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AB belt tension

msaeger

Well-known member
Printer Model
Formbot V2.4 R2
Use a pliers they say 🙂 so I used a pliers to try and tighten the AB belts and ripped the end of the belt off. My question is how tight should I be getting the belts by adjusting the length coming out of the carriage? Do I just get the belts even and use the front tensioners to get them tight? At what point do I use the front tensioners?
 
I loosen the front idlers all the way and get the belts equal length and as tight as I can get them by hand on the carriage. Then I adjust the front idlers equally until I find the tension I am looking for. There is some guidance on the docs site, but at this point, I know it when I feel it.
 
Yup, no need to use pliers, tighten them by hand and then use the tentioners that's what they're for.
 
Thanks for the replies. I used the tensioners and got them where they feel good to me. If am thinking of maybe get some of the electronics done so that I can test the movement before finishing the hotend.
 
That's most likely good enough to start with. The resonance testing is easy enough to do with a smartphone though. Also keep in mind belts will stretch with time especially at the beginning, you will likely need to add some tension.
 
It's probably not a new idea but thought I'd share as it could be a useful tip for others.

I've recently built a Trident and struggled with getting the belt tension right, as none of the phone apps suggested in the Voron docs seemed to give any consistent results.
Then I had a Eureka moment!
Being a guitar player, I have a guitar tuning gizmo to help tune each string to the right frequency. And it just so happens that the 5th string of a guitar in standard tuning is 110Hz - just the frequency we're looking to get when the A-B belts are tensioned correctly.
1683890460613.png
So, having set the 150mm spacing between the tensioner and idler centres (to leave the 150mm of belt on each side of the printer to twang) I placed the guitar tuner close to the belt and started twanging as I adjusted the belt tension. And it proved very satisfying to accurately get a tension that just holds the green light on (frequency spot on) or blinks the red lights to indicate frequency just too low (flat) or just too high (sharp). Much easier and more accurate than the other methods suggested.

The following link has a video demonstrating the process.

 
Since we are sharing, I have also used my mic from my Steelseries headset and some software to tune.
 
I bet a lot of new Voron owners overtighten their belts in the installation process, not sure if the mention of pliers in the manual is a good move. I just finished my build and i think mine are overtightened as well. I will leave it for the time being, to see if they stretch a bit.
 
I spent hours trying to get the right "twang", I am no guitar player and every time I plucked the same belt with no adjustment, it sounded different. I have probably over-tightened them; I am quietly waiting for the whole gantry to collapse from the belts being over-tightened, but up until that day I will keep printing.
 
Okay, sorry for Zombie-ing the post, but... my A/B belts are at about 175hz.

That seems... very loose.

I note the docs (https://docs.vorondesign.com/tuning/secondary_printer_tuning.html#belt-tension) says:
110hz equals roughly 2lb of belt tension here, which is on the lower end of the range. This should be a good starting point without stretching your belts too tight.

I put the belts on manually, used fingers to position before I locked them down, so either I have no clue how strong I am, or I'm missing something here. Idlers are 150mm apart, and I'm doing a series of plucks to make sure I'm not limpwristing it...

So.. If 110hz is the "lower end of the range", what's "too high"? I'm wondering if I need to back off my tensioners because the belts are too tight.
 
I am not sure there is upper limit, besides manufacturer's data on what belt can handle. And what your printer can handle.

Attached image is recommendation from Gates about belt tension for our application. This is for their original 2MGT GT3 belt, which can take higher load by - IIRC - 25% compared to GT2? Correct me if I am wrong. So for kit belts or older generations, get those numbers lower.

Just keep in mind that with increased tension, you are not putting load only on pulleys, bearing stacks and plastic parts - gantry may twist, micro-bearings in idlers may wear out, and plastic parts may crack. Motor bearings and shafts may suffer too. Common Nema17 motors' bearings are rated for 12 lbs, pulley plus belt going around it both sides lowers it to 6. You can safely increase belt tension if you mount pulley closer to the stepper by inverting one motor upside down like Clee does here, or if you support it on top, bottom, or both sides with bearing. You will need motors with longer shafts then.

Code:
6 lbs = 189hz
5 lbs = 172.6hz
4 lbs = 154.4hz
3 lbs = 133.7hz
2 lbs = 109.1hz


Credit to LJ of VORON Discord for providing links and numbers.

Gates belt tension.png
 
Thanks Sanity.

It sounds like I'm probably okay; I'll drop it lower, just in case, to be more in the midpoint of where I was, vs. where the "lower end of the spectrum" 110hz is.
Now for a little bit of additional tuning and then try a "for real" print.. calibration cube came out about as perfect as I've ever seen.
 
Thanks Sanity.

It sounds like I'm probably okay; I'll drop it lower, just in case, to be more in the midpoint of where I was, vs. where the "lower end of the spectrum" 110hz is.
Now for a little bit of additional tuning and then try a "for real" print.. calibration cube came out about as perfect as I've ever seen.
Awesome, can you post a photo of the cube?
 
Attached...

Corners are clean, no elephant footing, extrusion is clean.

Dims came out at 20.16 x 20.18 x 20.3. I'm pretty confident I can zero that better.
 

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