A hollowing question

[David Somers]

I am a newbie. Working on a first, rather overly ambitious bowl, but having fun. The bowl is a hollow form. Opening about 1.5inches. Have the exterior done, have the interior hollowed without blowing up yet. But....although most of the interior has a decent surface to it, one area where there is a transition from sap wood to heart wood has alot of grain tearing. Only one area however. The opposite transition area is fine. And, I can't seem to fix that.

I used an Ellsworth gouge to rough out the interior. No problems. All smooth at that time. I have tried using a Crown swan neck Beaver Tool for the remaining hollowing, but that is where I started seeing the tearing. I tried a round edged scraper, quite sharp, but am still tearing in that one spot. I ngdid find a posting here that describes some positioning for using a scraper inside a bowl. Next time I am on the lathe I will check my scaper use against that and see what happens.

Any thoughts?

I assume I am doing something very wrong with the Crown tool since it should be cutting, not tearing. It is quite sharp. I have had trouble with it clogging no matter what I do as well. I have tried opening the guard on it wide, closing it really small, and amounts in between. Have tried all that with light pressure, modest pressure and heavy pressure. I have tried running the tool high on the inside, low, and in the center line. Get the same result each time. Tearing in that one area, and constant, very fast clogging. I am obviously missing a technique here since people would despise this tool if this is how it actually behaves when it is used properly.

Thanks for all the help folks. Have enjoyed lurking about the forums and been waiting for a chance to ask a question. This seemed like a good one.

 

[john lucas]

Dave you may or may not be doing something wrong. Some woods just fight you. If your gouge is sharp and you aren't forcing the cut it may be the wood itself. I use thinnned lacquer to stiffen these areas. I thin it about 50 percent with lacquer thinner. Let it dry and then try cutting again.
There are other concoctions for this. I've heard of using white glue thinned 50 percent with water. Some people simply spray water on the area and then try another cut. Some poeple use wax and I've even heard of using WD-40 but I would be worried about finish compatibility with that.
The one dissadvantage of using lacquer is that you can't dye that area later, and sometimes stain won't take as well in that area.
Tool presentation can also cause this. Try to figure out what direction the grain runs in this area. It could be as simple as cutting from the center toward the lip that will solve the problem although this can cause tearout in other areas. Check to see that you are cutting at a very shear angle. That is the wood is passing the cutting tip almost parallel to the tip. This will give the cleanest cut most of the time.

 

[MichaelMouse]

If you supplied a touch more information, like for instance the grain orientation, it might help. However, with undercuts it's common to forget the "downhill" rule, which can lead to crumbling and tearing out. You may have to reverse the direction of cut to get support behind the fibers you're cutting.

 

[DWFII]

Dave,

FWIW, I am no expert but I've found that if I use a 30% cut of pure tung oil and let it sit for an hour or so, I can eliminate most of the tearing pretty easily. The advantage of using the Tung is that you can apply nearly any finish over it without worrying about it not "taking."

I just finished a bowl made from poplar or cottonwood...I don't know what it was, it was given to me as maple but I know from working with maple that it wasn't. Anyway, I had some bad tearout both inside and out. I almost gave up on it. Then I tried the thinned Tung oil and it was really no problem.


DW
In the High Desert of Central Oregon

 

[David Somers]

Michael,

Sorry, I guess grain orientation would be rather important! This is a standard orientation, not an end grain bowl. The wood is green Koa.

Mu cut direction is from the mouth of the bowl to the inside, since that is what I have seen detailed in descriptions of hollowing. I will try working from the inside to the mouth this evening and see if that changes anything.

The tearing is occurring where the sapwood changes to heartwood and the tear out is actually over the first part of the heartwood encountered by the tool, not truly at the boundary between the two. The Tearing runs mostly after the neck of the bowl to mid center. Again, this is all interior. Tearout does not occur on the opposite side of the bowl where the change is from heartwood to sapwood.

Thanks for pondering this Michael!! This bowl has turned out surprisingly well for a first effort that I though would end up winging off the lathe during some disastrous catch. I still have enough thickness on the walls of the bowl to correct this and I appreciate everyones input.

 

[David Somers]

John and DWFII,

Thanks for the tips. Will check my cutting orientation. Will also see what I have available to use as the suggested stiffener. This wood is green by the way. Will that effect the use of a stiffener?

The tearing is occurring inside the bowl where the sap wood transitions to heartwood. Not on the opposite side where it goes from heart wood to sap wood. I will also try MichaelMouse's suggestion of reversing the direction of the cut and get back to you all once I have tried this.

Thanks much!!

 

[Carvendive]

By NO MEANS am I an expert, but just another question along the same lines.
I've turned green but I use PEG on the pieces first and have had no problems. Used it for Carving green pieces and never thought of it but just did it as a matter of course when I started turning.

Those who turn green, is it worthwhile to use the PEG or have I just been lucky?

Edited: I hate acronyms - sorry PolyEthylGlycol (my spelling may be wrong).

 

[Matt Meadows]

By NO MEANS am I an expert, but just another question along the same lines.
I've turned green but I use PEG on the pieces first and have had no problems. Used it for Carving green pieces and never thought of it but just did it as a matter of course when I started turning.

Those who turn green, is it worthwhile to use the PEG or have I just been lucky?

Edited: I hate acronyms - sorry PolyEthylGlycol (my spelling may be wrong).

I turn a lot of green wood (which means 3 pieces a month since I have to work 40 hours in the cabinet shop before I can start up the lathe, lol). Personally I have avoided PEG and similar products because I've heard way too many stories of the wood causing PEG and Pentacryl puddles, since the wood has absorbed so much of it, and leaches it out over time. I know a guy that has several HUGE bowls made from green Macadukahogany (ie, some african wood he ordered as a whole tree that I can't pronounce)--- on display at a museum, all with neat little puddles around the base. They sat in his shop for 6 months before they ever went on display, so they didn't fully "empty" even then. He used Pentacry. I dunno if it's the exact same as PEG.


Anyhow, I just soak my small and medium turnings overnight in denatured alcohol and wrap them with a layer or two of newspaper and keep them in my house. In a week or so they are ready to be set out for complete drying. Works great.

 

[MichaelMouse]

Those who turn green, is it worthwhile to use the PEG or have I just been lucky?

Edited: I hate acronyms - sorry PolyEthylGlycol (my spelling may be wrong).

I used the PEG 1000 when the Moulthrop craze was at its height, but it really produces a darkened, slimy to the point where it's tough to finish, turned piece. I was a lot newer to the hobby then, and heard a lot of horror stories about bowls cracking, so I wanted to do my best to keep mine from that fate.

Then I looked on my shelves where I had bowl blanks drying in bags, out of bags, in shavings - well, I guess it's safe to say I tried whatever the latest was - I noticed that, with the exception of anchorseal and wet shavings causing nasty black mildew, the only stuff that cracked was stuff where I had the sides almost vertical. So I quit making those kinds of bowls.

Alcohol is the latest craze, having arrived after dish detergent, and I looked at it, in spite of the poor "science" upon which it was supposedly based. I found it to be purely a Pygmalion effect. You can't dry something by soaking it, and alcohol-soaked wood distorted to the same degree as unsoaked, so there was nothing to recommend it. Dish detergent will at least keep the surface damp(er) until the glycerine (glycerol) is removed, so I suppose there may be some of the same effect as PEG if you followed the same soak schedules and concentrations.

Wouldn't hesitate to use dish detergent to paint a carving. Should do for mildew while keeping the surface damper.

 

[MichaelMouse]

Michael,
Mu cut direction is from the mouth of the bowl to the inside, since that is what I have seen detailed in descriptions of hollowing. I will try working from the inside to the mouth this evening and see if that changes anything.

The tearing is occurring where the sapwood changes to heartwood and the tear out is actually over the first part of the heartwood encountered by the tool, not truly at the boundary between the two. The Tearing runs mostly after the neck of the bowl to mid center. Again, this is all interior. Tearout does not occur on the opposite side of the bowl where the change is from heartwood to sapwood.

If it's confined strictly to the change in wood type rather than the change in direction, you might just be experiencing a problem with grain reversal. Some trees twist right and left as they grow, and you can get those kinds of problems where that's happening. Five-six years left, then reverse. Lovers of elm know this well.

The other thing that happens with wood cut heart side down, since the annual rings don't show farther apart as rapidly as when you cut heart to bark, is that your cut width coincidentally matches the distance between two latewood ridges, and sort of drops in where the grain is at its longest, hooking out a small section as it does. Not sure this is a problem with your wood, as tropical woods are often much more even in their rate of growth.

 

[S. Clark]

Another Hardening Method

David, I have been successful using shellac to harden areas that tend to fuzz. It works fine on green wood, as it is an alcohol-based product. My approach has been to saturate the soft area just before making the final cuts. Depending on the porosity and moisture contentment of the wood, the saturation may only be a 32nd of an inch or so. Therefore there is no advantage to doing this earlier in the turning process. I apply it from a little squeeze bottle directly on the bad surface and allow it to dry for 10 or 15 minutes. You can tell by the smell weather it has dried. I sometimes run the lathe at low speed to let centrifugal forces draw it into the wood on inside surfaces. Increasing air flow by means of a small fan will speed the setup too.

You can apply almost any finish over the top of shellac. I find that shellac makes a good sanding sealer and I frequently use it for that on both green and dry woods. Note though that on lighter woods it will alter the color, typically darkening it with an amber or buff tone depending on the particular variety of shellac being used.

- Scott

 

[WoodDoc]

Any thoughts about drying in the oven? I've heard to heat a rough-turned green blank in the oven at ~200 degrees to dry it out partially, then leave to air-dry. A colleague of mine had also heard about using the microwave, though I'm very skeptical about this.

I DO know that bodgers will heat chair spindles in a box with a 100-watt bulb for a day or so to dry them out, so that they will then swell with ambient moisture to fit mortises on the seat.

I'm not very enthusiastic about PEG or other chemicals, though.

 

[David Somers]

Michael,

I don't think either of these is affecting this log. I have a good 12 feet of this log that someone cut into firewood length before giving it to me. For giggles I reassembled it to see if there was a twist along the length that I wasn't noticing from the short lengths that had been cut. It was pretty straight. The log also has modestly even growth rings. I live up high at 4,000 ft so we do have a winter season of sorts in terms of temps and growth rates. Also due to rainfall variances. This is fairly even growth. The heartwood of Koa is noticeably harder than the sapwood, but I don't remember anyone mentioning problems like this turning it. I will be working on the Island of Oahu Monday and will have a chance to talk to some turners and will ask them.

Will try the lacquer idea mentioned in an earlier post this weekend. See if that helps. I did look into the Beaver tool a bunch more and found that it is really meant for end grain cuting, not side grain as I am doing on this bowl so that did not help. Have played with the orientation of a scraper trying to see if I can present it differently and knock this tearout down but haven't found the right set of the tool for that yet. Still have some thickness in the bowl left to try and correct this.

I think I mentioned that this wood was Koa. Kind of young. Log thickness about 12 inches. Heartwood is about 1/2 the log.

Thanks again for pondering this Michael.

 

[Bill Boehme]

I have tried microwave drying just one time earlier this year and the results were very good. The wood was dripping wet green hickory. I finish turned the bowl all in one session and then followed the microwave procedure described in the following link on my woodturning club site, the Woodturners of North Texas Tutorials Page. I have seen numerous "recipes" for microwave drying, but I like this one because it is not nearly as agressive as many that I have seen. I think that pushing things too much will only lead to disaster, no matter what the process.

Bill Boehme

 

[David Somers]

Thanks everyone!

Well, because I travel for work it took me a while to experiment with everyones suggestions. Here are the results.

Folks suggested adjusting my tool presentation. That helped a bit but I was still getting a lot of tear out. Then I realised the ring tool (Crown Beaver) was really meant for end grain hollowing, not side grain so I switched to a scraper which was all I had on hand to use. Tearing was a little less, but still not nearly aceptable. I will be in my Oahu Woodcraft this evening and will talk about this with one of the sales people there who is a pro turner in real life.

I tried the suggestions for spraying a lacquer or shallac onto the tearing area to stiffent the fibers. Didn't seem to have much effect in this case.

I finally got rid of the tearing by taking a handball and mounting it on an arbor, gluing the hook side of velcro to it and draping it in a course sandpaper and putting it on a drill and using it to sand the inside of the hollow form. That took care of the problem for this project.

I will explore ways of getting a smooth cut in the future and hopefully avoid this issue in the future.

And thanks to everyone for their suggestions. I have tucked those all away for future use. Lots of good ideas to keep handy!!

Mahalo!!!!