Modified Tool Length Measurement

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30 Oct 2015 09:50 #64500 by LearningLinuxCNC
I am getting ready to implement the tool length measurement in gmoccapy. However I don't want to use the block height feature that is built into the standard gmoccapy procedure. I have been looking at the change.ngc file and I believe the only thing that I need to change is the following line
G10 L1 P#<tool> Z[#<touch_result> - #<_hal[gmoccapy.probeheight]> + #<_hal[gmoccapy.blockheight]>]

to
G10 L1 P#<tool> Z[#<touch_result> - #<_hal[gmoccapy.probeheight]>]

However as I am typing this I guess I could just leave the blockheight parameter set to 0 and it would have the same effect.

Am I on the right track here?

Also when running a program I will not always want to remeasure every tool, so I was thinking that I would use M64 P0 and M65 P0 to turn on and off the gmoccapy.toolmeasurement pin therefore enabling or disabling the automatic tool measurement. I can set up my post processor to turn on the tool measurement when I do a "manual toolchange" or turn it off for automatic tool changes (still manual for me but tool length is preset)

Does this sound like a good method?

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30 Oct 2015 19:53 #64513 by LearningLinuxCNC
I also think that I need to change the following line:
G91
G38.2 Z #<_ini[TOOLSENSOR]MAXPROBE>
G0 Z2

to
G91
G53 G38.2 Z #<_ini[TOOLSENSOR]MAXPROBE>
G0 Z2

This will make the tool length measurements independent of the work coordinate system. Does this seem correct?

I am trying to think all of this out before I try it.

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17 Nov 2015 02:38 #65353 by thor44
I think I have everything set to work correctly with the tool touch off in gmoccapy but I am struggling between a touch off pad or a button, what is your opinion?


Thanks

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17 Nov 2015 09:26 - 17 Nov 2015 09:28 #65362 by newbynobi
@Nitro,
Just write your own change.ngc, and do not use the gmoccapy probe and blockheight hal pin, than you can do what ever you want.
As I have not done it your way, I will not be able to help.


@Thor,
Button, no question for me ;-)

Norbert
Last edit: 17 Nov 2015 09:28 by newbynobi.

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17 Nov 2015 14:05 #65370 by LearningLinuxCNC
Norbert,

I am working on the modified change.ngc but I have not had much time to devote to it yet. I will post my finished results here along with a video showing it working. Thanks for the response.

Jim

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17 Nov 2015 14:10 #65372 by LearningLinuxCNC
Thor,

I would use a tool height sensor that has the following features.
1: Has an integrated switch so that it does not require hooking up a signal cable to the tool.
2: Has some spring loaded give to it so that you can do a relatively rapid initial probe to find the rough length and then re-probe for the final length at a slower speed.

The key is that the switch has to be very repeatable so you get the same reading each time. It also needs to trip the same at different locations on the touch pad otherwise tools with different points of contact will trip at different positions.

I am using a second touch probe from my videos as my tool height sensor. It is not perfect for this application but it appears that it will work within about +-0.0005". I will be trying other methods in the future (I like to tinker with things!).

Jim

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18 Nov 2015 15:01 #65433 by newbynobi
Hallo Jim,

has you seen my switch in the video?
That one has been sponsored for development from a forum member and with two times touch, first fast and second slow, it reaches an accuracy of about 0,01 mm

IMHO that is far good enough, otherwise you will have to go to more sophisticated systems. A friend of mine uses a digital indicator, connected to the machine, so he goes to the indicator with 25 mm measurement way and a resolution of 0,001 mm, stop in that range and read the value trough the RS232 to calculate the tool length.

Norbert

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