Hi folks !
I solved the issue on my printer 
Great result!
Did you use the “W 7mm with t” variant from the link you posted?
Yes, that’s the model I’ve used.
1 Like
So do you want to tell us that you changed all 10 pulleys with these toothed ones?
3 Likes
Optimal! and was it difficult to replace them, extract them? time?
Should the entire arm x be dismantled?
Could you tell me where I can buy them? Amazon?
Thank you
Luca
Please check the post I’ve linked, more or less everything is described.
I have a new X axis assembly and those pulleys on order.
I would really love to be free from trying to thread the needle of print speed to achieve good wall finish.
I just printed a couple VFA test:
- 20-200 mm/s (10 mm/s steps)
- 15-105 mm/s (5 mm/s steps)
Once I get the pulleys swapped I will run the same gcode to compare.
Okay, new X axis assembly arrived and I tore it down.
I actually found a way to remove the idlers without drilling an additional hole in the end brackets (do drive out the axles).
The only modification needed is to carve a bit off the carbon rod, so it can pass the idle axle. A cross cut carbide burr in a dremel makes very short work of this:
.
.
.
I got the assembly set up in my vise with a gentle grip using soft jaws, and importantly, the bottom of the bracket sitting solidly on the vise:
.
.
.
Here is where the axle terminates against a rib of the plastic:
.
.
.
You will want to find the largest flathead screwdriver you can, that will fit between the adjacent ribs, and get it resting on top of the axle:
.
.
.
Then, get something solid to support the tail of your screwdriver, so that it is just a little above horizontal. An extra set of hands would make this a lot easier, but I did it alone. You will then strike the screwdriver with a hammer, as close to the bracket as possible. You could even use a punch so that you can get extra close. The closer you get, the less elastic the collision is, so less force needed in the hammer blow.
.
.
.
Once the axle moves, you will feel/hear it. Stop. You can only knock the axle down flush with this setup, but it’s much easier from here. I reached in with a smaller screwdriver and pushed it down a little further. Then, I pushed it the rest of the way out with a 90* pick:
.
.
.
Be careful, as the axle can drop right out, spilling the idler and its tiny washers onto the floor.
I did order some toothed idlers from Aliexpress, but got impatient and got some from Amazon today. They are different in size, so I have to decide if I want to use them or not.
The stock idlers are: 12mm OD, 15mm flange diameter, 9.5mm tall, 7.9mm between flanges, with a 5mm bore.
The bracket height is 10.6mm and the stock washers are 0.34mm thick. So, you have about 0.42mm of freeplay in the stack.
My amazon idlers are: 12.27 OD, 18mm flange diameter, 8.6mm tall, 6.7mm between flanges, and 5mm bore.
3 Likes
Didn’t you damaged the little plastic rib that stop the axle ?
I drilled the hole at the opposite to avoid this, and to avoid to have to use force to extract the axle and damage something.
Regarding the pulley, with a 18mm flange I don’t think they will fit as is.
The toothed pulley I used are 10mm tall, that was rather difficult to put the washers back in place.
I’ve used thin tape to keep them in place while inserting the pulley, then centering them with a screwdriver before inserting the axle.
I’ve damaged two of them before been able to have them correctly in place with this technique.
No significant damage:
.
.
.
I was more worried about damaging that rib by drilling through the entire bracket, entering on an angled surface, and not knowing where exactly the drill would break though.
When you follow my approach, you just set the screwdriver tip gently against the rib, and then all your impact force goes down into the pin. It’s very low risk when done correctly.
I plan to put a drop of superglue on the end of the axle, so that it gets bonded back to that rib. What did you do for retention?
The 18mm flange idlers do fit in there with no problem. I’m more worried about how narrow they are between flanges. I’d actually prefer as wide a pulley as I can get, so there is less chance of interaction with the flange.
1 Like
Good to have an alternative approach to remove the axle.
I didn’t do anything special for retention, I just pushed the axle back in place.
He hasn’t move at all after more than a hundred hours of print.
Regarding the 18mm pulley, are you sure that the print head won’t touch it while moving ?
Mine are 15mm and they are at the border of the support.
Boy, you think it was hard trying to get the stack back in place with just the stock washers? Try adding an additional 2 printed washers!
.
.
.
Good call on the clearance though. While it does clear the end bracket easily, the flange protrudes beyond the edge and would hit the print head. I could grind down the flange diameter pretty easily, but since you had really good results with the specific Aliexpress pulleys, I’ll just wait for those. The fact that they have a wider flange to flange distance is good. Plus, you never know how good the machining is on the actual tooth profile. A mismatch there could defeat the the entire purpose of this mod. I could knock the flanges off one of my pulleys and inspect on my Keyence IM at work… or just be patient.
1 Like
How tall are your pulley ?
The one from Ali are 10mm, with 7mm for the toothed part, I can tell you it’s a nightmare to install the 0.3mm washers as the original pulley are 9.5mm tall.
Yeah, I bet. You go from a small amount of freeplay, to a very light interference.
My plan for that is to print a little mock axle, only 10.6mm high, and tapped for M3. I’ll build the pulley and washer stack on this, slip it in as an assembly, then thread in an M3 bolt and pull it out. The compression should keep everything in alignment to install the real axle.
Edit: Works beautifully. What took me maybe 10 minutes if super careful work with a flashlight and a pick, took me about 10 seconds with the printed axle installation tool.
1 Like
Here’s a quick video showing my installation tool. Gotta love when an uber simple part is a game changer:
2 Likes
Very good idea, hope it will be that easy with the taller Ali pulley and without the printed additional washers.
This is how I’ve installed mine :
I’ve done that on both sides of the pulley.
Once in place I’ve centered the pulleys with a screwdriver through the axle hole, then inserted the original axle to finaly remove the tape.
1 Like
I just discovered something quite interesting while browsing Bambu Lab web site:
Look at the pulleys, they are toothed. 
So that mean that they have well designed the axis, but for a crazy still unknown reason they have installed the wrong one.
1 Like
It would be nice to hear why they chose smooth pulleys for production!
1 Like
Perhaps to save 1 cent on each unit by reducing the amount of different parts required to build the printers ?
Perhaps wrong build instructions given to manufacturer ?
Perhaps build error made by manufacturer ?
I agree that we must have an official answer from Bambu regarding this issue, and a quick fix for new printers and actual one.
3 Likes