Custom hydraulic backhoe thumb

[Racerwannabe]

The hydraulic thumb on my Woods BH75 is complete and in-service! Could not have done it without the outstanding advice from this thread - especially DFKrug and Bumperm. The key was stumbling on a cylinder at Surplus Center that had the right 2.5" bore and exact same retracted length as the existing mechanical linkage. The stroke gave me 1/2" additional extended length than the mechanical linkage, but that didn't hurt me at all. Fairly minor fab which I did myself included the valve mounting plate on the dipper, cutting off and re-orienting the base cross tube on the thumb cylinder to get my ports on the side, cutting DOM spacers for the thumb pin/rod crosstube, and the little aluminum bracket for the valve switch. I'm into it for $325, not including my time or consumables, or replacing a sneaker that I got a bunch of Kubota Orange II overspray on.



I'm not really happy with the switch install. While perfectly functional, it still looks unfinished. Open to suggestions. The machine tools I used to make the bracket include a drill press, belt sander, Milwaukee Porta-Band, and a Dremel, so I'm pretty limited on what I can do.

One really dumb thing I did was cut the wires that tee off to go up to the switch too short. Only discovered it after I was completely done and testing the wire and hose routing for pinching over the full range of motion of the hoe. When the dipper and boom are fully extended (reaching as far away from the machine as I can with the bucket teeth), the wire up to the switch is uncomfortably strained. If I'm reaching down digging a hole I'll have a problem with that wire. So that's on the list to fix. Also gotta get some dielectric grease on the valve spade connectors. And get some hours on 'er to get all the air worked out. I'm shocked that I have no apparent leaks at any of the fittings, including the hardline compression fittings. I'm hoping that if I don't have any on start-up that I won't have any later (unless I whack something).

Do you guys think the hardline will hold up without being anchored/braced at the base end of my cylinder?

 

[Clipse3GT]

Awesome job. Looks very cool.

Would you be so kind to post the parts list you had to buy to make it?

Also, for the switch I think the control knob is hollow as well as the control tube. You could run the wire inside of the hollow rod and just drill the knob to accept a round momentary switch to work the diverter.

 

[Racerwannabe]

The cylinder is Surplus Center Item 9-8760. If you have a new Woods BH75 this is the cylinder you want.

The valve is a Hydraforce SV08-24-8T-N-12DS. I got that from my local distributor HydroAir Hughes in Connecticut. Good folks to deal with - I ordered it and they assembled it and shipped in same day.

Hoses and fittings were from Discounthydraulichose.com. Again, great to deal with. They pulled fittings and took measurements for the real tight plumbing I had to do around the valve. And they patiently tolerated all my hydraulics newbie questions. Had my stuff two days after order. Bill of Materials is very project-specific, so no sense posting it here. But if you're doing a hydraulic conversion on an identical BH75, PM me and I'll send you the BOM.

DOM tubing for pin spacers and switch was from Amazon. Link is elsewhere in this thread.

Marine wire from Ebay.

 

[dfkrug]

Do you guys think the hardline will hold up without being anchored/braced at the base end of my
cylinder?

First, it is good you are using a hardline there, as any protection is good. You should try to anchor
it at the base end, even if that means just tying it with zipties. I like your protected location for
the valve.

So far, I have not seriously damaged anything in the 7+ years since I built this, tho I recently
pinched my wires down by the hoe swing pivot, blowing a fuse.

 

[bumperm]

Racerwannabe,

Very nicely done! I especially like the solenoid valve mount, clean and out of the way. I may have to modify mine again - thanks a lot:ashamed:

I had my switch mounted like yours originally. Worked, but not so ergonomic. My current mount is a lot better - I like it a lot! Angled off to the side it's much easier and more comfortable to use, with my original one, like yours, I'd end up pushing the button with the side of my finger, clumsy.

I drilled out a length of Delrin rod, drilled and tapped the end for a set screw, then cross drilled at an angle to slide onto the joy stick arm. The switch threads, no nut, is a push press fit in. Wires pulled through as switch is installed. Quick and easy as with this sort of thing you kind of don't know how well it'll work until you try it.



bumper

 

[Racerwannabe]

Bumper - ya, in addition to not looking finished and being exposed, the ergos on my switch mount kinda suck. Initially I thought it would be good; just depress with middle finger and go to town, but the bracket is too close to the top of the knob. Amazon is my go-to for all purchases these days, and they have a one-foot hunk of black Delrin for $14. McMaster has it for $5/foot + shipping. I may do that, but I'm going to give it a day or two and prowl the aisles of my local dealer and Home Depot or Lowes. It occurs to me that I can use just about any kind of plastic as long as it's reasonably hard and machinable. Maybe I can come up with a Kubota branded screwdriver that I can cannibalize a handle from. Might be just the finishing touch I'm looking for. Thanks for the idea!

 

[massey240]

Have you thought about going to a foot switch for the thumb? You could also replace the know with a trigger style setup like in picture. You may can find one from an old bobcat that has the switch for 4:1 bucket. I really like the thumb you done great my friend.

 

[massey240]

 

[bindian]

I made my own switch knob. I got the knob from O'reilly Auto Parts and the switch from Radio Shack. Works great with my thumb. It is on my loader joystick, but you can buy 8 ball knobs with the switch on the side online. I have about $20 in making mine. 8 balls go for around $50 online.
hugs, Brandi

 

[avc8130]

I like this for the switch:

Cpi Weatherproof Switch, Push Button B7151-516 | Zoro.com

Zip-tied to the handle so you can hit it with your thumb is very ergonomic. I have 2 on my Kubota. One for the thumb on the hoe and one for the diverter up front.

ac