Your Inside Bowl technique

[Roger Chandler]

I was wondering what technique you use for making inside bowl cuts.......this assumes you are using a bowl gouge. Do you use step cuts, going from rim to bottom, or do you make one sweeping cut from rim to bottom ?

If you use step cuts, do you find that it cuts down on vibration of the rim. Do you just use step cuts when you get to the last few passes of the hollowing on a bowl?

[Scott Hackler]

Shallow bowls over 3/8" thick are done with a single pass from rim to center. Deeper bowls are from rim to bottom 1/3 with the bowl gouge and from that point to center with a "bottom feeder" gouge (very blunt grind to allow for riding the bevel to the center). Sometimes I will do rough outs with a giant curved scraper on the final pass, just to smooth things out. But I seldom use the scraper for a final.

Thin (1/8" range) stuff is ALWAYS done in steps in 1" increments from the rim to center and every couple inches I may do a shear scrape to blend the transition line.

[Dennis Ford]

Step cuts once a turning gets thin. What I consider thin enough to need step cuts depends mostly on diameter. Once vibration of the wood has started, it is very difficult to deal with; step cuts will help prevent it from starting.

[Hayes Rutherford]

At least 4 steps. First step establish thickness, then finish rim treatment and never go back. On a medium bowl that might be an inch or two in. Then second step. Third step for me is establish the depth, and the 4th step is tie in the transition.

Maybe some shear scraping from transition to bottom, but not usually necessary on sidewalls.

Steps cut down on vibration and you don't go back where the wood has distorted.

[Reed Gray]

Well, I rough it out with the scraper first, so most of what is left is finish cuts, and no steps. I have found the middle of the bowl to be much easier to remove if I am pushing a scraper straight down through the grain rather than across it. I work the rim to finish, then start down the inside. I am still experimenting. I don't like to start with a 60 degree bevel on the rim, and prefer a 45 degree bevel. Once it is started and down an inch or so, I come back and use a 60 degree bevel till I get to the transition. Depending on the bowl, I generally to through the last part of the transition with a 70 degree bevel. I have one spindle/detain gouge that I use if I am taking off over about 1/16 inch thick shavings. If I am trying to be more dainty than that, I go with the fluteless gouge from Doug Thompson. I always do clean up of 'difficult' woods with the fluteless gouge because I can roll it up so it is cutting at a 70 to 80 degree shear angle. Most standard gouges can reach 45 to 50, and more U shaped gouges can to a bit higher than that, especially if you roll them over on their sides. I do blend in start and stop points on the side walls with a scraper using shear scraping cuts.

robo hippy

[John Thorson]

I use Scott's techniques described above. I usually can 'pick up the cut' when going down in steps and avoid having to blend in the transition line.

[Roger Chandler]

I appreciate the comments so far.......I hope this will prompt more responses from others. This thread could become a learning tool for many newer turners.

What prompted me to ask about your inside bowl technique is this. I am currently engaged on a large bowl from ambrosia maple. Some woods are not consistently dense.....meaning they have areas that are denser than others in the same blank. Such is the case with my present project. I am finding that no matter what I do, I get some harmonics [vibration] I started out with a recess, to mount, began to turn it and then changed over to a tenon........then redid that tenon again and changed position in the chuck..........it helped some, but I still get the harmonics.

I am not all the way to the final cuts yet, but know that I am going to have to use the step method, because of the inconsistent density patterns in this particular piece of wood. It is both challenging and frustrating at the same time, but if I can get it pulled off the way I want, it will have real presence as a display or functional piece.

Have you ever had a piece with inconsistent densities and how did you handle it?

[Hayes Rutherford]

Roger, I'm thinking smaller increments. But there are lots of things like hand support on the outside, more or less tool pressure, speed, different tool, etc.

The first couple thousand are always the hardest.

[Prashun Patel]

I use step cuts. However, unlike many, I come back and smooth out the the transitions when I'm close to finished.
Yes, it cuts down on vibration.

[Thom Sturgill]

I don't think I have any ONE way to hollow a bowl. I do always define the rim first and make a starting cut with a parting tool. This gives the gouge a place to start so that it cannot skate backwards. SOMETIMES I define the depth with a drill or spindle gouge, but not always.

On shallow bowls after defingin the rime, I then start 'scooping' out from the rim toward the center creating the first step and then often start hollowing from the center, practising to get a smooth cut. I would not worry about steps if the final depth is only two inches or so.

On deeper bowls I use the method Jimmy Clewes taught in his videos. I step across leaving some mass in the center and then do the next step in a series of step to the center leaving more mass in the center. As I get deeper, I start removing the center cone and smoothing between passes. This also depends on the desired shape of the bowl and how the wood is cutting.

[Roger Chandler]

On deeper bowls I use the method Jimmy Clewes taught in his videos. I step across leaving some mass in the center and then do the next step in a series of step to the center leaving more mass in the center. As I get deeper, I start removing the center cone and smoothing between passes. This also depends on the desired shape of the bowl and how the wood is cutting.

Thom......you describe the situation I have now.......a deep bowl, a big bow, with a bit of an ogee shape to boot, and I am keeping my tools really sharp as well, but the grain just is not helping me on this one. It came from a very large tree and started out as a blank that weighed over 80 lbs, and only had bark on the smallest portion of the blank. That means it was like a big rectangle cut from the trunk with sides much wider than the bark area. The blank did not even go near the pith on this tree. I think the blank was somewhere in the 20 x18x 10 inch range in dimensions. It has been in my back shed for over a year, but had to move it and some more wood out, so my wife could store Christmas decorations there in some plastic bins.

The density of the wood changes from the one side to the other and it has minimal sap wood in it. That produces the vibration, so I will likely follow some step cuts and blend them in the final passes.

[Tony De Masi]

Roger, I used various methods on the inside depending on it's depth and it's diameter. On my larger bowls I do tend to use the step method and smooth the transitions as I go. But, from what you have mentioned in your posts you may be dealing with speed issues as well. How large a piece are you dealing with and at what speed are you spinning to do your hollowing? I tend to turn at the fastest and safest speed that the piece will allow.

[Reed Gray]

I have pondered the 'mass' in the center thing for a long time. I am not convinced that it stabilizes the wood rim on the bowl. Mostly is that it isn't connected to the rim in any way. Yes, it is connected to the piece, but not where it needs support. Probably the biggest learning hurdle here for me is how much I 'rub' the bevel. From some skew master, and I have no idea who it was, 'The bevel should rub the wood, but the wood should not know it.' It seems to be a natural tendency that when the bowl starts to vibrate, we clamp down on the tool in an effort to stabilize it, which actually increases pressure, or at least makes the tool rigid, so there is no play in the tool. Learning to feel that feather light bevel rub can reduce a lot of the harmonic vibrations that come up. The steady rest can do some thing like this, or I think it can. I never use one, mostly because I learned how to do it before I knew there was such a thing. Hand pressure = tool pressure. If your hand is getting hot, then you are using too much pressure. Too much pressure can deform the bowl as it turns adding to the harmonics.

robo hippy

[Roger Chandler]

Roger, I used various methods on the inside depending on it's depth and it's diameter. On my larger bowls I do tend to use the step method and smooth the transitions as I go. But, from what you have mentioned in your posts you may be dealing with speed issues as well. How large a piece are you dealing with and at what speed are you spinning to do your hollowing? I tend to turn at the fastest and safest speed that the piece will allow.

Hi Tony.......I am following pretty much what you say here........I have it about done. It is running truer than at any point since I began it, and I may go and make one or two more passes, just to thin it a bit, but this is one I want thicker walls on.........it is nearly 14" diameter, and 9 inches deep, with an ogee shape.

[Faust M. Ruggiero]

16" and 9" deep. That's a bird bath not a bowl. Well, a small swimming pool anyway. A bowl that size and diameter will almost force you to take the thickness down an inch at a time. I don't believe the "mass at the bottom" theory is as important as keeping as much thickness immediately below the inch you are working on. I also try to keep the finished thickness in proportion to the bowl size. Coincidently, I am hollowing a 16" cherry bowl now. It is a twice turned bowl. Last evening I took the entire bowl down to one inch and left it over night to stabilize. I had it in a cold room in storage. Between warming up in the shop and the stresses I probably relieved removing the uneven thickness, it is bound to move some more. I don't expect to make it much thinner then 1/2". I know that even taking the thickness down an inch at a time will get invite chatter unless I keep the tool really sharp and take very thin cuts until I am over half way down the side. depth. I try to match the cuts so as not to leave ridges or bumps even though tiny bumps sand away far easier than chatter, tear out or gullies. Those I avoid like the plague. Of course, by the time you read this you are probably already eating a gigantic salad from the bowl. have fun Roger, I'm sure it will turn out great.
faust

[Roger Chandler]

16" and 9" deep. That's a bird bath not a bowl. Well, a small swimming pool anyway. A bowl that size and diameter will almost force you to take the thickness down an inch at a time. I don't believe the "mass at the bottom" theory is as important as keeping as much thickness immediately below the inch you are working on. I also try to keep the finished thickness in proportion to the bowl size. Coincidently, I am hollowing a 16" cherry bowl now. It is a twice turned bowl. Last evening I took the entire bowl down to one inch and left it over night to stabilize. I had it in a cold room in storage. Between warming up in the shop and the stresses I probably relieved removing the uneven thickness, it is bound to move some more. I don't expect to make it much thinner then 1/2". I know that even taking the thickness down an inch at a time will get invite chatter unless I keep the tool really sharp and take very thin cuts until I am over half way down the side. depth. I try to match the cuts so as not to leave ridges or bumps even though tiny bumps sand away far easier than chatter, tear out or gullies. Those I avoid like the plague. Of course, by the time you read this you are probably already eating a gigantic salad from the bowl. have fun Roger, I'm sure it will turn out great.
faust

Faust.......I did exactly what you describe with thin cuts and sharp tools.......one exception.....I went about 1-1/2" on the steps as I hollowed it out. It is currently still on the lathe......no time to work on it today, but it is at about 5/8" thickness, and I have an itch to take it to 1/2" with about 2 more light passes. It has been through warming/cooling cycles in my shop for the last 3 days, so I know what you are saying about the bumps, etc. It is pretty true already, but I just want to make some final shear cuts on the outside to smooth and a couple of light passes on the inside.....its going to be a looker, I think!

I think this will be my last project on my G0698.......our turning club bought it from me earlier this month, and will deliver it to them when they get the new electrical circuit run for it, and I will be awaiting my new G0766......hopefully it will arrive by the latter part of February [fingers crossed!]

I will have to go small with my Delta midi 46-460 until my new green monster arrives! :D

[Thomas Canfield]

In response to a couple of posts about returning the 16" or so size, I have found that truing up the outside, and then truing up the inside will result in the outside being out of round due to reliving stress when cutting down the thicker sections truing the inside. I will jam the rough bowl inside against opened jaws of chuck, and with live center in dimple left in original tenon center, return the tenon and a section of the bottom to clear the chuck and headstock when mounted in the chuck. I then use a block to pad the live center to provide additional support to hold the bowl in the chuck and true up the outside with the bottom still facing the headstock. It is not the ideal way to cut, but does allow a more uniform thickness than would otherwise be possible. On 18"+D bowl went over 1/4" out of round after the inside was trued up. That is all the more reason to have a full 10% of diameter wall thickness on the rough piece. After getting the outside and inside trued up, then turning to final wall thickness is done in stages to help reduce the bowl going out of round and wall thickness variation.