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Author Topic: Mach 3 & Denford Orac spindle speed headache!!  (Read 5913 times)

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Mach 3 & Denford Orac spindle speed headache!!
« on: December 31, 2014, 07:31:39 PM »
Hi all,

 recently obtained a Denford Orac lathe and PC running Mach 3 ... It came from a firm that produced items in aluminium and so spindle speed wasn't an issue (nor was the ability to reverse the spindle) - and so I've completed the task (as all the break out boards and motor control was in situe, just needed the additional wiring to make it operational)

The problem I've run into is trying to do constant surface speed - mathematically it is always incorrect if my understanding of G-coding is correct.

G96 = constant surface speed in units per minute ... Mach 3 is running in mm as specified in the G-Code 'header', so my understanding is that G96 S20 should give a surface speed of 20m per minute however, when working out Speed (from Mach 3 DRO) in rpm x diameter x pi = something nowhere near the supposed surface speed!!!

The Orac instructions claim that the spindle can rotate upto 2000rpm, but this turns out to be an impossibility (unless I'm missing something very obvious) as the motor is rated at 1400 rpm, and the belt drive gives a step down speed of approx 0.6, so the max spindle speed can only ever be 840 rpm!! - Though the pulley ratio is irrelevant to one extent as the speed / timing / index sensors are on the spindle, so should always give the true spindle rpm?

Anyway I digress - I added a screen shot of Mach3 running in constant surface speed, and I'll let you do the maths and see if I'm missing something, or if there is indeed something wrong.

Please help as it's been 3 days of headache and measuring and re measuring and taking the belt drive off to measure pulley diameters and circumfrences and maths and countless scraps of paper calculations and I seem to be no further forward :(

Re: Mach 3 & Denford Orac spindle speed headache!!
« Reply #1 on: December 31, 2014, 09:08:51 PM »
Your screen is calculating in INCHES. (FPM)
Do your math and divide by 12 instead of 1000 (MPM)and you'll see.
It comes out much closer.
You must have a conflict in UNITS chosen.
Russ
Re: Mach 3 & Denford Orac spindle speed headache!!
« Reply #2 on: January 01, 2015, 05:39:41 AM »
to get 2000 rpm you'll need to run the inverter at 100hz or more.
« Last Edit: January 01, 2015, 05:48:41 AM by angel tech »
Re: Mach 3 & Denford Orac spindle speed headache!!
« Reply #3 on: January 01, 2015, 06:36:37 AM »
with regards to the units issue mentioned... if I set the feed rate to be 10 units / min, the slides move at 10mm / min (I've checked and measured. Also when typing in the code either via a loaded program or via the raw command line on mach3 the slides travel that given distance in mm... so apart from wanting to change the 'label' on the screen to be feed rate mm/min all seems fine - unless something had been set up wrongly by the company that used it (though I've seen the code and the parts produced and they are all done in mm and match the specifications)

with regards to the inverter frequency - the motor has a rating of 50Hz - so surely the investor needs setting to that too? OR is it the 1400rpm comes from when running the motor on 50Hz, thus if I feed the motor 100Hz it would then rotate at 2800rpm (thus giving an approx spindle max of 2000rpm). did the original Orac motor inverter drive feed 100Hz to the motor?
Re: Mach 3 & Denford Orac spindle speed headache!!
« Reply #4 on: January 01, 2015, 06:42:15 AM »
yes and yes.

The motor will run at 1425 rpm at 50hz, so increasing the frequency of the inverter you increase the speed of the motor.

The original inverter supplied with the orac would be set to  0-100hz.

Offline Hood

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Re: Mach 3 & Denford Orac spindle speed headache!!
« Reply #5 on: January 01, 2015, 08:38:42 AM »
One point to remember is that the speed set in spindle pulleys can affect the displayed value.
Or at least that is the case when using an external controller, cant remember if its the same with the parallel port as it has been a long time since I used one.

So anyway if you have a max rpm of 2000 you should set that in Spindle Pulleys so that the correct RPM will be displayed.
Hood
Re: Mach 3 & Denford Orac spindle speed headache!!
« Reply #6 on: January 01, 2015, 08:41:10 AM »
Check your Native Units setting as that is what seems to determine which divisor is used.
Both work fine here, but need to shut down and restart after changing.
Russ
HNY !
Re: Mach 3 & Denford Orac spindle speed headache!!
« Reply #7 on: January 01, 2015, 08:50:59 AM »
right, tried the inverter frequency, and it threw a hissy fit and had an error displayed (I did look it up and it was to do with current ratings. ... if it helps for this part of the question,the motor drive inverter is a Siemens G110

done the native units, and that works fine now for the feed label.

so, still no joy on getting the spindle rpm up to 2000 as claimed (partially as the motor is rated at 1400rpm and the inverter drive doesn't want to output more than 50hz atm) and still no joy on the css (g96) code yet - it still seems to misbehave, as at g96 s1 the motor runs at full tilt and warning comes up too fast for pulley. if I do g96 s0.9 it complains it's too slow for the pulley and won't revolve at all.

sorry for the loads of questions, bit I've struggled for the last few days on this, and decided it's time to ask for help :)
Re: Mach 3 & Denford Orac spindle speed headache!!
« Reply #8 on: January 01, 2015, 09:04:28 AM »
often with inverters there are several parameters that need to be changed to go above the default settings.

Offline Hood

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Re: Mach 3 & Denford Orac spindle speed headache!!
« Reply #9 on: January 01, 2015, 09:07:54 AM »
Ok first thing to say is be aware CSS doesnt work too great in Mach3, never has, never will.

If in Feed Per Min mode (G94) then it kind of works but to my mind CSS and G94 is not really using things as they should be, you will be keeping the surface speed constant but your feedrate will also stay constant so the chipload will increase or decrease as the spindle speed alters.

In G95 (Feed per Rev) it doesnt work as all it does is keep the feedrate constant to what it was at the start of the commanded move, ie it basically sees it as a G94 feed and keeps it at that.


Now your messages, probably you see the Too Fast one as you are commanding a CSS and a X move which will mean that your spindle will need to rotate faster than it is set in Spindle pulleys.
You can limit the max spindle speed from the code with a G48.
For example
G96 S200  (this will set your surface speed to 200 units per min)
G48s1400  (this will ensure that the max RPM never exceeds 1400)

Hood