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Sorby Hollowmaster



This was the first tool I acquired, years ago, that is capable of undercutting the rim of a bowl to form a semi-enclosed vessel.  It’s a good tool, easy to use, and with it I learned the basics of hollowing. It’s primary disadvantage, compared to other hollowing tools, is the relatively large opening the vessel must have for the shank and cutter assembly to pass through.


The Hollowmaster is available as full-size or medium.  A related item, the “multi-tip tool,” has a straight shank. Sorby also provides a smaller tool that is referred to simply as a “swan neck hollowing tool.” This and the Hollowmaster are shown in the photo below.



A distinctive feature of the Hollowmaster is that the shank of the tool is flat on the bottom.  This makes it easier to position the cutter exactly horizontal, and to some extent, makes it easier to counteract the twisting force produced when the cutter contacts the wood.


Two cutters are supplied with the Hollowmaster.  One, a rod with a semi-circular cross section, is used for shaping where significant wood removal is desired. The other, a disk, is used to refine and clean up a surface. It is not intended to remove large quantities of wood.


Grinds for the rod-shaped cutter


The grind I’ve come to prefer for general shaping and removing wood is a rather pointed V, as shown in the diagram below.  I advance the tool in a direction more or less parallel to one face of the V, and usually keep the depth of cut around 1/16” or less.  What I never do is advance the V straight into the wood so that cutting occurs on both sides at the same time.  The width of the cut widens quickly in this case, and severe chatter (or worse) is the result.  


The other end of the same cutter is ground like a round-nose scraper. With it I can take a very light cut and get a smoother surface than with the V, but it will remove wood quickly if I take a deeper cut.  


The Grind on the Disk


The bevel angle is somewhere in the neighborhood of 75 to 80º, which is typical for scrapers.  In fact, the disk should be regarded as a round-nose scraper. When it’s mounted on the swan-necked Hollowmaster, it becomes a round-nose scraper that can reach underneath the rim of a semi-enclosed vessel.  


Using the Hollowmaster


Adjust the tool rest to place the cutter at center height when the handle is horizontal with the flat side of the shank resting flat on the tool rest.   When using the swan-neck version, place the tool rest far enough away from the piece so the entirety of the swan neck extends over the rest.  This minimizes the twisting force produced by the cutter.

 

For your first attempt, my suggestion is to install the rod-shaped cutter and work on a test piece where the cutter is in full view.  It’s good practice to use the Hollowmaster to hollow the entire inside of a small, open bowl.  It may not go as fast as with a bowl gouge, but it’s good experience.


As an extra twist, if you’re new to hollowing, set the tool rest as shown in the diagram at right and use the Hollowmaster to reach around the rim to the inside of the bowl.  This setup approximates the geometry you encounter in hollowing a semi-enclosed vessel. Practice cutting without looking at the cutter, then examine the result to see if the shape of the resulting surface is what you thought it was.  


To get acquainted with the disk, I would suggest working on the inside of an open bowl as you did to practice with the rod-shaped cutter.  Set the tool rest so the cutting edge is at center height when the shank is flat on the rest and the handle horizontal.


Before you begin, check to see if there is a burr on the cutting edge. A prominent burr will make the tool more aggressive and hard to control.   A safe approach is to remove any existing burr and then reform a much smaller burr by honing lightly.  (Details on how to do this are given in the following article.)


Touch the disk lightly to the inside surface of the practice bowl.  If it feels aggressive or grabby, you probably have too much burr.  If you’ve just done the honing as described above, my suggestion is to remove the burr completely.  A keen edge will cut, even if no burr is present. You can reform the burr after you get a feel for how the tool behaves.


On the other hand, if the tool tends to chatter badly, even with a light cut, the cutter is probably not sharp or it has too little burr.

Don’t present the disk to a concave surface of almost the same radius of curvature as that of the disk.  This will result in a very wide cut, and the tool will be hard to control.  It is likely to chatter badly, or you may get a catch.  


Working with the disk inside a hollow vessel can be a bit tricky.  For one thing, you will not know exactly when or where it is going to make contact with the surface, and this is good reason not to have a grabby tool.  A safe approach is to present the cutting edge to the surface “in trail.”  


You can do this by rotating the tool counterclockwise a small amount so the neck of the swan points downward.  This will raise the flat shank off the tool rest, but that is of little concern. Lower the handle slightly while doing this so the cutting edge remains near center height.  Check this orientation out-in-the-open before you do it within a vessel.  



A Sorby Video


Here is a link to a video that shows the Sorby Multitip tool being used to hollow an ordinary bowl.  It is the straight-shanked version of the Hollowmaster.  


http://www.youtube.com/watch?v=cTDdPIW8WjQ


While the Hollowmaster and Multitip tool can be used to hollow an open-faced bowl, my impression is that they offer no advantage over an ordinary bowl gouge.  This and the impression that sharpening the cutters is a bit more involved than sharpening a gouge seems to indicate that they should be reserved for those instances where a gouge cannot be used.  



More about the Swan Neck and Bullet Cutter


Like the disk, the bullet cutter should be regarded as a round-nose scraper, one that can reach into the interior of a vessel.  It is not a primary hollowing tool for creating the cavity in a vase or hollow form, for example, but is intended for use as a scraper to clean up the surface left by another tool better suited for removing waste wood.  


Now having said that, a bullet cutter can be used to refine the contour of a surface, which may involve removing considerable wood. However, you must always take light cuts because the shank of the tool is not strong enough to support a heavy cut several inches beyond the tool rest.  


Set the tool rest so the cutter is at center height when the handle is horizontal.  


There is no flat on the shank.  When you are working blind inside a vessel, there is nothing to indicate when you have the plane of the swan neck level, and a slight rotation of the handle will cause the cutter to point either up or down.  It may be helpful to make a mark or place a piece of tape on the ferrule to serve as a reference.  


As before, begin your adventures with the bullet cutter on the inside of an open bowl.  Then move to the side and “work blind.”  


Making a Shearing Cut


After you gain experience and confidence in using the bullet cutter at center height and horizontal, you may consider tilting the plane of the cutter to produce a shearing cut in an effort to get a better surface. The extent to which this is possible depends on the orientation of the surface you’re trying to cut and the size of the opening you’re working through, but even a little shearing action makes a big difference.  


(See the article Scrapers: Part 3 if you need to review the details of a shearing cut.)


The plane of the cutter may be changed by raising or lowering the handle, and/or rotating the handle counterclockwise (CCW), which tends to point the cutter downward.  Another variable is the angle of the cutter on the tool.  


As an example, consider the case where you’re working under the rim of a bowl.  If you rotate the handle CCW and lower it slightly, the neck of the tool will be pointing down with the cutter somewhat below center height.  In this position, the wood will be passing the cutter at an angle, which produces the shearing action.  


To illustrate this, I cut a cove on a large spindle blank of ash and then, working from the side, used the bullet cutter on the headstock side of the cove.  The geometry of this cut closely approximates that encountered in working under a rim of a bowl even though the grain orientation is different.  


My suggestion is that you explore the possibilities for shearing cuts on the inside of an open bowl.  Just keep in mind that the reaction force on the cutter will tend to cause it to skate, and if it skates, make sure it will skate into thin air rather than deeper into the cut. This is explained in considerable detail in the article on scrapers.  


This same technique can be used with other hollowing tools as well. My go-to hollowing tools are Kelton swan-neck hollowers for hollow forms with small openings, and I use the shear cutting method routinely.


Final comment:  When working inside a hollow form with a small opening, be especially attentive as you withdraw the tool. Remember, the tool is not straight and some manipulation of the tool is required just to get it out of the hole.  If it accidentally makes contact with the rim, the design of your vessel can change quickly.


At first thought it might seem to be a good practice to stop the lathe before withdrawing the tool, but there is a hazard in dividing your attention between keeping the tool clear of the spinning wood and trying to locate the ON/OFF switch.  So my suggestion is to stay focused on the tool until it is well clear, and then stop the lathe.



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