Backhoe Building a thumb for a model 48 Backhoe

[dfkrug]

When JD fabricates the bucket, I think they use a mill to cut a slot in the boss BEFORE it's welded onto the bucket. That creates a square hole. Much easier than trying to drill a hole after the boss is welded on. You can see it here if you look closely.
Edit: added pic. View attachment 546149

OK, now I see. None of my JDs had that.

If you have a MIG welder, you can easily fill it in by backing up the inside with a piece of copper pipe
or rod.

That way, you do not have to ream out the bore.

 

[DanMc77]

Yesterday was a company holiday so I spent some time down in the shop and made this aluminum cap on the lathe. I wasn't convinced that it would be secure enough on the end of the pin to keep from getting knocked off after the first time in the dirt, but after adding the second inner O ring I'm pretty confident that it will stay in place. After pushing it on, it's very secure and even hard to get off. I had to make adjustments to the O ring grooves because the pin kept shearing the rings in half when I pushed the cap on. Now I've put the cap on and off quite a few times and it works well. The cap makes contact with the inner surface of the bore in the end of the pin and also comes up to the edge of the snap ring. So if a rock slams up against the end of the pin, the cap will protect the ring and keep the pin itself from being dinged up. A severe impact to the end of the pin would probably destroy the cap, but it will transfer the load to the inner surface of the bore and also the outer contact with the ring will transfer the force through the ring and to the thumb boss, rather than expecting the ring itself to carry the load with its groove in the pin. It was about 4 hours of futzing around and grinding specialized cutters to come up with this, but the next one will probably take less than an hour to make.

 

[Kernopelli]

Great project, just found it today. I have a small hoe that is already plumbed with a Aux. hydraulic circuit and I already have all the metal for a similar project.....all I need is time. You've done a great job on the fab work and making good use of that new lathe. Just an FYI, I have had great success buying lathe inserts and holders at National Product Sales | eBay Stores They almost always have a selection of inserts for sale and a little patient auction watching will get you specific size and styles. I have never spent more that $10 ( including shipping) for pkgs. of 10 for Iscar, Kennametal or similar quality inserts. It usually works out to 90-95% off retail.

 

[DanMc77]

Had some time yesterday to put the bucket and thumb on the backhoe with the new pin and see how it all plays. In general its all good. The 1/16" hole in the pin delivers grease to the thumb pivot and a few squirts later grease came out the dipper pivot tube, so that's all good. There's an interference issue with the dipper so I'll have to cut a notch in the thumb center frame. Finally, the grease cap traps air in it when it's greasy and the air keeps pushing the cab back off. I'll have to drill a little vent hole in the cap.
Have a blessed Easter. Shut off the computer and the phones. Spend time with your family and give thanks for the gift of eternal life in Christ.

 

[DanMc77]

Some progress with the thumb project. The first test fit (prior post) showed that there was an interference between the dipper and the thumb frame. That has been corrected as seen in the first photo, with the notch cut out. Now it retracts very nicely and tucks out of the way. The thumb frame will do an excellent job of protecting the cylinder, which will tuck very neatly inside the thumb.

 

[DanMc77]

More progress this weekend. Got the cylinder pivot done in the thumb.

Boring out the pivot hole. The cylinder pivot pin will span only the two bosses in the middle.


Test fitting the cylinder. Dang, I forgot to cut the opening in the pivot rail for the cylinder port. Had to hog that out later. Would have been much faster if it was done before welding. The shiny surface on the pivot rails will kiss the edge of the dipper. The zerk on the cylinder will just clear the dipper, but first I'll have to grind down a small area of the weld that runs down the middle of the dipper.


This is starting to get very close to being done.

As for the hydraulics, I'm leaning toward adding a switch to make double use of the spool that runs one of the stabilizer cylinders. You never need to run the stabilizer at the same time as the thumb. Now I need to find a switch, and also a bypass valve - I don't want to have any chance of blowing up the thumb cylinder.

 

[Peter 315]

I would get a foot valve ,So if both hands are on the controls you can run the thumb .. Looks like your doing a great job :thumbsup:

 

[DanMc77]

I would get a foot valve ,So if both hands are on the controls you can run the thumb .. Looks like your doing a great job :thumbsup:

That would not be hard to do! The stabilizer control is on the front of the spool tower, so I could just run a pushrod down to a pedal!!! NICE. Great idea!

Now to find a diverter valve. I think this would work. Has 6 ports as I think I will need.
Manual Hydraulic Multiplier, SCV Splitter / Diverter Valve

Then I'm in need of a relief valve for the extend circuit on the thumb cylinder:
PRINCE RV-2H Inline Relief Valve, 3/4 In NPT Port | eBay

I know I've been through this before, but that was back when I was thinking of adding another spool valve. I think this approach is simpler, and I don't need to cut into power beyond hoses that run the whole backhoe. Any hydraulics experts, please chime in!!

 

[aczlan]

I would disconnect the pressure in line to the backhoe valve, run it through a new valve such as this one: 1 SPOOL 3 GPM Cross BA1AXGA Open Center Hydraulic Control Valve w/Float | New Arrivals | www.surpluscenter.com and then use a double sided relief valve such as: 1/2 NPT 3 GPM 15-3 PSI Hydraulic Cushion Valve | Relief & Cushion Valves | Hydraulic Valves | Hydraulics | www.surpluscenter.com
Then you could connect the valve to a foot pedal (or just place it where the handle sticks out and you can push on it with your foot).
If you do want to go with a selector valve, this one is a lot cheaper: 3/4" NPT 3 GPM Prince Double Selector Valve | Prince Mfg | Brands | www.surpluscenter.com

Aaron Z

 

[DanMc77]

I would disconnect the pressure in line to the backhoe valve, run it through a new valve such as this one: 1 SPOOL 3 GPM Cross BA1AXGA Open Center Hydraulic Control Valve w/Float | New Arrivals | www.surpluscenter.com and then use a double sided relief valve such as: 1/2 NPT 3 GPM 15-3 PSI Hydraulic Cushion Valve | Relief & Cushion Valves | Hydraulic Valves | Hydraulics | www.surpluscenter.com
Then you could connect the valve to a foot pedal (or just place it where the handle sticks out and you can push on it with your foot).
If you do want to go with a selector valve, this one is a lot cheaper: 3/4" NPT 3 GPM Prince Double Selector Valve | Prince Mfg | Brands | www.surpluscenter.com

Aaron Z

Aaron, I so much appreciate your input! Dang, I've really gone full circle on this. An electric pump was supposed to be "simple", but it's not. The idea of going with a selector valve is that it would be "simple". But It's still about the same number of extra hoses as adding a new spool valve. In fact, adding the spool valve may actually be simpler - it only needs 4 connections whereas the multiplier valve needs 6, and operation is more straightforward. One of my concerns with cutting into the stabilizer cylinder lines is that those stabilizers move quite slowly. Getting into the main hydraulic feed would make it more peppy (or maybe not), and I'd be able to use everything without flipping a switch. Now I'm back to the spool valve approach. It's all good.

I have to remind myself: Open center means that the valve freely passes fluid through the center when the valve is in neutral, and the thumb cylinder lines will be blocked. Operating the thumb will steal pressure from all other functions of the backhoe. Having the float on the thumb spool valve may be handy so the bucket and thumb can both be tucked away at the same time, vs parking the thumb, then having to bring the bucket in separately. I like it. Now I need to go back and re-read the old posts talking about spool valves.