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I'm making a frame to hold a sprayer to go on the back of a small tractor and I'd like to make it easy to remove.
My idea is to have the frame slide on over a pair of tubes that are fixed to the back of the tractor - a cross section is shown below (I'm sure there's a real name for this type of connection)
[img] https://lh3.googleusercontent.com/y5TTNw3Iy2eflicVU4Y-ap88y_mWQQ7XcFk1mkQlAW8=w544-h209-no [/img]
Where the part A/B is made of two tubes (one inside the other) and is bolted to the tractor. C is the frame that will slide over C and secure with a pin or bolt going through both C and B.
My question is, how long should B protrude into C to give enough strength? I'd like to to be as short as possible without risking it bending.
B is 35mm box section steel with a wall thickness of 2mm and A/C is 40mm steel with a wall thickness of 2mm.
The weight carried will be no more than about 200kg (sprayer will weigh 110kg max) and is a maximum of 60cm out from the B/C connection.
A couple of things that would add strength and not need to increase the overlap length would be to plug or any least plate the end of B and over sleeve C to a little past either end of B.
We used to use to make 'a' frame set ups - the male side of the frame on the 3 point linkage and the corresponding female side on the implement - easy to make any very quick.
Look at 2" Receivers for some ideas: eg http://www.ebay.com/bhp/2-receiver-tube
They are common on the back of US vehicles. Nose weights on US trucks can be a lot higher. There is also a smaller receiver for lower loads.
The ring around the end of tube C will help prevent any splaying caused by bending moments. I am wondering if your tube sizes are big enough for something that will be suspended and bouncing around. + if you go for the 2" size you could fit a tow ball for moving trailers around if needed.
Oops, should have said that C will slide over B .... but you knew that anyway 😉
Nice ideas on plating B and a collar on C Mark, I'll do that.
Nipper, An A frame would be nice but the 'tractor/mower' is only small and doesn't have a 3ph (although it's an option).
Andy, I was wondering about the tube size but I can happily bounce on a single 40mm tube bolted to the tractor and I'm 95kg, so I think it should be OK. If it bends I'll make another!
Tractor is ready for a ball hitch if needed.
[img] https://lh3.googleusercontent.com/dnfSB4JxuhZt18nJsLPmwC6DZA4jI7kIRKFh-dephCQ=w844-h633-no [/img]
you dont say how long 'C' is or needs to be.
I would definitely go bigger with the diameter & wall thicknesses especially if there is no problem with trying to save weight - ie garden tractor and not an F1 car.
If it does bend the time and effort expended in making a 2nd one would have covered the slightly increased steel/raw material costs in making the 1st correct to start with!
In engineering terms, the overlap-length shouldn't make a lot of difference.
It does depend on how the load is applied, but I would assume it's loaded in bending. In this case, the highest stress will almost certainly be at the A/B junction, where all of the load is on tube B only.
The overlap is therefore only really important in keeping things well-aligned and the side-walls in contact. Without doing any sums on it (and, I'll be honest, as a somewhat lapsed mechanical engineer I'm not even sure what some I'd be trying to do here - not actually an easy situation to solve theoretically) I would have thought about 100mm or so would be sufficient. 150mm for comfort!
I would have said 70-100mm but using a decent size tube ( I know I keep saying it! ) and with a good close fit so they stay quite parallel and don't wobble around and reinforce the end of C to stop it deforming/splitting.
I assume your sprayer is lot wider than you so there will be twisting motion to take into account as it goes over bumpy ground and you said and it's cantilevered off the back not a point load directly above the connection.
Do you have a high mounting point that can be used to take some of the load in triangulation like a 3 point hitch or something?
Just saw the photo - that's a lawn mower with a bucket on the front 😉
Couldnt see any photos of the back but did see this -
Is that 2" receiver standard? I would always say go more heavy duty than you think. I've got one of those 12V linear actuators in the shed. Was going to use it to power my security gate but never got round to it.
Andy, yep it's a mower (a commercial one though!) .... and it's great! Didn'r know they did a loader for it until a few weeks ago and they stopped making them in '12 but I found a NOS one at a dealer in Surrey for less than half the original price. Handy [s]toy[/s] tool 🙂
The sprayer tank is about 32" wide but the frame is going to be connected to the tractor/mower with two of these tubes about 16" apart - not one so the twisting force will by little and obviously the load on each tube is about 50-60kgs each.
[img] https://lh3.googleusercontent.com/9j8P2CXCTBZIa0RNcdQRQ36KKQAm8NUZRy4NEdKcCbE=w476-h633-no [/img]
[img] https://lh3.googleusercontent.com/OwPJSIVvTG9gNwGEY_bXsNOlMKPOT5mWYiGsnCiGeUg=w476-h633-no [/img]
Yes, I could actually add some triangulation but seeing if I can do without for simplicity/speed of mounting.
ahh so there is two spaced apart? That sounds a lot better. 100mm in that case should be more than enough and you could get away with less. Weld a hoop of metal around the end of C as mentioned earlier. Consider a rose jointed turnbuckle to triangulate to a high point if you find it sags too much but you should be fine if you get a reasonable fit between the ID and OD of the tubes.
Looks like it is set up for a 3 point hitch? http://www.shopgreendealer.com/John-Deere-45-Gallon-3-Pt-Hitch-Sprayer-LP20840.html
edit: ignore that, your photos just loaded.
Looks fine with the two spaced tubed. 65-100mm overlap should do it. mock up the lower and see it how it goes as it will reduce the cantilever a a lot and keep your nose down.
Actually, something like at least double the tube diameter would be a good guess. Mock it up with short overlap but longer cantilever and see how it is and then chop down if it seems fine, adjust for longer if not.
Cheers guys 🙂