View Full Version : Limit switches keep activating

23-09-2012, 12:47 PM
Hi all
I am having issues with the limit switches i am using on my MDF special.
Possibly due to the vibration from the Trend T4 router i am running (its been fine for 4 months)
i keep getting false limit calls (most anoying when you go back expecting it to have finished)
i am currently using lever switches from RS Part No 159-4449 and it seems these are not ideal.
Could anyone suggest some reasonably priced alternatives.

23-09-2012, 03:43 PM
This will almost certainly be a noise issue not a faulty switch.!
Even the cheapest nasty switches can work ok and not trip, they just aren't very accurate. Also because there cheap and your only running 5V thru the switch's then this low voltage can cause the contacts of the switch to fuzz or burn thru them bouncing when machines working. After awhile this translates or worsens into a false trip. Setting the De-bounce helps handle this false signal.

If using Mach3 then try this first has a temp fix. In general Config in top right hand corner set the debounce interval. If at zero or very low number set higher IE: 1000. It's not unusual to have it set to several 1000's if needed has 1 unit = 40 microseconds.

Next check to see if any mains power cables run directly along side any input cables. If so then separate.

One of the reasons this happens is because the limits switchs don't get much use so it's a good idea to flick the swithcs every so often to give the a blast of current and clean the contacts. Putting some small capacitors across the switch's can also help avoid this if it continues. Thou I think you'll find de-bounce works.

23-09-2012, 10:12 PM
Thanks Jazz i will try debounce first.
i vaugely remember reading this in the Mach 3 manual but now you explain it it makes more sense.
i kept all the power cables separate from the outset and used screened cable for the steppa motors.
I have had great fun learning to use my MDF special and was glad that it was easily repairable when it inevitably went pear shaped.
Iv had good results in 2 and 3d
The only major problem with it is that it is soooooooooo slow.
i have been reading through the forums for some suitable designs for a more robust (and much faster) machine
Any sugestions/recomendations would be greatfuly recieved.
currently my machine has a cutting area of approx 800X450 as i am mainly interested in sign making although brass and ally would be nice.

yep: debounce did the trick nicely thanks