finishing cuts

[alex grams]

I am getting decent at turning, but still have some challenges when it comes to finishing cuts and getting a really smooth finish that required minimal sanding.

The biggest challenge I have is on bowls with sides that are 0°-30° parallel to the axis of the lathe. I get grain 'lift' and have a coarse surface there that requires a lot of sanding to remove. I usually touch up the gouge right before this cut to have a fresh, sharp edge, but it seems no matter which way I approach it, the rough surface still exists. It is worse in softer woods such as walnut sapwood on natural edge bowls. I've tried coming in from the outside and riding the bevel. I've tried the fluteless gouge. I've tried a shallow/shear cut on the bowl gouge coming out of the bowl, but no matter what, I still run in to it.

Any thoughts, methods, videos to help figure this out?

Thanks in advance.
-Alex

[Dale Gillaspy]

There are a ton of reasons that could be happening. My first thought is the direction of the cut. With cross grain like is usually done for bowls, you want to turn from the smallest diameter to the largest. People seem to have a tendency to start cutting at the rim and cut towards the foot, but if you do that, you are lifting the grain on those spots. If you turn from the foot to the rim, you are cutting with the grain.

You might also try putting a little shellac on the rough spots and re-turning. It will cut and sand away easily so it won't harm your final finish, but will stiffen the grain in that area.

The other thought is that if you are already hollowing the bowl, it could be flexing on you as it spins.

[Thom Sturgill]

There are a ton of reasons that could be happening. My first thought is the direction of the cut. With cross grain like is usually done for bowls, you want to turn from the smallest diameter to the largest. People seem to have a tendency to start cutting at the rim and cut towards the foot, but if you do that, you are lifting the grain on those spots. If you turn from the foot to the rim, you are cutting with the grain.


Depend on whether you are talking about the inside or the outside. Face grain you cut "downhill" so that the nest grain si supporting the grain being cut. This means foot to edge on the outside and edge to bottom on the inside. Endgrain is just the opposite.

A shear cut with the flute almost closed, that is one edge touching and the other nearly so, and angled at about 45 degrees can be done in either direction and gives the best finishing cut, IMO. Can also be done with a properly sharpened scraper.

[Reed Gray]

Well, a tough one to be able to answer without a hands on session. Sharp, well of course that comes first. A light touch, this is cutting the wood at a slow enough pace, pull or push cut, so that the wood does not tear before you can cut it. High shear angle. The higher the shear angle, the more gentle the 'lifting' action of the cut. Some days I get nice clean surfaces, some days things just don't go as well. For sure, softer woods will tear more than medium hard woods. Some times the really hard woods will want to tear more as well. I can use a negative rake scraper on most woods well, but big leaf maple is a bit too soft for it. Shear scraping can clean up a lot also, especially on the inside of a bowl. Again, it depends on the woods. Some times the bevel rubbing cut is the only way to get the clean surface. More experimenting......

robo hippy

[Edward Weingarden]

Someone mentioned that there is flex as the bowl spins. As the wall gets thinner, the amount of flex or vibration will increase, which makes it difficult to get a smooth finishing cut. One suggestion is to thin the outer most area of the bowl (rim area) and get the finishing cut before you thin the next area (going towards the bottom). Repeat the process with each area as you move towards the foot. This way, there will be some bulk of wood to reduce the flex of the wall immediately above. When doing the finishing cut in each area, blend with the already finished area just above.

[alex grams]

edward, that was exactly a thought I was having also. I know sometimes on those end cuts you can hear the wood start to flex and the tool loses its constant contact pressure, resulting in a rough, uneven cut.

I watch robo hippy's video on the fluteless gouge, but I swear he gets a lot better cut on his than I can seem to get on mine. I need to do some more learning with that tool to get to the thin cuttings he gets.

[Tony De Masi]

Alex, I think you answered your own question with your last post. Meaning, you need to do more learning. There MUST be a club local to Ft. Worth that you can explore and simply ask for some help.

[Geoff Whaling]

Alex, check out Glenn Lucas' or Mike Mahoney's DVD's on bowl turning. Both are production bowl turners and exceptional at their craft. If you get a chance also to see a demo of Tom Wirsing turning, jump at it, another turner with exceptional tool skills.

[alex grams]

I have managed to make it to one or two of the local turner club's meetings, but unfortunately I am usually working and unable to attend. :(

[Jeffrey J Smith]

Alex - you might look into the club's mentor program. Most AAW affiliated clubs have a mentoring program. These guys are available to answer questions and even offer hands-on help. Check the newsletter for your club for names and contact info. turning is, in some ways, like golf. A little hands-on help to get the basics down really helps.

[Prashun Patel]

Are you reshArpening before those final passes? I have the same issue. Sometimes a round scraper helps, sometimes a radiused skew, sometimes prefinishing then turning again. It has gotten better with practice but I havent yet found the magic bullet.

[Bob Bergstrom]

I have witnessed a number of turner who want to push the gouge at too fast of a feed rate or have to force the tool to stay in the cut. Try slowing the feed rate or increasing the rotational speed. You should proceed with a light cut without forcing the gouge to stay in the wood. When you watch an experienced turner remove his lead hand from the tool and it guides itself into the bottom of the bowl the tool is sharp, the feed rate is correct and the cutting angle is right. If there is a knocking sound or or flexing of the bowl wall usually the rake angle is wrong. Try moving the handle away from the bowl surface a little to increase the rake angle. On the inside to the right and on the outside a little toward the left.

[robert baccus]

Have you tried a bottom feeder grind. Take a 1/2" bowl gouge and regrind it to a 75deg. bevel and cut with the bevel flat on the wood. Makes a good finish cut on the outsides also. Should be curls and no dust flying in decent wood. I also do this to 1" roughing gouges for vase and bowls on the outside--never with the standard 45 deg. grind. The flat grind will simply not catch on the outside of a piece. It will boil shavings off green wood like crazy. Leaves a very clean cut in the bowl bottoms.

[John K Jordan]

... Sometimes a round scraper helps ... But I havent yet found the magic bullet.

I do often use a handled scraper (I like the Sorby teardrop shapes), but the closest thing I've found to a magic bullet for smoothing and finishing inside face turnings is a cabinet scraper. I have a variety of small curved cabinet scrapers, purchased from Highland Hardware, Woodcraft, and elsewhere. These are mostly thin and flexible, far thinner than conventional cabinet scrapers (although the thicker scrapers work fine.) Some are just an inch or two wide. I sometimes regrind them to shapes that work better for me. The flat scrapers have limited use on a lathe.

Properly sharpened, I find them hands-down the best tools to solve a variety of problems such as tearing grain in soft wood, punky wood, uneven surface due to technique or geometry, and problems with hard adjacent to soft. I reach for the scrapers before I ever reach for sandpaper which can make some problems much worse.

I hand-hold these at an angle, my hand may rest on the tool rest but the scraper never touches the tool rest. Speed is usually very slow and often with the lathe turned off. (With the lathe off is perfect for the inside center which can be tricky.) When sharp, a cabinet scraper will remove very fine shavings and leave a surface that needs little additional sanding. (I almost never power sand.) The curve of the scraper can quickly remove tool marks from a bowl gouge. I can get a better surface than with a scraper on a handle. Catches are almost impossible.

I use them both inside and outside of the work, but more often inside (which is usually harder to cut cleanly due to the geometry.) Just don't do what one guy tried - put his hand into a vessel with a fairly large scraper which got out of his control...

I have been using these for many years and have told lots of people but AFAIK only a few ever seem to try them, even after they asked me how in the world I got the inside of the bowl like that.

JKJ

[George Overpeck]

Some days I get nice clean surfaces, some days things just don't go as well it's great to hear a serious production turner say that cuts just vary sometimes without having a logical cause.

One thing I'm getting onto more and more is that the smoothness of the previous cut is going to affect the next one, specifically when one gets down to these finishing cuts. If you consider chatter marks for instance - clearly there is possibility there for the marks to set up a feedback loop where the chatter gets worse the next pass and leaves a larger field of ridges. Same with having a touch of tearout - you're likely to throw just enough vibration into the tool that it makes more tearout inevitable.

I deal with this in two ways, dependent on how willing I am to change the profile of the piece. One way - make a series of light cuts which don't extend all the way into the trouble area at first, but touch the leading edge and then progressively proceed further into it. Second - better, I think - sharpen again, make a deeper cut which extends well beneath the trouble area. Tearout is much deeper than we perceive. Cutting all the way down into clean wood gives you the best opportunity to start again, or to mess up again if that's going to be the way it is.

Typically the second method is going to be combined with Bob's advice on angling the gouge outward a touch.

[Prashun Patel]

John-
Circling back on this.

Just wanted to say thanks for this tip. When I started out turning I experimented with using a card scraper on turnings. However, I wasn't very good at using the lathe or the card scraper at that point.

This weekend I had a chance to revisit your technique above. Properly sharpened, I was amazed at how well the card scraper worked. I was able to keep my lathe spinning on it's slowest speed and got great wispy shavings. It smoothed my tool marks, and allowed me to start sanding with 180 grit. I have never been able to do that.

I had better luck on the outside of the bowl. I had moderate success on the inside (with a gooseneck scraper) - enough that I will definitely use this technique from now on - but the shavings don't clear as completely, so I quickly encountered some chatter. I think this is because my lathe doens't spin that slowly on its slowest setting.

Anyway. Thanks again...

[Damon McLaughlin]

John, I've seen the curved card scrapers both in the 3" or so size and some minis that are about 1" or so. What size do you use the most, or better put if one was to buy only one size which size would you recommend?

Alex, when I'm using softer woods I find that a coat or two of sanding sealer and then very light cuts works well for me in most circumstances.

[John K Jordan]

John, I've seen the curved card scrapers both in the 3" or so size and some minis that are about 1" or so. What size do you use the most, or better put if one was to buy only one size which size would you recommend?


I use the smaller ones the most, except for flatter surfaces like platters and wings of squarish things I often use a large scraper with a very slight radius like the large one in the left of this photo:

356165

Note that you can take old scrapers, maybe from a yard sale, and cut and grind them to any shape, just be careful not to overheat. I like the thicker scrapers are better. This was the first one I ever used on a woodturning, cut from a large curved scraper with a metal-cutting disk on a Dremel then touched up on a grinder.

356166

I sharpen these and roll up a cutting edge just like cabinet scrapers have been sharpened since the beginning of time.

JKJ

[Damon McLaughlin]

Thank you John. Now I know what I'm going to get for myself for my birthday this weekend :-)