Author Topic: Home and limit switches  (Read 1991 times)

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Offline cobber52

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Home and limit switches
« on: March 13, 2017, 11:38:36 PM »
Hi everyone Newbie,
I am an retired electronics tech and to keep my brain active design and make controllers for my and my friends pleasure.
To help facilitate this I bought a little chinese router cnc 3020t which I hoped would speed up board fabrication.
This unit had no home or limit switches and the internal bob has no circuit diag and would probably require reverse engineering to get one. I therefore inserted another parallel card into my hp desktop and another known bob with cct diagram to run my home and limit switches.
My problem is that when I ref all home in mach3 the x and y axes move as they should. x to the left and y down. So 0,0. as per convention. Great Now when i go to jog either the x or y axis I must use the opposite key i.e left arrow for x right  right arrow for x left. the same for the y axis. I can remap the keys ok but the DRO reads negative when I move the x axis to the right and the y axis to the top. Its like mach3 thinks the table is reversed. The homing switches work fine. All of the axes touch on the switch and back off so 0,0,0 can be set fine. If I reverse the motor settings active low in ports and pins, the unit then tries to set home at the top right hand corner of the bed. I know I have the unit facing the right way as all of the connections are at the rear looking at it, and standard home signals send it to bottom left, so mach 3 can drive it to home position and the thinks it is going the other way when jogging. All my limit switches and estop work fine in diags. I have not set any soft limits as yet. Would like to work out what I am doing wrong.
Any ideas or help would be greatly appreciated  as I can't quite get my head around the negative/reverse direction reading of the gantry, because with 0, 0 set for x and y any movement of the gantry i.e right or back should show up as a positive following convention.
P.s I have also tried reversing the direction in the homing/ limits section and the unit tries to set home top right.

Offline Tweakie.CNC

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Re: Home and limit switches
« Reply #1 on: March 14, 2017, 06:35:08 AM »
This right hand rule diagram shows the direction the cutting tool should move in relation to the work piece.

If your keyboard keys move an axis and the DRO's in the wrong direction then that can be changed in Config. / Ports & Pins / Motor Outputs by changing the Direction Low Active state.
If your keyboard keys move an axis in the wrong direction but the DRO's are correct then that can be changed in Config. / System Hotkeys.

Once you have that working correctly then set-up your limits and ref.

Hope this helps.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline cobber52

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Re: Home and limit switches
« Reply #2 on: March 14, 2017, 07:40:24 AM »
Thanks For that Tweakie.CnC
So you are saying check the axes directions are correct before any home and limit switches are setup. Set them up and then do the switches.

Cobber52.

Offline Tweakie.CNC

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Re: Home and limit switches
« Reply #3 on: March 14, 2017, 08:13:03 AM »
Yes sir, axis directions should be set-up first but remember it is the tool direction relative to the work that counts rather than the actual direction of axis movement. If that makes sense.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline cobber52

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Re: Home and limit switches
« Reply #4 on: March 15, 2017, 03:23:53 AM »
Tweakie,
Tried all that you said but still wanted to ref all home to top right so I let it as all my x and y axes limit switches work on one pin.
Scratching head i then noticed the home neg setting to the right of the home /limits settings.
Changed, reset and ref all Zero and lo and behold  the dro counted down negative to the bottom left corner and everything works as I was taught about the 3 finger rule 40 years ago. Aint maths great.
Now to fine tune my motors and set soft limits and rout my first board.
Thanks heaps. You saved me a lot of time. Even with reading all the manual and forums I forgot the one simple rule, KISS and was trying to get everything working at same time, so was masking my mistake with multiple errors.

Cheers Cobber52      ;D

Offline Tweakie.CNC

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Re: Home and limit switches
« Reply #5 on: March 15, 2017, 03:36:48 AM »
I am pleased to hear that you have got it sorted.  ;)

Don't forget to post some pictires of the things that you make with your new CNC, we all love to see pictures.  :)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.