Mach3 Problems problems problems.

[Clive S]

Whilst running a small program with G20 in the first line the program executes moves that are wildly incorrect. A move of Z0.100" makes the Z axis move continually in the + direction until physically stopped by operating cycle stop. After lots of messing about a G21 was inserted in the second line of the program. It worked perfectly and accurately in Imperial moves. Absolutely no idea why!!!

Before you start setting the soft limits you need to check what is setup wrong. You seem say when using G21 you are getting accurate moves with inches. Are you saying that if you command the machine X0 2 it moves 2" or 2mm?

[magicniner]

It doesn't matter if you use inch or mm for setting up your motor steps per, if you've done it right the machine will run imperial or metric code accurately.
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The body of each feature in the code is simply in numeric units and G20 or G21 in the header tells Mach 3 if those units will be interpreted as (G21) mm or (G20) inches.
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G20 specifies imperial, G21 specifies metric so if you are getting accurate Inch moves with G21 then you have configured your system incorrectly and your steps per out by a factor of exactly 25.4 and your initial commanded moves in inches with G20 will have been simply huge!

- Nick

[JAZZCNC]

It doesn't matter if you use inch or mm for setting up your motor steps per, if you've done it right the machine will run imperial or metric code accurately.
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The body of each feature in the code is simply in numeric units and G20 or G21 in the header tells Mach 3 if those units will be interpreted as (G21) mm or (G20) inches.

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Not exactly correct as explained above.!! . . . It will scale the moves but not the feedrate.
Try it load road runner and put G20 on first line or type G20 in MDI before running.
The Feedrate in Gcode will be in inches minute but motors tuning is relative to MM/min. This is why you have to retune the motors if you change from metric to imperial units.

[magicniner]

Thanks for that Jazz, that's interesting.
Given the simplicity of the conversion I'm shocked that they didn't make motor tuning/feed rate automatic for changes in G Code units, I had assumed this was the case but only ever work in Metric,
Regards,
Nick

[ECCO]

Many thanks for your replies. The mill is having mechanical parts modified at the moment and as soon as it is reassembled I will do some investigation and get back to you all. Once again thanks.

[ECCO]

Right the mech parts are now modified ok, back to the problems. could you please check over the following calculations for steps per.
By the way this is a fully licenced version of Mach3. Have re-installed Mach3 and chosen inch base units.

Motor Steps= 1.8deg =200 steps per 1 motor rev.

Motor Micro steps =10 therefor 200x10 = 2000 micro steps per 1 motor rev

Pitch of ball screws = 5mm = 0.19685 inches per 1 motor rev

No of motor revs to move 1 inch = 1/0.19685 = 5.08 revs

No of micro steps per 1 inch move = 2000 x 5.08 =10160 micro steps per inch

Z axis is a 2:1 reduction ratio so 10160 x 2 = 20320 micro steps per inch

Many thanks ( More to follow )

[JAZZCNC]

Yes that's correct go to top of the Class.