Elbows
Member
Success at last! Just in case anybody's interested in the extended saga...
I was going to demagnetise the original ram but couldn't find a suitable scrap transformer to make a demagnetiser out of. Also, if the ram had become magnetised once then it could happen again so I decided to make a new one out of 316 stainless. I found some suitable tubing on eBay but then found that the internal thread in each end was 19tpi, an unusual pitch which my standard set of lathe change gears couldn't manage. So the first job was making a 38 tooth change gear so that I could cut 19tpi threads. I ended up making a new plastic drive nut as well as the thread inside the original was quite short. Making the drive thread the full length of the nut seemed sensible as it would reduce the rate of wear. Of course this meant that I could have used whatever thread I wanted in the ram as a matching new fitting for the outer end would have been easier to make than a gear, but by the then I'd already cut the thread in the ram.
Put it all back together and it was a definite improvement but the compass heading was still changing as the unit operated causing it to hunt in and out. After a spot of testing it turned out that the threaded drive rod had also become magnetised and as it rotated it affected the compass. I ordered some 316 stainless studding but when it arrived it too was slightly magnetic. Turns out they'd sent me 304 by mistake, but my researches revealed that even 316 can become magnetic if it is heavily cold worked. Studding is usually produced by rolling the thread which certainly counts as heavy cold working, so I decided to go for brass instead just to be on the safe side.
Made the new brass drive rod and also fitted a new toothed-belt pulley as the original was a bit cheap and nasty and it was getting chewed up with the constant dismantling. Put everything back together yet again and it worked! Nice steady compass reading as the ram moved in and out, although it does change by about 5 degrees when it nears full extension. I think it's the steel circlip which holds the slider onto the nut getting close to the compass, but that doesn't matter when the tiller is hard to starboard anyway.
But now I had a new problem - excessive vibration! The brass drive rod had a very slight bend in it which I thought wouldn't matter as the rod is only constrained in 2 places, but turns out it does matter. So took it all apart yet again to get the rod as straight as I could, reassembled it and this time everything worked perfectly.
So, it's been a ridiculous amount of work and I must have dismantled and reassembled it at least 20 times. I've ended up remaking more than half the internals as well as adding the microswitch mechanism, but it hasn't cost much and it's been an interesting project. I'm (reasonably) confident that it will now carry on working. Time will tell.
I was going to demagnetise the original ram but couldn't find a suitable scrap transformer to make a demagnetiser out of. Also, if the ram had become magnetised once then it could happen again so I decided to make a new one out of 316 stainless. I found some suitable tubing on eBay but then found that the internal thread in each end was 19tpi, an unusual pitch which my standard set of lathe change gears couldn't manage. So the first job was making a 38 tooth change gear so that I could cut 19tpi threads. I ended up making a new plastic drive nut as well as the thread inside the original was quite short. Making the drive thread the full length of the nut seemed sensible as it would reduce the rate of wear. Of course this meant that I could have used whatever thread I wanted in the ram as a matching new fitting for the outer end would have been easier to make than a gear, but by the then I'd already cut the thread in the ram.
Put it all back together and it was a definite improvement but the compass heading was still changing as the unit operated causing it to hunt in and out. After a spot of testing it turned out that the threaded drive rod had also become magnetised and as it rotated it affected the compass. I ordered some 316 stainless studding but when it arrived it too was slightly magnetic. Turns out they'd sent me 304 by mistake, but my researches revealed that even 316 can become magnetic if it is heavily cold worked. Studding is usually produced by rolling the thread which certainly counts as heavy cold working, so I decided to go for brass instead just to be on the safe side.
Made the new brass drive rod and also fitted a new toothed-belt pulley as the original was a bit cheap and nasty and it was getting chewed up with the constant dismantling. Put everything back together yet again and it worked! Nice steady compass reading as the ram moved in and out, although it does change by about 5 degrees when it nears full extension. I think it's the steel circlip which holds the slider onto the nut getting close to the compass, but that doesn't matter when the tiller is hard to starboard anyway.
But now I had a new problem - excessive vibration! The brass drive rod had a very slight bend in it which I thought wouldn't matter as the rod is only constrained in 2 places, but turns out it does matter. So took it all apart yet again to get the rod as straight as I could, reassembled it and this time everything worked perfectly.
So, it's been a ridiculous amount of work and I must have dismantled and reassembled it at least 20 times. I've ended up remaking more than half the internals as well as adding the microswitch mechanism, but it hasn't cost much and it's been an interesting project. I'm (reasonably) confident that it will now carry on working. Time will tell.
