Max length of GT2 6mm

Hi, i want to build a large cnc. I chosed to use GT2 6mm belt because is cheapest. I have a dubt on how much it can afflict my precision and how much is strong(Fiberglass reinforce is strong and low elastic). I need to move a axis with 2kg of weight and i have 2 belts, so 1kg per belt. Also the total length of the belt will be 1700mm.
My question is:
The belt will bend on itself weight?
The belt will be enough strong to don't stretch and loose precision?

I'll also use belt tensioner.

As a matter of physics, no nonsolid object will remain perfectly straight with gravity at play. It's a matter of negligibility. I have steel reinforced GT2, 6mm but I haven't used it yet. At that distance, and for a CNC, so long as your structure and linear motion system are solid and sturdy enough, you should be fine. I hope your belt tensioner isn't spring loaded, those will allow your belt to lengthen and shorten with enough force.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

Yes, it's a spring. Do you advice me to not use it or use something else instead?

I've never used them, so I can't say anything for sure. I just don't like the idea of something that can be pulled with enough weight, in my simple mind that removes the point of reinforcing the belt since it will have a stretch factor to it with the spring.
I always have moveable parts to tighten belts. Like have a motor on a moveable mount, or the idler pulleys, or the belt attached to a screw that can be screwed in to tighten.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

Hi Yaro.

I was down the same path, whether should I use a 6 mm GT2 or something else. Eventually, I found a 10 mm gt2 belt steel reinforced, which I'm gonna use to move my 2 pound all metal extruder over 1000 mm of x-axis, using two 10 mm wide gt2 belts running in parallel. The reason I went with 10 mm instead of 6 is, I'm trying to avoid the guitar string effect. Wider belt, combined with steel reinforcing, should do the trick. I hope it helps.

Quote
val c.
10 mm gt2 belt steel reinforced

I'm looking for ~10mm GT2 belt, and what did you use for pulleys, can you provide a link.
Tks.

I wanted to avoid same problem, but i didn't find GT2 10mm belt and bore compatibles with good prices.

I use T2,5 belts on my large 3D printer and acuracy is very good. I do however run 2 belts with a 8mm shaft connecting the pulleys to ensure the gantry stays square.

Your problem is more than likely going to be the belt skipping teeth on a cnc as soon as there is resistance on the cutting head, that may be preferable to no give and a broken bit but it could still be a pain.
For the play in the belt from a spring tentioner i've seen a few nice designs on thingyverse the one that comes to mind is a belt clamp with 2 3mm screws that tension the belts, or you can have the idler pulley on the far side adjustable for tentioning the belts.

What about using GT5 belts?

I have steel reinforced 9mm wide 5mm pitch belts (don't know the exact designation- they came out of a piece of industrial scrap) on the X and Y axes of my printer. The Y axis span is about 700mm. It used to bounce a lot as the printbed moved and I considered putting a piece of soft sponge or something against it to control the bouncing but never got around to trying it. I did put a 1/2 twist in it so that the smooth backside of the belt wrapped around the untoothed idler pulley and discovered that the half twist stopped the bouncing almost completely. The twisted belt caused a noticeable improvement in print quality that I suspect resulted from the reduced bounce more than from the smooth side of the belt riding on the smooth pulley.

As i understood if i have a rigid structure with tensioners and maybe belt with 1/2 twist it will be good? I may try to add a belt support, but it will be really complicate to add it to my project.

Length-wise, you are fine with GT2 and even your weight shouldn't be a problem.

Redsalamander nailed it, resistance and teeth skipping will be your biggest problem. More teeth engaging is the fix but requires larger pulleys, larger pulleys decrease resolution and torque. Larger pulleys will allow for steel reinforced though, which work better with larger pulleys. There are also Kevlar belts (about 3 times the cost) which work better with smaller pulleys.