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vladson

X-Y axes straightness

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Hi all! I'm in process of building self-sourced Ultimaker Original and already sourced all the parts needed and built the frame and some of other stuff. And now I encountered issues with rods, which I ordered from Aliexpress. All the X and Y shafts are not straight: they have curve from 1 to 3 mm. As gantry alignment is one of the most important things for good print quality, can anybody recommend anything on rods straightening or is big issue at all (suppose yes).

Thanks in advance!

 

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It is a very big issue!

If your rods / shafts have straightness errors of 1mm or even more, then you can throw them right into the bin (or at the supplier.. ;))

Imho, even +- 0.1mm error is not desirable (but seemingly very hard to achieve).

Not only will you get issues with part dimensions, but you also increase friction ( = wear) in the gantry system if there is uneven movement.

Many people buy 2 or 3 times more shafts than they would need, and then use the best ones they get.

The best supplier for precision shafts (and other stuff like linear bearings, bushings, ball bearings, leadscrews, couplers and so on) that I know is Misumi. Japanese precision shafts rock, period :)

They also chamfer the shafts nicely, and have very good surface quality and hardness.

But they only supply companies, you can't make a customer account as a private person. And of course their premium quality comes with a high price.

If you have the possibility to buy from them via your company, then it's probably the best address there is.

 

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All the X and Y shafts are not straight: they have curve from 1 to 3 mm.

 

The thick rods or the thin rods?

That's pretty bad.

If the error is on the thick rods definitely throw them away. This will indeed cause stress and friction and binding.

On the thin rods it will cause exactly as much error on the part as on the rods. So if the error is on the far left of the X rod then parts will have a bend to them on the far left of the print bed. By the same amount. And there will be no extra friction or binding as long as the bearings slide okay. If the thin rods are overly bent then you cant slide the bearings along the rod.

 

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If the 6mm shafts are bent downwards like an "U", then the printhead will scratch the build plate near the center. If they're bent like an "n", then you will get a bad first layer near the center - maybe even failed prints.

In any case you will get inconsistent results which is bad.

So either way - I wouldn't mount any shafts that are noticeably bent.

 

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Thanks!

The error is on both thin and thick rods. Today I managed to measure actual error with mirror and caliper. It seems that axes have only one point of binding (in the middle). For the thick ones (8mm) the error from the plane is 1 or 1.1 mm. For the thin ones (6mm) it is 0.4 and 0.5 mm. So it is not so enormous but still unacceptable. I'll try to straighten them carefully, maybe it'll work.

 

JonnyBischof are you experimenting with direct X-Y drive? What sizes of thick rods do you use? As I can see They should be apprx 1.5 cm longer, are they?

Thanks again. Trying to find local source of rods with quality control.

 

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It depends on what mounting bracket and flex coupler you want to use. I needed only a 7mm longer shaft, because I'm mounting my coupler very close to the frame. But I noticed that it gets quite hard to mount the motor bracked with such little space, so there should be better solutions around...

 

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Thanks!

The error is on both thin and thick rods. Today I managed to measure actual error with mirror and caliper. It seems that axes have only one point of binding (in the middle). For the thick ones (8mm) the error from the plane is 1 or 1.1 mm. For the thin ones (6mm) it is 0.4 and 0.5 mm. So it is not so enormous but still unacceptable. I'll try to straighten them carefully, maybe it'll work.

 

JonnyBischof are you experimenting with direct X-Y drive? What sizes of thick rods do you use? As I can see They should be apprx 1.5 cm longer, are they?

Thanks again. Trying to find local source of rods with quality control.

 

There is an alternative to new rods: https://www.youmagine.com/designs/bearing-adapter-for-direct-drive-um-original

On the other hand, if your original rods are not really straight, then this is the ideal reason to buy new ones... ;)

 

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Thanks to all!

It turned out, that getting good shafts is indeed big problem: being impatient as I am, I managed to buy a long one 8mm rod from local reseller, but it was also bent a little (less than chinese ones but still tangible). After cutting with Dremel (oh! 2 hours and a ton of dust) and installation, I've been able to get my first print done! It was marvelous! I was very surprised to see my Um printing just after building completion.

Unfortunately, my happiness disappeared pretty soon: I could not help, but noticed, excessive friction in the gantry on the thick 8mm rods. On the one shaft friction is not linear, it is periodic (like sinusoidal alongside with rotation of the shaft), on the other it is quite linear, but it is was so big, that sometimes stepper could'n turn the shaft, which resulted in shift of the printhead location.

So, now I'm here, where I started: need more precise rods (no way to get Misumi rods alas) from local precision shafts factory, and any possibility to get rid of sliding blocks friction. Is it a good idea to add some grease? or should I use reamer to slightly treat my sliding blocks bushings?

 

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Don't use grease on the shafts (the grease from the UM1 kits is only for the leadscrew), but you definitely need to oil the shafts and bushings!

Use some standard universal machine oil.

But you can't do much if the shafts are bent, or even "not-perfectly-round".

 

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