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Mach3 Turn CSS Mythbuster
« on: October 09, 2013, 06:15:18 PM »
I thought I’d share my experience with Mach3 Turn using Constant Surface Speed (CSS). 

Attached is a short dissertation that could be used to bridge the missing information in the Mach3 Turn Manual.

I cover the use of G96 (CSS On) and G97 (Cancel CSS and return to RPM mode), as well as some tips on using G52 Offsets for gang tooling equipped CNC lathes.

Below is a video clearly demonstrating that CSS works well with Mach3 Turn, if you follow the rules outlined in my attachment.
 
The video also shows how I use Alodine 1200S to chromate convert aluminium parts.  Please note that Alodine 1200S is not ROHS compliant as it is a hexavalent chrome.  However, if you do not drink the stuff you will be OK.

http://youtu.be/2TsKji7VkYo

Enjoy

Chris Humphris
Re: Mach3 Turn CSS Mythbuster
« Reply #1 on: October 11, 2013, 05:46:26 PM »
OK,

I've had a few inquiries regarding the chromate conversion process. 

Attached is a procedure I have written which includes where to get Alodine 1200S in Queensland.  Basically it is available from Henkel Chemicals worldwide.

Regards

Chris Humphris

Offline Tweakie.CNC

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Re: Mach3 Turn CSS Mythbuster
« Reply #2 on: October 12, 2013, 01:46:12 AM »
Very useful information Chris, thank you for sharing.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Hood

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Re: Mach3 Turn CSS Mythbuster
« Reply #3 on: November 08, 2013, 04:08:37 PM »
I had never tried CSS when using the parallel port but it has never worked correctly with any external controller. I asked many people who used the PP if it worked for them and at first all said yes it did but then when I asked a bit deeper then they discovered it didnt. Also I am almost certain (could dig and find it to be sure) Art has said it does not work correctly in G95 and it is impossible to make Mach3 work correctly with CSS/G95.
Can you definitely say that the feed per rev stays constant, ie whatever you have it set to. So for example going from large dia to smaller the axis sill speed up and keep the FPR constant? In all the tests I have done and all the tests others have done the axis will start off at its FPR but from that point on the FPR will actually be treated as the base point for FPM.

Hood
Re: Mach3 Turn CSS Mythbuster
« Reply #4 on: November 08, 2013, 05:11:37 PM »
Hi Hood,

You raise some points I hadn’t considered.  I have not tried CSS with a parallel port connection, as my lathe is controlled via USB Smoothstepper.  So I can’t say for sure if a PP connection would work.  However I can’t see why not, as my understanding of Mach3 (which is not great; my understanding not Mach3, that is) is that the Mach3 PWM Spindle Control stream is simply passed through the Smoothstepper and not manipulated.

I cannot say categorically that the feed per rev remains constant but it appears to do so, both for diameter changes along the X Axis and linear cuts along the Z Axis.  I guess I could measure it but I am very happy with the way it behaves for me. In early days of development of my gang tooling setup, I found out that very large diameters slowed the spindle RPM to below the lower limit I set in Mach3, triggering the lower limit function of Mach3.  The upper limit is set to 1500RPM, well above the 1200RPM limit set in my Danfoss VFD, so I never reach the upper limit.

FYI, I use Mach3 Version R3.043.056 exclusively for both my lathe and mill.  The mill is PP controlled.
For the USB Smoothstepper, I use Plugin BETA Ver 0.015meg.  I tried later versions of the Plugin, but reverted to BETA Ver 0.015meg when I found that they would not report the spindle speed to Mach3.

In summary, given that G95 and G96  is not documented in the Mach3 manual, I have always believed that I have been lucky to strike something that works, and that it was more luck than good management.  I can’t recall why I even started down the CSS route, but I have vague recollections that I read somewhere that others had used it with success.

PS I searched the forum and found this:
http://www.machsupport.com/forum/index.php/topic,5503.0.html

Regards

Chrisjh

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Re: Mach3 Turn CSS Mythbuster
« Reply #5 on: November 08, 2013, 05:33:51 PM »
Well I would be doubly surprised if CSS is working correctly for you knowing you use the SS.

Should be relatively easy for you to see, if you start at a large dia and move in to centre you should see the FPR DRO decrease  as the feed, when CSS is enabled, gets based on the FPR and RPM at that time.
Also if you start CSS on a large dia and then move in to centre and then without calling a further  G96 just command the X to move back out to the starting Dia, I suspect you will see a hige difference between the time taken to move in and that of it moving out.

I tried searching the Yahoo group but couldnt hit on the exact post by Art (the search in Yahoo is really pathetic now since all the changes there, in fact the whole online Yahoo layout is now that way, it used to be difficult to follow things at times, now it is almost impossible). I did find some posts that mentioned Art had previously stated it was not possible to make Mach work correctly with CSS in G95 but that is all. will keep searching but look forward to your results if you can get some time.



Hood

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Re: Mach3 Turn CSS Mythbuster
« Reply #6 on: November 08, 2013, 05:47:56 PM »
Well managed to find some info on Yahoo, this was regarding a discussion where some said CSS worked, others said it didnt and basically it boiled dow to some saying it used to but not now, anyway heres what Art said on the matter.
Hood

here it is
Quote
---- Original Message -----
 From: G_Mouer
 To: mach1mach2cnc@yahoogroups.com
 Sent: Monday, April 09, 2012 10:21 AM
 Subject: [mach1mach2cnc] Re: CSS thread, Brian care to weigh in with your thoughts?



 Is this one of those things that used to work way back when, and went funny over the different versions? Just curious.


Hi:

 Ill kick in on this.. no , it was never different really. Due to the restrictions on the driver/interface doing proper CSS was
 near impossible back then, so a spindle pwm contol doing CSS was the best I could shoehorn in at the time. Proper
 CSS required things that a buffered trajectory path just wasnt compatible with. Lathes were not heavily used so dev time
 was at a minimum. I know care is being taken to allow proper lathe control in future..

 Thanks,
 Art
 www.gearotic.com
Re: Mach3 Turn CSS Mythbuster
« Reply #7 on: November 10, 2013, 04:24:10 AM »
OK,
I had assumed that because it appeared to work for me, that CSS capability was an undocumented feature of Mach3. You have aroused my curiosity, so I performed some measurements.
 
This is what I did.
   Setup some stock in the chuck and calibrated the X Axis.
   Using the MDI, I issued the command G96 M3 S50
   From the MDI, I requested G01 X50, X45, X40, X35, X30 , X25, X20, X15 in succession
   At each of the diameters listed above, I recorded using an independent tachometer, the actual Spindle RPM, and the reported RPM from Mach3 DRO (S True)

Listed below are the results:

Ø (mm)   Calculated RPM   Measured RPM   Mach3 DRO RPM Reading   Tangential Surface Speed (Metres/min)
50   318.31   348   349   50
45   353.68   380   380   
40   397.89   420   420   
35   454.73   471   471   
30   530.52   540   540   
25   636.62   636   636   
20   795.77   785   785   
15   1061.03   1034   1034   

Calculated RPM is from the formula:
 RPM = Surface Speed (in Metres per Minute x1000) / π*Diameter

I repeated the measurements at a couple of random diameters and the results were totally repeatable.  I also noted that the speed transition was very smooth, regardless of whether the diameter was increasing or decreasing.

I think the measurements prove that my combination of Mach3 and USB Smoothstepper is capable of at least approximating CSS.  I am happy it works for me.

One thing that annoys and frustrates me is that at the first use of Mach3 Turn, CSS does not work as intended, and the spindle speed drops to below the Mach3 low speed limit.  The workaround for this is to stop the program, rewind and start again. The lathe then behaves normally for the rest of the working day, even if I change part programs.  I think this is a result of my initial conditioning code, and I haven’t solved this problem yet.  I have simply learned to live with, and expect, this behaviour.

Regards
Chris Humphris

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Re: Mach3 Turn CSS Mythbuster
« Reply #8 on: November 10, 2013, 05:03:51 AM »
Excellent work Chris.

(Interesting about only working correctly after the second run).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Hood

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Re: Mach3 Turn CSS Mythbuster
« Reply #9 on: November 10, 2013, 05:10:02 AM »
If I am understanding your above tests they are showing the RPM is close to what is required for a given surface speed. That really has never been in question, what is in question however is whether the feedrate adheres to the commanded feed per rev.
 For example a feedrate of 0.3mm/rev at 100rpm should be also 0.3mm/rev at 1000rpm. In all tests I have done and others have done that is not the case and it seems Art has said that it can not be done in Mach3, certainly Brian has said that.
What actually happens is the moment of a feed being called in G95 and CSS the feedrate is then translated into a feed per minute and that is the rate that will ensue for the duration of the move and thus the axis will contnue to move at the same velocity. What should happen when using CSS with G95 is the axis should speed or slow to keep the 0.3mm/rev constant.

Hood