Flying Mango

Flying Mango · 10-12-2008, 05:25 PM

Today I was rough turning a piece of curly Mango I got from Kalai. It is much too pretty a piece for a beginer like me to ruin, but "NO THANKS, I think I'll keep it anyway".

Once I shaped the outside, I moved the tool rest and started to work on hollowing it out. I had only cut maybe 1" into the end. All of a sudden, the wood flies out of the chuck and into the yard. I could see a place on the rim where the gouge grabbed, but it wasn't deep enough to break the hold of the chuck. Glad my vehicles weren't at the garage door cause it really took off. Same thing hapened last week with a piece of Walnut. I know I'm doing something wrong, but I can't figure out what it is. It's pretty scary.

I have a Rikon 12-16 with a Nova precision chuck. I was running the lathe at 810 RPM, next to slowest speed. Mango had a 2" tennon 5/16 deep. Nova chucks call for a dove tail shape on tennon so it had been shaped. Bottom of bowl looks flat, but maybe it could be a little flatter. Would this make a difference? The block started a little wobble a couple of times and I stopped before it actually came off. It had slipped and was not fitting square on bottom. The blank started at 5 1/2 dia. and 4 1/2 high.

Does the bowl bottom around tennon need to be exactly flat?
How deep does tennon need to be inside chuck jaws?
Although this chuck is recommended for up to 12" bowls, could I be using the wrong one?

Thanks for any suggestions, but I'm still keeping the Mango!

WoodWrangler · 10-12-2008, 05:33 PM

Originally Posted by skeeter

Does the bowl bottom around tennon need to be exactly flat?
How deep does tennon need to be inside chuck jaws?
Although this chuck is recommended for up to 12" bowls, could I be using the wrong one?

Okay, let me ask the simple question first ... are you absolutely sure you are using a bowl gouge and not a roughing gouge? Because my first two bowls about a year ago did the same thing ... but my problem was the type of gouge.

To answer those questions you may want more of an expert, but here's my take and understanding:

The bottom of the bowl should be flat, or as flat as possible so that it seats well and evenly.

Usually I would guess my tenons are 1/4" min and 1/2" max (if that). Never really measured, just eyeball it. It's worked so far.

The chuck is probably fine. Just double check the tightness after a couple of minutes with the gouge in use. I usually give mine another snugging twist.

Let's see what everyone else says ...

FredP · 10-12-2008, 05:59 PM

I can assume you are using the correct tool and it is sharp.

I sharpen after a few cuts and everytime I sharpen I snug up the chuck.

wood compresses.... after the blank is round I use much more speed than you are.

dont know if thats a good idea or not but I'm a little on the crazy side and I like speed!

I get fewer catches that way and the blanks tend to fly better too!

I AM NOT GOOD AT THIS TOOL!!!!

so follow others advise before following mine.

work for me and um I never stand in the line of fire.

when the wife asks what was that I just say Im turning planes.

DaveO · 10-12-2008, 06:00 PM

The "cheek" of the tenon needs to be flat (at least where it contacts the top of the chuck jaws), just like in square work this area is what gives it greater stability. The tenon shouldn't bottom out in the chuck, as long as it doesn't it can be as long as you desire. Chucking with a tenon does require periodic re-tightening. A tenon is subjected to the wood fibers being crushed. With a straight tenon this is a bigger issue, with a dovetailed tenon you have a mechanical advantage that can hold it in place even if the jaws get loose.
I tend to chuck with a DT recess, I find that I waste less thickness that way, and if the bowl is too large to reverse and clean up the foot a recess doesn't look too bad.
Are you hollowing from the center out?? A catch with that much force that early into the hollowing process makes me thing that you might be starting out near the outer edge

.
Your bowl gouge will go where the bevel is pointed. I start with my gouge handle across the bed from where I am standing, and slowly rotate it towards me as the cut engages and roll the flute more towards the top.
I am a self taught turner, except for a brief lesson with Big Mike that really opened up my eyes to how the gouge works. So take my advice for what it's worth

Dave

Mike Davis · 10-12-2008, 06:07 PM

I have never had a bowl come off the lathe, lucky I guess.

I make an indented foot and set the bowl onto the chuck about 5/6 inch, Slightly dovetailed.

The bowl I'm working on today almost came apart at the bottom. Surface check I think. I turned it 45° in the chuck tightened it back and kept on working. I'll glue the crack before I oil it. If it had been any worse I would glue it first or maybe even put it in the burn pile.

I always stop if anything feels even a little bit wrong or different. Check everything and try to move the bowl in the chuck. If it moves at all I tighten it or sometimes take it loose and seat it firmly again then tighten it.

Glennbear · 10-13-2008, 12:21 AM

"when the wife asks what was that I just say Im turning planes.

"

Good one Fred !!!

walnutjerry · 10-13-2008, 10:07 AM

Charles----------when I took the turning class at the folkschool, I found out I had been doing things a little different than the instructors do.

1) the spigot/tenon was made just a little bigger than the closed diameter of the inside of the chuck jaws. reason given: there is more contact around the circumference of the spigot to tighten up instesd of 8 "points" on a bigger radius spigot.

2) the lathe speed (around 400 rpm)they use is much slower than I had been using to begin with.

3) Their tools were kept sharp with frequent "touch-up" using the vari-grind jig. (that produces that long grind on the bowl gouge).

4) Tool control----angle of entry, rate of feed for the gouge all have a part in the results. I had been trying to cut too big a cut too fast.

I found out how far I am from being a "turner". Both the instructors could lay the bowl gouge on the tool rest and guide a pass from beginning to end with one hand and have a smooth cut on the outside of the bowl.

It is the transition area inside that gives most people problems----that is where you roll that bowl gouge when starting outside working toward center.

I also have experienced a workpiece getting loose in the chuck, even the one-way 4 jaw chuck. i am not sure if it is vibration or compression of the wood or some of both. It has made me check the chuck more frequently.

Hope this helps a little-------take it with a grain of salt because I am not a pro by any definition.

Jerry