Making a Longworth chuck from acrylic

At the end of yesterday's Brighton Mini Maker Faire, a few members were discussing the next community/group challenge and when would be a good time to start one. Given we're still putting the finishing touches to our previous challenge entry, it seemed a little previous - but then again, there's nothing like starting a new challenge (or being dragged down by completing an old one) to inspire the mind....

At BuildBrighton, we've a fancy new (new to us anyway) Myford lathe. It's a beast of a machine and comes with lots of clever attachments for doing lots of clever things. But it's a proper, manual lathe. Meaning you have to have a bit of skill and understanding of lathing to use it. It's also quite scary.

So we've been kicking around the idea of a desktop sized CNC lathe.
One to make little chess pieces out of solid acrylic rod for example.

Having (almost) completed a CNC machine with controllable x/y axis and a multi-speed spinning head, with a little re-configuration, a lathe shouldn't be too difficult. Should it?

Well - the one thing that could prove a bit of a headache is the lathe chuck.
So this evening we've done some digging about and found plans for a DIY lathe chuck. It's usually used by woodworkers who are looking to increase the size of their lathe head, but we thought we'd have a go at making a smaller version out of acrylic (and perhaps eventually 3D printing one).

Following the description at http://www.woodworkersguide.com/2010/10/17/how-to-make-a-longworth-chuck/ and after some introductory lessons in using Inkscape, guidelines and drawing arcs from circles, we managed to create something that worked just like the real thing:

It's a multi-layered disk built using 3mm acrylic and M3 bolts:

On the back, we put a "spacer" disk, with larger cut-outs to allow the bolt heads to move along the arcs

The finished Longworth Chuck

Full details about how to make your own in Inkscape complete with diagrams and dxf cut-ready patterns to follow in a future post......

Longworth Chuck 4layer

Cut out and flip one of the duplicated shapes over. Tap the small circles with a 3mm tap and screw these onto the ends of the bolts in each of the four arcs. For a really cool finish (and perhaps more grip) once assembled, cover the pegs with heat-shrink and give a quick blast of hot air.

EDIT: To make your own, any size, click here