Thumb Home made thumb for mini excavator

[voodoo]

As usual, participating in these forums has got me wanting something I didn't know I needed.
The latest is a thumb for my 1.5 tonne mini-excavator. (Any of you wanting to see it can have a look under photo section).

After browsing search history form many late nights and plagerising ideas, I came up with this design. It's not the most original, but primary objective was to use a length of 5" "C" channel that I had sitting about, as well as some 4" box section off cuts.

All drawings are my own. Drawing package is Google Sketchup, and for all you budding mechanical engineers, the basic package is a free download from Google.

Nigel

 

[voodoo]

Primary design was to use C channel for thumb, box section for bracket and standard Cat 1 top link for brace. All these I had lying about.
Also wanted it to be as neat as possible and to be minimum weight.

Box section design was to split and drill with bushing / blocking to strengthen in key areas and provide additional bearing surface to pivot pin for durability.
I reckon there is insufficient rotation and usage to warrant drilling and tapping for grease nipple, but I can always do this at a later date if required.

The brackets will be welded directly to the dipper boom.

 

[voodoo]

I wanted to be as neat as possible with the stowed position maintaining the top link within the thumb and protected from any bucket damage or material when closed.
This seemed the best design.

 

[voodoo]

Here's the actual thumb.
In using the base of the "C" channel to protect the top-link, I may have compromised the teeth of the jaws. Maximum gripping effect may be diminished if the material in the jaw is bulky and hits against the flat plate.

I was also concerned about the bending of the jaw "arms" against an irresistible object, so I have included a solid round bar at the top of the mouth.
This was the only space available as clearance is minimal when the bracket is folded back.

To reduce weight without reduction in strength, I have shown the plate drilled out. I think it looks quite modern and hi-tech as a result.

 

[voodoo]

I've started to the fabrication, but no pics as yet. It's not easy keeping the camera clean when getting dirty and greasy!!

The pin holes are cut in the channel and support brackets are made. The bushings to the brackets have been fitted and provide a snug fit to the thumb itself. The toplink, brackets and channel have all been fitted together and work nicely.

I've just started to cut the weight reducing holes on the plate. Boy is it slow cutting 100mm dia holes in 5mm steel with a blunt hole saw on a 1/2hp pillar drill!!! One done, one to go.

Before I go too far, the design could perhaps be improved upon. Have any of you knowledgeable kind guys anything to add to improve, or anything obvious I might have missed.

PS: Apologies to all when I swap from imperial to metric. Old habits. UK is definitely a dual measurement country.

Nigel

 

[3RRL]

Looks like a pretty clean thumb to me. I like your jaw design and the reinforcement between it. Just make sure the adjustable brace is strong enough to hold the clamp force from the bucket. There is a lot of force there.
Great drawings too.

 

[voodoo]

Thanks for the kind words Rob.

I got a bit more done this evening. All holes are cut and all parts made up for welding.
Bad news is I managed to burn out my chop saw in the process. Guess it will have to go back under warranty. I'm only on the second blade from new.

The strength of the front jaw still concerns me. Too much scope for bending.
I've introduced a gusseted angle piece "vee'd" to let the brace fit when closed, which should do the job.
I'd still like some deeper stronger teeth for biting, so I guess it's back to the parts bin a rummage.

 

[mrutkaus]

When will you have thumb thing to show us?

Mike

 

[voodoo]

No pics until its finished. That way you don't see the messy welds along the way.

Oh, I'm just teasing. I'll post whats done to date later today.

Nigel

 

[voodoo]

OK,
Some pics as promised.

These first two pics show the mounting brackets. The main pivot bracket needs to resist torsional forces as well, so I incorporated these bracing blocks into the walls. They're only tacked in place at the moment for positioning.
The other bracket is only for pining the unit in closed position, so only a bushing for it.
When I have them pinned in place, I run the hole arbor down through them to ream out evenly. Works a treat.