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Thread: Hollow Forms and How I Turn Them

  1. #1
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    Hollow Forms and How I Turn Them

    [Originally posted in this thread. - VM]

    The following information on hollow forms is being presented with the beginning turner in mind. It is the simple intent of this post to expose the beginner to the various steps involved in creating a hollow form.

    The normal disclaimer: I am not an instructor and have learned what I know through active participation here on Family Woodworking and the SawMill Creek forums as well as trial and error. These photos offer only a few of the many possible ways to turn hollow forms. Most importantly, my methods work for me… if something doesn’t look or ‘feel’ safe to you – DON’T do it!

    List of tools:

    Jet 1642 EVS 2 hp Lathe, 7 bags of concrete
    Chainsaw
    Talon Chuck and various jaws
    6” Faceplate, came with the lathe
    Homemade Steady Rest
    ½” Bowl Gouge
    1/8” Parting Tool
    Monster Captured Hollowing System with Laser
    Cheapest electric drill I could find
    2” sanding disks, various grits

    I start with green (wet) wood and chainsaw the blank from a log using the procedure that Bill Grumbine demonstrates in his video “Bowl Turning Made Easy”. (this is an excellent video and I still study and learn from it!)

    I use the chainsaw to ‘round’ the blank as much as I can so it is easier to rough out. You don’t have to cut the corners off the blank first but it makes everything faster and a lot easier on your body.

    Roughing out the Hollow Form

    Step 1: Here I have a large blank on the lathe. The blank is mounted using a 6” faceplate and some good steel sheet metal screws. The tailstock is brought up to support the blank. The first step is to shape what is going to be the bottom portion of the hollow form and also to form the tenon. I’ll showcase the tenon in another photo later. At this step I usually run my lathe around 200 to 400 rpm depending on how out of balance the blank is. The general idea is SLOW speed until you get the blank rounded. Also, when shaping the form the only tool I use is a ½” bowl gouge. It’s not the only way to shape the form, it’s just the tool I prefer.
    Attachment 16856

    Step 2: Once step 1 is completed, remove the faceplate, reverse the blank and mount it in the chuck using the tenon. Bring the tailstock up seat into the blank. Now that the blank is somewhat more balanced I increase the speed a little which helps to remove stock faster and also gives a smoother cut.
    Attachment 16857

    Step 3: This is where you form the face (top) of the hollow form. Figure out approximately how large the opening is going to be and adjust your design so that the face and opening flow together with a continuous curve.
    Attachment 16858

    Step 4a: The outside of the form is now complete and I setup for hollowing. I remove the tailstock and install the steady rest. As you can see, it is a very simple design made out of scraps but it works very well! The wheels run on the largest diameter of the form and support it while hollowing. 4b shows the back side of the steady rest and another view of the way the piece is held in the chuck.
    Attachment 16859 Attachment 16860
    Attached Thumbnails Attached Thumbnails Rough 1.jpg   Rough 2.jpg   Rough 3.jpg   Rough 4a.jpg   Rough 4b.jpg  


  2. #2
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    Roughing Out continued…

    Step 5: Rough out the inside of the form. I try to leave the walls at least 10% of the diameter of the form. This is usually more wood than necessary but it does allow for small design changes once you finish turn the piece.

    Roughing out green wood is about as messy as it gets. You’ll have to stop often and remove wet shavings from the inside of the form but it is a great time to play with whatever tools you have for hollowing and figure out how each works. I found that the square bits work well for cutting and fast stock removal and the curved bits are for smoothing out the ridges the square bits left behind. Green wood is fairly forgiving so just play with each bit and see how it feels.

    For me, the best rules for hollowing are: Make sure the cutting edge is on the centerline or below, use light cuts, sharp bits and smooth movements as much as possible. If you have to push – then chances are your bit is dull or you’re not close to the centerline. Couple of other things to remember is to keep the tool rest close to the work as this will help reduce vibration. Also try to keep the tool bit parallel to the bed of the lathe. If the bit is allowed to rotate down – the edge will not contact the wood and if the edge rotates up above the centerline you will have what is known as a catch and bad words will be said!! I should also mention that I use sweeping motions just like when turning the inside of a bowl. Start at the left and move towards the center of the work and headstock.

    When hollowing, everything inside is cut strictly by feel. If you want to actually see how the hollowing tools work, then I suggest a practice session using a green bowl blank. It might give you a better understanding of what’s happening when you are hollowing.
    Attachment 16861

    Step 6: Remove the blank from lathe and DNA soak. I use the DNA method that Dave Smith developed and found that Dennis Peacock has an excellent tutorial already on SawMill that covers the DNA process and he included photos! Check it out here http://www.sawmillcreek.org/showthread.php?t=34370
    Attachment 16862

    Step 7: After DNA I let the blank dry for 20 minutes or so and then write the date on the tenon with a gel pen. Wrap the form in brown paper bag and leave an opening over the entry hole so the hollow form can breathe. I also date the outside of the brown paper bag and place up-side-down on a rack to dry. Depending on where you live the blank may be ready to turn in just a few weeks. I usually let mine dry for a couple of months and then start finish turning.
    Attached Thumbnails Attached Thumbnails Rough 5.jpg   Rough 6.jpg  

  3. #3
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    Finish Turning a Hollow Form

    Step 1: Mount the roughed out hollow form using the Talon chuck with whatever jaws fit the opening. I also bring up the tailstock and, using the original tailstock divot, center and secure the hollow form.
    Attachment 16863

    Step 2: The blank will have warped during the drying process – so the first priority is to true up the tenon and it’s shoulder area. This is an important step because not only does the grip on the tenon hold the work in place, it also determines the centerline for the form! I use a bowl gouge to true the tenon and my parting tool to clean the shoulder area.

    Hint: Make sure the tenon and shoulder are perpendicular to each other and the length of the tenon will not bottom out in your chuck! Please note that I use a Talon chuck and true everything up accordingly. The chuck you have may require a different tenon profile but the concept is the same!

    After the tenon is formed I then go on to shape what will become the outside bottom of the hollow form. This is where having a little additional wood left over from the roughing out process allows you to make small changes in the profile.

    A lot of folks get concerned about RPMs or speed of their lathe during all these steps. There are charts out there with recommended speeds for a given size of turning. I turn at whatever speed I’m comfortable with at the time but remember the general rule “the bigger the item, the slower the speed.” I turn the outsides of the form around 400 rpm while it is warped and from 550 to 700 once it is trued.

    After finishing with the shape I sand the form. This is where you will notice tear out, ridges, dips, etc. I turn the lathe down slow and use the cheapest electric drill I could find and 2” sanding disks. I work through the grits starting with 80, 120 or 180 (depending on tool control) and ending with 320.
    Attachment 16864 Attachment 16865

    Step 3: Next step is to shape the face of the form. Mount the blank into the chuck. I push and rotate the blank towards the headstock with my right hand while at the same time visually making sure the tenon is fully seated and tighten the chuck with the left hand. To check that the blank is centered correctly just give the piece a small spin and confirm the area you just turned is running true. If not, loosen, rotate the blank slightly and try again. There are times when I use the tailstock to support the form while shaping the face, usually when the piece is very large or has a number of cracks that I’m keeping an eye on. In the case of this photo, I did not use the tailstock but I highly recommend using it whenever possible!

    Because the face of the form is warped, I start turning around 400 rpm and then increase to 650 - 700 once the face is trued. I use a variety of pulling cuts as shown in Bill Grumbine’s video, starting close to center and pulling towards me. I find with practice you can cut an extremely nice surface and that gets rid of a lot of sanding!

    Once you have the face shaped the way you want, it’s time to sand. Before you sand – make sure you have the final shape that you want. Take a step back and look at the form from a number of different angles – this is your last chance to change anything before you start hollowing!
    Attachment 16866 Attachment 16867
    Attached Thumbnails Attached Thumbnails Finish 1.jpg   Finish 2a.jpg   Finish 2b.jpg   Finish 3a.jpg   Finish 3b.jpg  


  4. #4
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    Finish Turning continued…

    Step 4: At this point I set up the steady rest and captured hollowing system. Again, the steady rest rides on the largest diameter of the form and provides support.

    Remember the warped wood I spoke of when I first started finishing the roughed out form? Well, it’s warped on the inside as well and that makes for some real bumpy – grabby cuts. Using very light cuts and working in small sections helps. It was because of the torque that develops inside the form and unexpected grabs and catches that I decided to move up to a captured system. The support frame that holds the d-handle removes most of the fight involved in cutting through the warped area inside a form.

    Hollowing at this point is just a matter of working through the bits. I use the square bits to cut the walls to get close to whatever thickness I want for the form. I would love to be able to turn hollow forms with a 1/8” consistent thickness but I’m not there yet. To get to ¼” thickness I cut the walls down to about 5/16” to 3/8” and then switch over to a curved bit and smooth out the walls.

    A note about the square bits… when the bit is sharp it is very easy to get aggressive with your cuts and that usually results in tear out or a sudden groove. While it takes a while longer to complete the hollowing if you take light cuts, you’ll save time by not reworking an area to remove the damage.
    Attachment 16868 Attachment 16869 Attachment 16870 Attachment 16871
    Attached Thumbnails Attached Thumbnails Finish 4a.jpg   Finish 4b.jpg   Finish 4c.jpg   Finish 4d.jpg  

  5. #5
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    Finish Turning continued…

    Step 5: With hollowing complete the next thing to do is remove the tenon. While there are a number of ways to accomplish this, I use a homemade donut chuck. Very simple to make and they work great on most pieces. I bring up the tailstock to hold the piece in place while tightening the bolts. With the piece mounted in the donut chuck I make sure the form is running true by backing off the tailstock and giving the chuck a little spin. The tenon should run with minimal wobble – if not, you’ll notice that the divot was pulled to one side when compared to the tailstock center. Tighten the bolt on the opposite side of the direction of the pull and it should pull the center of the piece back into alignment.

    With the lathe running around 500 RPM, I use the bowl gouge and very light cuts to remove the tenon. I like a slight concave foot which allows the form to sit without wobbling and doesn’t subtract from the profile of the piece.

    Sand the foot area and remove the form from the donut chuck.
    Attachment 16872 Attachment 16873 Attachment 16874 Attachment 16875

    Step 6: For all purposes the hollow form is complete. Sign and date the bottom of the piece – it’s ready for whatever kind of finish you wish to apply.
    Attachment 16876

    Remember, there are many different ways to achieve the same results. The steps I’ve listed here are simply what I do at this time. As we are all learning, please feel free to ask questions, offer suggestions or comment.
    Attached Thumbnails Attached Thumbnails Finish 5a.jpg   Finish 5b.jpg   Finish 5c.jpg   Finish 5d.jpg   Finish 6.jpg  

    Steve

  6. #6
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    Just a post to bump this thread. It was suggested as a tutorial, so I copied it over here.
    When the going gets weird, the weird turn pro. - Hunter S. Thompson
    When the weird get going, they start their own forum. - Vaughn McMillan

    workingwoods.com

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