Why linear broze bushings in XY slide blocks?

[tommyph1208 55]

So... I have disassembled my entire UM1 with the intention of giving it a neat Glossy White paintjob (for that all-important WAF) as well as make an E3D hotend, and possibly a heated bed, upgrade...

I did not assemble the printer myself, and so the exact parts and way they are all assembled has not become fully apparent to me before now...

During disassemble one thing that puzzled me was why exactly Ultimaker has opted for the linear bronze bushings in the XY slide blocks, rather than (linear)ball bearings as everywhere else on the printer? Seems to me that ball bearings ought to work slightly better/provide slightly less friction?

 

[xeno 108]

I have also wondered about that.

I thought that the bronze bushing has less play then the ball bearings (on my UM1)

 

[tommyph1208 55]

I have also wondered about that.

I thought that the bronze bushing has less play then the ball bearings (on my UM1)

 

That might be it... I dont know... Hoping that someone with intense knowledge of the design decisions that went into the UM1, will pick up on this thread.

Seems counter intuitive though that the extrusion head itself has ball bearings, while the XY slide blocks that its attached to has the bronze bushings? In the end they move in exactly the same way right?

 

[foehnsturm 969]

Nope ;-) the four rods are rotating as well, while the other two don't. Linear ball bearings are designed for linear movements only.

[tommyph1208 55]

Alright... See now that makes sense... So its the fast rotation of the long X and Y axis that make the bronze bushings more suitable than ball bearings... Thank you for clearing that up