B21 Backhoe Thumb

[100 td]

I would be happy to answer any questions.

Thanks Pat, I think I will have to copy/save this thread for future!

 

[100 td]

Hey Pat,
Still haven't decided I want one, and my use may be going to loamier soil and a smaller block so the 4 in 1 bucket will probably do, but I just love coming back here and re-reading this thread and looking at the pics. Well done again!

 

[downsizingnow48]

Thanks for the note!

I find that 90% of the use is in demolition - breaking up old structures, pulling up footings, etc.

 

[downsizingnow48]

Adding a postscript to update this thread:

After a while I added a quick coupler to the backhoe so I could change easily between digging bucket, landscape bucket, ditching bucket, and root ripper. That changed the relative positions of bucket and thumb and messed up the thumb closure.

I tried to live with it but too much functionality lost. Last winter I decided to make a new thumb. Photos show the wood template, cleaning up the main rails, tacking everything together, and final installation. Fit is again perfect. I added a bit of extra curvature because the factory thumb was too flat, had a tendency to squeeze stuff out.

The main rails are 1/2" steel, all the gussets are 3/8". I followed the design of the factory thumb on bracing.

Photo 1 - template.
Photo 2 - cleaning up the main rails after plasma cut.
Photo 3 - tacked up.
Photo 4 - test fit.

 

[100 td]

BRILLIANT!

 

[Smokeydog]

Always enjoy a good fabrication story. Good job!

 

[Tractor Seabee]

Adding a postscript to update this thread:

After a while I added a quick coupler to the backhoe so I could change easily between digging bucket, landscape bucket, ditching bucket, and root ripper. That changed the relative positions of bucket and thumb and messed up the thumb closure.

I tried to live with it but too much functionality lost. Last winter I decided to make a new thumb. Photos show the wood template, cleaning up the main rails, tacking everything together, and final installation. Fit is again perfect. I added a bit of extra curvature because the factory thumb was too flat, had a tendency to squeeze stuff out.

The main rails are 1/2" steel, all the gussets are 3/8". I followed the design of the factory thumb on bracing.

Photo 1 - template.
Photo 2 - cleaning up the main rails after plasma cut.
Photo 3 - tacked up.
Photo 4 - test fit.

First time I saw this thread, went through it all. Outstanding piece of work, very professional. I have considered adding hydraulic to my BX thumb but haven't got their yet. Only question I have on your project is why put the operating valve where you did by the seat? Isn't that cumbersome when facing aft? I figured a way to add a valve to the mound on the BH so it is handy.

Again great job, Ron

 

[downsizingnow48]

Thanks folks, I appreciate the feedback.

On valve placement. I wanted a valve that could be used for other things when the backhoe was off. Also I wanted to put in a two-spool valve so that one part of it could be used going forward to FEL attachments. So I put it in the mddle of the tractor, between the fender and the seat. The forward valve lever falls under my left hand for operating the grapple or 4-in-1 bucket. When the seat is reversed, the rearward valve lever falls under my right hand for operating the thumb.

Somewhere here is a thread from a fellow who bought an extra stack valve segment and put that in the backhoe stack valve. Tthat is the slickest thumb-only valve setup I have seen.

 

[joea99]

I would be happy to answer any questions. I made some drawings at the time but don't have them now.
The basics:
Cylinder - this is the exact same as on the B21 stabilizers. Perfect for retracted length and stroke.
Thumb - this is the part used on the Kubota BH77 mechanical thumb. It is easily converted to hydraulic.
Links - these are made from 3/4"x2" flat bar. The holes are 6.75" OC.

I deleted my weekend post, the answers to my questions were clearly stated, if only I had exercised prudence and read through the entire thing.

In any case this is very impressive, as I am sure you know.

I have a mechanical thumb, that is useful but could be better. I was going to convert the existing one to suit.

Couple of questions before deciding. My current thumb jaw is only a few inches wide, about the width of the stick. Any real advantage to going wider? It is about 19" from center of pivot hole to the end. I suppose it could be split and made wider during "refit", but may not be worth the effort.

Your breakdown shows, as I read it, a VERY low price for the cylinder. How did you manage that? Did I miss something there as well?

 

[dfkrug]

My current thumb jaw is only a few inches wide, about the width of the stick. Any real advantage to going wider?

My homemade hyd thumb on my backhoe attachment is only about as wide as the dipper stick, about 4". My homemade hyd thumb on my mini-X is much wider, about 10".

Why the diff? My wide thumb is often used to hold dirt in the bucket when digging. The reach of the mini-X is not great, and dirt can fall out w/o a thumb. The downside of this wider thumb is that you have to be careful not to twist it when grabbing something off-center. The B21 and my 2 units all use 25mm pins and can deliver some very powerful forces.

I grab a lot of heavy rocks and logs with my hoe, and often sandstone will shatter. I really wanted the narrow thumb to avoid damage to the thumb.