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Gouges, Part 6

Cuts in Rough Turning a Bowl


(Note: a tip cut is perhaps better known as a push cut, and a wing cut as a pull cut.)


This article describes the various cuts that may be used to rough turn a bowl using 1/2” and 5/8” bowl gouges.  The objective is to rough out the form and turn the wall thickness down to about 10% of the diameter.  The blank will then be set aside to dry for several months before the final finish turning is done.


Truing up the outside profile.  We begin by removing waste wood from the blank with a chainsaw, attaching a faceplate, and mounting it on the lathe.


The first task is to remove the projections, the corners, working from the side rather than approaching them head on.  I used a 5/8” bowl gouge in a tip cut, guiding the tool along the rest.  The speed of the lathe was set at about 400 RPM, and it ran with minimal vibration.


A quick way to true up and shape the rest of the profile is to use a wing cut with the bevel rubbing.  Pull the cut from near the tail center toward the rim.  Once the blank is round and balanced, the RPM can be increased to about 600.


The tenon can be formed either with a parting tool or with gouges. Since this article is about gouges, let’s go that way and use a 3/8” spindle gouge with a fingernail grind.  Small cuts are made in steps to avoid overloading the small gouge.


True the rim.  I like to clean up the rim at this point (or even earlier).  A cut that works well for me is a variation on the wing cut. The gouge is positioned so the bottom wing will engage the rough surface of the rim in the trailing mode.  Then, with the handle down a bit, it is pushed across the rim an inch or so.  The shavings fly!  


Hollowing issues.  A complication often arises as you hollow a bowl with steep sides, and that is the degree to which the handle must be swung to the right in order to keep the bevel rubbing.  As the sides get steeper, the swing must increase.  It’s not at all unusual for the handle to be swung past the centerline of the lathe. When the swing gets extreme, it’s sometimes called a “chicken wing.”  


Having to swing the handle “way over” is not a desirable aspect of the hollowing process. It is a far cry from having the handle tucked against your side and is much less stable – and more dangerous.  Your control over the tool is simply not as good.


You can avoid the chicken-wing effect by using scrapers and hollowing tools designed specifically for this task.  If the side of a bowl turns in sharply at the rim, these tools may be required.  


Another problem with hollowing deep bowls is that the rim of the bowl gets in the way of the handle as you attempt to make a bevel-rubbing cut in the region where the side transitions to the bottom.  Whether this problem will arise depends upon the details of the bowl and the angle of the bevel on the gouge. You may have to use a scraper instead of a gouge (See Scrapers, Part 3).


Hollowing the blank.  Once the outside profile is completed, the blank is reversed for hollowing.  It is mounted in a scroll chuck which grips the tenon formed at the foot.


The basic tip cut is not necessarily the best for all situations. There are other cuts that will get rid of the waste wood quickly and efficiently.  One is a wing cut, pulled from the center toward the rim.


With this method, cutting is done with the lower wing.  The cut can be bevel-rubbing, or not.  On rough surfaces, just place the cutting edge in trail and drag the tool across the face of the piece.  Holding the handle low results is a shearing cut that will bring away a lot of wood in a hurry.  After the surface is smooth, you can switch to bevel-rubbing cuts, which seem to be a bit more efficient.


I’m a great believer in using tailstock support for blanks mounted on a faceplate or in a chuck whenever it’s possible to do so.  For example, when hollowing a bowl larger than about 5” in diameter, I pull the tailstock up and seat the live center against the piece.


An obvious disadvantage of using tailstock support is that it gets in the way of the hollowing.  However, there are ways to work around it so that a lot of wood can be removed.  This wood is the most distant from the chuck or faceplate, which means that forces exerted in cutting this part have the greatest leverage in regard to twisting or pulling the piece off the lathe. This is where the additional support is needed most.


The tail center does not get in the way of a wing cut except for the region closest to the center. Leaving the wood near the center leads to the formation of a pedestal, which is removed later.  On the positive side, the pedestal allows the tailstock to keep the blank pressed firmly against the chuck.

 

An aggressive wing cut pulled too close to the rim may cause surface splintering that may extend onto or across the rim.  To avoid this, I switch to a tip cut and work from the rim toward the center. Once the cut is well below the top of the rim, this is no longer an issue.


A wing cut below the rim can be made with the tool handle positioned almost parallel to the axis of the lathe.  This provides a means of removing waste wood on the steep side while avoiding the tailstock.  The tool handle is kept low to ensure a shearing cut. In doing this, you must keep the cutting edge in trail.  The cut becomes very aggressive if you open the flute a bit much. Do not attempt a bevel-rubbing cut – it’s too risky.  


As the hollow deepens, I find the diameter of the pedestal gradually increases because the start of each successive wing cut is slightly displaced from the one before.  To remedy this, you can make a tip cut down the side of the pedestal.  It’s a bevel-rubbing cut in which the bevel rides on the side of the pedestal, much like making a cut on a spindle. It is easily controllable.


A convenient cut that will deepen the hollow is a tip cut that advances at about a 45º angle to the axis of the lathe. The tailstock does not get in the way of making this cut.


At some point, it will be time to remove the tailstock.  The first task is then to remove the remainder of the pedestal.  A few cuts made down the side make quick work of this.  However, if you’ve already turned it down to a small diameter, it’s quite possible that a tap on the end will break it off near the bottom, to save a bit of turning.  It will be more likely to break if you can undercut it, perhaps using a diamond parting tool.  


Whether you use tailstock support and fiddle with the pedestal is, of course, up to you.  My preference is to use it because it gives me the confidence to take heavy cuts without having to worry about the piece coming out of the chuck.  With heavy cuts, the hollowing goes faster and more than makes up for any time lost in dealing with the pedestal.  With the blank shown here, at least 80% of the hollowing was done with tailstock support.


Complete the hollowing.  After the tailstock and the pedestal are gone, the hollowing can proceed in the usual fashion with a bowl gouge.  A mark of skill among turners is to start a tip cut at the rim and carry it all the way to the center without dropping the cut.  This assumes, of course, that the geometry is such that a bevel-rubbing cut can be maintained over the entire surface.


That’s about it for bowl gouges.  Now, wonder what a detail gouge is good for - details?


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