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Mill Z Axis gas lift

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philf:
In which case why not make the linkage fixed solid to your z-axis and offset so that the cylinder is always parallel with the slide?

picclock:
Hi Philf
That was my first thought, just a hanger off of the z axis head plate. But I wasn't sure how the turning moment would affect the head movement as it is applying a clockwise moment exacerbating the large turning moment caused by the head. It may be that I can align the base of the cylinder close enough that the effect will be of no consequence. Using the linkage the force will exert a slight counterclockwise moment.

In many ways the over the column with a pulley trick is superior as the head could be supported at its centre of mass. The snag with that is that it makes it impossible to rotate the mill head, consequently the z axis head plate is the only place to attach to.

As an alternative I suppose it would be possible to use a single cylinder with a pulley and a steel cable over the top of the column. The only reason for using a cylinder instead of weights is to reduce the  acceleration mass for the Z axis.   

I have not yet received the mill as I failed to mention I needed R8  :palm:, consequently it will take another couple of weeks. The Z axis will be the first thing I alter. As std the machine has a gap of 150mm at the lowest head position to the table, which is too large for stuff mounted directly to the table. I will increase the size of the column cut out to give an extra 100 mm of z axis travel, and that combined with a ballscrew and stepper will give me easy movement of the axis. The next thing which I will do is motorise the X and Y, which I will probably do both together. It seems to take about 150 turns end to end so I think that will get old very early on  :loco:  - battery powered drill to the rescue I hope.

Best Regards

picclock

picclock:
Having thought about it a bit more I think the following ticks all of the boxes. The bending forces on the column are minimised and there is little additional mass to accelerate. A single 32mm cylinder should do the job. It looks a bit crude but the functionality should be excellent.

Best Regards

picclock

philf:
Picclock,

Looks better but...... the Z-axis on my CNC (which is based on an Alexander engraving machine) lifts the knee and X-Y table via a 2505 ball screw and I don't have anything to take any weight off. Are you sure you'll need to do anything? Much heavier machines (e.g Bridgeport size) lift the knee and table without cylinders, counterbalances or gas struts. The other thing to consider is that, unless you spend a fortune on zero backlash ball screws, balancing the weight of the head will mean that you may see more problems with a counterbalance than without. Just my opinion - I'm happy to be proved wrong.

Phil.

Brass_Machine:
Hi Picclock...

You second drawing is similar to a design I saw that I wanted to emulate for my mill. He had hid his inside the column.

I will see if I can find the link.

Eric

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