Green Wood Checks - Whilst Turning
A green wood rough out in Honey Mesquite.
Working with green timber offers numerous advantages over it’s more expensive and colour compromised kiln-dried cousin. Not only is green timber plentiful in most areas, it is available in larger sizes (up to several feet in diameter) and many times it can be obtained for free, or at low cost. Another reason working with green wood is so popular is that it offers you the opportunity to recycle a resource that would otherwise go to the local dump, be processed into mulch or be burned as trash. For many of us, that’s an important consideration.
For all of the benefits that working with green timber offers, it is not without its own unique challenges. Since green wood still contains a lot of moisture, we have to season it ourselves. Many of us rough out projects on the lathe like bowls, platters, or boxes and then dry the roughouts by various methods. Some days/weeks/months later, we finish turn the fully seasoned project on the lathe. That’s a well-proven method for working with green wood most of the time, but the gods of wood can sometimes throw you a curve ball when turning green wood…
Some green timbers seem to be born to check, others can easily check if you do not take basic precautions and still others seem relatively impervious to checking. For all that is written about working with green wood, relatively little information exists about how to prevent checking whilst you’re turning a green wood project on the lathe. Through the years, I have had several occasions where I was working with a particular timber and I had to employ various protocols to prevent checks from forming, whilst the project was being actively turned on the lathe.
If you’re working on a large project on the lathe (say a large hollow form), the end grain areas may be exposed to the open air for quite some time before you complete hollowing the project. If your studio is air conditioned or heated when you’re turning your project, the additional drying effects will be even more pronounced. The drying effects of the projects rotation on the lathe, coupled with the effects of HVAC systems can accelerate checking, particularly in timbers that are susceptible to rapid checking. This effect can be further exacerbated if you live in areas with very low ambient humidity levels.
Another area where checking can occur when working with green wood is when you’re working on a project that you cannot finish in one session at the lathe. If you need to leave it overnight, or for a few days until you can return to finish it, proper storage is critical to preventing checking on exposed end grain surfaces and high figured areas. How you store the project and the materials used can mean the difference in returning to a project with no checking whatsoever, or one that will give you ample opportunities to practice your inlay techniques.
Preventing Checking Whilst Turning
There are two main techniques I used to forestall checking whilst I’m actively turning larger green wood projects on the lathe: 1.) Isolation of suspect areas by application of surface barrier films, 2.) Spray wax application to crack prone areas. For routine protection against checking on larger turning projects, I typically use spray waxes. Spray waxes are easy to use and can be reapplied as necessary. If the timber needs more robust protection against checking, I apply a barrier film to the exterior of the project.
Many different types of waxes are available in liquid form
for use on green wood turnings on the lathe.
Spray Waxes: Spray waxes are great to use if you need supplemental or temporary protection when you’re actively working on a project. For example, when you begin your initial roughing out, you can spray the end grain areas for additional protection as you continue to refine the exterior profile. When you turn past the wax layer, it can be easily reapplied when you stop for a cup of tea, stop to clear the shavings from the inside of your hollow form, or when you stop to examine the surface on other projects like bowls or platters.
A few quick sprays and you’re back to business. Years ago when I was doing so much production work, I used spray waxes routinely for this task. They allowed me to concentrate on turning my form, without worrying about whether the endgrain was checking because of the cumulative effects of the seven ton air-conditioning system, the 6” dust collection hose that was right next to the edge of the project, or the supplemental dust collection (ceiling mounted) equipment and circulation fans in the studio. This little trick worked quite well and I have used this technique for many years.
I still use spray waxes when I want temporary protection that I can easily turn away as I’m working on the piece. I can spray an area and get extra protection during turning and remove it any time I want with another pass of my gouge. Spray waxes are simple, efficient and a relatively inexpensive way to prevent checking in green wood projects, whilst actively turning them on the lathe.
You may be wondering if spray waxes will inhibit your subsequent finishing efforts. In my experience, using spray waxes never caused me any finishing problems, but most of my use of was on pieces that were being actively turned, so the wax was turned away as the piece was completed. I also use spray waxes from time to time on projects that are roughed out and allowed to season before final turning.
I’ve never experienced any finishing challenges with these projects either, since the surface layer of wax was turned away when the piece was trued up for final turning. Had I been concerned about potential wax residue, I would have applied a solvent wash of Naphtha to remove any residual wax that may have been left on the surface.
Small rolls of plastic film are very useful when working
with green wood projects on the lathe.
Barrier Film: Another method to prevent green wood checking whilst turning on the lathe is to apply a barrier stretch film. I like the kind sold by moving companies that stretches and is sold on small rolls. It is designed to stick to itself, but nothing else. Larger width rolls are also available, but usually prefer the smaller rolls since they are easier to store and manipulate around the project when needed.
This barrier film will not only prevent surface checking when turning larger projects on the lathe, but it’s also useful for helping to secure delicate projects that feature lots of negative space (voids or holes). Since the plastic leaves no surface residue, it is suitable for use during the final finishing phase of the project on fully sanded surfaces.
A few wraps around the exterior of the project helps to secure fragile projects, or those that you just feel more comfortable turning with some additional protection. One significant advantage barrier films have over spray waxes is that the barrier film leaves no surface residue. However, it is not as easily turned away as a spray wax. Barrier films are great, but they work best when the outside form has been completed and you do not need to remove any more of the surface to complete the form, or when applied for temporary storage of turned items.
If you’re working on larger projects, you can get the stretch film in wider rolls. I typically stock the smaller rolls unless I know I’m going to be doing a series of large hollow forms. This film is also great for wrapping the exposed endgrain on turning squares and bowl blanks if you don’t have the time to wax them right away. It’s a great way to prevent checking until you can get some free time to wax them properly. If you’ve never tried this stretch film, get yourself a roll and see how useful it will become in your studio!
Preventing Checking During Temporary Storage
If you need to store a green wood project for a few days or more, there are a few options. The challenge is deciding how to store the uncompleted project. As we all know, it’s usually best to not remove a project from its fixing (chuck or faceplate etc.) until you are finished turning it for that stage of turning.
The reason for this is that every time you remove a project from its fixing and you try to remount it later, you can rarely get it back into the original rotation. There is usually some variance in the way the wood fibers are re-compressed, which changes the rotation of the project. That means that you may have to turn away more of the surface of the project to get a true running surface again, which may not be acceptable.
If the project is in a scroll chuck, or mounted to a faceplate you could take it out and simply place in into a plastic trash bag, or into a plastic trash can (my favorite method) with a close fitting lid. You could also just wrap it up on the lathe, still mounted to the spindle but I do not like doing this because sometimes it causes my lathe spindle shoulder to rust, especially if I’m turning Red Oak, or other high acid timbers. Paper bags also work very well and I use these often as well, depending on the size of the project.
If it’s off the lathe and in a bag or in a trashcan, the chuck or faceplate is the only thing that is going to suffer. In the early days of my studio I was hesitant to leave green timbers in my chuck overnight, but I learned quickly that chucks and faceplates are only tools and they are not going to remain pristine for very long in my studio. Besides, a quick swipe with a steel wire brush mounted in a rotary tool brings the surface back to new in no time. Luckily for me, I rarely need to leave a green wood project in the fixing overnight, but it does happen on the odd occasion.
When I do need to provide temporary long-term storage, I dismount the project from the lathe (whilst leaving it attached to its fixing) and place it into a plastic trashcan equipped with a tight fitting lid. If it’s too big to fit into a trashcan, then I wrap it up in plastic wrap (the kind sold to cover items when painting), or stretch film. When I return, it’s good to go and I can get back to turning in short order with a project that is free of checks. Give these tips a try in your studio the next time you are going to be turning a larger project on the lathe. You’ll be glad you did!
Safety Note: Always follow all manufacturers safety instructions before working with your lathe, or any of the tools or products you may use. If you are unsure about any operation, obtain competent professional instruction before proceeding. Use and wear all necessary safety devices during turning and observe safe woodturning practices to prevent accident or injury.
|Steven D. Russell is a professional studio woodturner, teacher and writer. He has written numerous articles for international woodturning magazines, which have been published in more than 78 countries around the world. Steve has demonstrated in numerous cities across the United States. His studio, Eurowood Werks, specializes in bowls, platters and hollow forms with unique visual and tactile treatments. |
Steve is also a regular featured writer for the Guild of Master Craftsman's "Woodturning" magazine, published in London England. Woodturning magazine is the world's leading magazine for woodturners. Look for his monthly articles covering technical topics, or project based articles in each issue.
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