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Thread: Best of a bad job

  1. #1
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    Best of a bad job

    Had a small welding job to do on the headstock of a Kuhn 5f master 120 plough- the pin welded just above the top link holes on the rear of the headstock which the turnover ram hinges on had cracked 2/3rds of the way through. To make it easier I stripped the headstock of the turnover ram and a few other bits before removing the circlip and cover for the mainshaft adjusting nut, then the lockwashers and the nut, that was when the job suddenly became a bit more complicated!

    It started with the smaller front bearing coming off the hollow shaft with lots of damage to its inner flange and the 90mm step on the hollow mainshaft was in a poor state, it looks like the former owners may of had a similar issue and the damage was built up with weld, then ground back to fit another bearing? Probably because a new hollow mainshaft is around the 750 mark!

    If you look at the first photo you can see the sort of damage which I covered up with a layer of weld. The next stage was to somehow come up with a way to accurately grind back the weld to the required 90mm.








    So after much thinking it was time to make a simple guide to hold a 4-1/2" grinder that could be slid across and along the straight part of the shaft so the disc would grind at a consistent depth all round just like the pro surface grinders!!

    Using a section of channel with a slotted 10mm hole to mount the grinder by the spare handle mounting hole in the gearbox casing and angling the inner edges of the channels inner/underside so that slides around the shaft smoothly. Now time to see how it performs










    Using some 3-in-1 oil to help the "tool" slide easily, it soon started to make a decent job, I had buffed up the welds with a flap disc, using a simple stop-go gauge to get near the 90mm target size, then it was a matter of slowly working around the shaft in 4 stages. It took 6 discs using just the outer edge to complete, changing discs with only approx 1mm worn off the edge- all six went back up on the wall, perfect for further use


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  2. #2
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    Re: Best of a bad job

    Once we were down to within 0.5mm of the target 90mm diameter things changed to polishing the built up section with emery tape and then repeated offering up of the bearing so it marked any highspots, with gentle tapping of a rawhide hammer on and off soon all the highspots were dealt with so that a good final polish with the 2m of emery tape got it down to a gentle slip fit. All that then remained was to tidy up a few threads and fettle the nut where Mr Bodger the previous owner had used a pin punch to "adjust" the nut!!

    Turning the casting and shaft was easy once I had tacked a tube to the bench and slid the hollow shaft over it, then it was a simple job to use the nice little 500kg electric jib crane to rotate it. Should of acquired it years ago, makes juggling lumpy thing on the welding bench really easy to do on my own.

    All that remains now is to make good the ram mount that was the original object of this exercise


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    Re: Best of a bad job

    I like how you hooked up the grinder to the channel iron (3rd picture - second row).

    I wonder, if you had started by using some thin washers (or 1960s GM upper control arm shims) between the channel iron and the grinder, could you have avoided having to replace the grinding wheel as often?

  4. #4
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    Re: Best of a bad job

    Quote Originally Posted by Ironhead View Post
    I like how you hooked up the grinder to the channel iron (3rd picture - second row).

    I wonder, if you had started by using some thin washers (or 1960s GM upper control arm shims) between the channel iron and the grinder, could you have avoided having to replace the grinding wheel as often?
    There was no need, it worked out just right with that size of channel and the shafts diameter, to get the disc edge near to the work meant the grinder was quite offset to one side which meant that by simply sliding the bolt & grinder 1 or 2mm along the slot took about 0.5mm more off the workpiece. I really changed the discs more to keep a decent square face to them, more in the latter stages. After smoothing down with a flap disc there was 3-4mm to knock off to the point where I could see there would be 99.9% no voids or gaps so that "used" a couple of discs, and then another 4 disc edges were needed to get to the fettling/polishing point.

    It all worked reasonably well because the shaft had a nice parallel section between the races to work the channel on, if it had been like most axles etc with a taper we'd of been stuffed!!
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