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variable pitch pulley and cnc drive
« on: July 01, 2011, 11:56:20 AM »
on my shizuoka mill it has the pitch drive for the rpm change. i would like to use this with a stepper motor for rpm and have the vfd to just turn it on and off.
i have seen pics where it is done but are wondering how this would be controlled in mach 3?????

i was thinking of installing a tach to the spindle to read true speed. i dont think i can get mach to read this and act on it huh?

i have searched but cant seem to get the right key words..... ???

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Re: variable pitch pulley and cnc drive
« Reply #1 on: July 01, 2011, 12:14:21 PM »
Suppose you could have a brain looking at the spindle speed DRO and have it jog one way or the other depending on what the commanded DRO says. Have my doubts how good it would be though as I think it may constantly be trying to compensate and be rattling back and forth.

If there was a way you could "home " the stepper to a known point then you could easily work out the amount of steps for given speeds and adjust that way via your spindlespeed macro.
Hood
Re: variable pitch pulley and cnc drive
« Reply #2 on: July 01, 2011, 01:59:41 PM »
omg this sounds complicated! lol
how does this brain work?

i dont think the spindle rpm moves in equal values on the crank. like the first bit moves small amounts of rpm and then the upper half like doubles it....

thanks

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Re: variable pitch pulley and cnc drive
« Reply #3 on: July 01, 2011, 02:05:42 PM »
I think I would forget the brain, it may be possible to get it working but it would be hard I think and not even really something I would want to attempt.

Differing speeds with sheave position would not be a problem, you would just have to know what steps were needed for each speed. It would obviously not be infinitely variable speed but you could get it in ranges, just depends how large you want to make the macro as to how small the ranges.
Hood
Re: variable pitch pulley and cnc drive
« Reply #4 on: July 01, 2011, 02:35:32 PM »
i just dont know anything of macro's.
i am very good at mechanical things but i am lucky to have made it this far with computers. lol

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Re: variable pitch pulley and cnc drive
« Reply #5 on: July 01, 2011, 02:57:18 PM »
The macro wouldnt really be a problem, all you would be doing is treating the stepper as an axis and commanding it to move a set amount of steps depending on the speed you call.

Say for example you homed the axis so it was at the slowest speed then that would set that axis machine coords as zero.
Say that "zero" position was equal to 50 rpm and to get 100rpm you needed to move the stepper 10 units and 150 rpm needed 50 units from the zero then the macro would have  something like

If GetRPM= 50 Then
Code "G0A0"
End If

If GetRPM= 100 Then
Code "G0A10"
End If

If GetRPM = 150 Then
Code "G0A150"
End If

and so on.

The thing is you would really need to home each time you started Mach although I suppose it shouldnt really change much and having persistent DROs should keep the values in the DRO. Maybe over time it would drift but would be easy to command a move to slowest speed or below via MDI then set the machine coords for the axis zero again.

Doing things this way would mean really you would need to command speeds in specific numbers such as S50, S100, S150, S200 etc or whatever steps you thought suitable whilst remembering the closer the speed steps were the larger and more cumbersome your macro would be.


Hope this makes sense, its kind of hard to explain whats in my head sometimes ;D
Hood
Re: variable pitch pulley and cnc drive
« Reply #6 on: July 01, 2011, 05:14:37 PM »
hey thanks! that kinda makes sense.
after having lunch i thought of having the spindle set up a little more simple. try and follow me........

it now has hi/lo gear knob
85-505 lo
635-3800 hi

if i had it so i could "call" out for hi or low gear then i could use the vfd for final speed.
i would like to get rid of the variable pulley and go 1 timing pulley. aim for 4000 rpm on the fixed speed.

with hi gear almost picking up where low tops out @ i think this might work good.

making a air ram to switch the hi/lo knob would be easy and just require a signal to a 3 way soleniod.

make sense?

so i would need a g or m code or to say hi or lo gear and then mach would need to also be in hi or lo pulley ratio.  can this be done?
« Last Edit: July 01, 2011, 05:16:55 PM by turbothis »

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Re: variable pitch pulley and cnc drive
« Reply #7 on: July 01, 2011, 06:39:13 PM »
Yes that should work, you could use the pulley ratios in Mach and you could likely do all from your M3 macro without needing to call a different m code.
Hood
Re: variable pitch pulley and cnc drive
« Reply #8 on: July 02, 2011, 12:58:44 AM »
so in the g code file there is a comand to change the pulley #? 
i just want to have to switch it in the menu
like if you where cutting a part that used both hi and lo gear. 

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Re: variable pitch pulley and cnc drive
« Reply #9 on: July 02, 2011, 04:22:21 AM »
What you would do is have the m3 macro do the switching of the ram  by activating or deactivating the output dependant of the speed called. The spindle pulleys could also be set up in Mach so that the rpm input is corrected for the different ratio, assuming the speed sensor is on motor rather than spindle.
How the VFD would react I am not sure as I have no experience with them.
Hood