Westbury Cam Turning Jig

[Clive Brown 1Participant @clivebrown1]

In the Jan. ’82 issue of ME, Ian Bradley gives an outline description of a 30cc engine he made. In the article he refers to a camshaft turning jig based on an Edgar Westbury design. A sketch is attached. Another sketch shows the jig mounted between lathe centres on the “arbor”.

I can’t see how this jig works. Any ideas?

[JasonBModerator @jasonb]

It is the same principal as turning the radius edge on a flange. The jig allows the edge of the cam to rotate at a distance from the lathe’s ctl line so that the flank radii can be turned tangent to the base circle diameter. You can do the same thing with a boring head set to swing an external cut. Just imagine the lower half of that flange was missing and the shape would be a cam lobe.

[Roderick JenkinsParticipant @roderickjenkins93242]

Looking at this article below I’m not sure if the jig is intended to cut an offset radius for each flank since reference is made to indexing at 5 degree intervals, sort of more like an analogue CamCalc

Article from ModelEngine News

Rod

[ChrisLHParticipant @chrislh]

Rod. The 5 degree cuts are to form the minor diameter part of the cam, the bit which is marginally clear of the tappet so the stepped effect doesn’t really matter. The major contacting parts of the cam are continuous curves formed by the eccentric turning at single settings of the camshaft in the jig. You are left with handwork for the cam nose but that’s easily done.

[Roderick JenkinsParticipant @roderickjenkins93242]

Chris, agreed.  I’ve just braved the storm to retrieve the appropriate MEs from the workshop.  The relevant pages are below.  Looking at the references given in the MEN article, Chaddock describes a method for developing the full R theta form, of the sort that CamCalc produces, for cutting in a lathe with indexing on the lathe spindle and a flycutter on a milling spindle attached to the cross slide.

Anyway, hope this helps,

Rod

[Author]

Posts