Luke11CNC Build Log ,I'm so naïve

**Jonathan** · 07-09-2011

This should keep us out of trouble for a while :heehee:

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Edit: Just dropped one bit on the lawn and made a hole ... will be in trouble if I do that again!

**luke11cnc** · 08-09-2011

Yes Jonathan I can wait

I'm going to install Micro switches on my machine are this the right ones

http://www.ebay.co.uk/itm/AC-125V-1A...ht_2168wt_1139

Thank you for looking

James

**luke11cnc** · 09-09-2011

Well I've received my spindle today and

nobody warned me how heavy they are??

I may even put the spindle in between Y axis for support or is this over kill. I must admit I've never seen this done but how hard will it be

spindle weight is like trying to control a brick on the end of my little finger but that is just my own view

with all that weight at the end of a CNC machine no wonder there is issues with twist

James

**Jonathan** · 09-09-2011

Originally Posted by luke11cnc

Well I've received my spindle today and
nobody warned me how heavy they are??

They're heavy as there's lots of copper/steel in there. Be glad it's 3-phase as otherwise it would be heavier.

Switches:

http://www.rapidonline.com/Electroni.../Microswitches

The best switches (I think) are these, but they're a bit more expensive than the rest:
http://www.rapidonline.com/Electroni...switches-73549

You don't need the roller.

**JAZZCNC** · 10-09-2011

Originally Posted by luke11cnc

Yes Jonathan I can wait

I'm going to install Micro switches on my machine are this the right ones

http://www.ebay.co.uk/itm/AC-125V-1A...ht_2168wt_1139

Thank you for looking

James

Don't buy cheap micro switch's for home switch's they wear to fast and not accurate enough. You only need 1 for each axis (2 on slaved axis) so buy decent switch's like honeywell or Telmanique they will pay for them self's in the long run and give hassle free service.

Another thing to beware of with cheap micro switch's for limit switch's (not so much home switch's) is the potential for switch bounce or noise, esp with low voltage, low current setup's that most folks use IE: 5v straight from the BOB. . . This will show it's self as false E-stops.
It's a common ocurrence with cheap switch's due to poor quality contacts and the fact the limit's don't get used very often.
What happens is over time the contacts degrade and become pitted and dirty, this cause's noise on the signal line which can fool the controller(Mach3) into thinking a limit as been tripped or an E-stop occured. This often happens when taking heavy cutt's or on machines that vibrate a lot which make the switch's trembel slightly, when really worn/dirty or very crappy switch's used it can even happen when the machine is stood still or just with spindle running.
Also Another thing regards spindles and really crappy switch's used on low voltage setup's. If using a VFD then it's very likely you'll come across some noise issue at some point making it another good reason to buy decent switch's. (And use sheilded cable)

There are various ways to help stop this, using 24v or 12v for limits is the better way and the way it's often done on industrial machines. Thou for DIY just using decent switch's and tripping the limit switch's every so often helps greatly. . . . Also the use of a small 0.1uF capacitor across each switch helps keep the switch contacts clean by charging up to around 5v when the switch is opened then sending a short high current burst through the switch when it close's shorting the capaictor so cleaning the contacts. If you do this and trip the switch's every so often then the contacts are kept clean and noise free.

Please don't think I'm scare mongering because I'm not and noise on the signal lines is one of the most common cause's of electrical trouble folks have, often they don't even know it and blame somehing else like BOB, drivers or motors. When often it's down to cheap switch's and poor control box setup IE: Unshielded cable or bad earthing practices.

Personally I dont use limit's just good quality Home switch's and Mach's soft limit's.

**luke11cnc** · 10-09-2011

Excited going to watch my parts being cut on Jonathan's CNC today taking my Camera so lots and lots of Photo's to bore you with later

James & Luke

poor Luke he's at school until 4.30 so he will just have to watch a video and photo's of it

**Robin Hewitt** · 10-09-2011

Originally Posted by luke11cnc

I'm going to install Micro switches on my machine are this the right ones

Hi James

Microswitches bounce when they close, not when they open.

If you want to avoid bounce, without extra circuitry, set your position when the switch opens.

Do you "do" electronics?

If you want maintenence free precision consider an opto-slot with Schmitt trigger.

If you want zero hysteresis consider a standard, photo-transistor opto-slot and feed it into an op-amp wired as a comparator.

best

Robin

**JAZZCNC** · 10-09-2011

Originally Posted by Robin Hewitt

If you want zero hysteresis consider a standard, photo-transistor opto-slot and feed it into an op-amp wired as a comparator.

Hi Robin,

Great advice robin, thou you might as well be talking Marshen if folks are not into electronics:rofl:

Don't belive James/Luke are into electronics to that level, did consider suggesting opto switch's but didn't want to cause info overload.! . . . simpler to just say use good switch's and warn of the dangers of cheap bad switch's I thought.:question:

I've considered using opto switch's on my machine when the existing switch's start playing up. . . Thou I'm a bit unsure if they'll be ok due to flying debrie passing the opto falsely triggering switch.? . . How do they handle flying Ali chips.?

My machine must hold the world record for slinging chip's.! . . . They even make it into the house 20yards away.! . . . Thou my boots may play a part.:naughty: