Timing Belt Opinions

[Project_Hopeless]

For my DIY CNC router I'm thinking about using 2GT-3M timing belt and pulleys, 1:1 ratio for my Z axis. It will reduce the machine height compared to my direct drive concept.

I was thinking 30 teeth, 9mm width. What size pulley would you choose, number teeth, width?

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[__Britt]

Is that a belt drive going to a ballscrew, or a direct mount of the Z to the belt?

[Arjay]

A 9mm 2GT belt is awfully small. Those are better suited to a no-load application like a 3D printer.

[wizard]

Timing belts would be fine for a certain class of work, so the first question is what are your intentions.

Beyond all of that timing belts for most router implementations are almost always undersized on DIY builds. I work on a lot of pick and place robots (extractors) and special function machines and the belts used there are often 50mm wide, sometimes wider. To get the positioning accuracy needed the belts are tensioned very tight. This tensioning requirement is the second big issue on home builds, you can easily bend or warp a light frame or gantry beam. The mechanical arraingement of the drives is also important as you need to minimize belt slap or oscillation.

Belt drive isn’t impossible but it might not give you what you need.

[peteeng]

Hi Hopeful - 9mm is too narrow. Needs to be at least 16mm wide depending on the stiffness required. I'd use the widest pulley you can put on the motor shaft. My router has 16mm wide belts on all axis and next time I'd use 25mm. Prefer 32mm but too wide to get onto motor shafts. Usually height is not a problem. Direct drive is best so if height is actually not a problem (like it has to fit into a certain height space) I wouldn't use the belt. Cheers Peter

[Project_Hopeless]

Is that a belt drive going to a ballscrew, or a direct mount of the Z to the belt?

Yes it will drive a 1204 ball screw.

I'm trying to get the CG lower on the machine. Direct drive will have the motor high in the air. Seems like a lot of mass up high during high speed moves.

Pictured is the Z axis at the extreme stroke limits, left two images direct drive, right belt drive.



Nothing has left the drawing board yet!

[peteeng]

Hi Hopeless - I personally would not worry about the height, your gantry rail spacing is very big, it will cope easily unless you are aiming at 1G plus moves? . You are using rails for the Z yet round shaft for the gantry? Rail is much stiffer? I'd only use the belt if you needed a gear ratio. If 1:1 works then go direct.. Peter

I also think your saddle plate and Z plate need to be thicker or have webs on the sides. They will wobble quite a bit when they are thin and flat when cutting, a much bigger concern then the high mass.

[RCaffin]

I use GT2 belts myself between motor and ball screw, motor and harmonic drive.

The 6 mm ones are usually quite enough for that: they have incredible strength which few seem to understand - and many pulleys and belts can be bought from ebay for low cost. You would need to be pushing very high accelerations to justify going up from 6 mm to 9mm between motor and ballscrew. You should note however that Chinese GT2 belt profile is slightly different from Gates GT2. Not much, just simpler. The original profile (in the patent) was an attempt to block copies by being excessively complex. It didn't work

For direct drive something a bit wider could be advised. 16 mm with correct tension should handle many routers. Going up from there is expensive and of questionable value. Note however 'correct tension'.

Z axis web plates - yeah, a bit light.

Cheers
Roger

[teamloks1]

where did you all find big belt i only found 9mm belt currently using 9mm belt with 1kw servo driving 40kg z axis

[RCaffin]

6 mm GT2: used on little 3D printers, so hordes of Chinese suppliers.
Wider than that: European or USA suppliers only. A bit more $ of course.


Z axis. 9 mm GT2 belts bought in, Gates brand. Pulleys with GT2 profile and custom taper lock: I had to make these myself.

GT2, correctly tensioned, does not have detectable backlash. This set replaced the original 'timing belt' as that older profile does have backlash. I can measure a 0.8 um single step resolution with this with a Z axis touch probe.

Cheers
Roger

[__Britt]

I'm not a mechanical engineer... so this could be a totally bogus notion... but... how about putting multiple 6mm belts on it?

[RCaffin]

Those GT2 elts are much stronger than you might think.
I have seen 3 or 4 V-belts in parallel, on proper pulleys. It should, in theory, work here too. Need to handle the tracking problem.

Cheers
Roger

[Arjay]

Multiple belts? Why not just pick a different belt?

[RCaffin]

I would not pick a 'different' belt - I would stay with the GT2, but I would buy a wider belt if needed.
It's just that the 6 mm size is very cheap from China - that's all.

Cheers
Roger

[Arjay]

I would not pick a 'different' belt - I would stay with the GT2, but I would buy a wider belt if needed.
It's just that the 6 mm size is very cheap from China - that's all.

Cheers
Roger

I've got a couple of 3d printers with the 2gt belts and they seem to work well for a low inertia application with no cutting forces. Can't see them handling an aggressive cutting load though.

[RCaffin]

Can't see them handling an aggressive cutting load though.
Chuckle. Check out the specs. I machine steel and titanium with my machine.

Cheers
Roger