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Mill Z Axis gas lift

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picclock:
VM32B mill Z axis lift for future CNC conversion. I am not sure if this will pan out but the idea is to use two pneumatic air cylinders either side of the column with hangers attaching to the Z Axis These will extend around 450mm. They will be connected to a pressurised vessel, 3-400mm of 6" steel pipe, which will be pumped up such as to give a minimal load for the Z axis ballscrew which I will be fitting. Will probably use 20 or 25 mm cylinders with a working pressure of 80 or 50 psi.

The base of the cylinders will be connected to a plate secured to the base of the mill. Bearings at all three ends should keep everything sweet, and lifting from both sides keep it true.

I figure that if I can reduce the apparent weight to about 10lbs this will minimise wear on the ballscrew and allow fast(ish) movements of the z axis. Also possible to overdrive such that the head will 'fall' upward but can see no benefit in this.

Any ideas or thoughts much appreciated.

Best Regards

picclock

philf:
picclock,

Why the pressurised vessel?

I used pneumatic cylinders to counterbalance safety guards on various bits of equipment but only used a relieving pressure regulator. I can't see the point of a pressure vessel. (Or are you thinking it will stay at pressure without running a compressor?)

Cheers.

Phil.

picclock:
Hi PhilF

Pressure vessel is to maintain constant force from cylinders regardless of position.  Change of force over extension distance is ratio of displaced volume to total gas volume ~ 2.5% min to max extension.

Once pressurised only cylinder seal leaks need to be compensated for - probably top up pressure every3-6 months depending on how good the seals are.

Best Regards

picclock

philf:
OK - I understand your plan now relying on minimal leakage.

Having now seen your drawing what I don't understand is the linkage between the end of the cylinder rod and the vertical slide! Unless I'm missing something obvious the link will always end up in line with the cylinder rod if all three points are supported by bearings allowing free rotation.

Phil.

picclock:
Hi Philf

The linkage is because the shortest height of the cylinder is larger than the attachment point distance to base. The overall length of the cylinder without extension is about 4" greater than the top of the z axis column slide at its lowest position. This is the part I have some concerns about as I don't want any bending stresses on the cylinder.

Best Regards

picclock

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