Continuing with my personal learning on the Kel M coring system.
If you have not watch the Dale Bonertz video on using this system, I recommend you watch now. He is very experienced user.
https://www.youtube.com/watch?v=mS2yIb0HAU4
The part I had trouble with was replicating his method to position the knife.
I placed the knife over the bowl, but I had a difficult time tracing the curve back "in the air".
My solution was to make a half circle template for each knife. In theory each knife is a part circle. I used a compass on paper to determine the actual circle for e.g., the outer circumference.
I then draw a half circle on a piece of card. I cut out the half circle keeping the outside pen mark. I also drew a line to represent the inside edge and the 90 deg mark.
I cut grooves in the face of the blank to represent the cores I want to make. I find it is easier to enter the knife in the blank when there is a groove. The actual groove also helps in positioning the knife.
This picture was taken after removing the first core, but shows the groove for the second core. I made the grooves prior to positioning the knife. Dale uses pencil marks. The grooves are easier to see for knife positioning.
In the above picture you will note a piece of PVC pipe. I cut this to exact length so that the knife cutting edge will be at exactly top dead centre. No need to measure, just install the turret and piece of PVC and good to go.
I mark top dead centre on the bowl blank and lock my headstock.
Positioning the knife was a two person operation. One person had to hold the knife and the other to sight down the face of the blank.
I made a simple jig to hold the knife in position. Clamps to the lathe bed.
Front picture. Made from scraps. I needed a wider top support and the wider scrap was not deep enough, so I attached this to the vertical portion with bolt and barrel nut.
Rear picture. Vertical portion is glued to horizontal portion. I cut a piece to fit in the underside of the lathe bed and use a carriage bolt with a simple knob on the top.
This works well. The knife is actually at a slight angle. I can move the support front to back to meet the desired angle.
Now I can have the knife supported while I sight the angle when working by myself.
I leave the support in place for use, just to make sure I do not allow the knife handle to drop which would not be good if the knife in the core were to go above centre.
I use the template with the diameter parallel to the top dead centre position and the outer edge of the template at the outside of the relevant groove. A quarter of the circle over the bowl blank and a quarter of a circle over the knife - once it is positioned in the groove.
I hope this makes sense as you read.
I have observed that my friend and I find it easier to go too deep, so do not worry about repositioning the knife during the cut to make a tighter radius - it may be needed.
Let me know if I need to clarify any details.