Wight Woodturners

Club Meeting - 28th April 2016

How to make a Longworth Chuck

A Talk and Practical Demonstration by Roy Groves

The April meeting of the Wight Woodturners was well attended and all were treated to an informative and entertaining talk by one of our members featuring the construction of the Longworth Chuck.

First of all, the meeting was opened by our Chairman, Mike, welcoming both guests and members and giving us details of our Exhibition at the Rembrandt Gallery in Newport which runs from June 21st to the 25th June.  For full details members should read the April Turning Points elsewhere on this website.  Mike also informed us that the Club would be introducing some basic Health and Safety measures over the coming months which are needed safeguard members and guests and to fulfil our insurance and legal obligations.

Following an impromptu Show-and-Tell with Ron’s elm bowl, Peter’s bobbins and Paul’s carbide cutter tool the evening got under way with Roy Groves talk.

The Longworth chuck was developed by Leslie Longworth of the Hunter Valley Woodturners in Australia in the late 1980s.  The chuck features a self-centring mechanism that easily and quickly adjusts to the size of your turning.  It uses a pair of disks which rotate against each other, drawing in and out the attached rubber buttons on a series of opposing arcs.  A wooden version of this chuck can be easily made in the home workshop using readily available hardware.  You will be able to find many, many references on the internet on how to make this chuck but an excellent article by Walter Hall was printed in the Woodturner Magazine in 2010 and Roy recommends this as a good reference.  See the Resources section below.

In his talk Roy describes the general construction methods and gives us many practical tips on how to make this useful chuck.  Roy’s talk together with Walter Hall’s article and the Step-by Step Layout Geometry crib sheet should enable every member to make one!  Who was it who said Roy was going to have a Longworth Chuck Competition?

Just click on any of the small images to bring up the bigger picture

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This is an example of the useful Longworth chuck that Roy will show us how to make. It is used to hold bowls by the top rim so that the base can be finished. This often involves the removal of the chucking dovetail spigot.
The chuck shown is a smaller 6 button version made of MDF.

Roy explains one of the first things you need to decide is “how to mount the chuck on your lathe”. Options are a screwed-on metal faceplate, a threaded wooden boss, a face plate ring or a wooden dovetail spigot to suit your chuck jaws. The material for the chuck disks needs to be flat and stable. Roy says good quality ply or MDF board are both suitable.

Here Roy has a chuck with a metal faceplate ring. He advises you should NOT use wood screws into MDF as the fixing is not strong enough. Fit metal inserts into the MDF and use machine screws (see resources). Roy says for occasional use MDF is ok but good quality ply will give a more robust job for repeated use as the slots will not wear.

Extract from Woodturning Magazine No 212

This excellent diagram from Walter Hall’s article in Woodturning shows all the component parts of a typical Longworth chuck. The diagram shows a composite design with an MDF front plate and a ply backplate.

Here Roy explains the geometry of marking out the plates. As the slot geometry on the rear and front plates is identical the plates are machined together. After the slots are cut, one plate is flipped-over so that the arcs “rotate” in opposite directions. For a detailed step-by-step guide on marking out geometry see “Resources” below.

This is a close up of Roy’s layout diagram for an 8 button chuck. The slots will be cut with a router passing completely through both plates. Note that for an 8 button chuck alternating slots are reduced in length so not to compromise the strength of the disks.

Now Roy is getting the router ready by attaching the circle cutting jig and setting up the pivot pin for the correct radius. Before starting make sure you have clearly identified the pivot point for each arc on the marked out pivot point circle.

Here the plates are temporary screwed together at the corners to prevent relative movement then clamped to the bench before the routing begins. Roy has made sure there is nothing to restrict the router movement like protruding screws or G cramps. The circular disks are cut out after the slots are cut.

Roy reminds us that MDF dust is very fine and particularly nasty – hence the dust mask! Remember, the dust will stay suspended in the workshop air for many hours! (If you’re using a dust extractor when working MDF the filter must be suitable for a particle size of at least 0.5um.) Above, Roy assembles 2 plates “he made earlier”.

Now Roy shows us how the buttons are mounted. Here plastic thumb nuts are used to tighten the buttons – much safer than metal wing nuts! Ideally, the button fixings should be shouldered bolts with the plain portion of the bolt running in the slots for better accuracy.

Here is one of Roy’s button assemblies. The button, which needs to be quite hard, may be a demijohn bung, a wine bottle stopper or a button borrowed from a set of Cole Jaws. The bolt is a 6mm cap head bolt. Washers are needed either side of the rubber button.

Here’s an 8 slot ply chuck but with only 4 buttons fitted in the long slots so that they may slide right into the centre to hold small bowls. Again, for maximum accuracy the centre fixing bolt providing the pivot should be a close fitting shouldered bolt. Note also the 4 finger holes in each plate to enable a grip to apply pressure to the bowl.

 

Roy now mounts a bowl in the smaller 6 button chuck we saw at the beginning. Once mounted, a little bit of nudging may be needed to get the bowl to run perfectly true.

 

As the bowl is only held by the friction of the rubber buttons Roy recommends that when using the chuck the speed is restricted to a maximum of 500 RPM. Cuts should be fine and gentle as aggressive cuts or a catch could well launch the bowl into orbit!

 

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Wight Woodturners Visit to Axminster Tools

At the invitation of Jason Breach of the Axminster Tools Skill Centre a group of 21 members and guests enjoyed a day at the Axminster Tools facility.  There were two turning demonstrations in the superbly equipped Skill centre, guided tours of the CNC machine facility and warehouse together with a chance to spend as much money as we wanted on kit from the Axminster range of tools and accessories!  Our hosts Jason and Colwin Way made us most welcome and of course impressed us all with their turning skills!  Many thanks to Axminster for a most enjoyable day.

Here’s Jason in the Skill Centre Woodturning shop giving us a whistle-stop tour of holding methods and the best ways to use some of the latest Axminster kit. All sorts of useful tips.

Using Axminster button jaws Jason also shows us some of the effects an off-set and tilted work pieces can produce – similar to the work of Nick Agar (who also teaches at the Skill Centre).

In the afternoon it was back to basics as we were treated to a leisurely bowl turning demo by Colwin Way. Wow! - he just makes it looks so easy.

 

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Resources for Roy’s Longworth Chuck

 

·           Walter Hall’s excellent article on the Longworth Chuck  is on the Woodworkers Institute website here
Or for a printable version see Wight Woodturners “How to Do “ documents in the members area

·           For a Step-by-Step guide for Roy’s marking out geometry see the “How to Do “documents in members area

·           Threaded inserts for MDF may be found here or here and here

·           Cap head bolts may be found here and may from many sources on eBay

·           Nylon thumb nuts (safer than wingnuts!) can be found here

·           Buttons may be obtained here

·           If you thought Roy’s dust mask looked “cool” information on these efficient dust masks may be found here
Scroll down to the bottom of the page and download the Catalogue for full info.
Masks may be purchased here, here or here. But make sure you get the right replaceable filter.

 

 

Please note that the above links to external websites are valid at the time of writing
but may well change or disappear in the course of time

 

Peter Smart

15th May 2016

 

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