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?