Sunday, 7 December 2014

Linear Carriages

I have started printing the linear carriages and the first batch have turned out well.   They are designed to have 2 x LM12LUU linear bearings fitted, which are clamped by the means of 4 x M4x16mm cap screws and 2 circlips on  each bearing to stop it moving up and down.  They were printed on my Up Mini at a resolution of 0.2mm, fine quality and 1/4 fill to keep the weight down. I will say though, make sure the part is printed with teh pockets for the balls facing upwards and if facing down, even with smart support the pockets are not radiused correctly.

I  am using GT2.5 open ended belts so the carriages are designed to grip both ends.  I printed and tried a few integrated belt gripper designs before I settled on the one below.  It is made so the belts pass over each other and are secured so the ends pull from the opposite side of the carriage, pulling the print layers together, not apart like it would if each belt was attached from the top and bottom.  This is important especially if the chamber is heated as I don't want any delamination of the part.   This also means I don't need to worry about too much belt tension breaking anything.   A 6mm  long piece  of 1.75mm filament is pressed into the eye where the belts fold over and becasue the teeth mesh together they cannot pull out. I yanked on both belts really hard and there was no movement so I am very happy.

carriage with belt fitted and securing nuts and bolts

close up showing the belt fed into the carriage and the small pieces of filament
locking the end loops

The belt grippers are located dead centre between the linear rods in both the x and y direction so there will be lateral forces on the bearings from the belt pulling the carriage up and down.   This also means that the steppers are mounted off centre to keep the timing belt centered to the carriage.

Like the end effector each carriage has a 10mm diameter N42 magnetic ball JB welded to it.

Complete carriage assemblies fitted

close up of the
 carriage assembly with bearings fitted