I'm using my Cat 325B clear cedar in central Texas but would like to have my thumb rotate further so I can grab cedar closer to the cab. I feel the lifting (ripping) capacity is best when the dipper is more or less straight up and down but without my thumb closing far enough, I can't get a good bite close in. When I extend the boom to get a solid bite, I'm lifting up the rear on the moderate to bigger brush. I assume the easiest is moving/adding the thumb cylinder bracket down the dipper a bit but the tradeoff is the thumb won't move out of the way as much when stowed. And it would require a good welder to come out. I thought about extending the ram or even trying to add something between the cylinder mounting point and the thumb but nothing is obvious yet. Trying to find something simple I can fab up myself and take to the machine. Any ideas on the best way to extend the range on my thumb?
The best way is not cheap or easy, but effective. On a machine that big, you really need a progressive link. I would bite the bullet and either fab one up yourself or start the search for one. If you have not had one yet, they are really like having a hand. I can reach in tight until the bucket is flat enough to be no longer usable, and reach out away from me till it is completely horizontal without dropping something. When the pressures are right, it is a wonderful thing. https://www.machinerytrader.com/lis...chment/for-sale/200060007/cws-progessive-link
Longer hydraulic cylinder may work .
Yes, What skyking said, You are looking for a progressive link thumb. It will basically mirror your bucket linkage. You could definitely fab one up if you had a good design to copy. But might be less of a headache to buy. Good luck!
Progressive would be the cats meow, but on the cheep perhaps replacing the cylinder with a trunnion mounted cylinder or a 2 stage cylinder?? This way the distance stays the same but you could use a longer cylinder.
I like all the input! Yes, a progressive link would be great. I didn't realize that's what they're called but it's obvious they work great on the bucket where its curling has significant range of motion. A 2-stage cylinder might also be the ticket but I need to figure out how far it would need to go before it binds or loses it's force as it goes past the bottom. Seems like the angle of force (between the cylinder ram and thumb) will be very shallow as it keeps swinging which means it's losing a lot of it's force. The trunnion is good idea but I don't know if I have the pivot room for clearance. I thought about a longer cylinder but again, I haven't done the hard measurements to figure it out yet. I didn't state it earlier but the thumb is at full extension in my pics. Now you have me thinking about adding a progressive link. I can easily get a local fab shop to cut out the dogbones and H-link with their CNC plasma table (I have all the lathes, mills, welding to finish) but I'll need to design them first. I'm looking at my dipper set up and scratching my head trying to figure a layout. Even if I went the route of buying one like suggested above, I still have to make sure it would fit and function. Studying how a progressive link moves (see attached pic), it looks like the magic happens when the distance between points A and D (AD) is shorter than BC, causing the 'curling' action when the cylinder is extended. AB, BC, and CD distances are fairly equal... it's the AD that must be shorter for it to curl under. When I try to imagine a similar set up on the thumb cylinder side where E is ram pivot point compared to the bucket cylinder side, it looks like my thumb cylinder has to move up a bunch to add a progressive link. Hmmm. You definitely have me scratching my head on this one....
Yes, unfortunately it does appear the existing thumb ram mount would need to move up to make everything normal. Or, you could make a "custom" one, you would have to sacrifice either the thumb returning all the way up, or it would not curl all the way down and around like a normal one would. Like most things a simple idea quickly becomes a large job
you need to tape measure and get the dimensions of a good existing setup. It will take a while and hopefully you can get to operate the machine through the ranges of motion to see how it pencils out. I swear, if you had your own lowboy, it would almost be worth the rental costs to bring in a machine
If those pics are of your thumb all the way extended you do not necessarily need a progressive link thumb it’s just that thumb is spec’d/set up wrong. Either wrong cylinder or wrong thumb kit on the machine. That set up will work just fine and that thumb will give you all you need but the cylinder needs to be adjusted up to the proper length. Trying to make that set up work will be give/take for any adjustments and still not function or store properly.
Go find a machine with a working thumb linkage and steal the design. It does take a longer thumb cylinder to work properly and the linkage dimensions have to be right or they may crunch up or fold over. Unfortunately what you have can only be adjusted to go so far open and store flat. If you move the thumb cylinder base forward, the thumb will not store flat and will get in the way of digging. I have seen a thumb installed with its own mounting boss and not on the main bucket pin. The problem with those was that the bucket would hit the thumb boss when it was fully closed.
That's not the right thumb for a quick coupling and it won't close much farther than it is in the picture. It will hit the top of the bucket . Bob
Agreed it's not the optimal spec or set up but I'm making do with it so far. From the pics Lachua posted (thank you!), it seems pretty straight forward when using the existing bucket boss and the cylinder height is already correct. My calibrated eyeball is saying to mimic the bucket setup (or just slightly smaller). I think I have 3 options worth pursuing: 1) Adding a progressive link by moving the existing cylinder up the dipper and fabbing up the dogbones, H-link, etc. I'm not opposed to welding on the dipper but know this requires an expert to not screw it up. I'd have to look at my current set up and see if this is simple. 2) Adding a progressive link by replacing my current cylinder with a two-stage cylinder and fabbing up a few parts. This will effectively "move" the cylinder up but also keep the extension correct. 3) Fabbing up a modified thumb mounting riser that puts 6-10" inches more of effective stroke. I could also move the pivot point as needed to keep ram from getting too close to camming over for full extension. If I do it right, the riser would be a pin-on so I could use it/remove it as needed. The stow position isn't too much of an issues as I really just clear cedar. I have plans down the road for digging out a stock tank so something removable would be good. It's not about trying to find the lowest cost but more about what's feasible without going overboard. 1) is the ultimate solution, 2) is a tradeoff and 3)is a ranch version. All good input and much appreciated.
I think a cylinder with a longer stroke would help. But unless the rod eye mount is relocated further down the thumb the cylinder could be bent when it is fully extended. I am just getting parts together to convert my fixed thumb to hydraulically operated. I am in the midst of figuring out how far I want the thumb to extend from fully retracted and then to how far I want the open bucket position. Mine is on a T/L/B.
I've done a few progressive setups years ago, for what it's worth, here's a couple thoughts using your picture: 1) The length from A to B for your thumb links needs to be such that the cylinder has some clearance away from the stick when fully retracted and fully extended, shoot for about equal. 2) The current D to E is probably fine. 3) The thumb link B to C can be measured once you get the rest figured out, just make it short enough that the thumb will lay all the way back to where the stops land on the stick.
I'd be curious to see what it looks like with the cylinder fully retracted, maybe it was placed a bit too high up on the stick and should be moved down. Progressive link is nice, but $$$. I can't really say my thumb gets in the way much when not in use, definitely not enough to want a progressive link. Really depends how much machine is used, and it's value. A $40k machine isn't worth a super expensive thumb like a nearly new $150k machine is.
Thanks Lantraxco- good advice. I'll definitely need to measure and figure it out before I start cutting/welding. Suladas- The travel stops on the thumb hit the dipper when the thumb is fully retracted. When retracted, I don't remember any additional travel available from the cylinder but I can double check. Look at the pic to see where the ram wipers stop - not much left for additional retraction.
The thumb cylinder should 1/4" of travel remaining when the thumb is fully retracted and it is against the stop on the dipper. That would prevent the cylinder piston from bottoming out whenever it is fully retracted. IMHO !
Here is that thumb with another 22 degrees of rotation. Looks like it's setup fine for that bucket/coupler.
A progressive link thumb is designed to extend the thumb to the same line as the stick when fully extended. The direct connect thumbs usually gets you somewhere just over 90 degrees to the stick.
My direct connect weld on thumb has 134 degrees of rotation. I think that's pretty normal for most non progressive setups. An additional 22 degrees of rotation wouldn't be possible without a linkage but just wanted to show that the thumb doesn't look like it'd be into the coupler or bucket. I figured that the OP's thumb is only getting about 115 degrees of rotation from the stick.
I think you did a good job of that. You showed the limitations of the direct connect thumb through an illustration that makes perfect sense.
Agreed and appreciate the nice drawing. Definitely allows a visual understanding of the limitations. I did find this setup when surfing the web a bit which is a unique type of progressive linkage. I show it because the thumb cylinder is lower than the bucket curl cylinder-- somewhat more similar to my setup. Also notice the thumb does not flush up against the stick with stowed- it's definitely taking up some space when not in use. The pic is a screen shot at 11 seconds into this video
whoops- just realized the thumbs in Lachou's pics also have a similar setup with the cylinder pin being slightly inward of the dogbone/h-bracket pin. cool video seeing the linkage in motion at least...
Interesting, they use a longer link arm to get more throw out of the cylinder stroke. I remember fighting the short stick issue where the butt end of the thumb cylinder would hit the boom if you mounted it too far back. Cool.
I found a Cat brochure (attached) that shows the range of motion for the Cat Pro (direct mount) and Cat Pro Plus (progressive linkage) thumbs on page 3. My guess is the only difference between Cat Pro and Cat Pro Plus system is the Plus comes with the progressive linkages and the actual thumb is the same. Is someone has access to those assembly/part numbers and can verify, it would help. As for my plan forward, I'm thinking it would be straight forward to use my existing setup and just fab up a similar progressive linkage (I'm afraid to ask Cat what the cost is for just the linkage...if I even knew what part numbers to ask for). Looking page 4 of the brochure, I should be able approximate the lengths and have them cut with a simple plasma table. I think I'll need 1) a new pin for point A 2) two dogbones for ** 3) H-link for EF 4) two small pins for F and G. Also, if anyone has the Cat installation instructions/specs for a Cat Pro Plus thumb for a 325B, I can see if my current cylinder setup fits within the window. My eyeball is saying yes by looking at the setups in the brochure but any actual documentation would help. Thoughts?
[QUOTE="Tinkerer, post: 945219, I am just getting parts together to convert my fixed thumb to hydraulically operated. I am in the midst of figuring out how far I want the thumb to extend from fully retracted and then to how far I want the open bucket position. Mine is on a T/L/B.[/QUOTE] Tinker, Have you got a thread going on your project? I think about it every time I use mine, but how to do it is a stumper. Think I'd have to cut the mount(s) off and start over. It's one of those Chinee cheap ones that have been discussed here before. Joe H
It is here, Joe ! HeavyEquipmentForums
Great, thanks. I missed that somehow. Joe H Damn, only the second picture in and I'm jealous already of the brand new tire. Need a pair of 16.9x28 & wallet sez no.