Backhoe Thumb...weld or bolt?

[Dataway]

dfkrug,
Thanks, for the input. While I was eyeballing things the forward position did seem to me to be the most useful position.
I was up in the air about using a top link because of strength worrries..but today I examined the 1" pin top link I had lying around and it seemed pretty beefy. I don't mind removing it for storage because my simple design was probably going to require that anyway.
You've helped me make up my mind, top link it is.
JohnnyB

 

[dfkrug]

I was up in the air about using a top link because of strength worrries..but today I examined the 1" pin top link I had lying around and it seemed pretty beefy.

Johnny, CAT 1 toplinks have only 3/4" pins, but they hold up OK on the
3-pt with lots of box blade use. They are plenty strong enough for a thumb
brace. Someone actually sells a thumb kit with a CAT 1 toplink, I do not
remember the vendor. The one you had lying around is a CAT 2 toplink?
If so, that's super-strong.

For a fixed thumb, I had no issues with using only 3/4" non-pivoting
pins. But with a hyd thumb, I went to 1" pins with grease zerks. For the
thumbs' main pivot on the dipper, I used cheap sched 40 pipe (no zerk)
for fixed, and 1.00 ID DOM (greasable) for the hyd. The stresses and
wear are quite different for the 2 types of thumb.

 

[lostcause]

1.00 ID DOM (greasable)

sorry to hijack/sidetrack, but can you elaborate on what this is? is it a specific ready made piece, or is it a specification for a steel shape? i'm familiar with all structural steel shapes, but i have little to no knowledge of some of the more specialized shapes that are available.

i'm looking for some sort of pipe/tube with inside diameters and thick walls that have tolerances tight enough to use with standard size pins, such as 3/4, 7/8, 1, etc. it would be nice if it was also available in stock lengths that can be cut to fit the application, such as 1/2" to weld to a plate where a pin passes through, or 4" long to weld to the top of a forklift tine.

thanks.

 

[dfkrug]

i'm looking for some sort of pipe/tube with inside diameters and thick walls that have tolerances tight enough to use with standard size pins, such as 3/4, 7/8, 1, etc.

DOM=drawn-over-mandrel

I keep on hand 2 sizes: .750" ID, and 1.000" ID, both with .25" walls
It is pricey stuff, about $1/inch, depending on where you get it. If you
can't find it in your area, buy it mail-order.

I use this stuff for pin bushings (see photo). You need pins that have
.010-.015 grease clearance, so I often use 25mm rod stock with the
1.000". In the photo, I am using a piece of DOM tubing to align my
holes for welding.

I also use the .750 for CAT 1 pins, which are not greased. CAT 1 pins
fit tighter, so weld heat management is tougher.

 

[RFB]

When I set about to fab my thumb, I called the BH (Rhino) Mfg. They said welding onto the stick would void the warranty (heat).

I bolted.

 

[dfkrug]

When I set about to fab my thumb, I called the BH (Rhino) Mfg. They said welding onto the stick would void the warranty (heat).

Nicely-made brackets, RFB. Some have found that the bolted brackets
will slide on the dipper under the force of use.

Your 85 bkt seems to be of the older non-curved style. How long IS the
warranty?

 

[RFB]

df,

Thank you.

I did this when it was about 1 month old, and the warranty was 1 year. Rhino said that they were concerned regarding the welding heat on the stick.

I thought about slippage, and that is why I imagineered the upper plate to rest against the weld boss of that diamond shaped gusset plate. If it were to slip, the force vector is up towards that gusset, and it would have to spread the bracket to climb the weld boss. I also used right-angle partitions on the brackets to preclude any leverage induced angle shifting. I used grade 8 hardware throughout.

RFB

 

[Dataway]

dfkrug,
Wow...I like the look of that thick walled DOM. I've been looking for years for some kind of stock I could keep in the shop with .75 and 1.00 ID's and had at least .25" walls...that gives you enough to machine a flange on if you need it etc. All kinds of possiblities.

My biggest problem will probably be to drill the parts first, then weld, or weld then drill. Easier for me to drill first, but I suspect the welding will tweak things enough that the pins might get real tight. Would you recommend welding first than setting up the whole thing in the mill for drilling?
I just hate moving the vise and rotary table off the mill after spending so long getting them straight
JohnnyB

 

[dfkrug]

I thought about slippage, and that is why I imagineered the upper plate to rest against the weld boss of that diamond shaped gusset plate. If it were to slip, the force vector is up towards that gusset, and it would have to spread the bracket to climb the weld boss.

I went back to look closer at your photo and I see what you are talking
about. Excellent idea, RF. Some folks underestimate the 1000s of lbs
of force experienced by the upper bracket.

BTW, I doubt that ServisRhino used any exotic steels in the dipper...it
is probably just A36.

 

[dfkrug]

My biggest problem will probably be to drill the parts first, then weld, or weld then drill. Easier for me to drill first, but I suspect the welding will tweak things enough that the pins might get real tight.

I have experimented a bunch with heat management to reduce the
unavoidable welding distortion you will get. Pin alignment fixes after
welding requires a long reamer, to do it right. I no longer have to do it
that way, and I have sold my 1.000" reamer.

Put simply, you want your main weldment to be very hot before you weld
your bushings. Furthermore, making an alignment pin for the welding phase
helps a lot. I made a pin that is about .998 to fit into the 1.000 bushings.
Since the final pins are about .985, you do NOT want to use that. The
steel has to cool before the alignment pin can be removed.

I do not drill holes over 1" anymore; I cut them with a plasma cutter and
circle guide. I want them a little sloppy for fine tuning the alignment before
welding. You ARE talking about drilling 1.5" holes if you use this kind of
DOM tubing, correct?

 

[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.