Sorby spiralling

[duncanh]

At a demo at our club towards the end of last year the Sorby rep did some work with the spiralling tool. He said that he thought there was an formula to help you get an accurate spiral - what angle to use etc. This makes sense - some of settings shouldn't work for some diameters as the circumference of the piece needs to divide by exactly by the distance across the grooves. Has anyone come across such a formula? It'll save me the bother of working it out if it's been done before!

I've not used the spiralling tool much and I'd like to experiment more with it but other than coming across such a formula the only way is to get a bit of wood, turn it round, try a setting and if it doesn't work turn a bit off and try again. There really must be a better way which doesn't waste wood! Ideally I'd like to work on the side of large bowls (but I'm pretty sure the sides would have to be parallel to the lathe bed).

Any ideas?

Duncan

 

[spasm]

Hi Duncunh,

My first proper use of the spiraling tool was forlast months chalenge did the stem of the candle holder but didn't take any notes doh, so i also would be interested in any formula.

Spasm

 

[mpax356]

I am not aware of any formula in common use by Sorby spiral tool users and I have seen several demonstrators including one from Sorby. Most folks suggest not setting the angle setting more than 1 1/2. I would not want to spiral on too much surface on a curve bowl. In other words if the diameter of the piece changes too much you are like to get some unclean spiraling. Mostly it takes some practise like using any tool. I suggest playing with it before you get too hung up on deriving a formula. I have had some pretty good luck with spiraling. I do the outside of the bowl before I hollow. If the spiraling is not clean I can take it off and try again.
Here is a sample.