Information on the Longworth Chuck
Fred,
The article in Woodturning magazine was based on a two part arcticle in the Newsletter of the Hunter Valley Turners Club which is based in Newcastle in New South Wales, Australia. Leslie Douglas Longworth who was a member of that club died in 1988. The design was made available to the turning community by Mr Longworth so I suggest getting a hold of either copy the article and just rehashing it. If you can't get it let me know I will send you a copy.
Les Fortescue
Secretary
Woodcraft Guild Australian Capitol Territory
Note: The following material was forwared to my by Les Fortescue, but appears to be only part two of the article referenced. I am making this information available for what it is worth. I have also requested permission to post the full article from Woodturning magazine at this web site but have not heard from them as yet. The following information was from the Newsletter of the Hunter Valley Turners Club.
SELF CENTERING BOWL FINISHING CHUCK
(Details of the curves used for the slots on the discs. Continuation of the article from Vol 5 No. 7)
It was most interesting to see a reproduction of Doug Longworth's self centering bowl finishing chuck in the center fold of our last issue. Doug has been asked how he obtained the curves for the sliding jaw buttons and I observed that they are identical to the curves used to obtain a French handrail wreath used in stairbuilding. Chris Medlicott, being the wide eyed editor that he is, immediately gave me the task of reproducing a drawing with explanation for this issue.
The curves are known by various names, the main one being logarithmic. A study of Greek architecture shows that they used them extensively in design, the most well known being the Ionic Volute, used in scroll decorations at the top of the pillars at the Parthanon and other great buildings. Some of the designs are exceptionally complicated and demand a high degree of geometric knowledge in order to understand or reproduce. It must be kept in mind that all this was achieved without the aid of computers.
In 1864 a Frenchman named JEAY submitted a paper to the Royal Society of Arts setting out a design for a handrail wreath, where the handrail finished over a newel or cluster of balusters at the foot of a staircase and for his efforts he was awarded a Silver Medal. This design was received with great appreciation as handrail geometry was reaching its zenith or culmination, ending all the guesswork and trial and error methods. The English method was and still is, based on the eight centered Roman Volut'e or Scroll, which while it overcame many problems and logically set out a pre determined method of obtaining the finished article, failed to give a pleasing visual easing of the curves because the rail diminishes in four distinct
Jeay's method however, is simplicity itself and by placing a pin in the eye of the scroll template and by rotating the template a limited number of various positions can be obtained. Any person engaged in designing should have a plywood template of this wreath design as it has limitless applications. I have a number of them that I have made from plywood and when I am designing furniture or setting out staircases or handrail easements or bends, I find that I can draw a curve freehand to the shape required and then by placing the template[ over the drawing, true up the lines, so that they not only answer to the problem but look pleasing to the eye.
It should be obvious to everyone that a "French Curve" used in technical Drawing and drafting is in reality a number of these templates joined together and reproduced in plastic. The trouble however with a plastic French curve is their limited size and the ease with which they can be broken, so it makes sense to make up some templates in plywood, in an assortment of sizes that will give you years of use.
To obtain the shape of the wreath take paper or plywood and draw line A. B. with C.D. intersecting at right angles at center E. With E as center divide each quadrant into four equal parts. Determine the position of 0. From 0 draw a line at right angles to A. B. to point 1. Draw a line at right angles from I to give 21 from 2 a line at right angles to give 3 and so on, continuing around the spiral till you have reached the point desired.
As can be seen, I have shown two positions on the wreath where a straight handrail can join, but for the purpose of making a template, the spiral should be continued for at least three or four convolutions. To obtain the outer handrail lines shown, it Is necessary to step up half the width of the rail each side of each point using 2 compass, but for the purposes of a template, simply join up each point freehand. After cutting out using a fret saw, a piece of heavy sand paper should be used to give a smoother spiral to the edges. If it is not possible to obtain a French curve to join up all the points, then It would be advisable to make two patterns, the first being heavily sanded to give a truer line and then this pattern being used to set out the second pattern.
Don't restrict yourself in regards to the size of the pattern, for the bigger they are, the more uses they can be put to and when it came, to designing furniture full size, a pattern measuring at least 900 mm to 1.000 meter across is invaluable.
—David Lindsay.
Note: Drawings from the newsletter follow:
1. To view drawing Number 1, Select Here.
2. To view drawing Number 2, Select Here.
Note: The following Material was supplied by Jon Schilling:
Technical Comments about the Longworth Chucks by Jon Schilling & Carl Asch
My woodturning neighbor Carl Asch and I made three of these Longworth chucks and I have listed our recommendations and observations below:
1. Make the chuck as large as your lathe can turn. This chuck will easily adjust to turn the largest or the smallest diameter that you have, and I think it could take the place ofthe cole jaws except for the diameters under 7 or 8 inches. (Item D )
2. We used 3/4" MDF and 7/16" birch plywood 'cause we already had it on hand.. (Items C& D)
3. Have a woodturner friend help you and make two chucks. It helped, especially when routing the arcs to have two sets of hands and eyes.
4. Use a 6 or 7" waste block if your chuck exceeds 16 or 18". I feel this gives more stability and strength to the chuck. As with any other waste block make sure you use suitable wood. you den't want this block splitting and coming apart. (Item B)
5 . IF YOU ARE GOING TO USE THIS CHUCK FOR OUTBOARD TURNING, be sure to read the instructions carefully concerning construction for outboard turning. (Item 8)
6. Use nylon washers 7,16" X 7/8" against both sides ofthe chuck. (Figure 3)
7. We spent a great deal of time sanding the slots. We found that having these slots clean allowed for more free movement of the chuck. (Item 10 )
8. We recommend cutting some fingerholes in the MDF disk, too. NOTE: Be careful and don't place these holes on the same arc as the holes that you cut into the plywood disk. you don't want these holes to coincide with holes in the other disk, because of the danger of getting a finger caught. (Might not seem apparent to you now, but when you get ready to cut them, it will make sense) (Item 9 )
9. Instead of using screws to attach my faceplate to the waste block I made it so that I could easily remove and reinstall the faceplate. I did this by countersinking 4 1/4" dia bolts to the waste block before gluing and screwing it to the ND)F circle. (You have to layout the holes to match the faceplate for easy installation) You countersink from the side that will be glued to the MDF, drill the holes, insert the bolts and attach the faceplate to the waste block before you glue up the MDF and the waste block. By using this method your face plate will always be accurately centered every time you reinstall the faceplate from some other project. (Figure 3)
10. Take your time when you actually reverse the plywood disk and insert the bolts. There are two different places where each arch intersects another arc. Place a bolt into an intersection and attempt to rotate the disks. It won't move freely in the wrong intersection, but will move freely when you have the bolt in the right place. (Item 11)
11. I have used the chuck to turn the bottom of 3 large platters and using approx 200 rpm's it worked very well. Bert Stanford turned the bottom of a 12" dia and 10" deep walnut bowl and it worked well for that size too. Here is my point:
a. Be sure to use slow speeds.
b. When gripping an object, loosen the bolts holding the rubber jaws about a 1/4" and tighten the chuck by using the finger holes. Then, tighten the bolts holding the rubber jaws and you will gain more pressure with the jaws.
c. If you have concerns about tightness, take a rope or some twine and tie it around the jaws and you will also increase the holding power and insure safety of your object.
The LONGWORTH CHUCK - List of materials Needed
Secures Object
4 Rubber Jaws (#8 Single Hole Beaker Stopper #201-640)
(Nurnberg Scientific 503-246-8297)
Secures Rubber Jaws ;
4 1/4" x 3" HexCapScrews
8 3/8" 3 7/8" Nylon Washer & nbsp;
(Vancouver Bolt 360-699-4406, or 503-289-1261)8 1/4" Flat Washer
4 1/4" Wing Nuts Secures Waste Block to Face Plate
4 1/4" x 3"FlatHeadBolt
4 l/4" HexNut Centers Plywood to MDF
1 1/4" Brass Flat Washer Attach MDF to Waste Block
8 # 14x 2" Wood Screws
1* 24" x 24" x 3/4" MDF
1* 24 X 24" X 1/2" Hardwood Plywood
1 8" x 8" x 2" Hardwood Waste Block
* NOTE: Adjust sizes of MDF and plywood to meet rnaxirnurn size for your chuck.