Alan's Excavator Thumb

Latest project is a thumb for the 307 Cat excavator I will be running this summer. Manufactured ones cost $1300 (plus install time) for that machine, I figure I'll bring this one in for about $800 installed. This is the mounting plate that will be welded on the dipper and the thumb and brace will hook to.


Gravity Works
I had the thumb on sawhorses while I was cleaning it up. Tried the pivot pin and found there was a little welding distortion that made the pin a hammer fit. In the process of getting it back out it slipped off the horses. If anybody here has ever watched an animated movie called "Fern Gully" they might remember bat knocking himself silly and falling from a tree while Robin Williams voice said "Gravity works!" Nice to know it was still working this morning, that's a strong 150 lbs resting comfortably on the ground while I waited for reinforcements to pick it back up.

Here's the thumb after my son showed he's stronger than I am now. HE put it back on the horses alone. No way I was going to do that. The tines are 3/4 x 5 flat stock. Most of the welding was with .030 flux cored wire for a root pass and then 7018 for additional passes.

I put the thumb on today, got pictures of it all rigged out, and stowed, along with the stowage provisions for the brace arm. And then the computer wiped out virtually everything on the camera memory card. I have two left from today, this one showing the thumb in the stowed position under the dipper, and one more.

Sounds almost like "Wain Roy"
The coupler on this machine is a Wain Roy. They make a lot of digging attachments. I just had to get in my own ego trip on this one.

I see the computer damn near ate this one too, judging from the bottom third of the picture. (Picture cropped to remove damaged data).

Everything is mild steel. The forks are the 3/4 x 5 that I mentioned, all the gussets are either 1/2 or 3/8 plate. The spine that the bucket (stowed) or brace (in use) hook to is 3/4 x 3. The main pin is 1 15/16" cold rolled and it fits in 2" ID x .500 wall bushing stock. There's another piece of the bushing stock tying the forks together where the brace attaches. The bushing stock is pricey but I needed heavy wall there and it was easier than trying to find Sch. 80 or Sch 160 pipe in a size that would work. The brace is 3 x 3 x 3/8" square tube and the pins that hold it are 1 1/4" cold rolled. When the thumb is stowed the brace mounts on pins I put on the blade arms. I figured that if it wasn't kept on the machine it would never be around when I needed it.

I had a good picture that showed the thumb in working position and the bucket I rebuilt last month. It's a 46" cleanup bucket that was pretty well beat up. I put on a new, and much heavier than stock, (3/4 x 6") cutting edge, replaced about half the bucket bottom and both side plates. Most of the cleanup buckets don't wrap the edge around the corners of the bucket but I got this one overly long (60") and with some discreet heat and a bit of grunt work I wrapped the edge around the corners and up he sides 7" or so. I also applied a good crosshatch of hard facing to the sides. Once I see just where the wear will occur I'll do more hard facing if needed. I added five strips of 3/8 x 3 T1 wear bar on the back of the bucket as well, the old bottom was about worn through from the heel getting dragged through the dirt.

At some point I'll retake pictures of the thumb and some of the bucket as well.

Putting It To Use
I got to use the thumb last week. Clearing several lots over the next couple months, which is the project it was originally built for. The area is densely forested with Hemlock and a collection of assorted hardwoods and junk woods. One Poplar (aka Cottonwood) was on the order of 80' tall and 20" on the stump. That one was too big to carry. The thumb is coming in handy for such chores as stacking firewood, like here.

Or handling brush; (This one is about a 60 footer and 16" on the stump, it came along in one piece) Incidentally, until today I have been finding frost around the bases of the trees. There's enough old leaves on the forest floor to insulate it, combined with the lack of sunlight getting through the dense canopy it takes a while for the effects of a cold winter to go away. Last Thursday I pulled one slab of frost that was still hard enough that I threw it in a low spot and set the machine on top of it while I was pushing over a tree. The frost was still in one piece after quite a bit of bucking and thrashing. The machine is only 15,000 lb class and it's right at its' limit on this job.

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