Alan, the soap soaking is for making the wood easier to sand out. All the pine trees tend to have a lot of resin in them, and that will clog up your abrasives. It does nothing that I could ever tell to keep the wood from cracking. To prevent cracks, round over all edges, especially on the rim. Have an even wall thickness. I use the stretch plastic film over the rim to provide a bit of compression and to slow the drying at the rim, which is the area must likely to crack. Knots also tend to start cracks. Haven't turned the Norfolk Island Pine though....
robo hippy
Thanks for answering. Here’s where I got the idea of soaking green wood pre-turning. From
www.ronkent.com:
“The liquid I tried and now find so useful is...are you ready for this?....concentrated dishwashing detergent: Costco’s Kirkland brand sells for about $7.00/gallon in Hawaii, quite possibly less in other parts of the country. ( My guess is that this is their private label on a similar product with familiar major brand name, and that many or most other brands will deliver the same results.)
What are the benefits that I find? First there is the advantage of stabilizing the wood; a great deal less "moving" and warping both while working on the vessel and after it is taken off the lathe. A second favorable difference shows up in cutting. The shavings are a delight! Clean, long, cohesive ribbons, both for fine trimming and for the macho adversarial plunge-cuts that characterize my favored rough-shaping "technique". It feels almost as if the wood has been lubricated and allows the edge of the tool to slide smoothly through the cut. I never did figure out what "conditioning" means, but whatever it is, I’ll bet detergent does it!
Ah, and on the rare (Hah!!) occasions when I resort to using sandpaper....it is a whole new sanding experience. For one thing it allows sanding work that not only is green, but even wood that is soaking wet. The sandpaper still becomes clogged, mind you, but a couple sharp slaps on the bed of the lathe clears the grit and allows reuse again and again.
And with dry wood...well. you have to try that to see for yourself. The closest I can come to describing the difference is to compare it to certain special woods (ebony comes to mind) where the dust seems to be tiny beads rather than that with which we are more familiar. Again the sense of lubrication.
Technique
Now back to my story. Though the experimentation never ends, I currently use a dilution ratio of one part water to one part concentrated detergent. (I’ve also tried diluting with isopropyl (rubbing) alcohol and suspect I get better penetration, but am not sure it justifies the added expense.) Even after this dilution the result is a viscous, syrup-like liquid, leaving me to suspect that further dilution would heighten the economy without losing effectiveness. I vary the proportion each time I mix it, still seeking an optimum ratio.
I do, however, regularly add eucalyptus oil to the mix. It is available at most drug-stores; I use about one teaspoon per gallon. What does this add to the process? A distinctive, pungent scent It just smells good!
Green wood
All of my work is on logs that I get from local tree-trimmers. They bring it to me as soon as the tree is cut, and I’m likely to start turning it the very next day. The wood at this stage is not only green, it is soaking wet! I strip the bark, mount the log, and rough-turn the shape to about one inch thick. (Attention NASA Engineers: Please read as 2.54 cm.). I remove the work from the lathe and slather on a thick coat of the mix., wait a few minutes for the foam to soak in, then repeat. Maybe as many as a half- dozen times, inside and out.
I haven’t...yet...adapted detergent to my old "trick" of total immersion. (For many years I have used an open vat of Varathane...75 gallons of the stuff...for multiple immersion of completed turnings ). A detergent" pre-soak"----at an early stage of turning---seems the logical next experiment to try. I’m planning a five-gallon tub for starters. (I also have begun experimenting with the mix as a "sealer" on end-grain of cut logs, waiting in my wood-pile. I suspect it will decrease splitting and checking. As for other woods...woods not as porous as Norfolk Pine...well, I’d be very interested in hearing from you if you find out.)
After the soak – by what-ever means – I set the work aside for a few days to allow detergent to permeate the wood, and become surface-dry.
Before I started using detergent this was a chancy thing to do. When I was lucky the vessel-to-be only warped. I wasn’t always lucky. There was a definite risk of losing the work altogether due to checking and cracking. With this new technique my experience to date has been minimal "moving" and zero checking .
At this point I re-mount the workpiece and proceed using the usual tools and procedures, enjoying the benefits to cutting and sanding described earlier.
Dry wood
I use the same procedure on logs that have dried out standing in the wood-pile, and I find the benefits are even more marked. Norfolk Pine dries and spalts very rapidly in Hawaii’s humid climate. Spalting typically starts within a month of the tree’s cutting. By the fourth month the wood is almost completely black. Though there still is considerable moisture in the log, the wood acts as if it were dry. It is significantly more difficult to cut smoothly, and it is easily subject to bruising and tearout. This dark-and-dry wood drinks up detergent like a camel in the desert, but the overall process differs mainly in quantity. My goal is to penetrate...permeate...the wood with liquid detergent. Sometimes I start working the piece right after the soaking, before the detergent has even had a chance to dry. More often, though, I will subject the rought-turned form to repeated soakings over a period of days, then allow up to two weeks of standing before I finish the piece. Did I mentioned "conditioning" and "stabilizing? Let me now add another word of description: This wood acts as if it has been rejuvinated.
Effect on Finish
I told you about trying acrylic wax and rejecting it because of its effect on the final finishing process. Detergent, on the other hand, seems to actually enhance my own particular technique. Remember: my finishing process consists of multiple cycles of soak, oil-sand, and dry. The detergent-treated vessel is fully receptive to absorbtion of the oil. It is difficult for me to be certain, but it seems to me that I am achieving even more dramatic translucence from the oils when using wood that was treated with detergent during forming of the vessel. How will detergent affect other finishing techniques on other woods? I haven’t tried it, so I do not know, but my strong expectation is that, once dry, the detergent-treated wood will accept any of our standard, traditional finishes and that it might greatly improve cohesion of the new water-based products.”