Making a form tool to turn globe lubricators on the lathe

Discussion in 'Tutorials' started by Rob Pulham, May 15, 2021.

  1. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    A fellow modeller asked me how I made my form tool that I recently used to turn my whistles.

    I was planning to have another go so I made another form tool and took photos as I went along.


    Using a second cut file I filed away approximately half the thickness of the bar (in the event it was nearer to 35/40% than half).


    Then I used a centre drill to drill a 1.5mm starter hold which I opened out to 2mm. I think my 2mm drill bit must need sharpening because I struggled to get it to go through the last bit.


    I had drilled quite close to the end so I put the rod drilled end upwards in my vice and tilted it forward to file away until I had just over half the hole exposed.


    Then I transferred it to the lathe. I put my cone shaped grind stone in the collet chuck and ground the inside of the hole to put my rake on it. The black pen mark on the stone was at the 2mm diameter mark so I didn't inadvertently make the hole bigger.


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    Next, I used the diamond cutting disk to grind back the outer edges to refine what I had filed and get it nearer to final size. But before removing the tool from the cross slide I marked with a pencil the angle which I had ground at to make replacing the tool at the right angle easier should it need regrinding.


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    Then I hardened and tempered the cutting end. I did this by heating the end using my Microflame to a red heat then I quenched it in a jar of water. I repeated the process but only heating until it changed to a blue colour before quenching again in water.


    I tried cutting a globe but I made a couple of mistakes:


    The material I was trying it on was too thin (2.5mm diameter) and I had predrilled the centre thinking that I was going to thread a rod through it.


    The 'globe' broke off long before it remotely resembled a globe and I realised that even with thicker material I needed to grind more off the tool to make the forming half circle shallower. At this point I used thicker material but still predrilled it.


    Another try; another failure and another regrind.

    The forum won't let me post more than 10 photos per post so I will finish off in a second post.
     
  2. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    The last go was cut from 4mm bar and no predrilling and I also took some of the edge of the 'globe section with a diamond file prior to applying the form tool.


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    Having done all this I now think that I may get away with thinner rod now that I have refined the form tool and my technique.


    Of course, the law of sod dictated that not 15 minutes after finishing the successful lubricator the postie came with some brass bearings that I had ordered from China and wasn’t expecting for another three weeks or so.


    The subject of those will make another posting at some point.
     
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  3. My7mm

    My7mm Full Member

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    Rob that's a great tutorial, informative and handy for fellow modellers who build their locos from scratch.:thumbs:
     
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  4. Rob Pulham

    Rob Pulham Happily making models Staff Member Administrator Feature Contributor

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    Further to my last post, when the brass bearings arrived I knocked one up into a lubricator to see how I would do it.

    It was a bit interesting drilling out the bearing but following advice given I got a short length of tube the same diameter as my bearing and made a slit in it to make a split collet. This I gripped in one of the collets on the lathe and then I centre drilled it. Followed by drilling right through. They are slippery little blighters and one flew off into space as I was attempting to load into the lathe collet. Surprisingly I found it a couple of hours later.

    I was fortunate to have some 1mm square bar in stock so I drilled right through one way and then half way on one side. When I fitted the rod through the bearing and into the square section I filed half of it away for the last millimetre which gave me a bit more room to solder the piece in that goes into the boiler.

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    With the obligatory scaling piece.

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    As with all such things in modelling making one is sometimes the easy part making another or several is more difficult. So it proved with the second one

    I ruined one bearing when I hadn't quite tightened the collet enough and the bearing wasn't centred, then I didn't get enough solder on the cross pipe so that came adrift as I cut it short and I ended up having to re-drill it in the pillar drill before I could solder it back in.

    But get a pair I did. My collection of bits for the D2 is slowly coming together.

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