Using a photocell as a carriage stop

[The Landshark]

Not necessarily. If you stop the motor all motion stops. If you forcibly stop the carriage and the motor keeps running something may break.

Especially as theres no slip clutch on this machine

 

[DMS]

I have seen modifications to the 7x series of import lathes that used a mechanical linkage to disengage the feed lever, so it is possible even with a single motor driving the system.

Take a look at Gadgetbuilder's site

http://gadgetbuilder.com/ThreadingTools.html#AutoStop

 

[stupoty]

Rather than a photocell, I would recommend a slotted interrupter. Less chance of room light effecting it. If you arrange for the slot to be oriented down, then swarf should not be much of an issue. I have a similar setup on my CNC mill for the home and limit switches.

Yeah sloted sensor is probably best for an optical meathod, and their used as inter locks on lots of small equipment. As you say they dont seem to be affected by ambient light.

Stuart

 

[hman]

Rather than a photocell, I would recommend a slotted interrupter. Less chance of room light effecting it. If you arrange for the slot to be oriented down, then swarf should not be much of an issue. I have a similar setup on my CNC mill for the home and limit switches.

+1 on this one!

I've used a huge number of Omron EE-SX670 series slot-type sensors on various assembly line machines I've built over the years, and would suggest this as very good choice. Datasheet: http://datasheet.octopart.com/EE-SX670-Omron-datasheet-5390888.pdf

Note that there's a large variety of shapes and orientations available. The active sensing area is 0.8 x 2.0mm, and the actual transition point is very reproducible. I once checked a (clean, new) one and found it to be good within .001" That said, your results will of course vary if there's any oil, swarf or whatever in the slot area. Orienting it downward will help, and you'll want to be able to access the slot area so it can be cleaned with a Q-tip or similar.

One of the very nice things about the Omron (and makes it worth the higher cost than most other slot-type sensors) is that it has a built-in power supply for the LED and an amplifier for the sensor. All you need is 5-24 volts DC, no external components. The output has a current capacity of either 50mA (PNP type) or 100 mA (NPN type). There's also an indicator on the device, so you can verify that it's operating and sensing.

Hope this helps.