reverse chucking

Hello,

I use three main methods to reverse chuck bowls and platters. 1.) Jumbo jaws outfitted with sacrificial wooden faces. 2.) Large 3" to 4" thick round wood sections attached to a faceplate and 3.) Extended friction cylinder chucks. I've yet to jump on the vacuum bandwagon, as I rarely encounter a form that cannot be easily rechucked with one of the above methods.

1.) I use the wooden jaw modified jumbo jaws the most. I do not use the plastic knobs for securing bowls. These are the 20" diameter set, outfitted with 3" thick wooden faces. To rechuck a bowl, the jaws are extended slightly, a recess is turned in the wooden face that matches the rim of the bowl. The bowl is then loaded into the recess and the jaws secured. This works very well and offers near 100% contact with the rim. In addition, no tailstock support is required with these jaws, so you can completely turn, sand and finish the piece under power. Very delicate rims can be held this way without damage. It's easy to add tape to the outside of a bowl, if the situation warrants this additional precaution as well. Think of this method as an adjustable friction chuck... :-) I use this method 90% of the time for my production and artistic work.

2.) This is a standard friction chuck type mounting method. I prefer soft Maples for the wooden face of the jam/friction chuck. This type is only used with very small bowls that cannot be mounted in the jumbo jaws. These work well, but require the tailstock to be used, or they must be taped onto the face for finish turning. I use this method 5% of the time on production and artistic pieces.

3.) The extended friction chuck is a cylinder of wood (various lengths) with a turned dovetail tennon turned on one end and a slight concavity turned on the other end of the cylinder. This cylinder is mounted in a scroll chuck's dovetail jaws and secured. The bowl is then inverted over the end of the cylinder and the tailstock is brought up and secured. This style works well for natural edge bowls. The end of the cylinder is covered with smooth leather, or high density foam. The cylinder have been soaked in a thin, penetrating epoxy to harden the cylinder. The bottom of the bowl is finished down to a 1/16" tennon and finished off by hand after dismounting. I use this method 3% of the time on production and artistic pieces.

3A.) A favourite variation of #3 involves the use of ultra high density foam faces, in lieu of the wooden cylinder. This is the same foam used when they built the Alaska pipeline to protect the Arctic Tundra. You can run a truck over this stuff without any damage. Sections of the foam are glued together and trued up with a slight concavity at the end. The opposite end of the foam is glued to a wooden keeper, which has a dovetail spigot for securing it into a scroll chuck. This acts as a basic friction chuck, but it is non-maring and allows very delicate pieces to be finish turned without fear of damage or burnishing. I use this method 2% of the time with artistic pieces.

Good luck to you and best wishes in all of your woodturning endeavours!

If you use a recess, you can finish the bottom prior to reversing to hollow.

If you're an outside gripper, you can reverse to jam between a tapered (for centering) plywood circle and the tailstock, trimming the final tip off with a curved knife.

All the methods I know of( except mine, of course) require either turning a face plate grooved to match the bowl lip or turning an extra amount on the bottom to match a chuck. What I found in Wood Magazine # 45, Sep 91, p.

84 and stupidly listed in their on-line index as being for plates is this:

I turned one disc to the max diameter my lathe would take. Then turned a second set of discs, same diameter but different size holes at the center, padded the hole insides with rubber. Glued a piece of scrap wood to the bowl bottom, fastened that to a face plate, turned the outside and inside and finished them. Removed the face plate,then put the bowl on my solid disc, picked the second disc of appropriate diameter and fastened it with matching bolts to the base disc, turned away the scrap wood and finished the bottom. Just finished two today and it works like a charm. If you can find that wood article, you should read it first. There are probably more details than I am giving here.

Bob Moody

If you have the Vicmarc chuck, why not make a set of jaws?

What is the configuration of the wooden faces, Steven? Do you just secure some rectangular strips to the jumbo jaws, or triangular sections, or what?

I hadn't thought of this option--I like the concept.

Max

This sounds like the same technique Judy Ditmer describes in her book, "Basic Bowl Turning." (Schiffler Pub.) I haven't tried it yet, but it seems like a reasonable method for fabricating a reverse chucking apparatus that will work with many different bowls of similar diameter.

Max

The reason I made this inquiry was to see if you experienced turners used jumbo jaws for reverse chucking. So far it would appear that a variety of methods are used.

Max

Max, Usually I reversed the piece and jammed it between a tail center, narrow enough to expose all the bottom except a tiny nib, and some sort of driving device that didn't damage the vessel. The bottom was cleaned up, decorated or not, sanded and later the nib was carved off.

I made a narrow revolving tail center that extended about 2in. from its bearing. This made the bottom more accessible.

The variations mostly had to do with the driving device that jammed the vessel against the tail center without damage. Usually this was a simple wooden cylinder held by the scroll chuck, the other end knobbed and of a size and shape to fit the cavity bottom. The knob was covered with a material that would resist slipping yet not score the vessel. Ex. vinyl sheet, sandpaper, leather, canvas, balloon wrap. I've never used it, but urethane foam can be molded into a form fitting driving knob.

I threaded different lengths of 5/8 in. CR bar to hold various sized and shaped knobs. To extend, they could be screwed together like a gun barrel swab or maybe slipped over a tube like a trombone. I threaded a dovetailed disc for the spindle ends to fit into. Holding the disc in the scroll chuck saved the time taken to remove the chuck for a separate attachment.

I've never used a Cole jaw/scroll chuck set up, but I have used a large aluminum plate with a foam/vinyl backng to jam a smooth rimmed vessel. IMO, faceplate clamps, dogs and such are best left to machinists, Also jamming a vessel's rim into a turned groove on a wood disc was a pita and not worth the time spent.

I've considered making an 'internal compression chuck' by inserting a small inflatable ball attached to a shaft and inflating it to fit just snug enough to drive. Sort of a soccer ball on a stick. I haven't got roundtuit yet or even thought it through and I probably never will. :)

The use of a vacuum chuck is self evident, but the details are complicated and probably should be the subject of an entire thread.

Max, I used the past tense in the nonsense above because I mostly (87.3%) use a faceplate and sacrifice some wood, which is plentiful in Fl, That way the blank is firmly held and I don't need to reverse the piece to finish its bottom.

Arch

Fortiter,

Hello,

The wooden faces are fabricated from solid sections of a soft Maple, or Poplar and are cut to match the pie shaped pieces of the aluminium jumbo jaws. The jaw mounting area is cut-out in the wood face to allow attaching the jaws with the two screws in the chuck body. The jaw faces are 3" thick, sometimes a bit more and are secured from the rear of the jaws with screws in the furthermost holes in the centre and the outer edges. These areas are not typically in the area of the jaws you will be using when turning the rim recess.

I have used many different methods to rechuck bowls through the years and I like my wooden face modification the best. When set-up, the rechucking is fast and accurate. Many times, the rim recesses can be used for several bowls, if the diameter is the same, or nearly the same. When doing a long production run of bowls, I can frequently use a turned recess many times before it needs tweaking.

I have used this as the primary method to rechuck several thousand bowls over the last few years. It works very well and is very fast. Time is money in a production studio, so if I keep something around the studio and use it, it's because it works. I use the large jumbo jaws offered by Vicmarc on a dedicated chuck for rechucking. When the wooden faces wear out, simply replace them and you're good to go for a few hundred more bowls. Works for me... :-) Take care and all the best to you and yours!

Guess I'm not envisioning this method very well. I'm assuming you're talking about sacrificial wood at the base, similar to a glue block? So, if you part the bowl off, don't you need to finish the bottom? I'm so confused. :-)

Max