Hi, I think this is my first post here. I have been lurking here for a little more than a year when I bought my first lathe. It is a mini (10 inch). I have one of Raffan's books, have taken several turning books out of the library, been to many websites (Around the Woods is my favorite), and don't have a clue how to search this group for ruts in concave turning. On concave pieces - plates and bowls I get "ruts" on the inside surfaces after using a bowl gouge. I've only turned one green bowl and everything else was with dried wood. I am using a Benjamins Best bowl gouge with the grind it came with. I've turned cross grain and crotch pieces so far. What I end up with are what look like ruts in the bottom. I also have trouble with the nubbin in the center. It dosen't come off cleanly - sometimes leaving an indentation.. I eventually get the ruts out with a round nose scraper and sandpaper. .It seems to take forever.
I am hoping that someone might recongize these "symptoms" and provide some advice
Darrell, to make sure you don't even have a moment of self doubt when sanding, please use the more common name I am trying to get into the turning language: "The 80g finishing gouge". The "g" is actually spoken to keep from having any confusion with other tools, and it should be noted that the "g" style gouge comes in different sizes as well, like the 100g and the 120g gouges.
I would add one additional item to check. If the tool rest is not smooth it will make it difficult to slide the tool smoothly and each stop is a potential rut, OK that's what I found :)
if you have a heavy enough gouge, with a reasonably sharp fingernail grind, and you rotate it properly as you go from rim to bottom, you do it all in one smooth cut and there are no ridges - my guess is that you are stopping and starting, and are not changing the angle from nearly horizontal to nearly vertical (for the flute) as you go from edge to bottom. - you can also shear scrape with the gouge coming from bottom to rim but that takes more practice to avoid a rather spectacular catch.
I'm not sure what grind the Benjamins Best bowl gouge has on it, but my experience says that most bowl gouges from the factory do not have a good grind on them. If the gouge happens to be a 5/8" shaft, I would recommend purchasing the Ellsworth Grinding Jig and put the Ellsworth grind on your gouge. This gives you a nose bevel angle of somewhere between 60 and 65 degrees and good swept back wings. This particular grind will allow you to cut from the rim to the center of the bottom of the bowl in one smooth pass. Normal, factory ground bowl gouges will not let you do this. Unless you have the Ellsworth Grind or a very similar one, you will need two grinds on your gouge to cover the area from rim to center. A gouge with a 45 degree nose angle will cut smoothly about 2/3 of the way down the side of the inside of the bowl. You then need a gouge with an angle of between 60 degrees and 70 degrees to continue on to the center of the bowl bottom.
With the Ellsworth grind, you can cut from rim all of the way to the center, including removing that little nubbin at the center if you finish your cut exactly on center. When you get close to the bottom center, the wood is moving very slow so you must move your gouge very slow and smoothly to avoid tearing out the center point and having a detent instead of a nubbin.
The ridges you are talking about generally come from moving the tool to quickly and not moving it smoothly. I think that most of this will all be eliminated with a well ground bowl gouge and lots of practice. When it comes to good woodturning, nothing beats making lots of shavings; i.e., practice, practice, practice!!!
Welcome to woodturning and good luck with your turnings. As others have said, the last resort is the 80 grit gouge, which also leave grooves in the wood. I can remember when I started turning many years ago, that the 40 grit gouge came in quite handy to start to smooth the bottom of the bowl.
Some other reference material are videos and DVD's on turning and three US magazines devoted to woodturning: American Woodturner published by the American Association of Woodturners, More Woodturning published my me, and Woodturning Design published by one of the large publishing companies.
Welcome to "the club". Since I mentioned clubs, but have no idea where you are, I'd suggest you find out if there are any woodworking groups/clubs near where you live. The members can be a great way to get a few tips to make turning easier. Books and tapes can only do so much, no matter how good you are or how much "natural talent" you have. A few moments with a "coach" can make for some really large improvements in style and the results you see. With anyone (book, video or live coach) take the suggestions as food for thought. Look at them and determine if they work for you. If not, try something else.
Everyone is different and as long as you are working safe, there are a lot of "absolute" rules that just don't apply to some people. (as an example, I've been told several times that I "have to" cut from the bottom of the bowl to the top when hollowing end grain. Though this should produce a better finish due to the mechanics of cutting with the grain instead of into it, I rarely cut that direction with a bowl gouge because it just doesn't feel right to me. For one thing, the geometry just seems wrong, and on deeper bowls, there's no way to angle the handle to miss the opposite wall of the bowl without leaving the cutting edge unsupported. The biggest issue is using sharp enough tools that you don't end up with torn grain, which is really hard to get rid of.) Others may have mentioned the 80g gouge... Here in Hawaii it's known as an 80-Grit gouge, and comes in a variety of versions (I have down to 24 grit for the extreme cases or for working on thinner, large diameter sections that can't easily be dealt with using a gouge). No shame in using them, as sanding something into submission is sometimes the only way to keep it in one piece and get the result you were looking for. It's not necessarily all of the techniques you use but the end result that is important. If it looks great when you are done, then it isn't any better if you did a final cut with a gouge and went to 150 grit sanding, than if you had to sand with 40 or 50 grit then progress through to the finer grades. In the end, it's often a matter of how much time it took to do the job. A full time professional turner will often develop the skill to consistently move directly from gouge to 150 grit, but I know a number of people that are making a living turning that don't always meet that goal, and they put out some great work. For myself, I don't hesitate to whip out the coarse grit sanding discs if things aren't working well with the regular tools. It's much less frustrating that way, and I still produce work I'm not ashamed of.
I've found that when I cause grooves (ruts) it's usually because the tool either hung up on the tool rest, or I was pushing too fast. No big deal when hogging out most of the wood, but once I get within a quarter inch or so of the desired curve, I have to take a lot thinner cuts to avoid them. Taking my time and making a follow up light cut typically takes care of the too fast problem, and checking the tool rest solves some of the others. In other cases, I just whip out the power sander. For me, life's too short to be frustrated about something like this, and there's always another piece of wood around the corner. As for the nub in the bottom, it's nearly impossible to cut it clean with a gouge for most of us, and sandpaper works a trick there too.
That all said, after you're in this awhile you may end up using other tools to supplement the bowl gouge. For most of the salad bowl curves, I use a disc tool I made that uses round carbide inserts typically used for metalworking. With a special tool rest with a fulcrum pin, I can set the tool rest such that the tool pivots on the pin instead of my left hand, and I can cut a salad bowl curve in one smooth sweep. by sharpening the carbide insert (on a drill mounted mandrel) with a diamond paddle, I can get an extremely sharp edge and reach the "final cut and 150 grit sanding" goal with little effort, but it's not a bowl gouge.
Make sure your tool rest is smooth and slick. Whenever I notice a nick in mine, I sand them until smooth and apply a paste wax (like Johnsons in the yellow can, which also helps keep down the rust on things like table saw and band saw tables). With it smooth it is easier to move the tool in the continuous arc that you need for the bottom and side of bowls (concave surface).
This may sound funny, but learn to listen to the wood. If it tells you (through whatever means, odd vibration, strange cutting action, or just a feeling something isn't right), listen to it. If it sounds like a Zen or metaphysical approach, perhaps it is, but it works... I used to have a shelf in my shop up near the ceiling with the pieces of bowls where I didn't listen to the wood, and as a result they came apart on the lathe. The shelf was about 20 feet long and had regular replacement of the items there until I learned to listen to the wood... Haven't blown up a bowl in over two years now, but now that I've said that I'm sure one will humble me again pretty soon...
Just re-read the above and an idea popped into my head. Try to notice whether you are always supporting the edge of the tool. The bevel of the bowl gouge (behind the cutting edge) should always be in contact with the wood, supporting it and allowing you to properly control the tool. Ideally, you should be able to cut with very little pressure and without holding the tool in a death grip. With the bevel riding, you control the amount of cut by rotating the tool slightly to adjust the angle to the wood. If you don't ride the bevel, you end up using the gouge more like a scraper, and if you don't run the right angle, you can get ruts (or worse, a major catch that can make a really large gouge in the wood or pull the tool from your hands). If you find you are noticing fatigue in your hands while turning, perhaps you are trying to manhandle the tool instead of having the bevel support the cut. This is sometimes difficult for the relatively inexperienced turner to determine without someone else watching to see... I've even seen experienced turners that were getting tired slip into a position where the bevel wasn't riding the wood, which typically resulted in a minor catch or groove... Minor ones can be a wake-up, major catches can be dangerous. At least half of the items on the "shelf of shame" in my old shop were from catches from one reason or another.
While on the topic of catches and such, make sure you always wear eye protection. I wear a full face shield and have had many cases where I was very thankful I was. Ducking an exploding bowl should be a rarity, but when one happens, a full face shield gives you that extra edge a pair of goggles doesn't, and doesn't fog up quite as much as goggles either. I wouldn't turn on my lathe without a shield on first, unless I'm done turning and sanding and am in the finishing stage. Working safe is the only way to do it for a lifetime.
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