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Chuck Jaw Size for Coring

I don't often turn, or core bowls over 14 inch diameter, but do go up to 16 inches some times. I use a recess, and use my Vicmark 120 chuck. The jaws are about 2 5/8 wide. Pretty sure that is a metric measurement. I would think with a tenon, you would want 4 or so inches for the diameter of it, maybe a bit more if you are twice turning. I use the McNaughton coring system.

robo hippy
 
Thanks robo. I also have the McNaughton. It would be rare for me to core a 16" blank, but just want the capability if I come by a blank that large. Do you find a recess to be more secure than a tenon?
 
I’ve cored a number of bowls with my McNaughton system using a tenon and #3 jaws in my Oneway Stronghold chuck. Most of these were 10-12”, but a few in the 14-16” range.
 
@Reed: You're right, the official name for the standard jaws for the VM120 is 68 mm, but if you look at the dovetail model range, the sizes may be metric by name but the imperial "translations" and intervals tell another story. The sizes are close to 2½", 3½", 4", 5", 6", 7", 8" and 9"
Lars
 
@Ed: For coring, I use a locally made bowl saver with cup shaped carbide bits making a rather wide kerf.
For that, I use 4" jaws and find the the hold very well and control the process perfectly. A had some vibration using the standard jaws, but I use a spigot mount, not a recess.

Lars
 
@Ed: The 4" measurement is the outside diameter of the jaws almost closed (2mm apart).
The jaws wil fit a recess of 4" and a spigot of around 3½". My go to jaws for coring.
 
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When I used the Woodcut Bowlsaver I normally used the 2" Nova jaws as the pieces were 12" or less. Now doing 16" or 18" pieces with the Oneway I use the Nova Titan either 5.75" jaws or the Titan 6.5" jaws. I always use a tenon. Chris Ramsey starts with the smallest and cores towards the biggest. I start all my bowls on the Nova screw in the chuck and I core from the biggest to the smallest. I start each successive core on the screw. That way I always have a tenon already on when I go back to finish each core.
 
I use the 2 blade Woodcut system, and have cored several 14”-15” bowls. I have used Stronghold #3 and #5 jaws. The #3 had plenty of grip for coring. I like the larger jaws to provide more wall support when finish turning the bowl. I use a tenon, and finish cut the foot after hollowing the ID, removing the large tenon. I core from smallest to largest bowl, one after the other, then mount with a jam chuck between centers to cut a tenon, then finish turn.
 
Thanks for all the feedback. I have Powergrip jaws for my SN2; I'll give them a try. If they don't provide for a secure mount while coring, then I'll probably invest in the 130mm jaws.
 
Doug Freeman said:
I use the 2 blade Woodcut system, and have cored several 14”-15” bowls. I have used Stronghold #3 and #5 jaws. The #3 had plenty of grip for coring. I like the larger jaws to provide more wall support when finish turning the bowl. I use a tenon, and finish cut the foot after hollowing the ID, removing the large tenon. I core from smallest to largest bowl, one after the other, then mount with a jam chuck between centers to cut a tenon, then finish turn.
Click to expand...
Hi all, from a Woodcut Tools perspective we recommend at least a 4" spigot/ tenon is made to establish a nice wide grip held by a large dove tail chuck. Our friend Phil Irons recently produced a video demonstrating the process to create a Dovetail Spigot or Tenon for bowl coring
View: https://www.youtube.com/watch?v=VdnV4C-bF4k&t=113s&ab_channel=Woodcut-Tools
 
I do have a video up about Mounting things on the lathe. The argument about which is stronger never stops. The point I make is that when made 'correctly' there is no holding advantage to either one. I prefer a recess as my finished bottom. I sand it out and sign in the recess. I do now use a dedicated NRS with a left side sweep for finish cuts inside the recess rather than the dedicated dove tail tool. I have turned bowls up to 16 inch diameter with the 2 5/8 wide recess, and no problems. I have learned how to do this through trial and error, correcting as I go. The biggest bowl I have ever turned and cored was a 22 inch diameter piece of madrone. I used a 4 inch recess on it. My biggest coring blade left about a 3 inch tenon on the core blank and I had to beat on it to break it off. Didn't damage the recess at all. I do once turn all of my bowls. My process might differ a bit if I was twice turning, but I like the warped bowls.

For mounting the blanks in the first place, I drill a 2 5/8 inch recess in the top and use that to expand into. No problems with the sides being straight. No screw chuck to put in, then take out. No face plate and screws either.

robo hippy
 
I use the Macnaughton and routinely core virtually every blank from 12 or 14 inches to 20 and 23" once in a while. I use a 4-1/2" tenon on vicmark dovetail jaws for virtually all coring and roughing. The jaws optimize at 4", but roughing out I leave the tenon at 4-1/2" so it can be trued when twice-turning the roughouts later on (they'll generally fit into the same jaws saving me a chuck change).

A 4" tenon is plenty strong especially since the Vicmark dovetail jaws accommodate a longer (1/2") tenon without bottoming out.
 
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