Re: Knee for z-axis control?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "industrialhobbies" <admin@i..
.> wrote:

> Eric,
>
> You might want to think about going with a pneumatic cylinder, an
> accumulator, and a regulator instead of gas springs.
>
> It gives the advantage of being adjustable (varying table load) and
> if the accumulator/cylinder ratio is high enough it's fairly

constant

> lift force.
>
> Unlike gas springs which force becomes exponential with compression.
>
> Incase you don't know the math:
> Radius ^2 @Pi (3.14) * PSI = Lift force
>
> On a 4" bore cylinder that works out to:
> 2^2 = 4 *3.14 = 12.56 Square Inches of piston area. To hold up 400
> LBS you would need about 32PSI.
>
> You could make a little chart and mount it to the side of the mill.
>
> 32 PSI empty table
> 38 PSI 1 Vise
> 44 PSI 2 Vise
>
> This way loading on the axis motor would be more or less constant,
> plus you could use a smaller motor.
>
> Check on eBay cylinders are cheap.
>
> Good luck on the knee. You'll love the travel.
>
> Thanks
> Aaron Moss
> www.IndustrialHobbies.com
>

I like this idea alot. Does anyone know how to calculate the size of
the accumulator that would be needed based on the different cylinder
diameters and strokes?

Thanks
David