Re: [CAD_CAM_EDM_DRO] Power Transmission? was: Does this make sense?

Vince Negrete wrote:

>Jon,
>
>I'm having trouble understanding what you mean by "power transmission
>grade".
>
>I have something similar to this:
>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2549803136&category=12577
>
>
>

That is not a power transmission grade screw. The Saginaw, Nook and other
low-cost screws (new cost runs around $12/foot for 1/2 or 3/4" screws, and
$40 or so for single nuts) is often black with a very grainy (nitrided?)
surface, and the company's catalog lists them as "power transmission
grade". Thay are used for elevating pieces of machinery, anything like
the hand-cranked wheels that support the front end of semi-trailers
when not attached to a tractor, to moving boxes around in packing
machines.

That black, grainy coating is a giveaway that these screws can't accurately
position a machine tool.

You can (barely) see such a screw on my photoplotter
http://jelinux.pico-systems.com/photoplot.html
attached to the stepper motor at the right. (The silver thing below it
is a Thompson guide rod.) This was a proof of concept setup, I
have later replaced that arrangement with a BSA plastic-nut and
screw that has a backlash compensator. it works MUCH better,
but wouldn't be suitable for a machine tool.

Here's the EXACT same thing on eBay right now, black screw and
I recognize the nut as a Saginaw, exactly the same as was in my
photoplotter:
<
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2549546354&category=25276
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2549546354&category=25276>

>

Jon