Re: Advice on small mill table conversion

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<dave_mucha@...> wrote:

>
> You need to put thrust washers on the handles to make sure the screw
> does not move axially. that is the easy part with your design.
>
> The nuts can be made pretty easily, I think. you did not show the
> drawing, but it might be possible to add a second nut, and bolt it to
> the first with some tiny screws on the perimiter.
>
> The more you tighten these, the less backlash and the more friction.

It has thrust washers (i.e. plain washers) but I was thinking thrust
bearings to prevent the axial movement. I am a little limited in terms
of space, anything of greater diameter than that collar will catch on
the bed, however I think I would probably be OK, there would still
need to be something to prevent radial movement though, there is
nothing at the moment, a needle roller would be compact enough or a
flanged radial mounted in the end of the extrusion.

One thing I am a little bothered about is the fact that since the
castings already stick out about 3" from the bed once I add space for
a coupling or a motor Everything sticks out a long way, this is a
niggle really but I prefer to make it more compact if I can. Perhaps
I could use a belt drive putting the motor above the casting. I also
wondered about fixing the leadscrew rigidly to the stepper motor using
the motor as the thrust bearing, these motors seem to have massive
bearings but I worry about long term reliability. It would allow a
compact direct drive installation though and the motors are so cheap.

In terms of the nuts, I'm trying to find a ACME tap of the right size.
I know people have made these but I don't have any acme rod either,
I'll keep searching. Perhaps if I use the self forming method
described in another post I can make the starting threads using just a
normal metric tap before "cold forming" the rest of the threads. A
long delrin nut had been my first thought, I don't think there is
quite enough meat in the current nut to make it antibacklash but I
will look into it, I might be able to make a fine cut and add screws
to allow it to sprring.

thanks all

Graham