Exterior Bearing mounts.



Once the frame has been constructed, you can then build the exterior rails that simultaneously support the moving ‘x’ shaped X/Y stage and also rotate to drive the spectraline that moves the x/y stage. This very elegant use of the linear rails is the principal innovation of the Ultimaker that makes it stand out from other gantry based Cartesian bots.
Several criteria need to be considered when this approach is used:
  • The rails need to be extremely straight; the run-out tolerance of the rails needs to be in the region of 80microns per metre or lower- the 10mm shafts that I purchased were not sufficiently straight and it took 2 further replacements before I got some that were straight enough.
  • The XY ends that move up and down the shafts have to use bushings rather than ball bearing based linear motion bearings (eg LM10UU). Linear bearings generally are not designed to cope with rotational movement of the shaft they run on. For the Ingentis I am using press fit Bronze bushings from SDP-SI. An alternative would be the printed PLA bushings that are used on the original Tantillus design. http://www.tantillus.org/Build_3.html#bushings
Bronze Bushings from SDP-SI
As the Ingentis is so much bigger that the Tantillus, I have opted to use 10mm linear shafts as opposed to 8mm on the (metric) Tantillus.  I have also deviated from the T-Slot Tantillus design that uses a single printed bracket on each corner to hold the t-slot together and simultaneously support the bearings that support the outer shafts at each corner. 

Original T-Slot Tantillus Corner Bracket
My alternate design uses separate bearing holders that require much less material to print with, I also found the T-Slot Tantillus brackets were very hard to print with ABS without warping. It is still possible to utilise the original brackets if you wish – the bearing mounts will accommodate for the 6900ZZ (10mm  shaft) bearings as they are the same OD as the original 608ZZ bearings used in the Tantillus. 

Anyway. To build the external rails (using the Ingentis Bearing mounts) you will require the following:
Start with the upper Mounts, all four of these are the same part. (10mm Shaft Bearing Mount Upper V2)
Insert a 6900ZZ bearing into the appropriate aperture in the bearing mount and secure the mounts in the upper corners of the front and back sides of the frame. The mounts should be oriented so they are attached to the vertical parts of the frame with the bearing facing outwards. The diagram below should be used as a guide. The mounts should butt up against the underside of the upper horizontal t-slot.
Note the sides have the additional horizontal extrusion.
Next, we move on to the lower mounts. These are slightly different from the upper mounts as (for some fairly practical reasons) these mounts have a few mm shaved of there bottom side (when orientated as show in the above diagram) - This is a fudge the horizontal t-slot (that supports the Z stage) to fit in place while not preventing the motor/shaft herringbone gears (covered later) from meshing correctly - it's an inelegant fix for a problem I discovered during prototyping but I've avoided a re-design at this stage.

So, you need to print:
 2 x 10mm Shaft Bearing Mount Lower A V1
and 
2 x 10mm Shaft Bearing Mount Lower B V1

These are then installed in the same way as the upper mounts. Please take care to ensure the bearing mount has the 'trimmed' edge facing downwards. The bearing mounts have a small downwards facing arrow on their outer face you can use as a guide.
The mounts need to be positioned so their upper side is 20mm from the base of the horizontal T-Slot above them. Use a piece of 20mm-slot as a shim to space them correctly. 




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