Hollowing a large project with steady rest
. See what happened when we used an 8 arm steady rest. We only used 3 arms which will work well if evenly spaced as with the standard version Clark Steady Rest however, the 8 arm steady rest is designed for a minimum of 4 arms. We only used the bottom 2 mid positions and the 2 o'clock position which left a large area of the log unsupported. See the first video on the main hollowing system product page.New External Shaping Modification
- I am excited about a new idea to use the hollowing system to rough and shape externally! All that is necessary is to add a second base ($50). The 2 bases are mounted at 90 degrees to the lathe bed and connected on the side of the lathe using the tool post in much the same manner as one would hollow. In this configuration an extremely aggressive removal of wood is possible and "catches" become a thing of the past! Now the hollowing system can double as a roughing an shaping attachment. I also now have a 1/2 inch diameter square cutter ($25) which is 4 inches long. It mounts directly into the end of the hollowing bar - no flexing and no mercy on any type of wood either hollowing or externally shaping! Roughing a log with knots etc takes no effort. I tested the system externally and was able to put my little finger inside the hole in the end of the bar and with only that finger touching the bar was able to hog off material! It is quite impressive and satisfying to see how well it works. Watch the videos on using the system.
Update and Tips
- From September 2012 through January 2013, hollowing systems were not shipped in an effort to test some improvements. Some modifications are minor, while others are major. I am very thankful for feedback received from many wood-turners over the past 10 years or so which has helped me refine the Clark Deep Hollowing System. Overall, the original design has proven to be excellent! However, the original (2001-2006) cam-follower bearing design and slot in the hollowing bar suffered from binding. The second generation (2006-present) adjustable ball-bearing and better machined slot provide smoother operation without binding - a very significant upgrade in performance. The Fulcrum Support Tube and a new way of connecting the Swivel Pivot Apparatus have proven to be significant advances!
Recently, I have been blessed to work with Jon Leggett. Jon turns full-time in Virginia and has become an expert with the Clark Deep Hollowing System. He has challenged me to extend the system's performance envelope. Together we are defining hollowing depth capabilities and providing specific recommendations for cutting tools, accessories and techniques for various depth ranges.
There are other hollowing systems on the market that cannot hollow well beyond the 8 inch depth range. I know this because I get calls from turners who are not satisfied with other systems they have purchased. The standard Clark Deep Hollowing System can easily hollow to 15-18 inches and to about 22 inches with a very careful and slow technique.
Some of the variables influencing results include; type of wood, type of cutter, angle of approach of the cutter, position of the cutter relative to center-line and features of the hollowing bar itself. Of course, a major factor affecting depth capability of all hollowing systems is flexing of the bar. During deep hollowing, the tool tip is suspended a long distance from the tool rest. Tremendous forces are generated which can lead to unsavory vibrations. Vibration can be minimized by larger diameter bars, less aggressive cutting tips or very slow removal of wood. Larger bars are cumbersome and slow removal of wood is no fun! With new accessories the Clark Deep Hollowing System is potentially capable of aggressive, relatively rapid hollowing up to and possibly beyond the 30 inch depth range with the new Fulcrum Support Tube.
- please turn safely!
The Clark Steady Rests are an integral accessory for hollowing. Forces exerted by the hollowing system are tremendous. The wood can be much more easily torn from a faceplate or chuck without a steady rest. Any wood-turning task can potentially be dangerous! Proper protection, instruction and experience are necessary.
Almost any hollowing tool will work with the Clark Deep Hollowing System up to 15 inches or so deep. Beyond that depth can get tricky and will be easier with less aggressive cutters. New turners will certainly appreciate the smaller cutters and especially guarded cutters. Hollowing can be difficult, and there is definitely a learning curve. Consistent practice and experimentation with variables being discussed will certainly be fruitful.
15 INCH DEPTH HOLLOWING
- 19 mm round, carbide cutter
There are really no changes from the basic system required to hollow to the 15 inch depth. Any cutter will work well to the limits of the wood and the cutter itself. Between 15 to 23 inches deep is better controlled with a less aggressive cutter and delicate technique. The 19mm round carbide cutter I sell is shown on videos at www.theokspindoctor.com.
Some have suggested that this cutter will not work well because it is too large. Our experience has been excellent - it removes wood quickly and has great longevity. Yes, it can be aggressive if too much force is used. Jon Leggett has used the same cutter to hollow 22 large vessels (many were hardwood) to the 20+ inch depth. He did not even have to rotate the cutter to an unused edge. However, rpm has to be slower than expected, and the cutter is very sensitive to angle and position relative to center-line. When Jon and I were demonstrating at the Virginia Wood-turning You Turn 2 Symposium in September, we were hollowing an 8 inch diameter hardwood log at about 18 inches deep with the 19mm cutter. I turned on the lathe and set 800 rpm. Jon began hollowing and experienced bad vibrations to the point that he could not hollow. We incorrectly thought the vessel has warped overnight or that the log had moved in the chuck. I was very surprised that problems were solved with an adjustment down to 280 rpm! The cutter must be set at center-line. During removal of wood at the bottom, the angle of the cutter should be slightly down about 10 degrees from horizontal. Side removal works better with a wider angle from horizontal. The most difficult area to hollow is at the junction of the side and bottom when very deep. Removing the nub right at the center is easy if the tip is at centerline and angle is closer to horizontal.
30 INCH DEPTH HOLLOWING
- the Fulcrum Support Tube Accessory
- See videos that follow for very
Here is the really tricky issue; using a 1.25 inch diameter bar to hollow extremely deep with the Clark Deep Hollowing System. Turners typically use very large diameter bars to get to this depth and beyond, but the bars are heavy and can be difficult to control. Jon Leggett has used this system to hollow to 30 inches with the standard bar and an 8 inch Fulcrum Support Tube Accessory. This accessory mounts on the tool rest provided with my system and greatly stabilizes the bar. Extreme depth hollowing produces vibrations in the bar due to flexing of all the components from the base to the cross bar and the hollowing bar itself. With a secondary banjo under the Fulcrum Support Tube there is even more stability. Any turner desiring to frequently hollow beyond 15 inches consider a 12 inch Fulcrum Support Tube. Those looking to hollow beyond 15 inches may like a longer Fulcrum Support Tube. Some lathes with a tall banjo, such as Oneway lathes, will need a shorter secondary banjo to use the Fulcrum Support Tube.
- John Leggett suggested installing a grease fitting to the swivel-pillar mechanism. It was a wonderful suggestion! The screw holding the pillars together must be tight. If play develops then there will be a source of vibration which will limit depth of hollowing. With the joint lubricated with grease, the screw can be much tighter. The pillars turn much easier and there is no binding.
- Any curve can be created but the ones shown are for closed forms since one can reach under the upper shoulder to hollow.
The blowup in the lower right corner shows the round cutter. These can be ordered straight or curved holders. They can be ordered almost any diameter but usually 1/2” or ¾”. These are made in Switzerland of high tech carbide and never need sharpening. I believe they actually cut rather than scrape the wood away.
Cutters and Holders