Backhoe Thumb...weld or bolt?

[Dataway]

Thanks for the tips. I'll be TIG welding most of it, so it will have time to get pretty hot
Welding is part of my vocation, but I very rarely weld anything thicker than 1/4", I do mostly light industrial stuff, custom shelving, brackets, funiture etc.
I'll be MIG'ing the stuff to the dipper, .045 "outershield" wire....so there could be some more tweaking there...although I'll probably "box" the brackets a bit with some 1/2" plate to try to keep them stable.
Below is a basic image of what I have planned.

My largest drill bit is 1 7/64, so I was thinking I'd work up to that, then use the boring head in the mill to take it out to exactly the fit I want. Or maybe drill, then weld, then put the whole bracket in the mill and align bore the holes...assuming my boring bar is long enough.

The dipper is only 3" wide...not going to be a lot of room for bushings. A Cat 1 top link is 1.5" wide at the pivot, so 3" minus the two 1/2" plates leaves 2" between them, or 1/4" of free play on either side at the top end of the top link. At the bottom I may offset the side plates outside the dipper to get more width for stability at the hinge (an idea not shown in the image)...so bushings will be called for there.

Before I start I'll tweak the images and submit for final comment
Thanks for the advice folks.
JohnnyB

 

[dfkrug]

Johnny, the bracket you weld near the end of the dipper is mounted
to some pretty thin steel, so you may want to have it wrap around the
dipper so the tension forces do not distort it.

BTW, I just scored a set of annular cutters and an arbor for my drill
press....hole drilling just got a lot easier. I will post a thread.....

 

[Gale Hawkins]

I am going to get a price on the Bro-Tek bolt on when I get a digital camera cable so I can upload marketed up dipper pictures so I can get a quote for one to put on the JD 310B.

 

[Dataway]

dfkrug,
Yep, that was a worry of mine. Do you think wrapping some 1/4" flat around there would be enough? I'm thinking the 1/2" would be a bit much. Maybe just some side plates to sandwich the dipper?
JohnnyB

PS. I'd like to hear how those work... makes a lot of sense...why remove all the metal when you just need to remove a ring of it. The BP drills good holes...but it's time consuming stepping up to the big sizes.

 

[dfkrug]

Do you think wrapping some 1/4" flat around there would be enough?

Here is a photo of the parts for one of my mechanical thumbs....I put it
in the form of a kit for the last guy I sold it to. The dipper bracket for
the thumb pivot is just 1/4" steel, but it extends along the sides all the
way to the other side of the dipper. Forces are distributed along the SIDEs
of the dipper, and the welds are in shear, not tension. 1/4" is strong
enough, but thin enough to install below the level of the other 2 dipper
pivot hole bushings, which sit proud of the surface by maybe 5/16-3/8".
That way, the bucket action does not hit the thumb bracket. All of these
(six total) have stood up well. My dipper is only 3/16" thick!

The photo is from one of my thumb threads....you can see the dipper
bracket welded at the lower left.

 

[Dataway]

dfkrug,
Yep, I should be able to squeeze some 1/4" between the bucket pivots and sandwich the dipper as shown in your image. Same issue on my dipper..it's 3/16" too.

Better safe than sorry, I tend to abuse things.
Got some of the DOM 1/4" wall tubing in today from McMaster... will come in handy for numerous things.
Thanks again for the help and advice.
JohnnyB

 

[Gil Case]

You guys have way too much time on your hands, for 2-300 bucks you can get a bolt on thumb from Michigan Iron and be up and running in 15 minutes.

 

[toolbox5]

i just welded my whole assembly to a piece of 1/4 " plate and then welded it to the dipper boom .Been working great for the year it's been on . I also used a piece of 2" square tube for thumb brace.

 

[Dataway]

You guys have way too much time on your hands, for 2-300 bucks you can get a bolt on thumb from Michigan Iron and be up and running in 15 minutes.

It's what my financial advisor calls "Sweat Equity". If I can spend some time that I would otherwise waste, saving $30/hr building my own thumb...then that money stays in my bank account. If I was pressed for time I would buy something, but in a rare twist of fate I've got some spare time right now. If it's profitable for a company to build them and sell them...then it might be profitable for me to build my own and save the money. If I had a $50/hr job waiting (which I often do) I wouldn't be taking the time to build a thumb.... I'd buy one, do the other job, and pocket the $20/hr difference
JohnnyB

 

[akpilot]

I agree with dataway......everyone is "hard wired" different, I get way more satisfaction out of building rather than buying, however as dataway said there are times it doesn't make economic sense.
I haven't used may thumb very much to give much input...however I have been digging in the frost for the last several days, That bottom thumb mount takes a beating, soooo........ make it tough or you will bend it!! The cross tube for the pin adds a lot of strenght, so far mine has done well.