Re: Mariss' Surplus Center Motor - Encoders - location - Long

> Is the motor or the leadscrew better in such a case ?

Dave,
Not an easy answer. There are a bunch of ways and tradeoffs.
1. On the motor - real easy to mount, theoreticaly loose accuracy due
to belt stretch between motor and screw. This is the way my Tree Mill
is rigged and I don't see any problems.
2. On the leadscrew - Not always so easy to mount. May prevent you
from mounting a hand wheel (big argumnet if you need one on a CNC or
not. I got ones and want them. If nothing else for a future learn
mode. Also nice for setup.)
3. On a separate belt from the screw to the encoder, different from
motor belt. One of my axis was done this way and its amazingly good.
The encoder presents no drag so belt stretch isn't an issue.
4. A linear encoder on the table - Best solution if you have a zero
backlash leadscrew and a stiff drive train. I've got the leadscrew
and drive train but can't afford the encoder. US digital's strips are
not high enough resolution and I can't afford a real encoder.

I don't think this issue matters much on a hobby class machine. My
mill uses a differnt strategy on each axis and to the limits of my
measurements I can't tell the difference. On a mini mill or a RF-45
clone the slop and bend will hide any inaccuracy in encoders anyhow.
I consider myself real fortunate to have bought a 7000# comercial
mill and tooling with a blown controller for peanuts. I didn't have
to think about lead screws, servo mounts or encoders. They were there
and probably much better done than anything I could have cobbled up.

Roger S