Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Obviously I am missing something .
Shadetreemotorcycle talks about needing a collet chuck for machining the PM globe valves ??
 I have looked at their castings and instructions I have and the castings are Hexagon not round
 I thought collet chucks are for round ? And hexagon usually goes in a three jaw .
Can some one please educate me as obviously i am doing something wrong in my workshop.

Cheers
Dennis

Dennis,

You are reading WAY to much of your own personal opinion into my posts.
  I said a collet lathe is MY prefured shop tool, not in any way required to turn things round. l have been machining for 35 years. The primary advantage to a good collet lathe is the ability to take the work in and out (multiple times) of the collet and remain true. Often 3 jaw chucks will only repeat within .002 (some worse) so you have to get an indicator out.
  Point 2: you CAN hold hex stock in a ROUND collet, I do it all the time! There are 6 "points" on hex stock and 3 splits in a 5C collet, you just have to rotate the hex stock so none of the points line up with the splits in collet. I do Not recommend this for precision work as the points on brass are soft and can be deformed by to much collet clamp pressure.
Point 3: they MAKE Hex 5C collets and my last shop had a full set...picture enclosed.
Point 4: the long center stem (what the knob attaches to) is Not hex stock and many people have struggled to turn that long thin part...then when they do get it made it bends or break when they run a thread die over it. One of the solutions I saw a fellow steamer do is only turn about 1/4" at a time so your working close to the chuck, leave .0015 oversize and polish to size when long.
  The traditional way is to turn between centers. I do not yet have my Globe valve kit so after I get them and study the drawings I may do mine differently.