Hyd. thumbs

[coopers]

What's the difference between direct and progressive linked hydraulic thumbs?

Blake
WA

[badranman]

I'm pretty sure a direct one will move the same distance for every inch the cylinder moves. For example let's say the cylinder moves 1 inch which causes the thumb to move 3 inches. The cylinder moves another inch which causes the thumb to move 3 more inches. Now a progressive one will do just that. The cylinder moves 1 inch and the thumb moves 3 inches. The cylinder moves another inch but this time the thumb moves 5 inches. The cylinder moves another inch which causes the thumb to move 8 inches and so on. Someone else will have to chime in with the benefits of each design and/or correct me if I'm wrong.

[coopers]

Hhhmmm, okay, so for instance....our JD 120C excavators have a thumb made by CWS that will close against the bucket even if the bucket is curled all the way out....but our 200C LC, which also has a thumb by CWS will not close against the bucket if it's curled all the way out. Instead, the thumb stops about 3/4 of the way. Why it does that I don't know, well I do know but why we purchased that make I don't know...our kubota 121-3's do the same thing, they do not go all the way to the bucket if the bucket is curled all the way out....


Blake
WA

[Dwan Hall]

Hhhmmm, okay, so for instance....our JD 120C excavators have a thumb made by CWS that will close against the bucket even if the bucket is curled all the way out....but our 200C LC, which also has a thumb by CWS will not close against the bucket if it's curled all the way out. Instead, the thumb stops about 3/4 of the way. Why it does that I don't know,
Blake
WA

I would think with the one that went all the way out you would loose some of your griping power. My TB070 only goes about 3/4 of the way and sometimes it is a pain when setting rocks because when extending the bucket the thumb stops and I drop the rocks. I have learned to be very carfull. on the other hand it does have good griping power.

[coopers]

Here's what the difference is. Yeah, I don't like the ones that stop 3/4's the way, the direct thumb. I like the progressive linked.


Progressive has a linkage that looks like the bucket linkage allowing more arc travel. This allows the thumb to follow the same arc as the bucket.

The Direct thumb has the cylinder attached directly to the thumb. They typically don't travel all the way.