Saturday, 28 June 2014

Huxley #710 Coupling Service...

One of the issues seen on Huxley #710 early on was Z axis coupling failure.

Alternate coupling fitted to Huxley #710
Any failure on a 3D printer tend to produce a mess but the nature of coupling failure experienced tended to be be when prints had been running a while and the Z axis has advanced. Probably as the stress on the coupling increases as the axis moves away from the bed and the heat from the table and motor tend to warm up the plastic parts. This of course is really annoying as there would be quite a bit of plastic wasted by the time failure occurred.

Failure seemed to happen either due to cracks in the printed coupling or movement of the clear plastic tube. Additionally fitting the coupling was tricky as the thread engagement on the design is difficult to achieve, particularly when on the last screw. The access is limited so this typically meant Huxley #710 had to be disconnected and moved to allow access to both sides of the printer. Then of course a bed leveling operation is implicit with coupling failure. Being prior to the glass bed and discovering that Huxley #710's Aluminium table is distorted so can not be levelled. This was a particularly trick task.

RepRap Pro produced an alternate coupling
which can be seen below with some pictures taken during fitting of the coupling.

Huxley #710 Z Axis Original Coupling Installation
Fitting of the new coupling will require a Z axis alignment validation. As its likely the bridge carrying the X axis will move during fitting. In fact it did and this was one of the reasons I put off changing the couplings out. But having been reminded of the issue today and having finished a number of prints on the current project.  I elected to make the change.

RepRap Pro Alternate Z Axis Coupling

Huxley #710 Original Z Axis Coupling Removed

Adjusted for the new coupling - Wish there was a little more tube
Fitting required a clean out of the 3mm holes, this is usual with RepRap Pro designs as they prefer to clean out with a drill. The nut should be pushed home into the bracket prior to placing the coupling on the shaft as the thread will not be long enough to engage when the coupling is placed over the clear plastic tube on the shaft. Fitting and sliding the clamp over the tube required the clamp was spread to clear the tube. The clamp was then carefully aligned and clearance checked. It does clear nicely!

Finally the print head height was checked and adjusted by rotating the motor to bring the X axis back into parallel to the table.

Huxley #710 with updated Z Axis coupling fitted

On the left in the picture you can see some nut covers I printed very early on to protect from the sharp edges on the ends of the threaded bar used to hold Huxley #710 together. I did this even though I spent considerable time dressing cut ends during the build. It finishes the build a little more cleanly and offers some protection from scratching.