, run behind the x plate, etc), but here is another way if you aren't happy with your tension with that method:

Zip tie the left anchor point first. Make sure the teeth mesh. Now, route it around the idler pulley that's mounted on the left frame piece, then run the belt behind the X axis plate, around the motor pulley, and back towards the X plate. Now, slide that X axis plate all the way to the left frame piece. You may want to put a piece of wood, rag, or something of that nature between the left frame piece and the X axis plate that is butting up to it because you are about to push that plate firmly into the frame. Now, at this point it would be great to call a friend, spouse, kid, whoever over to help you if they can. Its doable without a second person, but a lot easier on you if you can put someone to work for 3 minutes. Run the belt through the right anchor point. If you have that helper, have them grab the motor pulley, pinching the belt firmly to it, and then have them turn the motor pulley firmly clockwise. This is going to tighten the longest run of belt that goes behind the X axis plate and create slack on the run from the motor pulley to the right anchor point. This is what you want. Have your helper (if someone was nice enough to help you) place their free hand against the X axis bearing plate and push it firmly against the left frame. You need to take up all that slack they created as they continue to hold the X axis plate and put clockwise torque on that motor pulley. You can get more tension if you anchor this one with the back sides (the smooth sides) of the belt against each other, but consider using two zip ties to hold the belt if that's the way you go about it.

Let me know if there are any questions.

[kb9jlo]

I did the right side first and then when I got to the "pull that sucker up tight and zip tie it" point -- I used a clamp to hold the X axis against the side. Just a cheap HF quick clamp. Then I used my smallest vice grips to hold the belt teeth together while I did the actual zip tie. Easier to do then explain. When I strum it it has a good tone. I think that's what you told me.

I do seem to have an issue. I have the alum bracket as high as it will go and the belt wants to slip up the and off the bearings. It can't slip off since the belt hits the top of the square hole in the side panel. I'm thinking of loosening the alum bracket a little and putting a slip or two of paper under the top edge of the bracket to shim it out -- so it tilts out just slightly to keep the belt on the pulleys. I'm not having any issues like this anywhere else. Everything is good. Or should I put more washers under the bearings?

Never mind - was able to lower the pulley just the slightest bit and I think it will be just fine.

[Derek the Admin]

That's a great method Dan. A clamp makes for a good third hand.

I'm also glad you got the belt slip fixed. Honestly there isn't a real scientific approach to that "belt rides up or down" issue. That sequence of hardware is pretty critical because the slots are designed for 6mm but we needed to use 52mm bore screws. That m6 washer stacked against the m5 washer helps keep the bolt itself from rolling. Aside from that, its almost luck of the draw. The majority of the time I put them on the belt just rides dead center. Probably 30 percent of the time it wants to ride up or down. Shimming seems like a reasonable thing to do, but every time I have run into it I just do the loosen this tighten that routine talked about in the instructions and it starts riding center.

We looked at using a pair of flanged bearings there, but there were a couple reasons we stayed away from them.