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  1. #1
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    Lightbulb Is this possible engineering-wise ?

    I have sheared one of the shafts on my pole saw. Plenty of replacements available but mine is a 7 spline and most are 9 spline now. I can buy new 7 spline shafts & tubes but they are either too long which will make the tool very unwieldy or they are too short and no gentleman wants that.

    So my question is : Can such a small diameter 8mm shaft be repaired by welding a collar where the break is ? That part doesn't go through a bearing and it is not at the point where the splines engage with the coupling on the next tube.

    TIA for any input.
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  2. #2
    Senior Member T P's Avatar
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    Re: Is this possible engineering-wise ?

    Silver soldering a collar would be more likely to work than welding as the end result should not be as brittle. The only slight concern I would have is balance at the shaft I think runs at engine speed. Nothing to lose trying. Silver soldering is easy all you need is the heat to get the parts up to near red and the stuff runs on a treat. Needs to be clean and let it cool naturally don't dunk in water as it'll go brittle.Don't mistake the term solder for a poor joint, silver solder is a seriously strong joint and creeps into small gaps by capillary action. It's an expensive joint compared to welding but far more forgiving. Ask at your nearest motor factor/welding supplier for a few flux coated rods that look like these:

    http://www.ebay.co.uk/itm/Silver-Sol...MAAOSwU-pXrw2T

    Very good for one off repairs on delicate stuff but not economically viable for mass producing things cheap. Pulled me out of the doo doo many a time. you'll be back for more rods once you use them. Better value in small quivers @80-100 but you need to be doing a bit of work and store them dry. Big variation in price _best value usually comes from welding supply shops.

    https://www.wellyweld.com/products/s...ted-72591.aspx

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    Re: Is this possible engineering-wise ?

    Thanks TP. Would never have even considered soldering and have never done any silver soldering. Making a small collar is easy enough and I have gas to get things warm. So everything up to near red and just touch the collar ends with the rods ? Certainly worth a try. Are they the correct rods in your link ? If so I'll order some.

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    Senior Member T P's Avatar
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    Re: Is this possible engineering-wise ?

    Quote Originally Posted by zaza View Post
    Thanks TP. Would never have even considered soldering and have never done any silver soldering. Making a small collar is easy enough and I have gas to get things warm. So everything up to near red and just touch the collar ends with the rods ? Certainly worth a try. Are they the correct rods in your link ? If so I'll order some.
    Try to get the 55% silver ones if they are available locally, ebay are rip off prices. You need to be around the cherry red zone to get it to flow properly. I use a propane oxy cutting rig with a softer flame. I don't know if a plain propane blowtorch would cut it temperature wise as I've always had the oxy on tap. Size of flame depends on size of item being welded. Keep your collar a decent fi on the two parts. if you know someone wit ha hydraulic crimper they could give it a wee light squeeze before you do the joint.As we don't know the parent metals it's always a gamble but SS is very versatile and brilliant for delicate items, I've used it for donkeys to make up all sorts of fittings and repair everything from broken wardrobe hinges to leaking injector pipes.

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    Re: Is this possible engineering-wise ?

    Quote Originally Posted by T P View Post
    Silver soldering a collar would be more likely to work than welding as the end result should not be as brittle. The only slight concern I would have is balance at the shaft I think runs at engine speed. Nothing to lose trying. Silver soldering is easy all you need is the heat to get the parts up to near red and the stuff runs on a treat. Needs to be clean and let it cool naturally don't dunk in water as it'll go brittle.Don't mistake the term solder for a poor joint, silver solder is a seriously strong joint and creeps into small gaps by capillary action. It's an expensive joint compared to welding but far more forgiving. Ask at your nearest motor factor/welding supplier for a few flux coated rods that look like these:

    http://www.ebay.co.uk/itm/Silver-Sol...MAAOSwU-pXrw2T

    Very good for one off repairs on delicate stuff but not economically viable for mass producing things cheap. Pulled me out of the doo doo many a time. you'll be back for more rods once you use them. Better value in small quivers @80-100 but you need to be doing a bit of work and store them dry. Big variation in price _best value usually comes from welding supply shops.

    https://www.wellyweld.com/products/s...ted-72591.aspx
    T P - would it help him to drill a couple of small holes in the collar (middle or 1/3 of the way from each end) to help draw the silver down the inside of the collar?

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    Re: Is this possible engineering-wise ?

    I've been having a think. The tube that this shaft runs in is circa 24mm ID. Any collar could be 15mm OD and would easily fit inside the tube. The collar could be almost any length but it must not go down the male splines any further than where they engage with the female splines of the next section. Suppose I made a collar that sort of size and then drilled and inserted a couple of roll pins through the collar and shaft after it had been silver soldered ? Or is that the blacksmith coming out in me. Thanks to you all for the help so far.

    This is what the shaft looks like when not sheared.

    Shaft5.jpg

  7. #7
    Senior Member T P's Avatar
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    Re: Is this possible engineering-wise ?

    If you get the collar to fit snugly the joint will very very strong. I wouldn't be in favour of drilling the shaft as it will create a weak spot for cracks to propagate from. I was wondering if the splines were hardened or can you mark them with a file or hacksaw? On such a simple device possibly not hardened and the one you pictured had twisted rather than snapped. Not hardened is better for silver soldering as the process would draw the temper on a hardened shaft. If you put the twisted shaft in a vice and heated it to red it should be possible to "untwist it" so it would mate up to the original then out a collar over with perhaps a hole in the collar at the break to let plenty of solder flow in. It's one of those things that could be a great success or thrown in the scrap after ten minutes but that's how you learn things. Probably cost about a fiver to have a try so no worse than a nag in the national.

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