Thread: A tricky bit of turning

Hi Ken,
Your drawing hasn't come through. Have you tried to see if anyone has an old stock one?
Dave

Dave,

Forgot to include attachment, now fixed. Scrounged around gas stove shops and a recycling facility, no luck. I can buy the complete piezo lighter for around $35, but that means pulling the stove apart, and I consider $35 a bit steep for a $0.30 part.

Ken

Does it need to be exactly the same shape or will an approximation suffice? My initial thought was to cut out the underside profile 1st using a custom ground tool then shape the top slope as close as possible to what you want and part off. This would leave a flat top instead of the concave surface in your drawing.

I'm still thinking how to do the next step..... what material are you trying to use?

I would just hand turn it on my wood lathe out of Delrin or similar and cut the slots after

On a metal lathe using Delrin - Machine the outside dia. Face the end and cut the rear grooves. Then turn the outer elliptical shape with a ball turner or a rest and sharp tool and then part off? Wont give the concave face but otherwise all good...

or

make a mold and make the knob out of 2 pack polyurethane or similar?

cheers

Kevin

Hi,
I am not an experienced machinist but my thoughts would be to do as Rathkool suggests with his first idea, then remove from the chuck and mount on a stub mandrel made to closely fit the outer groove cut previously, perhaps using an adhesive such as shellac to hold it, and then remount in the chuck and using a ball turning attachment to cut the concave with the 30mm radius. If no ball turning gear available, and you just did the eliptical ?? diameter freehand, or by calculating the radius at various linear distances or by whatever other method you fancy, you could still make a simple tool holder to cut the 30 mm radius concave if your tool-post does not lend itself to swinging a tool at this radius. One idea might be (if your top slide has a T slot) would be to turn a cylinder of around 45 mm diameter and bore it for a close sliding fit on the tool-post hold-down bolt. Face both ends and make the length such that the tool-post bolt can just clamp it down. Next cross drill it at a height just below centre height, to accept a piece of drill steel of suitable diameter to grind your cutting tool. an old broken 1/4" drill bit should be fine. Then diametrically opposite drill another hole to hold a suitable length of bar for a handle. You could probably use Loctite to hold the handle and he tool, but if you prefer you could thread the handle and drill and tap another hole from the top to allow a small, say 3 or 4 mm bolt to lock the tool in place, at 30mm from the centre of the holder to the cutting edge. Adjust to centre height with shim washers - even light card like a wheetbix packet should do the job here. Those are my thoughts anyway, but as I said earlier I have plenty to learn on this subject, it would pay to confirm with more experienced machinists any of my methods. Best of luck,
Ropetangler