Re: [CAD_CAM_EDM_DRO] Re: Knee for z-axis control?

Guys,

All of these ideas may be viable but they seem to be overly complicating
things... I think KISS really applies here. I've had ove two years of
trouble free operation of my servo based system and all I use are two
$20 175lb gas spring from McMaster Carr one on each side of the knee.
I've had two 70lb kurt vices on the table and even with power off, the
knee has not moved! Mind you I would never work under the knee without
sliding a wooden block to 100% support the dead weight. Just do it...
Happy cnc'ing the knee.

Cheers, Peter



R Rogers wrote:

>Another option for the assist of a knee. Mount a single acting pneumatic cylinder inside the knee. Then use a two direction spool valve mounted in unison with the belt of the drive in this manner: Have a small toothed sheave of the same type as used for the drive axis mounted inside the belt enclosure. on the shaft of this idler sheave mount a cam that can rotate 180 degrees only. The cam would have to be able to slip on the shaft by way of a slip clutch which could be as simple as a belleville washer. The cam would then rotate back and forth and operate the spool valve. The cylinder sizing can be calculated by the area of the piston times the pressure in PSI to calculate the force desired. Have a regulator in circuit to adjust.
>
>It would operate like this: when the axis belt moves for a -Z transit this would rotate the cam and open the valve injecting air into the cylinder for assist. The opposite would occur for +Z releasing the air and allowing the table to descend. Believe me, the table needs no help coming down.
>
>Ron
>
>volitan712003 <volitan@...> wrote:
>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "industrialhobbies" .> 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
>
>
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