Ballscrew & Linear Rail Kit - Any Good

[A_Camera]

Thanks for the advice on the bearings!

I was not sure if they even came with bearings?

I will take an image if there is any kind of stamp on them.

Presume I just take internal and external measurements and order the replacements

They always come with bearings, one double bearing in the BK and one single in the BF part.

Once you remove the four screws holding the dust cover of the BK12 you will see two bearings. I think the BF12 has a similar (but only one) bearing, but that is the floating end, so it isn't really critical. They are simple 6001Z 28x12x8 bearings.





These are cheap, but never the less can be very good. 6001Z is one of the most common type, so they are cheap, even if you'd replace them with an SKF or similar. https://www.skf.com/sg/products/roll...oductid-6001-Z

Of course, if you replace them, you might as well replace them with the best ...or not. Replacing 8 BK bearings if you have four screws can cost between 250 - 400 USD (maybe even more), so you must take it as a fairly large cost for an improvement of a hobby machine. There is no need for rushing, it's easy to do even later on, once you have everything up and running.

Never the less, I would not recommend you to start with replacing them, since there is really no reason, unless you really feel some serious issue, or play. I know I can't feel any, so even if some people laugh at them, let them laugh. Replacing is easy, but you need a proper tool, because these are really tight sitting in their seats. Don't use a hammer to get them out because that might damage the seating. There are tools to remove bearings, get one if you not already have one. Anyway, I don't think you will need to replace them unless you really feel there is something wrong with them. When it comes to wear and tear, I don't think you'll ever wear out these cheap bearings. It's a difference if you'd build a professional placing machine with high speed servos running H24/7, but as a hobby machine with slow rotating ball screws you will never come near the performance limit. In fact, inlines and roller skate bearings get a lot more beating than these, after all, these always rotate on smooth surface and at comparably very low speed.

[Clive S]

They are simple 6001Z 28x12x8 bearings.

But they should be AC bearings back to back to get the preload. This is why I asked him to check !

[A_Camera]

But they should be AC bearings back to back to get the preload. This is why I asked him to check !

It should not be anything else than what they have specified. If you didn't ask and is not stated then that's it, be happy if the 6001Z is of good quality.

[JAZZCNC]

Never the less, I would not recommend you to start with replacing them, since there is really no reason, unless you really feel some serious issue, or play. I know I can't feel any, so even if some people laugh at them, let them laugh.

It's not about laughing at people it's about trying to let people know the difference between building the right vs the wrong way. Everything about these is Wrong and pointless for a CNC machine.
They are deliberately made and sold this way to keep the price low to make the kits look cheap with NO regard to whether fit for purpose or not.!

Those bearings in the BK mount are completely wrong for the application as they are not designed for lateral loads, they should have Angular contact bearings, not deep groove bearings like 6001ZZ.
They will wear excessively and they will introduce backlash, even if fit with SKF bearings because they are not designed to operate with lateral loads. Also, to get preload on the bearings and reduce backlash puts extra load on the bearings causing friction which robs power from the motors, again causing extra unnecessary stress on other components like drives, PSU, and lowering performance.

I don't understand why anyone would buy components that are not fit for the purpose, then spend more money on them to put or right and even worse spend money on them replacing bearings with the same inappropriate bearings. Especially when buying correctly the first time isn't that much more expensive and far less hassle.