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« on: October 16, 2012, 03:11:46 AM »
For me homing has to be accurate, if I run a part one day and want to run the same the next day I want to know I can just place in the soft jaws of the vice and press start and away it goes.
On a lathe it is especially important for the tool dia, I dont want to have to take a test cut each time I start the lathe, measure the dia and then set the tool offsets. I have a turret and I want to switch on, home and then when I call a tool and tell it to cut a diameter I know it will be there.
I use Index homing but I do it external to Mach as my servo drives support that homing feature. What happens is I send a signal to my drives from Mach, they start homing and look for the home switch input, when they see that input they then search for the index pulse from the encoder and then they stop and set that as home and send a signal to Mach which then sets the machine coordinates.
There used to be a board that could do similar, it was made by CNC building blocks but sadly Ed no longer makes them. It worked in a similar manner except Mach actually did the homing moves, it was just that the building blocks bob delayed the signal to Mach. Hers how it worked. Mach started homing and saw the switch being activated and reversed the axis, the BOB however would not tell Mach the switch had again closed until it had seen the index pulse of the encode. It would then tell Mach the switch had closed and Mach set the machine coords.
As mentioned in my previous post however if you use optical switches you can also get very accurate homing, that was proven by the tests I did, so if you dont have encoders and drives capable of homing then optos are a very cheap and accurate choice.
Hood