Having trouble visualizing what kind of 'spiral' you mean and how uniform
it must (or mustn't) be.
For an inside threaded straight hole, you could drill out the majority,
then use something like the auger at http://www.homedepot.com/h_d1/N-5yc1v/R-202935069/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=anchor&storeId=10051 to create
the spiral thread.
For a large worm-hole spiral maybe http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=202703690 , then a flex-shaft
drill, then back to the spiral.
For a 3" OD wormhole (that you could stick your arm into) I have no
idea.
Might wetting it slightly as you proceed help?
Let us know what you end up doing.
On 10/5/2012 5:40 PM, Nick wrote:
> As part of an installation an artist friend has asked me if I could bore a
> spiral hole of about 1" dia endways through a seasoned hardwood log. Log
> would be about 14" dia (ish) and about 3ft long. Dia of the spiral not too
> important but minimum about 3" OD. It is important to the artist that the
> spiral be contained entirely within the log. She will not encounter through
> drilling and plugging. I've done some oddball stuff for this lady over the
> last thirty years but this one has me stumped. She only asked me a couple of
> hours back and no doubt I'll be pondering for days. Hence this post.
> The final product would be only a minor component of the whole which is
> intended to have a practical and useful purpose. On this I am sworn to
> secrecy. I can say that there will also be a ballista type machine involved
> in the apparutus and the intention is saving, rather than taking, of life.
> The project is somewhat W. Heath Robinson, but it is food for thought.
> I'm in England and have always had a great love for WHR's designs.
>
> I know the above is daft but (1) the only daft question is the one that you
> don't ask and (2) anything is possible.
>
> Many thanks,
> Nick.