Messages

991

Show"N"Tell ( Your Machines) / Re: AL54b (lathe) project from New Zealand

« on: November 11, 2010, 10:40:42 PM »

Hi

Your AL54B looks very similar to my AL from Hare&Forbes. I have had it for a number of years now.

Comments:

* They are both made in China, with the inevitable consequences. However, the consequences are not always as expected. I find the bearings are still pretty good, the headstock alignment is pretty good, but all the fasteners are rubbish. Any cap-heap bolr which is active will have to be replaced with an Unbrako.

* I hope the ball screw has the same pitch as the lead-screw you are replacing, because the back-gearing is designed to work with the lead screw to get all the thread combinations. As this is very unlikely to be the case, you may have an interesting time getting the thread cutting going. Good luck.

* The use of a ball screw may place extra loading on the main lead-screw bearings. Check adequacy.

* The back gears do need changing for different threads. I hope you have left enough room/access for this. In addition, those cast iron gears get extremely filthy with iron and carbon dust after a while. Trust me, I KNOW!

* I have the standard small Qwik-change tool-post holder on my machine, and haven't had any problems with its rigidity. But I tend to machine fairly gently most of the time.

* The gibs on the saddle do need regular adjustment in my experience. But, that is not too difficult.

* I still have the 3 and 4 jaw chucks which came with the machine of course, but these days I tend to use an ER32 collet system as much as possible.

Cheers

992

General Mach Discussion / Re: For a new built machine, what would you change

« on: November 11, 2010, 10:14:47 PM »

My current machine works fine, but the physical layout of the electronics (done by a third party) is ridiculous. Everything is jammed in tightly together, and I have to deconstruct half the case to get at anything.
I would go for a very clean open layout which allows test probe access.

Cheers

993

FAQs / Re: Losing steps or something?

« on: November 04, 2010, 04:13:16 PM »

All that is attached to the parallel port is my cheater cable to which I have hooked the probe leads to the outer end.  Nothing else.  The 1V pulses concern me too.

I had better point out something you definitely need to test here. If the output PP is completely unloaded you can get fake signals on floating lines through capacitive coupling. The 1 V signal may be due to a broken connection somewhere at the PP output. You should check this by loading the whole cable - say with a BoB. If the 1 V signal disappears or changes much when the cable is loaded then try another cable! Or, as you suggest, another computer, or another parallel port card. That Dir signal is definitely wrong.

Step pulse "0" time:  .5uS min.
Step pulse "1" time:  4.0uS min.
Direction Setup:  1uS min.

The last line is the key one. The Dir line must finish changing state at least 1 uS before the Step line starts to change state.

Cheers
Roger

994

FAQs / Re: Losing steps or something?

« on: November 04, 2010, 06:02:27 AM »

img-0815:  HUH?
NO WAY!!!!!!!!
I do not know what is going on here, but no way should you get anything like that trace! It seems to show that the DIR line is pulsing in sync with the Step line. I have not put a CRO on my system, but I will stick my neck out and say this should NOT be happening! Dir is meant to be a 'static' state.
Second, and related: 1 v pulses? Something very faulty here.

Question: is this a bare PP output, or is there anything hanging off it?
Comment: either way, something has one (I hope just one) big internal fault. Either you have the wrong lines, or the PP has a major defect, or whatever is connected to the PP has a major defect. I just cannot believe Mach would pulse the Dir line like that. Far too much potential for disaster.

Step pulse is delayed about 2-3 uS on rise from Dir pulse.  Both fall together. 

Well, the step pulse making its rising transition a little time after the Dir pulse is right, but everything else is way wrong.

Positive news: you now have the means to properly investigate what is going on. With this gear you should be able to crack the bug.
Negative news: you have a fault somewhere ... but you knew that anyhow.
Also, I will be off the air for a week+ from Saturday. Sorry about that. Give you time to really explore combinations.

Cheers

995

FAQs / Re: Losing steps or something?

« on: November 04, 2010, 04:43:18 AM »

Corrected version - got interrupted for dinner...

Hi Dan

I would like to note that it is not as easy as it may look trying to capture the timing between the step and direction signals using a plain scope. Thing is there is also the motor acceleration factor and the step pulse stream is not going to be constant frequency. One could probably try a very slow speed and VERY small acceleration and even then it's not going to be easy.

True, true, but I think the arrangement I have described should work.

First of all, the CRO will trigger off the Dir transition in one direction only. That's the nature of CRO triggering, especially with something as simple as a BK Precision.
What will be seen on the CRO when it triggers off the Dir transition will be the Step pulses as they ramp up in speed, so their spacing will of course vary.
But if the machine is set to do 100 cycles back and forth, each cycle will be the same. So it should be possible to see the pulses on the screen. If 100 is not enough, try 200 ...

Cheers

996

FAQs / Re: Losing steps or something?

« on: November 04, 2010, 04:01:49 AM »

Hi Dan

I would like to note that it is not as easy as it may look trying to capture the timing between the step and direction signals using a plain scope. Thing is there is also the motor acceleration factor and the step pulse stream is not going to be constant frequency. One could probably try a very slow speed and VERY small acceleration and even then it's not going to be easy.

True, true, but I think the arrangement I have described should work.

First of all, the CRO will trigger off the Dir transition in one direction only. That's the nature of CRO triggering, especially with something as simple as a BK Precision.
What will be seen on the CRO when it triggers off the Dir transition will be the Step pulses as they ramp up in speed, so their spacing will of course vary.
But if the machine is set to do 100 cycles back and forth, each cycle will be the same. So it should be possible to see the pulses on the screen. If 100 is not enough, try 200 ...

Cheers




May be you could try in Incremental Jog mode, defining ONE motor step there...? But don't know if your scope can capture a single pulse.

Dan
[/quote]

997

FAQs / Re: Losing steps or something?

« on: November 03, 2010, 05:39:30 AM »

Does the Direction act as a pulse for each step? or does it change state for reversals of motion direction only, ie. steady state for duration of move in that direction?

Dir is a state, not a pulse.

My steps are set to "Low Active" in the Motor Outputs.

Is that what Gecko recommend? if so, OK.
Do confirm with the CRO that the negative going pulse on the Step line is narrow, with a wider Hi state. This is illustrated in the Mach3Mill doco. Check you can vary the width.

I would like setup instruction on using an O'scope as I do have a BK Precision 1530  30mhz scope.  If it could be hooked up to see the timing differences between step and direction it would be nice.  It is a simple dual trace scope, not a storage type.

Um ... putting into words what I do automatically ... Um! Interesting challenge!

OK. First, disconnect everything from the PP. Bare PC.
Hang channel 1 on Dir and channel 2 on Step. If you have a separate trigger channel hang that on  - um, try Step for now. Otherwise trigger off channel 2 for now.
Program the machine to do about 10 steps forward and 10 steps backwards, for many cycles. Adjust the CRO so you can see the Step pulses. The sweep rate won't be very high. The Dir channel will flip up and down. That gets the CRO going.

Now trigger off the Dir channel instead. You should be able to see the slow square wave on the Dir channel and the fast Step pulses on the other channel. Get this going. Now you will be able to see 'ground truth'.

Look at the timing between the Dir transition and the Step pulse downwards (leading edge) transition. What you do NOT want is for the Dir and Step transitions to be too close - that can confuse the Geckos. Also look at how fast the two signals go from Hi to Lo and Lo to Hi: the transition times. Record all these things - paper and pencil & sketches are fine.

Repeat all this with the BoB on the PP, looking at the output of the BoB. What do the pulses look like, and what is the timing like.

Repeat all this with other elements in the chain, up t5o the point of having a running motor. See if there is a shift in the timing between Dir and Step, or if the transitions times change, when some part is put into the chain.

You noted 'stuttering' at the start of a cycle - when Dir changes. This is where I would focus. You want to see what is going on here.

Hypothesis: you are getting a step pulse, or at least an edge of the Step pulse, or part of a Step pulse, while the Dir signal is changing state. This will confuse the hell out of the Geckos and most certainly cause 'stuttering' and screw up the movement of the motors.

Of course, if the stuttering has disappeared but the drift persists .. um ...

Cheers
Roger

998

FAQs / Re: Losing steps or something?

« on: November 03, 2010, 03:44:17 AM »

The Step Pulse parameter is how many micro-seconds are added to the base step pulse width (don't remember what it is). I think the label is wrong and it would accept values 0-15.

Ah - seems reasonable, albeit obscure ... :-)
Hum - at 35 kHz clock, you wouldn't want anything over 15 uSec, would you?
One day ... I will haul the CRO out there.

Cheers

999

FAQs / Re: Losing steps or something?

« on: November 02, 2010, 05:28:45 PM »

Don

Mach3Mill_1.84.pdf, pages 5-12 and 5-13, seem relevant.
Top of page 5-13:
"problems with the test moves (e.g. motor seems too noisy) first check that your step pulses
are not inverted (by Low active being set incorrectly for Step on the Output Pins tab of Ports
and Pins) then you might try increasing the pulse width to, say, 5 microseconds. The Step
and Direction interface is very simple but, because it "sort of works" when configured
badly, can be difficult to fault-find without being very systematic and/or looking at the
pulses with an oscilloscope."

Cheers

1000

FAQs / Re: Losing steps or something?

« on: November 02, 2010, 05:01:14 PM »

I was talking about the Dir setting under Motor Tuning. The value there is how many micro-seconds before the first step in the opposite direction, the Dir pulse changes state. You are correct about the direction line that its Hi or Low state essentially defines the direction of the motor rotation. But the timing is critical here. Change it too soon and you lose one step in the current direction, too late you gain one.

Thank you! I have been educated. I did wonder what those parameters were for.
By way of explanation: working with robotics in the past, I had to write the low-level driver code myself. So I could be sure the Dir state change did NOT clash with the step pulses. Ah well.

So the Dir parameter is the delay in microseconds between a Dir state change and a pulse?
Then what is the Step pulse parameter? I would love to know. it says 0-5, but accepted a 6 (I think).
Is this documented somewhere - I would love to read it up.

*******
Don: this is something to test! Some fine adjustment here might solve your problems.

Cheers