Re: how to safely stall a DC motor

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Lance Hopper"
<snaggletto@c...> wrote:

> I'm in the process of completely retrofitting an Emco Turn 120

cnc

> lathe. It's got an 8 position tool turret on a ratchet mechanism,
> driven by a small DC gearmotor (24VDC ~15watts) through a worm

gear.

>
> In operation, the motor spins the turret forward until the

proper

> tool location is found (a small sensor board senses each position)
> then the motor reverses and then stalls out holding the ratchet

pawl

> into the ratchet teeth. This in conjuction with the gearmotor and
> worm drive help to hold the turret in postion during machining.

Far

> from ideal I know, but at this point I want to make the existing
> setup work rather than redesigning/rebuilding the whole tool

turret.

>

Just curious, why are you retrofitting the machine? The Emco T1
control has features and an assortment of canned cycles that you may
not find in a retrofit controller.

The turret design is not the best type, as long as tools are set so
the cutting force is downward it's not a problem (CW spindle
rotation, cutting force against locking pawl). When single point
threading right hand threads conventionally (from tailstock towards
spindle) the tool needs to be upside down with CCW spindle rotation
so it's best to specify more than the usual number of passes,
especially in coarse threads, since the cutting force can slightly
override the holding force of the motor.

BTW, I have a 120 that I bought new and we still use it almost daily
in production even though I have bigger, newer machines. They're
great machines, mine can still easily hold +/-.0004" all day long.

Doug