Homemade Articulated Mechanical Thumb

[schmism]

Coolant will definitely help....even air.
Good luck with the new drill press.

well that was what caught my eye in your fab pics ... seemed you worked all your stuff dry which i thought was odd based on the amount of material you were hogging out....

 

[tlbuser]

OK,
What do you think so far?
I'll try to go up this weekend and attach it, if Loretta can get off work.
Otherwise we'll have to wait another week.

Well, of course it looks like a pro made it Something about the linkage though.....I don't know why. Can't decide if it would bind or maybe have a tendency to "over center". Tried putting all 3 pics on the same page, but that wasn't much help. As a precautionary measure, after tacking it on, maybe unpinning the cylinder and rotating the bucket / thumb assembly by hand would be prudent.

 

[3RRL]

Well, of course it looks like a pro made it Something about the linkage though.....I don't know why. Can't decide if it would bind or maybe have a tendency to "over center". Tried putting all 3 pics on the same page, but that wasn't much help. As a precautionary measure, after tacking it on, maybe unpinning the cylinder and rotating the bucket / thumb assembly by hand would be prudent.

tlbuser,
Thanks for the compliment.
And I agree with you 100% that I will be mocking up the location before I weld it so that it doesn't do that ... "over center" business. I'm bringing several giant clamps to hold the pivot points while I move the bucket back and forth to see what REALLY happens. You know the old story about it "looks good" ... but I am planning on testing the fixed pivots first. My thoughts about adding the additional pivot holes are for that reason too, in case I screwed up and did not allow for enough travel to avoid the "over center" condition. I don't think it will bind as I've thought that out pretty good and spaced to avoid that condition. I'm pretty confident in that respect.
Wish me luck and thanks for the reminder.

schmism,
You might have noticed the air nozzle in some of the machining photos. I keep a constant stream on the cutter and chips so it cools and blows the chips away, out of my face. I've learned a few things over the years (since 1964) cutting steel. Some are pretty good and some are pretty crappy and dangerous, but still have their place in a pinch. Just think how we used to cut and grind all those geometries before CAD and CNC? Shapes are basically the same, just different ways to machine now. Then think about those guys who made guns and screws and plows etc. back in the 1800's!
No Harbor Freight then.

 

[63DH8]

63DHB,
I have "curled" the bucket on the CAD to see how the thumb moves in relationship to the bucket. I'm wondering why it would not grab if they are approaching each other?
.

When you curl the bucket, curl the thumb in the same direction as if you have a baseball between the thumb and bucket. Simulate uncurling the bucket/thumb combo to drop a load into a dumptruck. You'll see what I mean by the the thumb will drop it's load. The thumb and bucket has to share the piviot pin to keep from going from an underbite to overbite or vis versa.

 

[EddieWalker]

Rob,

Put me down for wanting to see a video of it in operation!!!!

It's very impressive to see it coming together from an idea to reality.

Thanks for sharing,
Eddie

 

[HomeBrew2]

When you curl the bucket, curl the thumb in the same direction as if you have a baseball between the thumb and bucket. Simulate uncurling the bucket/thumb combo to drop a load into a dumptruck. You'll see what I mean by the the thumb will drop it's load. The thumb and bucket has to share the piviot pin to keep from going from an underbite to overbite or vis versa.

NOW, I can visualize what you're getting at! From lots of experience with just a baby BH and cheap static thumb, I know how the load is always trying to shift while lifting into dump trailer or tall pile, or just manuvering around stuff ... I can't imagine the trouble I'd have with the thumb constantly moving relative to the bucket

 

[dfkrug]

When you curl the bucket, curl the thumb in the same direction as if you have a baseball between the thumb and bucket. Simulate uncurling the bucket/thumb combo to drop a load into a dumptruck. You'll see what I mean by the the thumb will drop it's load. The thumb and bucket has to share the piviot pin to keep from going from an underbite to overbite or vis versa.

With this kind of articulated thumb, curling the bkt will always further
close the thumb. Conversely, uncurling the bkt will open the thumb. In
order to roll an object between the 2, as you describe, the thumb would
have to move in the same direction as the bkt. It never will. This is
confirmed with my wooden mockup AND using a thumb pivot point just
aft of the bkt pivot point. If you have an independent hydraulic
thumb, you can do what you describe.

Rob:
As for drilling steel at low speed, good luck finding any non-industrial
drill press that spins slower than 180RPM. I would love to see 100 RPM,
but have found that you need a geared head or other industrial
machine costing over $1K. Seems that vendors of cheap (under $1K)
presses think their customers are only drilling wood. I know you have a
nice milling machine, which does a great job drilling, but I am still
resisting that kind of purchase.

 

[scott_vt]

Just think how we used to cut and grind all those geometries before CAD and CNC? Shapes are basically the same, just different ways to machine now.

Hey Rob,
Those rotary tables and dividing heads are just a distant memory

 

[3RRL]

Hey Rob,
Those rotary tables and dividing heads are just a distant memory

I know what you mean Scotty, but I still have all that stuff here in the garage since I have no CNC here. Have to make do the old fashioned way.

Dave,
You might be able to switch either the motor pulley or spindle pulley to get a lower speed? You will more than likely need that more than high speed for wood. I'd look into that as it will make drilling those larger holes a breeze on your unit. That is, assuming it's got a pulley system for speed changes?

You are right about the thumb approaching the bucket when curled and it only opens (moves away) when uncurling. That's why I think this should work. Once I curl the bucket and grab an object, I can move the dipper stick and boom without loosening the grip....only when I move (uncurl) the bucket. I don't see it working any other way.

 

[dfkrug]

Dave,
You might be able to switch either the motor pulley or spindle pulley to get a lower speed? You will more than likely need that more than high speed for wood. I'd look into that as it will make drilling those larger holes a breeze on your unit. That is, assuming it's got a pulley system for speed changes?

You are right about the thumb approaching the bucket when curled and it only opens (moves away) when uncurling. That's why I think this should work. Once I curl the bucket and grab an object, I can move the dipper stick and boom without loosening the grip....only when I move (uncurl) the bucket. I don't see it working any other way.

My old and new drill presses have 3 step sheaves (pulleys). The center
one rotates on a pivot to tension the 2 belts. I looked into buying or
making a replacement center sheave, but ran into a dead end. The
motor's step pulley is already being used with its smallest diameter. I
also considered a slower speed (less than 1720 RPM) motor, but buying
one can be as much as the new press! I want to stay w/ 120V. I have
not changed my old drill press from the lowest speed in 10 y.