Spoon bit geometry

[W.Pastuch]

I hope I'm not asking to reveal some secret, but I'm wondering on what is the correct geometry for spoon bits? What makes them work the way they are supposed to? I haven't learnt to drill by hand yet, but I'm planning to, hence the research.
From what I've seen on different photos and a couple of ones that I've seen in Mimmo's shop, they're basically a round rod, with the point ground to the desired shape (which is the shape of the bottom of the bowl), and ground flat through the half of it's diameter. Is that correct? Is the flat part actually flat (concave maybe)? Is that 'flat' part ground exactly along the middle of the bit?
Thanks for any advice, sooner or later I will get some spoon bits and I'll hopefully learn to use them without hurting myself too badly

[W.Pastuch]

So, a secret after all?

[KurtHuhn]

I was kind of hoping Todd J. or Brad would chime in, as I am far from an expert.

That said, what small amount I do know is this:
- rod stock profiled to the shape you want
- 48 to 49% of the rod ground/machined away
- flat, not concave, on the resulting face

And honestly some of that may be wrong, but at least it will get you going in the right direction without injury.

[W.Pastuch]

Thanks Kurt!
I still hope that Todd or Brad will give some pointers on this.

If that is correct, then the fact that the remaining part of the bit shoul be over a half of the rod's diameter, is already a very good tip. I imagine this proportion is crucial for a good cut.

[PremalChheda]

You would also have to cut the shank down for gripping in chuck in case you want to chuck it in a tailstock, and harden it before final grinding. The time you would spend trying to make one may be better spent making a pipe. Plus, a professionally made one runs only about $100.00 from Brad. I think it would take me about 6 or more hours to make just one bit ( and maybe hurt myself a little) , and in that same time I could almost make a complete pipe that sells for at least $350.00.

[W.Pastuch]

Thanks for your advice. I'm not actually planning to make one myself, but I'm looking around for some precision metalworking company here in Poland, who would be willing to make this kind of small accessories for me, and a spoon bit is a good place to start.
I would love to buy one from Brad, but ordering almost every little pipemaking thing from abroad is already a big expense for me so saving some cash is always good when you can. I guess for the cost of the bit plus shipping to Europe I can have it done here and save a couple dozen bucks.
Besides, I just want to know how it works I think learning the mechanics behind the tools we use is almost as important as using them properly- less chance of screwing up if you're familiar with the theory!