Re: [CAD_CAM_EDM_DRO] Rotary to linear translation - an interesting idea.

beer@... wrote:

> Here's the interesting part, that I haven't been able to get my head
> around.
> The guy claims that by pressing the pulley farther and farther into
> the shim stock, causing greater and greater deflections ( adjusting
> tension as required ), the pulley diameter is effectively changed - a
> given amount of linear travel will cause more or less rotation.

I can't see how changing the preload on the shim stock is going to
change the effective diameter of the pulley. However, if you put the
pulley directly opposite a single bearing, put a slight crown on the
pulley, and provided means to accuratly adjust the pulley/encoder
mechanism in a vertical plane and maintain pressure against the shim,
you could easily make minor changes to the effective dia. In fact, this
is exactly how a TravDial works. For that matter, you could drive the
wheel directly against the table like TravDial does. If any gear train
was included, it would need to be anti-backlash.
TravDials are not impervious to coolants/swarf, but with nothing more
than a simple foam pad (with slot for the edge of the wheel) they manage
to keep most contaminates out.
The first Prototraks I saw simply replaced the needle with a rotary
encoder for position feedback.
Too bad TravDials still command such a premium. If one could locate a
couple cheap enough, it'd make a great start.

Jon