BarleyTwist Dimensioning

[darkside5374]

I want to create a double open barleytwist using my small lathe.

My piece of timber is 40mm diameter, I have drilled a 10mm hole all the way through.

Normally with a 20mm radius, I would mark 20mm segments along the length giving me a full twist in 80mm. If however I have reduced the amount of timber depth by 5mm (radius of centre hole) then would I make the segments 15mm (20mm - 5mm) resulting in a full twist in 60mm?

This way I see the open twists being 15mm in diameter each

Comments please

Tony

[Skew ChiDAMN!!]

It depends on what "air gap" you want between the spirals, but in my opinion you're on the right path.

With 15mm twists doing a full turn every 60mm then you will have a 15mm air gap between each strand. ie. it's the same as the strand thickness, which I think looks best.

There are times when you need to change the air gap, but usually only when doing show-off pieces, such as trapped balls, etc. (Which I've never managed to succesfully pull off, but one can dream. ;) )

[darkside5374]

I felt if I used 20mm segments then my spiral would be 20mm x 15mm, oval not round

[Skew ChiDAMN!!]

This is where the air gap I mentioned comes in.

If you marked it out in 20mm segments and kept the spiral cross-section round at 15mm radius, the air gap to the next segment would be 25mm. (The 20mm mark plus the 5mm you 'took away' from the previous mark.)

Rather than confuse the issue, lets just say: "Yes. Marking it out in 15mm segments should give you what you want."