Homebrew PCBs

> A direct coupled gear head approach is certainly
> straightforward if somewhat of an expensive option.

I wouldn't consider $15.00 - $30.00 for a gearhead motor expensive. 
You can get one with encoder for $29.00.

> Then again there is the backlash in the gear train

A fraction of the lead screw backlash. Better than using belts 
(toothed or friction). Backlash at reversal is handled in software. 
This is a drilling setup, spurious movement in the backlash dead 
zone like with milling or routing isn't an issue.

>There is also the need to align both
>axises within a given tolerance to minimize bearing
>wear.

Use shims and a dial indicator or use a flexible coupling. I prefer 
proper alignment and rigid couplings. Yeah, machining and metal 
working savvy is beneficial.

>Actually the linear velocity is of more interest. 

20 IPM for a 12" X 8" travel. The milling table weighs 64 lbs. 
Drills 18 holes per minute (6" X 4" matrix).


--- In Homebrew_PCBs@yahoogroups.com, uhmgawa <uhmgawa@m...> wrote:
> derekhawkins wrote:
> >>For lead screw applications I'd keep the encoder on
> >>the screw. Doing so allows the screw to be driven
> >>indirectly and velocity/torque/rotational-precision
> >>to be scaled via simple friction coupling without
> >>introducing slippage error.
> > 
> > 
> > A DC gearhead motor is best for lead screw applications as it 
allows 
> > the screw to be driven "directly" without any complications 
provided 
> > speed and torque requirements are met. It doesn't get much 
simpler 
> > than this;
> > 
> > http://www.pbase.com/eldata/image/45200286
> > 
> > http://www.pbase.com/eldata/image/45200509
> 
> Depends upon what one is trying to accomplish.
> A direct coupled gear head approach is certainly
> straightforward if somewhat of an expensive option.
> 
> Then again there is the backlash in the gear train
> which needs to be factored-in when making fine
> adjustments via changing direction to minimize
> over travel.  There is also the need to align both
> axises within a given tolerance to minimize bearing
> wear.  These tend to be non-issues with frictional
> coupling.
> 
> BTW what type of rotational velocity are you
> getting out of this setup?  Actually the linear
> velocity is of more interest.  Hard to gauge from
> the jpg but the lead screw appears to be ~10TPI?
> 
> -- 
> uhmgawa@m...        www.gnu.org