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Author Topic: Mach3 Turn CSS Mythbuster  (Read 18264 times)

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Re: Mach3 Turn CSS Mythbuster
« Reply #10 on: November 13, 2013, 06:29:54 AM »
Hi All,

I haven't gone to sleep, rather been thinking long and hard, and performing some tests.

My tests (based on blind faith in Mach3's ability to report Feed per Revolution accurately in the F DRO in Mach3 Lathe) reveal that Constant Surface Speed is accurate but, as reported by Hood, Feed per Revolution appears to vary whenever the X Axis is in motion in CSS mode. I have concluded that, in my case, it doesn't really matter, but have proposed a couple of possible solutions to improve constant chip load.

My report is attached.

Regards

Chris Humphris
Re: Mach3 Turn CSS Mythbuster
« Reply #11 on: November 13, 2013, 10:00:29 PM »
I’ve been thinking some more and decided to look very closely at some of my parted off material. 

A true G95 motion should have a spiral with a pitch equal to the distance per revolution.  (In this case 0.05mm)

The attached photo shows that the pitch decreases as the parting blade moves from the outside diameter of 38mm towards approx.  Ø12.5, then reverts to a smooth 0.05mm per rev to the centre, when the VFD reaches maximum RPM.

Regards
Chris Humphris

Offline Hood

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Re: Mach3 Turn CSS Mythbuster
« Reply #12 on: November 15, 2013, 04:31:22 AM »
Chris, I had hoped you had found the magic combo but really knew it would not be the case. Anyway until I junk the ESS from the lathe I cant really use CSS anyway as sadly the ESS  and USB SS  have issues with a step/dir servo for a spindle anyway.

Hood

Offline BR549

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Re: Mach3 Turn CSS Mythbuster
« Reply #13 on: November 17, 2013, 01:04:36 AM »
Just curious but could you not just look at the Xdro as diameter and use that value as a percent of Spindle over ride.

When started it would see the X value as the base to start from then as you moved towards the center mach3 would adjust the Spindle overide to increase the speed same with moving out it would slow down.

Am I missing something ??

Just a thought, (;-) TP

Offline Hood

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Re: Mach3 Turn CSS Mythbuster
« Reply #14 on: November 17, 2013, 05:43:44 AM »
Spindle override would be far too limiting, for example a very conservative surface speed, say 50m/min, so you start at 100mm Dia so RPM is 159rpm, now the max you could get with spindle override would be 250% or is it 300%? anyway we will say 300% so get to 10mm dia and you require 1592rpm but that 300% has limited you to 477rpm, so effectively the spindle override became ineffective at approx 33.35mm Dia.


Better option would likely  be to use the Feed Override and compare to actual spindle speed (Mach does a decent job of controlling RPM in CSS) there is actually a guy that has done just this via a plugin, he posted recently on the General part of the forum,. It worked in my testing but I had some issues but more importantly for me the ESS has even greater issues in its spindle control which makes me not want to test further, roll on Mach4 so I can use the CSMIO on the big lathe and according to Brian CSS is done so this wont be a problem.

Hood

Offline BR549

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Re: Mach3 Turn CSS Mythbuster
« Reply #15 on: November 17, 2013, 02:11:28 PM »
OK instead of using the SSO then just update the Sspeed dro then you have unlimited response up to max spindle speeds. I have a working model running in a macropump.

It can be started/programmed via a macro M96 as to on /off ,base diameter and Max spindle speed that it cuts OUT and does no further adjustments. Once started it follows as to the position of X being the control radius.

Interesting, (;-) TP
Re: Mach3 Turn CSS Mythbuster
« Reply #16 on: November 17, 2013, 02:47:39 PM »
Hi all,
just for test purposes I have created a macro that calculates and set the speed and feedrate at the line where it is coded.

May be not free from issues

attached the macro and a sample G-code
#1 is surface speed  in meters per minute
#2 is feedrate in mm per rpm
#7 is max rpm coming from the macro


alex