Woodcut was too small, Oneway was expensive for my lathe, So I purchased a Kelton Jumbo. On my second try - first on walnut - I ruined one of the bowls because I was unable to estimate the correct entry angle.
Here is what you do not want. A funnel instead of a bowl.
This happened because I had not left enough wood at the bottom when I cored out this walnut blank. Fortunately this was not the biggest bowl but the next to biggest. It is important to start the cut at the correct angle so that the coring knife finishes at the correct depth.
I am sure this comes easily to those who have used this coring system frequently but I needed some guidance as I was starting out. Though I watched the Mike Mahoney video but it was still unclear how to estimate the entry angle.
So here follow two ways to establish the entry angle:
1 Measurement technique:
To calculate the entry angle I made up this half circle on bristol board with the same radius as the coring knife. Cut out the template with some scissors so that it can be held up to the wood.
You do not need a complete half circle. A quarter circle is fine. (See examples page)
5.5 – 4 =1.5
5.5 is the total wood
thickness,
The four is obtained by
adding the three 1 inch thick bowls and the three 0.33 inch cuts. (3+3 cuts of
.3 inch each)
I obtained this angle by moving the template so that the line down the center of the template is slightly angled. An imaginary line drawn through point #1 and 1.5 inches on the centerline will be parallel to the face. Holding the template to the face at this angle will generate the correct entry angle.
To explain this further imagine using the straight cutter which would generate a perfect cone. If you made a conical (triangular) template in the same style as this template, you could apply the same principles.
For my lathe a back and forth rocking motion seems to help the knife enter the wood without jamming in the groove. However it is important not to pull on the handle but try to push the knife into the cut. Pulling on the handle causes the knife to jamb in the groove as it does not follow its own curve.
I do like the coring process as it is faster than carving out the whole interior and one gets to keep the wood for more bowls. I now have the jumbo set of cutters plus the most curved of the standard set. When using the standard cutter the holder height has to be adjusted from that needed for the jumbo set.
For another example click here
Also see below for an alternative:
2 Center hollow technique
Here is another technique which may appeal to those who do not like all the measuring.
Use
the outside of the bowl to establish the initial angle. This works well
if the coring knife has about the same curve as the bowl exterior.Here is another technique which may appeal to those who do not like all the measuring.
You can also make a small hollow in the center of the bowl to be cored and use the angle created at the edge of this depression to establish the entry angle. (See picture bottom right.)
The picture below shows the entry angle as established by the hollowed center of this bowl (picture bottom right) but with the toolholder moved to the entry location.
