I Found a good way to make closed loop GT2 belts

I have a reprap Prusa I3, but this applies to any situation where a closed loop belt would be nice.
I wanted to make the extruder motor turn the big gear attached to the hobbed bolt run via belt, not gear.

I think it would have been done like that from the beginning if it were not for difficulty of getting closed loop belts of any size.
So I needed one, and tried gluing with neoprene glue. Not impressed, too weak a joint.
I then thought of sewing the loop together, and got out my sewing kit (ok, my wife's), and found a nice fine quilting needle.
I got some nylon thread, and tried using that to put a couple stiches through some scrap belt.
It was way too thick of thread, no go.
So I got out some really fine thread from my trout "fly tying" materials, and tried a couple stitches.
It worked well, so I used that.

I found that the best workflow was to cut the belt right in the middle of a tooth, so not a skew joint, straight accross. So each side is 1/2 tooth, and sewing them together forms a whole tooth. It seems like a better idea to do a skewed joint, so more length to sew along, but lining up the teeth is impossible.
It is rather fine work, and I justs did what i might call looping stitches like a spiral notebook, nothing tecnical.
I used a metal thimble on one hand, and needle nose pliers in the other. Wax the thread to keep it from tangling too much.
Its very hard to push the needle through, so use the pliars to do that, then pull from the other side with pliars.
Once you have a stitch or two going, its easier as the belt stays in place.
I have printed for 20 hours so far with no sign of degredation from the seam, and no stretching issues.
I did about 12 stitches I recall.

There could be 20 variations of this, including gluing the belt, then sewing it.
The point is, it can be done with cheap materials and is durable. I was worried the rubber would split or shred from the thread stress.
Its been fine though.

I bet others could improve this, and then belt driven extruders could be the norm.
They are quieter, have no backlash, and allow you to use an aluminum gear on the stepper motor.
My pla plastic gear kept getting soft from the motor heat, then deforming and slipping as the set bolt hole elongated.
No more of that, perfect reliability now.

I should mention anyone could retrofit a typical gregs extruder to belt.
Get an aluminum small pully, and sand down the big gear to make it smaller.
Add some ridges to keep the belt in line, maybe with loops of copper wire or adding thin discs to each side, assuming that does not mess up the hobbed bolt spacing. I made my large gear out of 4 layers of 1/8 in pressboard. The two outer layers were larger dia so formed the track.
The important detail here is you do not need teeth in that larger gear. The belt friction is enough.
Elongate the motor mount holes to allow for belt tensioning.

So I am done with herringbone gears, belts are way superior IMO and can be made with a bit of fine sewing.
I'll post pics and a vid of the extruder soon.

Edited 1 time(s). Last edit at 12/19/2014 01:45PM by jmaeding.

Or you could cut at an angle, lay the two pieces together on a printed jig or pulley to get the spacing right, and glue a inch or two piece of the belt flipped around on the backside.

I'm itching to see this, i tried the glue on it's own and also rubber strip on the back, both failed pretty quick

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I tried that. It does not work as it messes up the way the belt bends. I was going to do that the whole length, not just at the seam, but it will not work with the aluminum pulley, the teethe do not line up.

I posted a vid to youtube:
video of belt extruder

If you look close, the seam is visible near the end of the video. Its not easy to see even in person unless you are looking for it.
I made the whole extruder from pressboard as I wanted something high heat resistant.
The motor is rotated a bit compared to normal gregs because it allowed better access to the motor mounting screws which you must tighten after the belt is in place.

Whats the advantahe of belt over gears?

The herringbone gears i use mesh really well with no slop on my extruder.
Theres hardly any wear that i can see in the hours ive printed with them.

Gordon

less noise, high heat resistance, no backlash.

My extruder stepper gets hot enough I cannot keep my finger on it for more than 4 seconds.
That heat transfers to the parts its touching, including the small gear.
I went through 3 gears, about 1 every 20 hours, and started to hate wondering when the next gear would fail.

So if yours is working, cool. I would argue a belt design covers a wider range of reliability issues.
I am keeping an eye on the belt though. We could buy them easier if an extruder design for them was published similar to gregs extruder.

My extruder motor gets warmer than the other motors but not so hot as to effect the gears.
All of my printer printed parts are abs though which has more heat resistence than pla.

Ive done well over a hundred hours on my last extruder without problems of heat.
Would have been longer but the extruder body was badly printed and split so had to replace it.
At the same time i changed to a slightly better design and different gearing so didnt get to the point where i had to replace the gears.

I have found that the fit between small and large gear is crucial. You have to take the time to tension the
hobbed bolt and bearings just right and make sure the motor is tilted just right in its mounts to mesh properly.
I could see how premature wear or the motor working harder could happen if they arnt meshing properly.
But cant say i have much noise coming from it.

Gordon

Quote
jmaeding
less noise, high heat resistance, no backlash.

My extruder stepper gets hot enough I cannot keep my finger on it for more than 4 seconds.
That heat transfers to the parts its touching, including the small gear.
I went through 3 gears, about 1 every 20 hours, and started to hate wondering when the next gear would fail.

So if yours is working, cool. I would argue a belt design covers a wider range of reliability issues.
I am keeping an eye on the belt though. We could buy them easier if an extruder design for them was published similar to gregs extruder.

Well, I think that working around the heat-generation of your stepper motor is actually also working 'around' the problem, instead of solving it. My stepper motor doesn't heat up much as I'm using a 2.5A rated motor, this works very well. It gets quite warm still.

I'm using a direct-drive with metal filament driver so that's also better than using plastic materials that connect between the motor and filament driver.

Nonetheless, it is again quite evident that working around a problem can actually create interesting results that wouldn't have existed otherwise. I'm curious to see how long the belt holds up. I am designing a belt-driven extruder myself, but instead of making it first and then looking for a belt, I'm trying to figure out which closed-belt sizes are most common so I can base the design around the belts that are available. I hope there will be more belt-driven extruder models in the future, as I was pleasantly surprised by the 00str00der's design.

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Its got to be a lot easier changing gear ratios with a belt and the ability to tension it properly.
Thinking about it thats got to be the killer benefit.
Just change the drive pulley smaller or larger to get just the right gear ratio for your motor.

Gordon

I solved this issue by cutting a length of belt about 1" (12 teeth) longer than I need. I then place the ends together teeth to teeth and the ends are even. I use a heavy canvas/sail thread and wrap it many times. I have also use the metal crimps. It may take you a little time, but once you get it positioned correctly, it will run across the timing pulley without a problem. The metal crimp takes up more space than the thread; that will determine which to use.

Quote
jmaeding
My extruder stepper gets hot enough I cannot keep my finger on it for more than 4 seconds.

My extruder motor was getting hotter than I could touch, so a I glued an aluminium heatsink to the end of it. Now its well below "hand hot" to touch even after prolonged use and I'm not adding much mass at all.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions