On Tue, Jun 23, 2020 at 6:27 PM Jon Elson <el...@pico-systems.com> wrote:

>
> That looks a bit like my X-2 hack (although mine isn't a
> real X-2, it is the same machine.)
> See http://pico-systems.com/minimill.html   for some photos.
>
> I found one big problem was the Y axis handle assembly did
> not have a ball bearing, but just a bronze sleeve and the
> handle jam nuts would slowly tighten up until the axis bound
> up.  The X has a pair of ball bearings with the handle nuts
> preloading them.  So, I cut the Y axis handle bracket to
> work the same way.
> You can just barely see it in one of the pictures.
>

I looked at the photos, can you tell me anything about how the machine
performed.  If you milled a circle how off-round has it?

Yes, the Mini Mill does not have a bearing in the Y axis.   I installed a
pair of thrust bearing that are held in place by the drive pulley and the
nut on the hand wheel.    It is really odd that Sieg did not put a bearing
on the Y axis when they used on X.  I wanted to keep this build VERY simple
so I made a plastic plate that screws to an existing hole on the mill and
then there is a pocket where the two bearings are press-fit into the
plastic.    I did not want to cut any metal as that would go against my
"simple as possible" goal.  I wanted this to be do-able with only hand
tools.   The goals is to say "look what can be done with a 3D printer
and a screw
driver."

I looked at your photos.  VERY similar design except I bought much larger X
and Y motors than you did so there was no need to gear them down. I have
torque to spare.  They run 1:1 for X and Y.      You wrote that you
found the smallest ball screw you could for the  Z axis.   I took the other
approach and used the largest one I could physically fit in the space.
Mine is a 16 mm diameter.      The difference is that your design spins the
screw, my design spins the nut.

I had planned to use aluminum like you did, then thought....  A 4 Newton
Meter motor can produce no more than 4 Newton meters of rection torque even
if it stalls.   Plastic can handle a load like that.   All the cutting
force is taken by cast iron dovetails

-- 

Chris Albertson
Redondo Beach, California

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