Fine tune your MK3 Y axis  

Re: Fine tune your MK3 Y axis

Just adding a little recent personal experience to this topic...and perhaps helpful info for some. Note: this applies to horizontal alignment only, not vertical.

I too previously posted about having trouble getting the Y belt to line up properly in the horizontal plane with stock PRUSA parts. My first attempt at fine tuning this in December (before this thread was born) was to add washers to the Y motor mount to move the motor 1.5mm to the left, so that I could properly center the belt on the motor pulley. However even though the belt was centered on the pulley, the entire belt path was certainly not centered. As I moved the Y carriage back and forth by hand it was easy to see the horizontal misalignment.

Since then, I have rebuilt the Y axis using MISUMI rods and bearings, and RHDreambox's reinforced Y motor mount (but I modified it to provide the 1.5mm of extra motor spacing that I needed on my first build). I've kept the stock PRUSA Y idler and Y belt holder. As I was rebuilding I decided to take some digital caliper measurements to ensure things were properly aligned, and I'm glad I did. Despite meticulously following the build instructions by leaving the Y rod mounts loose, then moving the carriage to each end of the frame to "align" the rods before tightening the rod holders, it turns out my rods were still skewed by ~1.5mm. Not good.

Using the calipers, I took the following 2 measurements at each of the four 'corners' of the frame: 1) inside of rod to outside of aluminum extrusion, and 2) outside of rod to center of belt at the (front or back) pulley. So eight measurements total, and I took each of them 2-3 times to ensure accurate measurements. After each set of measurements, I then adjusted three things as necessary: A) The rod holders, B) the position of the motor pulley on the motor shaft, and C) the position of the belt within the belt holder grooves. Measure again, adjust again, repeat...

After 4 full iterations of this process, I am happy to say my rods and belt are now as parallel to each other and the frame as is realistically possible for me, and the belt stays centered on itself and on both pulleys through its entire path. I can offer the following observations as a result:

1) The step in the Y-axis section of the manual titled "aligning the smooth rods" (step 30), is NOT sufficient to perfectly align your rods. Only by carefully measuring with calipers and applying a significant amount of lateral pressure to 2 of the rod holders to force them into place while re-tightening them was I able to get everything aligned properly.

2) Once the rods were accurately aligned, I was able to rather easily horizontally center the belt over its entire path using the stock Y belt holder and Y idler.

3) After aligning the rods and getting the belt centered, it appears the extra spacing on the Y motor mount that many of us expressed needing is no longer necessary, as there is now an extra ~2 mm of bare motor shaft between the motor and the pulley. (Although I might still add 0.5mm of spacing on the stock mount just to have a little extra "comfort" space between the motor and the pulley.)

So in conclusion, for my printer, it turns out it WAS possible to horizontally align the Y axis with the stock 3D printed parts it came with (R1 parts)...however NOT via the PRUSA build instructions, and not without a digital caliper. If you are having trouble aligning the Y belt and have a digital caliper, I would suggest carefully examining your rod alignment before assuming you need to print altered parts. YMMV.

Re: Fine tune your MK3 Y axis

Great post. Helpful for me as I added a 2mm spacer to get everything straight and now plan to use RHDreambox's reinforced motor mount which i was going to modify to add the 2mm I need.

But if you think there is a way to square it up, I am going to try that first.

I am still a little unsure of what you did to 'fix' it.. You said you adjusted the rod holders.. What sort of adjustment did you actually do?

Jon

Re: Fine tune your MK3 Y axis

Great post. Helpful for me as I added a 2mm spacer to get everything straight and now plan to use RHDreambox's reinforced motor mount which i was going to modify to add the 2mm I need.

But if you think there is a way to square it up, I am going to try that first.

I am still a little unsure of what you did to 'fix' it.. You said you adjusted the rod holders.. What sort of adjustment did you actually do?

Jon

In the end I had to laterally adjust all 4 rod holders, either left or right depending on the measurements. However with 2 of them I had to apply significantly more lateral force while tightening than I would have imagined, to coax them into the correct positions. I'm sure that could easily be remedied with printed parts that allow for more/easier lateral adjustments, but I was making an effort to see if it could all be squared with stock parts.

You may still want to add a bit of spacing to that motor mount, but after fully aligning mine the 2mm would be overkill. If I reprint my mount I'll likely just give it 0.5mm or 0.75mm.

Re: Fine tune your MK3 Y axis

Great post. Helpful for me as I added a 2mm spacer to get everything straight and now plan to use RHDreambox's reinforced motor mount which i was going to modify to add the 2mm I need.

But if you think there is a way to square it up, I am going to try that first.

I am still a little unsure of what you did to 'fix' it.. You said you adjusted the rod holders.. What sort of adjustment did you actually do?

Jon

In the end I had to laterally adjust all 4 rod holders, either left or right depending on the measurements. However with 2 of them I had to apply significantly more lateral force while tightening than I would have imagined, to coax them into the correct positions. I'm sure that could easily be remedied with printed parts that allow for more/easier lateral adjustments, but I was making an effort to see if it could all be squared with stock parts.

You may still want to add a bit of spacing to that motor mount, but after fully aligning mine the 2mm would be overkill. If I reprint my mount I'll likely just give it 0.5mm or 0.75mm.

What I don't get is that the holes are 3mm as are the screws.. So I can't see how much lateral movement you could move them.

I am still going to print mine +2mm.. At the end of the day, even if I do manage to square things up, it will just mean my pulley is further (2mm) down the shaft.. The default mount gives almost no adjustment as the pulley will have to go near flush with the motor.. But by adding 2mm, you have the entire shaft to play with (probably should have thought of a better way to say that 🙂 )

Jon

Re: Fine tune your MK3 Y axis

What I don't get is that the holes are 3mm as are the screws.. So I can't see how much lateral movement you could move them.

I am still going to print mine +2mm.. At the end of the day, even if I do manage to square things up, it will just mean my pulley is further (2mm) down the shaft.. The default mount gives almost no adjustment as the pulley will have to go near flush with the motor.. But by adding 2mm, you have the entire shaft to play with (probably should have thought of a better way to say that 🙂 )

Jon

There is definitely some play in there, but yes, there needs to be more. Fortunately I only needed like .5mm adjustment on one, and like .6 on another. But the fact that the holes are basically the size of the screw is clearly why I had to push so hard to get it where it needed to be. Obviously a better solution would be to either widen those screw holes with a file, or redesign them wider and reprint.

Ha. That's what she said.

Re: Fine tune your MK3 Y axis

If you do have a precise assembly RHDreambox, would you mind checking to see if a 16T pulley would align correctly to the other side? 🙂

So, @RHDreambox would you please upload the .stl file for this holder update ?

Here you go!

I've got both 16T and 20T idlers, think there is any advantage to adjusting this for 20T or does 16T seem to be a perfect fit?

Re: Fine tune your MK3 Y axis

I've got both 16T and 20T idlers, think there is any advantage to adjusting this for 20T or does 16T seem to be a perfect fit?

The advantage of 16T is that the drive belt becomes completely horizontal and fastened to the same level in the belt holder.
With 20T you can still make the drive belt horizontal (with a new Y belt-idler), but the ends of the belt will be placed at different levels in the belt holder (as it appears today).
So 16T should be the optimal solution.

Re: Fine tune your MK3 Y axis

I've got both 16T and 20T idlers, think there is any advantage to adjusting this for 20T or does 16T seem to be a perfect fit?

The advantage of 16T is that the drive belt becomes completely horizontal and fastened to the same level in the belt holder.
With 20T you can still make the drive belt horizontal (with a new Y belt-idler), but the ends of the belt will be placed at different levels in the belt holder (as it appears today).
So 16T should be the optimal solution.

Awesome, printing the last part for the 16T upgrade now, thanks.

Re: Fine tune your MK3 Y axis

Hello,
I read through this thread and still don't see an answer to my questions:
1. I understand the Pythagoras math behind the improvement but is there any prove that it will make a better print? Maybe absolutely horizontal, even, symmetrical belt mount tend to resonate? It will be great if someone could describe a case where this upgrade helped, improved the print quality.
2. Why PR didn't change the belt alignment after so many years of the same layout?

What I actually miss is a practical application and prove that the printer will perform better under load/max. speed, last longer ....
Otherwise I see a chance people might trying this upgrade, printing their own parts and make the printer perform even worth then with original parts.

Thanks in advance.

Re: Fine tune your MK3 Y axis

Hello,
I read through this thread and still don't see an answer to my questions:
1. I understand the Pythagoras math behind the improvement but is there any prove that it will make a better print? Maybe absolutely horizontal, even, symmetrical belt mount tend to resonate? It will be great if someone could describe a case where this upgrade helped, improved the print quality.
2. Why PR didn't change the belt alignment after so many years of the same layout?

What I actually miss is a practical application and prove that the printer will perform better under load/max. speed, last longer ....
Otherwise I see a chance people might trying this upgrade, printing their own parts and make the printer perform even worth then with original parts.

Thanks in advance.

Personally, the beefed up motor mount helped me out as Prusa's came in the mail warped.

As far as proving if the rest of it will make a better print or not, how do you expect to prove anything without printing one out and giving it a shot? Why should we put the time, effort, etc, to prove to you vs you doing it and proving it to us? It's three small parts and very little time to swap back and forth. 🙂

I am running with the GT2 16T version of this, and I feel that the bed has better movement. I also like the bed belt mount way better as it doesn't slip like the stock one does under tension.

Re: Fine tune your MK3 Y axis

I can't prove it because my MK3 will be delivered end March/April. Trying to get all the information I can get for the build.

My MK2/MK2S is printing almost every day with all the not perfectly aligned belts. It generates accurate and reliable prints at speeds around 30mm/s and S3D slicer. So I'm wandering if this X/Y belt improvements might bring some disadvantages. The old system is proven to work.
As already mentioned my concern is a resonance you might get on the belts because of the symmetry. This is something you might realize only under certain conditions (speed,model,temp,..). That's why I'm asking for experience who did that upgrade.

josh.w3 post was very helpful and I understand why Brigandier was looking for improvement.

Thanks for sharing.

Re: Fine tune your MK3 Y axis

Anyone have a link on Amazon to which 16T idler to get? What is the bore diameter, 3mm or 5mm? Which idler should I plan on getting? Also, if the idler is 16T, shouldn't the drive pulley also be 16T so that everything lines up properly? Are you also changing the belt?

Sorry for the questions, but this is my first 3D printer, and I am trying to learn as much as I can.

Re: Fine tune your MK3 Y axis

Maybe this one: https://www.amazon.com/gp/product/B075M3NCW3/ref=ox_sc_act_title_4?smid=A2K1WYI5NZ8QSW&psc=1

Re: Fine tune your MK3 Y axis

Can I take a step back and ask for some clarity..

As I read it there, are 3 different choices on the Idler...

16T
20T
Smooth (Stock).

Am I right in thinking that you use the same motor mount for all.. But you have to change the Idler mount and belt holder for each?

Do you use the same idler/holder for the 20T as you do with the stock pulley?

Could someone put together a post that links the various parts and options?

I don't mind doing it, but am a little lost as to what each combination is.

Jon

Re: Fine tune your MK3 Y axis

It would be great to have just one topic named "fine tune your mk3" and a first post kept up to date with all the improvement that can be made by axis and link to the files.

Re: Fine tune your MK3 Y axis

It would be great to have just one topic named "fine tune your mk3" and a first post kept up to date with all the improvement that can be made buy axis and link to the files.

I believe they lock the edit button on the first post after a time. Sucks 🙁

Re: Fine tune your MK3 Y axis

Can anyone confirm if this is the correct 16T idler to get?
https://www.amazon.com/gp/product/B075M3NCW3/ref=ox_sc_act_title_4?smid=A2K1WYI5NZ8QSW&psc=1

Also, if the idler is 16T, shouldn't the drive pulley also be 16T so that everything lines up properly? Are you also changing the belt?

Re: Fine tune your MK3 Y axis

Can anyone confirm if this is the correct 16T idler to get?
https://www.amazon.com/gp/product/B075M3NCW3/ref=ox_sc_act_title_4?smid=A2K1WYI5NZ8QSW&psc=1

Also, if the idler is 16T, shouldn't the drive pulley also be 16T so that everything lines up properly? Are you also changing the belt?

Isn't the pulley already 16T.. Which is why people are upgrading to the 16T idler, to keep the whole thing parallel.

Re: Fine tune your MK3 Y axis

Can anyone confirm if this is the correct 16T idler to get?
https://www.amazon.com/gp/product/B075M3NCW3/ref=ox_sc_act_title_4?smid=A2K1WYI5NZ8QSW&psc=1

Also, if the idler is 16T, shouldn't the drive pulley also be 16T so that everything lines up properly? Are you also changing the belt?

https://www.amazon.com/gp/product/B01H3EY4X4/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1 These are the ones in my Amazon order history that I can confirm are working fine. The ones you linked look the same. You might as well grab some 20Ts while you are at it for that X axis. 🙂

And yes, the pulley on the stepper is already 16T. With this mod you will have a 16T on each end and perfectly parallel belts. The Y carriage belt anchor is also better designed and less prone to slip. Make sure to look at your stepper mount as well, mine was heavily warped and a reprint helped quite a bit.

Re: Fine tune your MK3 Y axis

Here you go!

I just printed the16T belt holder and expected the writing to be on the bottom (GT2 16T), but it doesn't print.. Looking at the 3D view in CURA its there.. But the layer view does not show it...

Its a minor issue, but something that perhaps should be corrected since there are so many varients of these parts now.