On Dec 30, 2023, at 6:11?AM, Paul Fox <pgf@...> wrote:
chris wrote:
I like to make a distinction between the use of ¡®ground¡¯ and DC
return patch. It is simple. ¡°grounds¡± do not carry current. ...
Agreed -- that's an excellent way to think about it, and a good way to
describe it to others.
None of this matters in a simple Lathe. But some day you might
want to do a CNC conversion and add some motors to the hand cranks.
I did this to my HF mini-mill. ...
Have you written that conversion up, or do you have a pointer to
someone else's similar conversion?
On the electrical and computer side, it is just LCNC with three stepper motors, So the LCNC documentation applies.
But on the mechanical side, there is custom-made parts that fit the motors to the HF mini mill. These are VERY specific to the exact mill because screw holes have to line up.
As it turns out converting a mill is not hard. You don¡¯t need to make strong cast iron parts as the motor mount only has to handle the moter¡¯s torque reaction. A 4 Newton meter motor can only push with 4 newton meters of force on the motor mount. 3D-printed plastic is strong and rigid enough to handle that.
But, that style of conversion where you put motors on existing hand wheel makes the CNC machine only as good as the manualy machine because you are keeping the old lead screws and nuts and keeping all their slop and backlash. A better conversion would replace the lead screws with ball screws that have close to zero backlash. I did replace the Z axis system with a ball screw because the Harbor Freight Z system is very poor.
Yes it is written up in the CAD files. Here is a render from CAD. If anyone wants I can post a link to CAD files that could be turned into 3D prints. The X and Y axis are obvious from the picture but the Z axis is a complete replacement. You can see that the ball screw is stationary. It does not rotate. The ball nut spins and there is a big thrust bearing under it that takes the full weight of the machine head.
When I first started, I figured I would do the conversion using plastic parts, then use the mill to make better parts from metal. But the plastic seems to be mostly good enough (just one part has too much flex)
I have a home-made CNC mill
(running LinuxCNC), which is capable of cutting wood, and some
non-melting :-) plastics. It's very satisfying to use, but I'd love
for it to be more capable. Always seemed like converting a "real"
mill would solve a lot of problems.
paul
=----------------------
paul fox, pgf@... (arlington, ma, where it's 42.1 degrees)
