First large (for me) bowl

[Heath Warren]

Hi all,

I am getting ready to start my largest bowl (mostly I’ve done 6-7 inch bowls). I have a 12/16 Laguna lathe. My blank is a 10x3 piece of Macacauba. I’ll cut it round before I start. I have a new Vicmarc chuck with 100mm jaws.
My questions are:
1. For initial roughing and shaping should I turn between centers, or use the worm screw?
2. Tenon or recess to mount to the chuck for turning the rest of the bowl.

The shape I’m aiming for is flying saucer. 2/3 convex curve at the bottom, and a 1/3 convex curve on top. Then a concave recess in the top for the bowl part that’s about 1/3 of the bowl radius.

I’m a bit nervous turning something with that much mass, but I have pretty good spidey senses when something seems off.

Thanks for any experienced input I can get. This is for a charity silent auction and I have plenty of time to complete.

Here is a photo example of what I’m going for:

 

[Alan Weinberg]

If it’s your largest bowl and you are unsure, use screw. If comfortable turning, quicker between centers and retain ability to adjust blank to best position. As for tenon or recess (mortise), whatever you are comfortable with, but if you make a recess, don’t go deep (less than 1/4 inch), leave wood around it, and remember when turning the bowl that you have a recess so you don’t funnel it!

 

[Joel Daniels]

I also have a Laguna 12/16. I turn 12" bowls frequently. I always use a wood screw. I bring the tail stock up for the initial outside shaping. I always turn a tenon. For a 12", I usually turn a 4" tenon (less than 1/4" deep - maybe closer to 1/8") that becomes the final foot. I completely finish the outside before turning around to do the inside. For that size, I have to set the belt to the lowest setting to get the most torque. That limits the highest speed to mid-500's. Final cuts need to go slow with minimal shavings. Good luck!

 

[Dave Landers]

1. For initial roughing and shaping should I turn between centers, or use the worm screw?
2. Tenon or recess to mount to the chuck for turning the rest of the bowl.

In all honesty, these are personal preferences, and there are pros and cons to each. No absolute answer for "should I".

My personal preference is to start things between centers because 1) it's just easier and quicker for me, and 2) I can adjust the orientation. Between centers I can eliminate or highlight figure/voids/etc, balance grain patterns, or even change my mind about which is the top/bottom. With a screw, you lock yourself in once that hole is drilled.

But a worm screw in the right size hole, especially when backed up with the tailstock, is probably more secure in most cases. So if you're more confident that way, use the screw.

And for the bottom, I personally prefer tenons - mainly because they're easier to make when the tailstock is there. I also have more confidence in their holding power (maybe that's all in my head). But a recess might be the only way to go if you're short on wood and the recess needs to become part of the foot design. But you can also use wood inside a larger tenon for the base.

If you decide on a recess, remember the jaws are pushing out on the wood so leave enough "meat" there outside the recess for the jaws to push on.

 

[Jaramiah Severns]

Agree with Dave that these choices will vary depending on who you ask. I prefer to use a tenon over a mortise, especially if you’re a newer turner. Gives you a little insurance; if you go too deep, the tenon becomes a foot and you avoid a funnel.

 

[Don Stephan]

Never heard of that wood species. Nothing wrong with gluing up a blank of the same size using poplar and turn as intended. You may decide to change the design, before starting on the intended wood. Make sure your intended blank is completely dry before starting, not coated with wax and wet.. My 2 cents.