Re: stepper acuracy

Message: 16
Date: Mon, 06 Jan 2003 02:09:13 -0000
From: "maryonclan <obwan425@...>" <obwan425@...>
Subject: stepper acuracy

Hello Group,
I am a newbie and would first like to say hello and wish everyone a
happy new year..Now for the question.I am thinking of buying a
converted mill\drill from cnc masters the "cnc jr".This machine comes
with ball screws-x-y- and anti backlash on -z- 1000 oz\lb
steppers.What I am wondering is will a machine of this construction
be sufficiently accurate and fast enough to cut detailed geometry
such as a mold?Are servos the only way??Any advise would be fantastic
and appreciated.
Greg

[The CNC Jr is a pretty good retrofit of a basic Asian round-ram mill-drill.
The 2hp R-8 spindle is powerful enough to remove steel at a reasonably fast
rate, and the steppers are powerful enough to be pretty much immune to step
loss under normal working conditions. While servos are generally considered
to be better, it's certainly possible to do detailed and accurate work with
steppers. Whether it will work for your specific application depends on the
tolerances you're trying to hold. The limitations of this machine are mostly
due to the base machine, not the retrofit. The round ram is a problem, since
you can't raise it to load tools and drop it back into position accurately.
Some people get around this by mounting a laser-pointer to the head,
pointing it to a spot on the opposite wall, and marking the spot before
moving the head. Other problems may be due to roughness in the castings or
the machining on them that was done in Asia, the quality of which is
variable. If you need to hold very high tolerances and want to go really
fast, you might need to get a better machine, which will cost upwards of
twice as much. But in its price range, I don't think you'll find it has much
competition, unless you're stacking it up against do-it-yourself retrofits
or used machines.]

Andrew Werby
www.computersculpture.com
Disclaimer: I am a CNC-Jr reseller, and offer a small discount on them