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731

General Mach Discussion / Re: Has anyone actually got a C11 to control a KB speed control via Mach?

« on: July 05, 2012, 09:45:31 AM »

Well, apologies that I wasn't familiar with the C11 BoB when I first posted.  On looking at its manual (which is not entirely clear on this matter) the 0 - 10v output is internally opto-isolated, that is, it has two outputs between which it will output a voltage variable in this range, and these outputs are electrically isolated from ground so they can safely be connected to the KBIC. 

Looking at the KBIC manual, I think it is essentially the same as my controller except that mine comes in a metal box with control pot and mains switch.  However these controllers are NOT grounded, so the "0 volts" line at one end of the pot will be bouncing round at up to mains voltage, hence the need to opto-isolate the control input.

For the C11 to generate that isolated 0-10v ouput, it has to have an internal source of more than 10 volts that is itself isolated from ground, and I think it must have an internal floating dc-dc converter incorporating an isolating transformer to do this.  The C11 manual does say that for the function to work a +12 volt 20 mA supply for the function to operate (see page 15), which would be supplying the on-board converter.  Do you have this supply connected?  If it isn't then you would get anomalous behaviour.  See page 18 of the manual for where to connect it.  As far as I can see all the rest of the C11 only needs a +5 volts supply.  If you need to generate +12 volts then a small regulator off the stepper motor supply should do it.  My BoB on my lathe runs from the stepper supply (about 40v) which it reduces to 12v then 5v.

732

General Mach Discussion / Re: Has anyone actually got a C11 to control a KB speed control via Mach?

« on: July 05, 2012, 04:37:38 AM »

Which KB controller are you using?  On my Novamill I have a KBWM240 running a Baldor .5 hp motor, but as far as I can see the KB controller's pot must be floating around relative to earth since there is no transformer or dc-dc converter inside the KB to isolate it from mains voltage.  I decided that in order to control the speed from Mach 3 I will need to opto-isolate the variable duty-cycle output and smooth it on the "KB" side of the isolator.  If you try connecting direct, goodness knows what is happening.

733

General Mach Discussion / Re: Backlash compensation again - and Xbox controller

« on: June 22, 2012, 10:30:34 AM »

Another update.  I've now made much more progress having worked out how to change the shuttle accel setting.  Basically I think if you type a new number into this field and press "enter" the general config screen just closes, and the new number typed in is lost.  Technique seems to be to type in the new number, then click the mouse cursor to plave the insertion point somewhere else on the screen, then press OK or enter.  This then saves the new parameter setting.

So I set the parameter to .005 s and BC works much more as expected now and with a bit of experimental tweaking of the backlash parameters it works much more consistently.  I can see though that if the backlash varies along the screw then one could build up errors during a run.

My reason for wanting to get BC working is for taper turning away from the headstock, but I must say I can't see any reason why backlash should be a problem for any CNC operations carried out in a way which is eqivalent to manual turning (such as threading) - am I missing something here?

Ideally I would like to eliminate the backlash, but the problem with the Super 7 is that the cross-slide doesn't have enough room for a ballscrew of the usual diameters (say 12 mm) as the nut is too large.  I have found 8mm ballscrews that would fit but they are much more expensive.  Also converting the leadscrew involves major dismantling of the apron that I'm not ready to face yet!

Another small observation on the Mach documentation, I assume that the term "shuttle accel" in the general config screen has nothing whatever to do with the use of a "shuttle" as an MPG - the documentation is practically silent on its significance, so maybe its name could be changed and a few more words given on what it does?

Anyway, thanks once again for the assistance,

John.

734

General Mach Discussion / Re: Backlash compensation again - and Xbox controller

« on: June 21, 2012, 05:32:29 AM »

Thanks Rich.  I had another go yesterday with a bit more success.  One thing seems to be that you can't make a jog move smaller than the BC compensation distance on a parameter, so if I choose an incremental jog of 0.1 mm it doesn't work but 1 mm does.  The behaviour on an axis is then exactly as you described with the shuttle accel setting at 1.  Unfortunately when I try to enter a different shuttle wheel setting it is not recognised - maybe I'm having DRO finger trouble, but I was wondering how this "shuttle" is related to "shuttle express" which I used to use as a manual input device but now of course is replaced with the Xbox control.  I've also realised that there is a fundamental problem with BC because if it doesn't exactly compensate the backlash I guess it can get progressively inaccurate?

735

General Mach Discussion / Backlash compensation again - and Xbox controller

« on: June 20, 2012, 11:28:22 AM »

I am running the latest M3 lockdown version on my lathe and mill, and have also installed the addon for using the Xbox wireless game controller.  Backlash is (so far) not a problem on the mill which has ballscrews but is on the lathe (converted Myford) so at the weekend I decided to enable backlash compensation.  I measured the BL on the two slides and entered the right values in the DROs and set the speed to 20% as recommended.  I didn't touch the Shuttle Accel setting as the manual doesn't mention it though I see in some of the forum postings that it seems to be relevant - so probably set to the default value which seems to be 1.  The Z backlash is about 0.08 mm, Z about 0.18.

Then trying the lathe using the Xbox controller I found some very peculiar behaviour.  Continuous jogging using a joystick in one direction worked fine, but when I reversed direction, first I think it moved slightly in the same direction as before, then moved much too far in the other direction at a speed that varied wildly, first going at normal jog speed, then slowed right down, then speeded up again.  I haven't tried any actual cutting as this behaviour seems absurb, obviously something wrong.

So, questions if anyone can help please.  First, anyone with experience using BC on a lathe?  Or BC with Xbox controller?  And what is the significance of the shuttle accel parameter, is it relevant at all with the Xbox controller and if so what should I set it to?  

TIA - John.

736

General Mach Discussion / Re: Newbie Help Please to Stupid Question Number 2

« on: May 25, 2012, 04:42:43 PM »

And I think you need to smooth the PWM output with an RC filter...

737

General Mach Discussion / Re: Backlash and taper turning

« on: May 11, 2012, 11:38:59 AM »

OK, that's the one!  It has a wizard to turn tapers to faces, either way round.  Looks just the ticket, thanks for your help Hood.

John.

738

General Mach Discussion / Re: Backlash and taper turning

« on: May 10, 2012, 10:36:12 AM »

Ah, would that be "extra turn wizards" by zarzul?  I just found those attached to a post and downloaded them.

739

General Mach Discussion / Re: Backlash and taper turning

« on: May 10, 2012, 07:31:18 AM »

Thanks Hood - er, where should I search?  I can't find anything on this forum or google.  Please could you give me a hint?

John.

740

General Mach Discussion / Backlash and taper turning

« on: May 09, 2012, 12:19:39 PM »

This is probably a silly question but I'll ask it anyway...

I have now got both my lathe (Super 7) and mill (Denford Novamill) working under Mach3, generally pretty successfully.  The lathe uses the standard Z leadscrew though I made a new screw and nut for the X-slide because I didn't want to start modifying Myford's components.  Because I'm not using ballscrews of course I have some backlash in both axes.  From a static point of view I could compensate this by switching on backlash comp.

The normal taper turning wizard cuts towards the headstock with increasing diameter.  This means that the X-slide is at the "wrong end" of its play, and is only constrained to the taper path by cutting forces.  In particular as you reach the end of the cut and the tool runs out of the work, there is a danger that the diameter will increase by more than it should given the taper - in fact I think I have seen this behaviour.  The alternative would be to cut away from the headstock, but then you could have the same problem with the other axis.

Ideally one would start by grooving the work near the headstock and cutting the taper inwards towards the headstock so that both axes are being driven against their play, so to speak.

Am I right in my thinking here, and are any wizards available that work in this way please?  (Or should I write my own gcode?)

John.