I started by finding a scale drawing and using it to produce a rough sketch of the chimney with all of the dimensions in millimetres.
A length of 5mm dia. brass was put in the chuck with 18mm sticking out. This was faced off and turned down to 4mm dia. (bottom flange dia.) 16.5mm long;
With a pointed turning tool fitted at an angle the part was turned to 3.4mm dia. (top cap outer dia.), starting 2.3mm from the end;
The centre section was then turned to 2.5mm dia. (finished dia. +.2mm);
Using a parting-off tool a 2.5mm dia. recess was cut above the top cap, to clear the forming tool;
The top cap shape was formed using a 1.6mm wide round nosed form tool, specially ground for the job;
Touch onto 2.5mm dia, move tool along until it touches corner of cap, move tool along .75mm.
At first I tried forming the cap using a round needle file, however I wasn't happy with the results ( I scrapped 4!), finding it difficult to make both radii consistant, especially as I wanted to make 5 identical chimneys..
The bottom radius however was formed with a needle file, larger diameters seem to be easier to form with a file;
With the pointed tool re-fitted the centre section was turned to its finished dia., 2.3mm, 10mm long. Remember that a chimney often consists of a tube sitting between cast top caps and flanges, which fit outside of the tube ends. Turning this section after forming the cast top and bottom sections means that it won't be marked if the file slips.
Centre drilling next, then the chimney was drilled through 1.5mm dia. To form the flange the inside of the bottom of the chimney is filed to a bell-mouth shape using a needle file, to reduce the wall thickness;
Then the chimney could be parted off to 14mm long.
To form the flange shape I set the machine up as a drill press, held the chimney upright using a little mandrel and squashed the base of the chimney against a length of half inch dia. stock (much the same as I did with the Px48 chimney);
Job done;
All turning and drilling done at 2000rpm, apart from forming and filing, 685rpm, and parting off, 365rpm.
Click on the photos for a larger image.
Paul.
These look fantastic! I think I still prefer your recently turned buckets, but that may just be because I've at least seen good chimneys before but those buckets were far beyond the quality of any cast parts I'd ever come across.
ReplyDeleteThanks Mark.
ReplyDeleteI take the opposite view, to me the buckets are just simple turnings. One advantage of cast whitemetal for such items is that the finish isn't too far away from galvanised metal, whereas a decent turned chimney will always look better than a cast one (all to do with surface finish and a lack of mould lines).
True, I guess with the buckets it was that they looked much more natural that most castings I've seen given the more sensible handle placement etc. I agree though that these chimneys are much finer than castings given the lack of moulding lines etc. they are probably more robust than the whitemetal castings as well.
DeleteI have one more of these to make this weekend, which will be used as a casting pattern (I'll be taking a slightly different approach to forming the bottom). So, it will be interesting to compare a casting to the master.
DeleteYes, that will definitely be worth an other post to see the difference.
DeleteThis is very fine work...and yet you make it look so simple.They are little works of art!
ReplyDeleteThanks Iain.
ReplyDeleteThey were actually quite easy to do once I'd stopped messing about with files and ground up a profile tool. There's a lesson to be learnt there...
One day I'll show you my scrap pile.