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Belts pitch: 2 or 3 mm ? Your opinion ?

Posted by ARG 
ARG
Belts pitch: 2 or 3 mm ? Your opinion ?
January 24, 2021 02:09PM
Hello, I am new here. After starting at 3D printing with a Bibo printer, and spent a lot of time to ... fix it... I have understood 2 or 3 basic things:
- Industrial FDM printer are out of my price range.
- The consumers FDM manufacturing industry is driven by the price consideration and flooded by Chinese crap parts.
- Technical solutions are also driven by the profit consideration.
So, I decided, like many of you, to start from scratch, and build my own printer:
Briefly:
- Core X/Y geometry
- Inspired from the DD UMMD ( thank you DD thumbs up really useful writings ): rails, belted/worm gear lifted Z axis , separate Z frame, etc...
- careful attention to basics technical details: rigidity, for example.
I would like to hear you about this question :
Belts to move the X and Y axes :
My though was to use 12 or 15mm wide belts in order to reduce the ''spring effect'' of the belts driving a quite heavy carriage: probably near 2Kg once built.
I found GT2 12 mm wide 2mm pitch belts, and 15mm wide GT3 3mm pitch belts.
In your opinion, is there a real down side to use a 3mm pitch ( 0.9° motor) on the X / Y axes, instead of 2 mm ?
( from an accuracy point of view, with a standard 0.4mm nozzle)


The devil is in the detail.
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 06, 2021 01:23AM
is this a trick question...2
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 06, 2021 07:59AM
Yes, super wide belts will stretch less, but you will pay an arm and a leg for drive pulleys to fit your motors, if you can find them. The stretchiness of the belts is a small problem compared to the springiness of the motors.
And don't forget the flexibility of the frame. There would be no point in using extra wide belts if you're going to make the frame from 2020 t-slot.

I don't think 2 or 3 mm pitch makes any difference, especially if it is GT profile. My first printer had 5 mm pitch XL belts (steel core!) and it produced beautiful prints.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 06, 2021 10:16AM
I suppose you get faster with the larger pitch, and a new controller to divide the steps more.
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 06, 2021 03:35PM
Why would the belt pitch have any effect on the speed?


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 06, 2021 03:49PM
I've read 2mm pitch GT2 has better positional accuracy vs 3mm (4x according to the Shapeoko wiki: [wiki.shapeoko.com]), though as the digital dentist mentioned, it probably doesn't have much effect in practice, as there are other larger contributing factors to accuracy. I would still use 10 or 12mm wide belts though for stiffness (and GT2 2mm can be sourced in 15mm wide as well).


Modular Linear Slides for Aluminum Extrusions [www.exoslide.com]
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 07, 2021 09:01AM
in the same way a 5mm lead on a screw would be faster than a 2mm lead
ARG
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 07, 2021 10:38AM
Sorry to be back so late. I appreciate your time. I did some researches on my side, and I found :

- some answers here
- and a tool for calculations here

Quote
the_digital_dentist
I don't think 2 or 3 mm pitch makes any difference, especially if it is GT profile
I agree with you. The Prusa calculators helped me to visualise the real difference between 2 and 3mm pitch. It is near nothing in term of accuracy for a tool which extrudes melted plastic.

Quote
MechaBits
I suppose you get faster with the larger pitch, and a new controller to divide the steps more.
I don't think so : one full turn of a 3mm pitch driving pulley is the same full turn than a 2mm pitch driving pulley of the same diameter: it remains a full turn, and the length of ''moved belt'', is the same. So there is no gain, or loss for speed.
The improvement would be on the accuracy, through a better positioning.

Quote
gmedlicott
(and GT2 2mm can be sourced in 15mm wide as well
I would be glad if you can point me to a source of Genuine GT2, 2mm pitch, 15mm wide GATES belts.
After a lot of researches, if found in this document that GATES sells open belts in those dimensions :
GT2 2mm pitch: 6-9-12mm wide
GT3 2mm pitch: 4-6-9mm wide
GT3 3mm pitch: 6-9-15mm wide
I am not affiliated in any way to Gates. I am just the guy who dont want to buy chewing gum belts from nowhere-land, without any technical other infos than : ''GT2 compatible''

Quote
gmedlicott
as the digital dentist mentioned, it probably doesn't have much effect in practice, as there are other larger contributing factors to accuracy
Yes you are probably right. But...everything is in the word: ''probably''.
With this project, my goal is to try to remove, or bring back to near zero the most gray zones I can. ( the ''probably'' zones)
One zone/ problem at time.
Today was the belt zone.
Tomorrow will be another day/zone.

A little more precisions about my project: The idea is to collect quality parts for technically proven solutions, and, at the end, to design and build the printer.
At date, I have some components in hand:
- THK HRW17 Rails for all axes.
( I know it is overkill , but I found a good deal)
- Onedrives 1/30 wormgear (UMMD flavour z axis )
- Duet 3 Mainboard 6HC
- Duet PanelDue 7'' display
- 2 NEMA 17 / 60mm / 0.9° motors

For the design: the general idea is to use the ''halo'' solution for the top plate. A T slot rails frame. And rigid aluminum side pannels on all remaining faces. Goal: rigidity / mass / weight.
Mic6 Cast 1/2'' bed. Separate heater. 3 points manual leveling adjustment.
I think seriously to water cooling.

The final goal : a solid, reliable, finely adjustable workhorse printer.


The devil is in the detail.
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 07, 2021 11:42AM
20t gt2 is 12mm, but I wouldnt know the diam of a 20t gt3, they are more expensive.
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 07, 2021 02:44PM
One point with stepper motors and wide belts is that their rated radial load is not too great. Wide belts lever on the shaft more than narrow belts as narrow belts can be set closer to the flange. An excerpt from a datasheet below gives 28 Newtons (about 2.9kg or 6.3 pounds force) as the maximum for a fairly typical NEMA17. I think they are regularly used at or beyond this but think the gains in reduced flexibility from a wide belt could be lost in the flexing of the stepper shaft - besides the reduced service life.



Mike
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 07, 2021 02:57PM
Quote
MechaBits
in the same way a 5mm lead on a screw would be faster than a 2mm lead

Belts and screws don't work the same way.
Oh, I see, you're assuming an equal number of teeth on the 2mm and 3mm drive pulleys...


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
VDX
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 07, 2021 03:22PM
... hmmm ... I have two machines form Janome with "superfine" pitches belts, which are specified with up to 800mm/s and 0.01mm accuracy -- so finer belts could be of any good too? confused smiley

Edited 1 time(s). Last edit at 02/07/2021 03:22PM by VDX.


Viktor
--------
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Call for the project "garbage-free seas" - [reprap.org]
ARG
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 07, 2021 05:41PM
Quote
MechaBits
but I wouldnt know the diam of a 20t gt3
Misumi USA has everything to answer this question here

Quote
leadinglights
Wide belts lever on the shaft more than narrow belts as narrow belts can be set closer to the flange.
an interesting point: I must to think of it twice, before making the choice of belt width

Thank you :-)


The devil is in the detail.
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 08, 2021 01:27AM
I had to assume some things where = even though they aint the same smiling smiley
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 08, 2021 03:41AM
Different pitch like different modules for gears !


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Belts pitch: 2 or 3 mm ? Your opinion ?
February 08, 2021 06:11AM
A bit more on toothed belts, belt tension, and stepper motors. Firstly though, a bit of a disclaimer: I exceed the recommended figures by quite a bit on my Delta printer and I haven't had any real problems

I worked out the load from a site that has gone missing in the depths of time, but this one [www.mitsuboshi.com] gives about the same results - except that it barfs when I put in the true center distance of 780mm.

Specification 				Classical	
Tooth profile 				T5	
Belt width 				6mm
Number of teeth on large pulley 	20	
Number of teeth on small pulley 	20	
Revolution of small pulley 		600rpm
Center distance 			600mm

Calculation results
Initial tension (min) 			12.66N
Initial tension (max) 			19.12N
Static shaft load (min) 		25.32N
Static shaft load (max) 		38.24N
Deflection 				9.60mm
Deflection load (min) 			1.04N
Deflection load (max) 			1.45N

Please note though that the shaft load from the recommended tension goes up to 119.43 Newtons with a 15mm wide belt. Again though, a lighter tension will probably work fine, but the engineering specs will lurk in the room like an elephant.

Mike
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