How to cut a log

[woodfarmer]

I have been given a very nice pear wood log. It is 28 cm long and 47cm diameter. What would the best way be to cut it to make bowls? I can only think of cutting off two chords to make two 28cm bowl blanks then cut the remaining oblong to make two more 28cm blanks and one 20 cm blank leaving an 8cm off cut. Anyone have a better way to cut it? I would hate to discover there was a better way after I had cut it.

 

[paulm]

I think I would likely cut it along the pith so you have two half logs, each 28cm long and 47cm wide.

I would then take a half log and cut off either side to leave a 28x28 piece of maximum thickness from the centre of the half log. This would leave you with two side offcuts of 28x8.5cm approx'.

The 28x28 piece could then be cut into two same size pieces of reduced thickness, around 23.5cm each.

Repeat on the second half log.

That would give you four good size blanks and four offcuts I think.

May be the same as you suggested above, not really sure !

Cheers, Paul

 

[CHJ]

A great pity the log section was cut so short, ideally you want at least the length and diameter to match.

This PDF may be of use in giving you some guidance into the growth ring patterns that may manifest themselves when turned from any given slice or section.

 

[Neil Farrer]

I would suggest you cut it either side of the pith so you have three sections. Dont be greedy - cut a decent width out of the centre. From this board cut the same section as the depth of the board, essentially a spindle blank containing the pith and put that on your woodburner! If you are not going to use the wood immediately now slice the triangles from the edges of the semi circular sections so you now have a section resembling a round roofed house with vertical walls. Now slice a thin section of the roof off. The reason that you do this is that the differential between the radial and tangental contraction is that which causes the tensions and splits. If you interupt the tangental forces (shrinking around the circumference of the tree) you will stand a greater chance of avoiding it splitting. The greater the difference between the tangental and tadial contraction ratios, the greater the risk of splitting. The root of most splits is the pith, and to cut the log in half will inevitably leave sections of the pith in both sections as it is not dead straight. Typically a tree will contract tangentally between 6 and 12% and radially between 3 and 6%. The spindle blanks that you can cut from the narrow boards either side of the pith from the centre section will be quarter sawn and will be reasonably stable.

If you dont remove the top, the tangental forces will force the wood to cup putting presure on the centre of the tree to split.

Hope this helps.

 

[woodfarmer]

CHJ, Thanks, I have saved that file, it may well induce me to try turning some bowls differently than the basic half circle with the top from the middle of the tree.

Neil, thanks also, Had to read your post a couple of times before I fully understood what you meant. Because of that I will be sure to remove the pith from the blanks I cut AND the tops of the outer layers.

I have several pieces, fortunately most have similar lengths to diameters. Is "spindle turning" a green bowl a real option? or is it likely to split.