Re: Linear motion design Q

Ok, I've placed some pictures in the Photos section, in the
album "Kevin's CNC router".
The shots were taken with flash only, so I had to fiddle with
brightness and contrast to make things show better.

Each bearing is held in place by a cap screw and washers, into a
threaded hole in the carriage body, and with a regular nut added as a
locknut.
To adjust the bearing tension (i.e. to adjust for rail width and
errors in bearing placement), a pattern of slots is cut in the
carriage body plates, and a 8-32 setscrew set into the plate edge
pushes the bearings towards each other a bit.
There are a couple of design flaws here:

As this thread already mentioned, the CRS rails are not in general
accurately straight, but they can be machined to the desired
tolerance and/or replaced with more stable materials, and the bearing
tension adjusted accordingly.

The bearing tension adjustment needs a stronger locking mechanism; as
it stands, all the machining forces in one direction are absorbed by
the poor little 8-32 screw pressing against 6061 T6 aluminum. It is
certain to pound itself a little indentation and thus loosen up.

There is one bearing too many; the mechanism will jam or deform if
the front and back rails are skewed.

I have endcaps made to fit inside the ends of the box beam, but they
have not been installed yet. If possible I intend to place the Y
drive motor *inside* the beam, with the shaft sticking out the end
and pulleys and a belt to drive a leadscrew mounted on the underside.

Hope the pictures make it clear.
-Kevin

--- In CAD_CAM_EDM_DRO@y..., "hotaluminum" <zbadone@b...> wrote:
> Hi,
>
> I'm trying to picture in my mind how the bearing and CRS are mounted
> and used in ref to each other. Got any pictures or a diagram?
> That was my next problem, the Y-Axis. I believe I have my X-Axis
> settled as to form and function.