Centroid Community CNC Support Forum

cnckeith wrote: ↑Thu Jan 31, 2019 10:50 am hello.
we do not recommend using NO switches as they are susceptible to noise. use NC switches and 24 vdc.

Ahh! I used the switches that came with the machine. Does anyone have a recommendation on limit switches?

depends...what kind of machine and how are they mounted etc.., post link to photo album of machine tool shots.

It's in my signature. It is a 5' x 8' cnc router.

viewtopic.php?f=60&t=1728

I believe our machine uses the same switches. I found them on ebay and they had them in either NO or NC for the same price. they come from China so it takes a few weeks to get them in. Mine are here but I have been working on other issues so I haven't installed them yet. I went with them because the price was right and since they are the same switch with the same mounting, installation should be easy.

https://www.ebay.com/itm/Proximity-swit ... 2749.l2649

I’m going to try the same gcode that was having the limit trip interruptions and see if they happen with the inputs set to homeok instead of limitokhomeok. I’ll report back.

If you add an external 24V relay you can avoid all the false trips. This method still allow limit switches to work.
Russ

Russ,

I have normally open limit switches..

Yeah this method will not work with NO limit switches. Most commercial machines use NC limit switches, the idea behind that standard is if any limit wires get broken at any point the machine will freeze. When using NO limits a wire could break and you are not aware of this fact and the machine go slam into an end stop or worse.

Limit switches are cheap, optical sensors, Proximity sensors, which all work fine are more money than simple switches.

Russ

Russ.

I understand how a fail safe circuit works. Thank you for clarifying the application. I was able to get the machine running well by changing the inputs to HomeOk vs HomeOkLimitOk (or whatever they call it). I found a NC version of the limit switches on my machine. Starting to think about switching to these though:

https://www.automationdirect.com/adc/sh ... pnm6-cp-3h

I'm also thinking of switching to DYN4 servos on all three axis..

Thank you for your help!

slodat,
Yeah I actually run servos myself. What is nice about servos is they have a closed loop to the driver. Now Acorn can't close the loop, like their higher end products like the OAK board but I have not had an issue. The Servo and AMP ensure the motor never loses steps because it has instant feedback from the encoder. The Acorn sends its step/direction pulses and if you have that interface close and quiet everything works fantastic.

Proximity sensors like the ones you selected are also nice, because dust or debris normally does not interfere with their operations. Sensors like that are commonly used on commercial machines for that exact reason.

Steppers have their place and can work very well if you oversize them, so they have plenty of power for the given application. They make more noise and sound that servos which are typically very quiet and smooth. Also a stepper is typically 200 P/R or 400 P/R and then to get more resolution they go to drivers that support micro-stepping. Servo encoders run from 1000 P/R to 5000 P/R so their resolution is much finer. This shows up the most when working metal, as wood usually never requires that kind of resolution.

I don't think you will go wrong with your planned upgrades. Others are doing the same thing on the forum.

Russ