fabing a backhoe thumb

[toolaholic]

Hoe is around 16000 lbs. picked up AR 400 3/4" steel for tangs. will need longer 1 3/4" pins for bucket. what stock? cold rolled sufficent? will post all costs and pix. will take a little time . T B L is 1990 M F 50HX with extend a hoe. will be similar to smart thumb. non hydraulic. extending hoe operates thumb .
All suggestions welcome Thank's Tool

 

[Renze]

I think i get your idea... it looks like you're getting a nice low-cost thumb, and the idea of adjusting the stand of the tumb by the stick extension is nice too... this way you can allways have the same ground angle of attack, closeby the TLB as well as further away. Normally the thumb would be allmost horizontal operating within the first yard behind the backhoe, and vertical on maximum reach because the angle of the boom stick also changes.

now we'll keep waiting for the pictures....

 

[MadReferee]

How-to-Plans.com offers plans to build a thumb like what you are wanting to do. I am sure their plans have the info needed to get/make the right type pins. Personally, I would not use CRS as it's soft. A good tool steel would be much better.

 

[Renze]

Most machine shops have C45 medium carbon, surface ground shaft steel in stock. That's the best middle-of-the-road steel to use around the farm, as its high enough carbon to be wear resistant, and low enough to prevent any mistakes when welding it.
Usually machine shops also have some thick walled tubing in stock, of which you can have lathed and smooth bored some bushings. If you're using 1" pins i'd be using bushings of 1" width also, to weld into the cut sheetmetal to provide some surface to distribute the forces on, to prevent the bushings from getting sloppy.

Perhaps people feel more comfortable by actually buying a plan with detailed description, but for most fabricators, seeing a close up picture is enough to decide what dimensions and material thickness the are going to need... You'll probably want to over-build the thumb anyways because your MF 50 B backhoe is quite big when compared to the average weekend warrior's hobby machine...

 

[shaley]

If you cant find C45 steel, a long time standard and specifically produced as a shafting product is ANSI 1045 TGP (turned ground and polished). It is case hardened for wear and has a very tough core for impact resistance and torsional shock. Straight tool steel, while giving good wear will suffer from brittle fractures. I take it you are going to mount the thumb end on the 4 bar pivot pin vs a pad mount on the dipper.

 

[toolaholic]

Thank you 1 and all. there's a great video of a mechanical thumb operated by

extendahoe movement ,in and out. Punch up smart thumb. I have lots of welding experiance. was a certified pile butt years ago . thank's

 

[Mcfly89]

i had a certified butt pile once

 

[3RRL]

I'll be watching this thread very closely because I just started my "mechanical" thumb project today. I was going to build a stationary one but thought a moving thumb would be pretty cool. If it doesn't work out very good, I can always use the jaws and make them stationary. I'm using HRS and will case & carb the jaws and actuating bars. Probably turn out stronger than needed, as my hoe is a smaller 3pt subframe one.
Post some pics when you get them.

 

[toolaholic]

Interisting Mcfly89, but understandable. driving a Scout will do that!

3 RRL ,Hi neighbor. I'm up the road in San Rafael Ca.Probably a week out to fab the thumb . Will take lots of Pix. Hope you do also. Went to the equeptment rental yard today [ Hertz ] used a 1/4 " piece of plywood 12" x 48" and traced a thumb with a magic marker.took lots of pix with camera . tangs will be about 6" x 44" long . Didn't get nabbed. Tool

 

[3RRL]

Hi Tool,
I didn't know we were that close by. Your bio does not show where you are. Maybe we'll run into each other? Well, I'll be watching for your pics and narrative on how you do this. Looking forward to it.
BTW, to give you a size comparison, my jaws are only 24" long. I've already started some machining, but spent more time on the concept of the linkage so far. I want to include a couple of position holes for grabbing when the hoe is extended way out like for picking stuff up farther away, and also for when the bucket is closer to the tractor with the dipper stick and boom folded more. I'll start another thread soon and post my progress.
Thanks,
Rob-