I am going to build a hydraulic thumb for my New Holland LB75B backhoe. As I know everyone likes to see photos, so I have attached what I have designed so far. I still need to work out a few of the details. My biggest questions right now is what I should be using for bushings / pins. Should I worry about getting hardened bushings? Or would bushing made from DOM be sufficient? Do I need hardened pins? The best I can measure, the bucket pins on the LB75 seem to be 45mm pins. Does this sound correct? Thanks, Steve
Here's a link to another home built thumb. This one is not hyd. but it's got some pictures that show it off pretty well. In your drawings I noticed you don't have much support up by the ends of the tines on the thumb, I think you might want to add some. http://www.snowplowing-contractors.com/alans_excavator_thumb.html
95zIV, Thanks for the link, I should be able to get some good inspiration from all the photos. As far as support near the end, I have been thinking the same thing. I am just not sure what I want to do yet. I am debating between another piece of plate, or maybe a tube or pipe welded between the tines.
Also consider which is stronger the bucket curl or the thumb cylinder, so you don't bend something. Adjust your pressure reliefs to make sure one of them gives in a stand off. I would suggest the thumb cylinder pressure be set a little lower.
What you have so far looks pretty good, a little more support for the tines at the end would be a good idea. However I think you should put some thought into how you will plumb the boom and tie into the hydraulics on the machine. Seems like this may be the most expensive part of the job.
Norite, I already have AUX hydraulics running up the boom, so the plumbing shouldn't be too bad. I will just need to add a valve or two to get the controls the way I want. PDG, The plan was just to set the AUX relief quite a bit lower than the bucket curl.
Make it out of T-1 or Hy 100, 1" steel. They are heat treated, stress relieved, have every alloying element know to man. It will bend, but will return to straight. Clamp the living daylights out of everything, and then make a 1" long bead and then go to another spot and run another 1" bead. Then go take a 15 minute break while it cools; repeat. I found out why the Lincoln Welding manual has 50 pages about welding distortion... I made a self actuating model, the HoeClamp from Amulet Manufacturing in Cali. http://www.amulet.com/texts/HoeClamp.pdf I went to the local heavy equipment dismantler and bought a 1.5" diameter cylinder rod for the pivot pin. The chrome plating makes it slippery and it doesn't wear. If you use it a lot, I'd weld a doubler on the side of the tine and bore it for a bushing. Make it an interference fit, .002" would be plenty. Couple of zerks to lube it, you're in business.
Have a look at this http://www.tractorbynet.com/forums/build-yourself/125912-custom-hydraulic-backhoe-thumb.html There are probably 100 DIY thumbs on this site. Yes, for smaller hoes but the idea is the same. Joe H