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CSS - in meteres or milimeters
« on: April 26, 2016, 08:58:00 AM »
Hello Chaps-
Mach 3 on lather
I have units set as metric.

Setting CSS via gcode is G96 S????

Is the S word in metres or in mm?

My product cuts nicely at 900 rpm on a diameter of 100 mm
Is the following logic correct
100mm X PI= 314.16 mm per rev.
900 rpm will mean 314.16 X 900 = 282744 mm per minute
= 282.744  metres per minute
the block will read G96 S282.7   ??

Next thing is feed per rev that was set by G95 respected??
 
Thanks in advance

Fred

think of the trees-- use both sides of the computer paper
Re: CSS - in meteres or milimeters
« Reply #1 on: April 26, 2016, 11:19:25 AM »
Can't intelligently comment on your math but can definitely say that G95 won't work properly with G96.:(  G96 works well with constant FPM though, for what that's worth.:)
Milton from Tennessee ya'll.

Offline Hood

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Re: CSS - in meteres or milimeters
« Reply #2 on: April 26, 2016, 04:44:01 PM »
As Milton says CSS does not work correctly in Mach, it half works with G94 but to my mind there is not much point in having CSS in feed per minute as the chip load will change as the speed increases or decreases.
G95 itself works great but with CSS Mach looks at the feedrate when starting the CSS move and keeps it to that, in other words it looks at the feed per rev value and converts it to a value for feed per min and it stays at that feed per min throughout the G96 moves, no use at all :(

Regarding your calcs, yes they are correct.
Hood
Re: CSS - in meteres or milimeters
« Reply #3 on: April 27, 2016, 03:41:31 AM »
thanks Chaps--

so when I use css the "S"
 is entered as surface speed inmeters per minute? (Not in mm per minute)

many thanks

fred
think of the trees-- use both sides of the computer paper

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Re: CSS - in meteres or milimeters
« Reply #4 on: April 27, 2016, 03:51:32 AM »
That is right Fred, either m of Ft depending on your setup.

Also just in case you were unaware you can set a max RPM whilst in CSS, Usefull if turning a large dia that would be dangerous if spinning fast when the tool gets close to the centre. To use that you call a G48 S500 or whatever and the max RPM will be that value.

Hood
Re: CSS - in meteres or milimeters
« Reply #5 on: April 27, 2016, 04:04:50 AM »
Hood your experience and knowledge are always respected and gratefully acknowledge.

To elaborate on my present interest in CSS this is what i am doing
I am not using CSS as a control on facing the ends but  rather I want to control surface speed
along the axis as the diameter of the part reduces while machining the OD smaller.
I am machining nylon rods ( about 250 have to be done) from square blocks plus minus
130  X 130 X 280 long. I am machining the blocks down to 68 mm diameter X 250 long.
As all arel aware when machining plastic - there is a major problem with keeping
the swarf under control.
I would like to have the job run itself with minimal supervision so i have rigged a blower
and vacuum arrangement to remove the swarf close to the tool tip.

It works well except that as the surface speed at the cutter tip changes so the swarf
stream also changes direction and moves away from where the swarf control apparatus is
located.

I have found that a 900 rpm on 100mm dia. the swarf goes just where i want it.
However at 900 rpm on a diameter of 70mm ( much slower surface speed)the
swarf flows in a different direction. ( in fact around the tailstock rolling centre where
it fouls the centre and messes with the finish on the last cut)

Therfore I would like to have the surface speed at the tip the same from diameter
of about 120 right down to diameter 68

( sorry about being so longwinded )( maybe it is a sign of advancing age?)

all sugestions will be appreciated.

( please dont over look the meters and mm question ion the beginning)

regards
fred




think of the trees-- use both sides of the computer paper

Offline mc

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Re: CSS - in meteres or milimeters
« Reply #6 on: April 27, 2016, 04:31:16 AM »
Without seeing the part, would it be possible to break the taper moves into segments, then alter the spindle speed and federate for each segment?

As long as you've not got exact stop mode active, I'd think the segments should get blended into a reasonably continuous movement.

Offline mc

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Re: CSS - in meteres or milimeters
« Reply #7 on: April 27, 2016, 04:44:30 AM »
And just to clarify Hood's typo, CSS is specified in M/min or Ft/min depending on if you're in mm (G21) or inch(G20) mode.

Offline Hood

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Re: CSS - in meteres or milimeters
« Reply #8 on: April 27, 2016, 06:40:26 AM »
Fred,
 it may work but as the chip load will lessen as the spindle speed increases, and vice versa, it may end up no  better, only one way to find out I suppose.
With CSS working correctly then the RPM would Increase/Decrease depending on Dia and at the same time the axis would keep a constant feed per rev, CSS in Mach doesn't work correctly unfortunately :(


Hood

Re: CSS - in meteres or milimeters
« Reply #9 on: April 27, 2016, 11:13:21 AM »
Thanks everyone--

does css work on mach4 ?

think of the trees-- use both sides of the computer paper