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Reverse Turning Hollow Forms

Discussion in 'Woodturning Discussion Forum' started by Ed Weingarden, Aug 1, 2020.

  1. Ed Weingarden

    Ed Weingarden

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    When I'm about to complete a HF, I usually turn the area under the base to a small diameter with a parting tool, and then complete the separation with a fine tooth saw. Then I'll nibble away the sawed-off area with a chisel, followed by sanding using the drill press. I'd much prefer to reverse turn so that the bottom is finished as nice as the rest of it. However, I'm concerned that I'll mess-up the top when I reverse it. For anyone doing HFs, do you reverse turn for the bottom? What's your methodology so the top doesn't get damaged? Thanks.
     
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  2. hockenbery

    hockenbery AAW Advisor Staff Member

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    There are two basic methods of reverse chucking hollow forms.

    1 use a rod ( wood of steel) with a pad on the end. The opening of the form goes over the rod so that the end of the rod and the tail center are pressing on opposite sides of the bottom center.
    I use this method Most of the time and it is virtually impossible to crack the form or damage the rim.

    rubber chucky has a nice set of part to use to make these up.
    https://www.rubberchucky.com/store/p15/Reverse_Chucky/Mini_Reverse_Chucky.html#/
    The various pads go on the end of the rod and rest against the inside bottom of the for.
    The cones then slide into the opening and the nut holds them in place - no pressure this is just to keep the form from vibrating.

    2. The padded rim of a bowl shaped Jamb chuck or a vaccum Chuck is seated on the shoulder of the form where the side wall of the form turns at the top of the form. The rim and opening sit in the open space of the chuck.
    This method can crack a thin walled hollow form by applying too much tail stock pressure.
    With a small and opening this may be the only option.
     
    Last edited: Aug 1, 2020
  3. Ed Weingarden

    Ed Weingarden

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    hockenbery - thanks for the info and link. The Reverse Chucky looks very interesting.
     
  4. Roger Wiegand

    Roger Wiegand

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    Vacuum chucking also works, but can be tricky because you often have a bunch of short end grain that leaks like a sieve. I often seal the inside of the vessel with shellac so it will hold a vacuum. Any turning has to be done really carefully. And of course it doesn't work at all when you have holes and porous inclusions.

    I'd love to have a better way, but all the more secure methods I know about involve having the tailstock in the way. (I haven't yet tried making one of those donut holders that clamp the vessel in place.)

    I'm not worried much about the button in the center, but rather getting access to the inner rim of the foot. I'm always hitting the tailstock when I try to maneuver a tool into that area.
     
  5. Don Wattenhofer

    Don Wattenhofer

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    The method that Hockenbery described has been around for a long time from different sources but I personally have not bought one, instead I mount an appropriately long piece of white pine then turn it to fit through the opening with a close fit at the opening to maintain the axis of the form.
    The majority of the hollow forms I do usually have a threaded lid so when threading the piece I also make a short male threaded block that I can screw the HF onto for working the base. The tailstock with a live cup center is still necessary but it is easy to cut a cone shape from the cup center down to less than 1/4 " at the finished base then carve it off and sand without the tailstock in the way. The jig is mounted in a scroll chuck to the left of the picture. The threaded block is also useful for holding the piece for finishing.
    IMG_1239.JPG
     
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  6. Ed Weingarden

    Ed Weingarden

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    Roger and Don - thanks for the additional info.
     
  7. Damon McLaughlin

    Damon McLaughlin

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    I have the set up from Rubbery Chucky that Hockenbery mentioned. It works quite well as long as you stay within the size limitation. I find that I still use the saw, chisel and sanding method on occasion only because its quicker.
     
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  8. Ed Weingarden

    Ed Weingarden

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    Thanks Damon.
     
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  9. Mike Johnson

    Mike Johnson

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    The size and shape of the hollow form is determined by the wood billet you have available for each individual turning, many times this will require a different size or shape of Jamb Chuck to reverse mount the hollow form. Turning a wood piece for the jamb chuck and using a thin sheet of polymer foam as a cushion is an easy solution for the different hollow forms turned. You can save the various shaped wood jamb chucks in a box and re-use the ones as needed or modify one as needed for each new project. Half of the fun of operating a lathe is creating the tools and jigs you need to produce the new projects you are working on.
     
  10. Ed Weingarden

    Ed Weingarden

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    The good information keeps coming!
     
  11. john lucas

    john lucas AAW Forum Expert

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    I made my own version of the rubber chucky. I used all thread rod and ground a morse taper on one end. It doesn't have to be perfect because you aren't really using it do drive anything with any force. Then I glued nuts into wood that fit on the all thread and turned 3 or 4 cone shapes to fit the lip of vessels. I use my tailstock cone center with a small washer on the end to keep it from penetrating more than about 3/16". I then turn the bottom leaving that very small nubbin to carve off.
     
  12. Ed Weingarden

    Ed Weingarden

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    John - does the threaded rod have the same diameter as the spindle opening?
     
  13. Clifton C

    Clifton C

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    I first heard of this as the Kirsten-Kone. It's googleable, and might give you some ideas. I use a collet chuck to hold a 1/2 inch shaft with a repurposed sanding mandrel for a drive. The cone is maple with a side hole drilled and tapped for a set screw, no insert, just tapped the wood. As Al said, it's just the bottom pinched between whatever pad you have on the shaft and the tailstock, the cone just keeps things from flexing. I added a few strips of fun foam to the cone for a little give. A fun project and you can turn different size cones depending on your needs. I suppose you could also use a Jacobs chuck to hold the shaft...
     
  14. Don Wattenhofer

    Don Wattenhofer

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    To get enough steel to make a #2 morse taper I would guess would take at least a 5/8th 11 or 3/4-10 all thread and then to grind a morse taper that "doesn't have to be perfect" is not the kind of thing I would want to put into my head stock plus if it ain't perfect, which it won't be, it's going to wobble causing further damage to the morse taper socket - that is scary. The idea of using a washer to limit the penetration of the cone center doesn't make much sense when a cup center does the same thing only much better.
     
    Last edited: Aug 2, 2020
  15. DON FRANK

    DON FRANK

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    I have a few variation of this. Different size and lengths of pvc with a turned receiver that goes in a chuck. Because the pvc is hollow, the nub at the bottom of the hollow form doesn't affect how it sets. I pull the tailstock up and turn away everything but the last 1/2". IMG_5585.jpg
     
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  16. john lucas

    john lucas AAW Forum Expert

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    Drill.rod is soft and wont damage.the morse.taper. I did use 3/4". The hardest part is center drilling the all.thread to take your tailstock so you can grind the taper. After I center drilled.it I mounted the rod in my chuck with the live.center in the center divot. Then turned the lath on at slow speed and used my angle grinder with an abrasive disc.to get.the shape. Slow going but it worked. Got.it.close and then remove the live center and coat the taper with blue machinist dye. Insert it in the Morse taper and twist by hand. This shows where it runs. Put it back between centers and either grind more or use a hand file with it rotating to remove the high spots. A half dozen of these check and file and it was close enough to work. I made a wooden piece to.fit the end that has sand paper to drive the turning.
     
  17. Ed Weingarden

    Ed Weingarden

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    Don - any problems with getting the PVC to run true?
     
  18. DON FRANK

    DON FRANK

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    The pvc is not glued in place. It would be better if it was. I need to make an end cap for it that I can put on my tail stock and then glue it permanently once I know it's running true. It takes a little adjustment to get the hollow form running true. I have been green turning to final thickness and leaving the stub on the bottom for the tail stock. I come back with this to finish off the bottom, however, I think I'd be better off to completely finish the bottom and then I can always do this again to hold it on the lathe for additional sanding once it's dry.
     
  19. Ed Weingarden

    Ed Weingarden

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  20. Mark Jundanian

    Mark Jundanian

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    I'm just following this thread from the back row, but a question comes to mind. Would there be any roll for a steady rest in this work holding problem? Just some first cup of coffee thinking, but a steady rest might help with running true, dampen vibration and keep the HF from flopping about when the nub is cut off. If the diameter of the HF increases on the head stock side of the steady rest, the rest might also tend to hold the work on the head stock. Of course I have no experience with steady rests.
     
  21. William Rogers

    William Rogers

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    I use a vacuum chuck as described by Roger. However I also use painters tape and tape the piece to the chuck should there be a slight catch. You need to keep the tailstock up as long as possible and very light cuts to finish up.
     
  22. hockenbery

    hockenbery AAW Advisor Staff Member

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    generally no. There may be some forms for which it would be of value but I can’t think of one .

    1. Unless you screw up, there is no flopping around
    2 a steady rest will make compression marks on the hollowform so most peopl would leave a band for the wheels to run on that gets sanded flush to remove the compression marks.
    3. a hollow form is big enough to require a steady rest, it will be too big to reverse chuck.
     
  23. Randy Heinemann

    Randy Heinemann

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    @Ed Weingarden If you're so inclined to spend some money, ronbrownsbest.com sells what he has named a doughnut chuck. You can buy a combo of a longworth and doughnut chuck with inserts to fit a range of bowl and hollow form sizes from 2 1/2" on up. Basically the combo set is designed to permit remounting the bowl with the bottom exposed unsupported from the tail stock end. This allows you to turn the bottoms however you wish. To be honest, I just bought this and can't yet tell you whether I feel it was a good purchase. However, Ron Brown gets a lot of positive feedback on all of his products. The longworth chuck for sure works as that concept has been around for awhile. The only issue with a longworth chuck is that, sometimes, you still need to support the bowl from the tail stock side because of the shaper of the bowl or hollow form. With the doughnut chuck added, this problem should be solved. Again, this is only if you want to spend some money. If you are more inclined to make your tools/jigs, then there are a number of solutions which have already been described.
     
  24. hockenbery

    hockenbery AAW Advisor Staff Member

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    I use donut chucks for holding balls to hollow and they work great for small bowls.

    I would not use them for hollow-forms.
    Too much risk of cracking the form and the long bolts needed would be added complications I don’t want to deal with.
     
  25. Tom Gall

    Tom Gall

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    I always completely finish-buff-wax (whatever) my pieces while they are on the lathe. The tenon (or other mounting method) is dealt with last and finished separately. So, holding with vacuum is not a problem. Any holes can be covered with pieces of masking tape, or if larger (inclusions) I use that self-adhering wrapping film. If your tailstock is in the way for those final cuts try using one or more MT extensions, although I don't usually find that to be necessary.
     
  26. Ed Weingarden

    Ed Weingarden

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    Randy - thanks for the insights with respect to the Ron Brown options. For my bowls, I'm set up with a vacuum chuck, which I use on most of them to finish the bottom. After looking at a couple of the videos on Ron Brown's web site, I'm not sure the doughnut chuck system is appropriate for a 12" or 14" deep hollow form.
     
  27. Brandon Sloan

    Brandon Sloan

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    I’ve been using the reverse chucky from rubberchucky.com. It's a simple system, the only negatives are that it’s made from aluminum and the threads are very soft. If I had to do it again, I’d probably go with the kelton mandrel. I chose the rubber chucky over the kelton because I didn’t want to turn my own cone sections. Just used it yesterday for this piece.
     

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  28. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    What turners in the Mainland call a doughnut chuck, in Hawaii we call it the Jack Straka chuck. Jack came up with that in the 70's. I do not use one, I have seen it in action, and seen how many different lengths rods you need. It is very easy to make. I do not know why someone would pay for that. I have dozens of lids of boxes in a "lesson learned" bin, I always find one that fits the mouth of my hollow form, I then use the tailstock, cut the nub at the end.
     
  29. Don Wattenhofer

    Don Wattenhofer

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    Well I am on the mainland and it is only on this thread that I heard the name donut chuck and after looking at the plastic one being sold that I realized it was a very old idea being recycled. More than 20 years ago I made one for hollowing ornaments and then attaching apiece of wood for the hanging finial then after turning the finial I reversed it to mount a block and turned and carved a hanging eye. So Ya why would anyone pay for that? 6096-97.JPG
     
  30. hockenbery

    hockenbery AAW Advisor Staff Member

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  31. Mark Jundanian

    Mark Jundanian

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    What Ron Brown's Best did was to mate the donut idea to a Longworth chuck in such a way that the Longworth retains its function. So that's a step up from a simple donut (more of a longjohn :)). Certainly a person could design and make their own, but personally I had neither the interest nor the tools (CNC) to do as good a job. I use mine frequently, but I've never done a tall HF.
     
  32. Ed Weingarden

    Ed Weingarden

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    Brandon - thanks for the photo. That's a nice piece of wood.
     
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  33. Timothy White

    Timothy White

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    Cindy Drozda did a hollow form demo at SWAT a couple of years ago, she used blue painters tape and packing tape to hold the reversed HF on the Kelton. She kept the tail stock up, turned off most of the tenon, taped the HF to the Kelton cone, removed the tail stock, cut off the rest of the center and sanded the bottom.

    It’s not a good idea to put the packing tape (box tape) directly on the HF. The adhesive is very difficult to remove. This technique will work with the Rubber Chuckie also.
     
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  34. hockenbery

    hockenbery AAW Advisor Staff Member

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    . Good advice. Also if the form is thin it can pull a a piece out of the endgrain adding an unwanted hole.

    Cindy has many many good tips in her demos and classes.
     
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  35. Don Wattenhofer

    Don Wattenhofer

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    Please excuse my ignorance but what is a Kelton?
     
  36. Don Wattenhofer

    Don Wattenhofer

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    The idea that using tape to hold a hollow form onto whatever since if you are taking off a tenon you will have about 1/2" material to remove and if using a cup center to hold the piece to the jam chuck whatever that may be the final cuts can make a cone shaped nubin from the cup center down to the base to maybe 1/8" diameter.That nubin can be cut off and sanded just as fast as taping and finishing on the lathe.
     
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  37. Brandon Sloan

    Brandon Sloan

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    If you look at the picture I posted of the rubber chucky, the kelton mandrel is similar except you turn your own cones.
     

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