REAR-MOUNTED CRANE

[Aussiebushman]

G'Day from Oz

I have a jib that attaches to the 3PT linkage on my Ford 6000 but the usefulness of this is limited due to the lift height and a minor hydraulic leak causes the lift to slam up instead of raising steadily - fixing that is a job for another lifetime!

The ground here is uneven and lifting heavy objects gets awkward so Instead of building a fixed crane or gantry, an adaptation of the one in this picture seems like it could be a great solution and I have most of the bits needed including the steel and the chain block. There is no danger of the front of the tractor lifting due to the weight of the massive dozer blade holding it down.

• The two main frames will be made of 75 X 45 mm steel RHS 3 each metres long
• A collar will be made to bolt the two frames together at the head of the rig, control the height and hang the chain block
• Holes will be drilled at the bottom of each side frame to swivel on the pins in the 3 pt linkage
• The "back stay" (actually faces to the front of the tractor) will be a heavy cable running from a mounting point on one side of the tractor through an adjusting block and back to the other side - this controls the height of the frame. OR it may be easier to simply affix the head of the rig with chain that can be adjusted for length with a rated shackle .

I see the benefits of this concept being its mobility - the tractor and rig can be backed up to whatever needs lifting. The only problem I can foresee is the angle of the wire stay being too far back but I can't see an alternative other than adding a vertical "gin pole" OR running the cable right through the cab to the steel frame at the front - not desirable

Jenna (the German Shepherd in the picture) has already provided instructions but has anyone got a better idea (and I do not mean hiring a crane for a 3 hour round trip every time I want to use it).

 

[CalG]

G'Day from Oz

I have a jib that attaches to the 3PT linkage on my Ford 6000 but the usefulness of this is limited due to the lift height and a minor hydraulic leak causes the lift to slam up instead of raising steadily - fixing that is a job for another lifetime!

The ground here is uneven and lifting heavy objects gets awkward so Instead of building a fixed crane or gantry, an adaptation of the one in this picture seems like it could be a great solution and I have most of the bits needed including the steel and the chain block. There is no danger of the front of the tractor lifting due to the weight of the massive dozer blade holding it down.

• The two main frames will be made of 75 X 45 mm steel RHS 3 each metres long
• A collar will be made to bolt the two frames together at the head of the rig, control the height and hang the chain block
• Holes will be drilled at the bottom of each side frame to swivel on the pins in the 3 pt linkage
• The "back stay" (actually faces to the front of the tractor) will be a heavy cable running from a mounting point on one side of the tractor through an adjusting block and back to the other side - this controls the height of the frame. OR it may be easier to simply affix the head of the rig with chain that can be adjusted for length with a rated shackle .

I see the benefits of this concept being its mobility - the tractor and rig can be backed up to whatever needs lifting. The only problem I can foresee is the angle of the wire stay being too far back but I can't see an alternative other than adding a vertical "gin pole" OR running the cable right through the cab to the steel frame at the front - not desirable

Jenna (the German Shepherd in the picture) has already provided instructions but has anyone got a better idea (and I do not mean hiring a crane for a 3 hour round trip every time I want to use it).

Your plan is good.

I've got something similar.

The structure is 50X100 welded thick wall tube. The joined end is made with a pintle ring . The flat flange drilled for 18mm bolts.

The tractor end is a pair of female shackle ends (aviation discards) fitted to the ubiquitous pre-drilled draw bar .

I run a chain from the top link to the pintle ring. A come along/ power pull serves for fine lifting, else, it's just the tractor 3 pth doing the dirty.!

 

[davedj1]

I like the idea of having a jib back there from time to time. Is there any reason you can't add a spreader bar in line with the top link and actually use a top link?
Then if you feel the need for cables use them as a truss set up, a standoff at the mid point of your booms and then just tie the cable to both ends?

 

[Aussiebushman]

You mean like this V2 schematic? Not sure I understand the benefit. It seems to me that the higher the fixing point for the chain/cable the better, but a strut in the centre would certainly help firm up the structure.

Another option would be to bolt the bottom of each post to welded plates on the top of the scraper blade instead of onto the 3 pt linkage pins - see V3 schematic. Then the rig can be left in place even when the rear blade is in use and the angle of the chains/wire stay might be better

 

[CalG]

You mean like this V2 schematic? Not sure I understand the benefit. It seems to me that the higher the fixing point for the chain/cable the better, but a strut in the centre would certainly help firm up the structure.

Another option would be to bolt the bottom of each post to welded plates on the top of the scraper blade instead of onto the 3 pt linkage pins - see V3 schematic. Then the rig can be left in place even when the rear blade is in use and the angle of the chains/wire stay might be better

DON'T run a four sided structure! Triangles! Only Triangles.

The problem with mounting to the blade is the loss of lifting power with the distance from the lift arms, and loss of "daylight" between the load and the blade in the process.

Double negative! If you are lifting pipe, that won't matter. ;-)

 

[the old grind]

I'd only use version 1. CalG explained why. :thumbsup: I might even put a pulley on the jib and shackle a winch to top link base. Goal, to enhance o'all range of lift, offer snatch block to reeve 2 part, and no chains or ratchet latches to bust your hands. Lift cyl will hold more than it will lift, so higher max cap, too.

Strongest bits should be the lower legs. Top legs will be under tensile vs compressive load, could even be chains with grab hooks applied to adjust jib position relative to that of 3ph arms. (Flat bar top legs can offer adjustment too, pinned thru clevis etc.)

btw, I have a 3PH 'boom', and I suggest it's less attractive that what is proposed, less stiff/secure with a load that swings from side to side, and with a single point lift that's a given. Also, to connect bits, instead of just punching bolt holes at pivots or anchor points, can you make bigger holes and weld in bushes/hubs? (Tack & try out right on the 3PH and weld 'er up once for good?) t o g

 

[Dave M7040]

I see a number of large cranes with jibs which have this general design which gives a good angle to support the outer end of the jib.

Dave M7040

 

[CalG]

I see a number of large cranes with jibs which have this general design which gives a good angle to support the outer end of the jib.

Dave M7040

Dave

From an engineering standpoint, the structure makes good sense.

But practically, a little extra wall thickness at the memebers will cut the parts count to TWO!

You might figure how the economics might play out.

Plus, A simple boom stores most compactly ;-)

 

[Aussiebushman]

Interesting - It certainly overcomes the problem of where to anchor the rear cable. However, unless I'm missing something, the height of the jib is fixed relative to the ground unless the upper green line in your sketch is adjustable for length so the whole thing swivels on the lower pivot.

Raising or lowering the jib provides a distinct advantage in terms of getting it under trees.buildings etc before hooking on.

In practice, not sure your suggested arrangement is any more workable than the jib I already have. There is nothing to stop me from raising that jib to whatever height I want, then using a chain block to do the lifting. Cost of this option is NIL. BUT I have already mentioned that the 3 pt linkage slams rather than lifting smoothly - The proposed arrangement overcomes that problem because it provides the option of easily and smoothly raising/lowering the jib as well as using the chain block.

 

[Dave M7040]

Thanks for at least considering my suggestion.

I saw the red line as being a cable as on the cranes. A heavy turnbuckle providing some adjustment.

I saw the top green line to be a hydraulic top link thus being easy adjustable.

Where the three black line meet, the two crane arms could be hinged to allow more compact storage.

Good luck with whatever you do and plse report back so we all benefit from your experience.

Dave M7040