bounce off home switch.

**motoxy** · 27-08-2012

I noticed that on the x axis when it hits the homing switch it 'bounces' back a few steps. On the z and y axis it hits the switch and just stops. Is this a setting or does it just happen. using mach 3 btw.

Bruce

**i2i** · 27-08-2012

it should come back on all three axis

**JAZZCNC** · 27-08-2012

I could be off the switch but you haven't seen it move.? . . . easy way to tell is to go into diagnostics screen and check the " input signals current state" the M1,M2,M3 home led should be off after homing.!

Just watch the diagnostics screen while it's homing and you'll see the pin state change then go back to off.

**motoxy** · 27-08-2012

Thanks i2i and dean. I know its working just suprised that the distance was differant. I have a small problem that when the home switch is also a limit switch sometimes the z when it homes does not clear to allow the x and y to home. Have to check that out on wed as I actually have work for tomorrow.

Bruce

**motoxy** · 28-08-2012

Okay got home early and fiddled. When the z homes although the diagnostic says the switch is off the y will not home or it will do a couple of steps and stop. If I move the z down and then home the y its fine. I was curious as to why the x backs off maybe 1/2 a turn but the z and y almost appear to not back off at all although the switch does clear on the diagnostics???

Bruce

**russell** · 28-08-2012

Could it be the hysteresis of the switch (the difference between the on and the off threshold positions)? Or even backlash on the x axis?

Russell.

**motoxy** · 28-08-2012

Originally Posted by russell

Could it be the hysteresis of the switch (the difference between the on and the off threshold positions)? Or even backlash on the x axis?

Russell.

Do not think its backlash as the motor does not try to back it off. I was looking on the mach forum and realised that I have not connected the shielding to earth yet. Naughty me. So I will try that tomorrow and see if it helps.

Bruce

**russell** · 29-08-2012

Originally Posted by motoxy

Do not think its backlash as the motor does not try to back it off. I was looking on the mach forum and realised that I have not connected the shielding to earth yet. Naughty me. So I will try that tomorrow and see if it helps.

Bruce

Sorry, I'm not understanding. I thought you said that the x motor backs off by about 1/2 turn???

Russell.

**motoxy** · 29-08-2012

okay I think I have got to the bottom of the problem.....crappy switches.
When a homing switch is triggered then the motor will back off until the switch clears, as was said earlier. You can test this by homing an axis and the pressing the switch manually. If you hold it in the motor will keep backing off until you let go. Because these switches are, cannot think of the right word, flicking off then the motor winds back until it flicks back. Trouble with these switches is that they start to lift off the connection before they fully flick off. Therefore the circuit is broken and the motor only goes back a very small amount to make the switch. This means that the switch is resting on the gantry and any vibration at all will lift it off and so the next homing is reset early. Thats why when I backed off the offending axis the rest homed perfectly. This also explains why one switch, which must flick as it breaks, allows the motors to rewind a small amount before it flicks back.

Hope this makes sense to anyone else and serves as a warning on cheap switches.

All of this is what I think Russell indicated when mentioning hysteresis of the switch. I had to look that up

Bruce

Now I have to investigate why when I home the x axis the b axis which is slaved to it does not operate. So near and yet so far....