Last edited by John Bartley; 11-27-2010 at 12:08 PM.
Go watch your buddy, worth the time.
Also, lets see a pic of your bowl gouge, I'd like to see how it is sharpened, I found that most of my catches were mainly because I had the grind, way too long on my gouge.
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
William Arthur Ward
I'm no expert... in fact, I'm completely hopeless. I'm so bad at this there was some talk of making a nickname for me... you know it's bad when your whole reputation rests on blowing things up at the lathe, and people cite you as an example of how not to be...
That said, what's helped me is to really think about what's going on when there's a catch. Even to the point of turning off the lathe and holding the tool up to the workpiece, and moving the tool a little against the wood. What's actually going on in the few millimeters where the steel meets the wood fibers? Is your tool acting like a plane blade, or like a card scraper? If you twist it just a little, will an edge catch? Then, what happens when the turning forces come into play? Does the cutting action tend to turn the tool a little, so the edge catches? Does the steel flex a little, and then pop back? Do your hands subtly let the tool move out of position?
What helped me was seeing some book with a page called "an anatomy of a catch" It was almost like a series of high speed photos in stop motion... the tool rotated a little, the edge started to catch, and suddenly was cutting deeply... you could tell the next photo would be the chisel trying to get away and the piece flying.
Or try this: look at Bill Grumbine's recent catch photo, and try to figure out exactly what the blade was doing at the time...
Good luck. If it's any comfort, you're already way better than me at this stuff...
Last edited by John Bartley; 11-27-2010 at 12:08 PM.
Part of the problem we all experience from time to time is catches while turning. I used to get bad enough catches that I actually sheared off as 12" toolrest with a catch! I did my best at trying to duplicate what I did in tool presentation to the wood with the lathe off. All to find out that "I" moved during the cut causing the cutting tip to go at an angle that caused such a drastic catch. Needless to say...it was a lesson learned.
When turning the inside of your bowls, start with the bowl gouge flute pointing directly away from the side of the bowl and at an angle of about 45º away from your body. This will present the cutting edge about parallel with where you want to start the cut. Use your thumb on your left hand to push and keep even pressure on the tool and you will then be riding the bevel down inside the bowl. Go slow, remember you're not in a race to turn, but to turn a finished piece. I used to think I had to "hurry" and get this done, but that's not what turning is all about.
Now..as you progress further down inside the bowl, then is when you start pulling the butt-end of the bowl gouge towards your body and this will start your turning transition towards the actual bottom of the bowl. The transition from the side to the bottom is the trickiest part, so go easy and with lite cuts until you get the feel for it.
One thing I learned the hard way was to not change my grinding profiles. A change in profile will cause you to have to learn new angles of presentation of the cutting tool to the wood needing to be cut. The best practice is to get a grind you are comforable with, maybe like the Ellsworth grind and practice with that until you are getting the results you want with it and using the tool enough to where bowl turning becomes and extension of you. However, it is fine to experiment with various grinds as some grinds suit some better than others, but it's time you have to spend with each grind to see what grind/angle you like best on your turning tools. Remember that a bowl gouge can be used in many ways to accomplish various cuts. If you don't have either of Bill Grumbine's DVD's? I'd highly recommend getting both of them and watch them more than once. You will for sure learn a lot from watching and listening to Bill's experience as a turning teacher.
Overall, have fun, and relax at the lathe. There is no real substitute for time you spend in front of your lathe actively turning wood into little curlies.
Everyone has catches. The trick, or the goal, is to minimize them and spend more time turning and less time fixing problems caused by those catches. I posted the picture of mine recently to show that everyone and anyone can get them.
A catch occurs when the tool meets the wood at an improper angle. When I am teaching or demonstrating, I do a little segment called forensic woodturning. When a catch occurs, you can stop the lathe and place the tool into the catch to see what happened at speed. It gives you a good idea of how you were holding the tool when the catch occurred. This helps with self diagnosis.
It sounds to me like you are allowing the tool to cut on the left side of the sharpened edge, and that is when your catches occur. This cut can be made, but it is very difficult - an advanced cut. I call it the Dangerous Cut, because of its great potential for disaster.
When you are cutting on the inside of a bowl, the tool should be on the horizontal center line of the bowl, so that the force of the wood is pushing it down against the rest. Think of the artificial horizon when you are flying. If you have it up higher, you are fighting the rotation of the machine, and the machine always wins. You want the shaving to be coming off the right side of the point, just past the point of the gouge. If it is coming off the tool anywhere else, you are setting yourself up for trouble. The flute should be pointed towards the center of the bowl, and slightly up, say at about 2:00. This last bit is not hard and fast, and every gouge has a sweet spot. This cut can be made with any length of grind.
Use your left hand as a pivot and your right hand to swing the tool by the handle, pulling it toward your body. The closer you get to the center of the bowl, the slower you need to move the cut, or the less wood you need to take off, or both. This is because as you get closer to the center, the surface speed of the wood is tending toward zero, so you need to lighten up or there will be trouble.
Hopefully this will help you out some, and if you have questions after trying it out, I will be glad to try and answer them.
Thanks Bill. I did exactly what you said not to do today on a mesquite bowl. I was just humming along and everything was just going fine. Curlies were coming off right nicely. It then happened. I let the gouge get past the 2 o'clock position and wham it happened. The tenon broke and the bowl went sailing. I glued the tenon back on and then watched a little more carefully. Things went fine from then on. Only problem I had was the bark went sailing. So so I just burned the edge and finished. I use a long Ellsworth grind on my bowl gouges and haven't had a catch for a while so this was a wake up call.
Thank you again Bill for the reminder.
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