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Topics - Bobthebuilder

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General Mach Discussion / Understanding Backlash Compensation
« on: December 15, 2018, 06:34:42 AM »

I'm using Mach3 mainly because there is this thing called "Backlash Compensation". So I figured out what my backlash is for each axis using a dial indicator, when I stumbled upon this fundamental problem of this compensation. Maybe its just how it works, maybe I'm using it wrong.

Some numbers first. I set my X-axis to 0.07mm backlash. Without backlash enabled, if I were just to reverse the direction when milling and mill a 100mm pocket, the pocket would be 99.93mm long. That's why I enabled this 0.07mm compensation. With this, when I just reversed (!) direction, Mach3 will add another 0.07mm to the lenght of my desired travel and the pocket will become truly 100mm.

Now image I would just go ahead in that direction and extend this 100mm pocket for anoter 100mm. Now the pocket will NOT be 200mm but it will be 200.07mm. Because Mach3 will add another 0.07mm to my feed lenght, however I'm still going in the same direction as before hence in this case theres NO compensation needed. I thought BC is there to compensate for play in the axis travel.

Backlash Compensation should only be calculated when there was actually a change of the direction you're milling. (but here's the next problem: how should Mach3 know what my last direction I moved was? Should be doable programming wise for sure, but now things get complicated)

Right now, when I do g0x100 five times in in one sequence, I will end up with a 500.35mm track, because the program will always add this 0.07mm to every move I do... When there is no compensation needed at all!

Please tell me I am using BC not correct. Because If this is how this "works", I can't see whats the purpose of this is at all. Thanks.

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