Author Topic: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)  (Read 37484 times)

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #750 on: February 10, 2019, 10:05:16 AM »
To give me a means of bringing on the turret indexing 'fault' I wrote this little diddy to exercise it - the intention being to give it long and short moves in both directions. It selects tools in this sequence 1,12,2,11,3,10,4,9,5,8,6,7,6,8,5,9,4,10,3,11,2,12 and then it cycles back ad infinitum





Of course I left it running for ages and it never failed  :bang:
Andrew Mawson
East Sussex

Offline WeldingRod

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #751 on: February 10, 2019, 03:57:00 PM »
Excel spreadsheet.  Weigh all your tools, do the combinatorial thing (12 factorial or 12 11 x 10 x...) for lines, 12 columns for.positions, then do a net moment calculation for each opposite pair, and sum it up.  Lowest net moment is your best choice.
Or, just take the weights and match the heaviest ones across the disc.

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Offline Pete.

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #752 on: February 10, 2019, 04:08:20 PM »
If that thing needs 40 amps to operate why should a little imbalance bother it?

Offline mc

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #753 on: February 10, 2019, 05:04:21 PM »
Have you noticed it always rotates clockwise slightly when locking?
Surely if it's on position, it should pull straigt in onto the coupling with no rotation?

I can't remember how you said the position is measured, but I think I'd be nudging whatever it is around so it's pulling in straight.

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #754 on: February 11, 2019, 05:34:27 AM »
Moray yes I think that you're on to something there. I have long thought that there MUST be some way to set up the relative rotational positions of the Index pulse and the two pairs of Curvic Couplings.

The index position is sensed by a proximity sensor looking for a notch. When the turret is initialised the SMCC card seeks the index position and homes on it - you can see the drive dog for the powered tooling rotate, then finding the position go off it and back on for accuracy.

Now it's rather difficult to see what is attached to what within the turret, but certainly at the point that it is seeking Index the front curvic is fully engaged and the rear one dis-engaged. The listing of the SMCC program that I have shows that there are 2000 encoder points between tool positions so when it is asked to change tools it seeks Tn x 2000 pulses.

But what sets the relative rotational positions of the  Index to the other bits I am not clear. The Index proximity sensor is in a tapping in the turret casing so not rotationally adjustable.

This morning with the machine cold it resolutely refused  to run the Turret Exerciser program without failing. It was OK on anti-clockwise moves but failed to seat the curvic on clockwise moves.

There is a setting ('Offset') on the servo card that so far I have failed to adjust by the book - it requires that certain wires be removed and links made, but the terminal numbers in the book don't all correspond to the printed numbers on the card. Basically you enable the drive, and also it's 'inch' mode and apply 0v to the analogue input, and tweak the multi-turn offset pot until the servo motor stops turning. Now just using the system rather than links, for 0v input the servo motor IS stationary.

However this morning with the program failing every time, I thought - what the heck - tweak it. I gave it 5 turns anti-clockwise (I think that it's a 20 turn pot) and guess what, the program instantly started working. So somehow I need to bottom out the wiring and get the offset accurately set.

It is very difficult to see if the clockwise last minute rotation that Moray noticed is still as consistent as it was - the camera angle is such that the tool disk is moving away at an angle anyway as it seats so it looks to rotate anyway - I shot another video so I'll let you decide as it's easier to see in the video than in real life.



I've also included the Turret cross section for reference.
Andrew Mawson
East Sussex

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #755 on: February 11, 2019, 06:02:17 AM »
Well that last video was pretty useless - out of focus and still from a difficult angle. Hopefully this one is somewhat better:

I get the impression that there is still a slight settling clockwise on clockwise tool changes, but not so much on anticlockwise moves  :scratch:



Proof of the pudding will be tomorrow morning when it's cold again I suppose
Andrew Mawson
East Sussex

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #756 on: February 11, 2019, 12:56:08 PM »
Excel spreadsheet.  Weigh all your tools, do the combinatorial thing (12 factorial or 12 11 x 10 x...) for lines, 12 columns for.positions, then do a net moment calculation for each opposite pair, and sum it up.  Lowest net moment is your best choice.
Or, just take the weights and match the heaviest ones across the disc.

Sent from my SAMSUNG-SM-G891A using Tapatalk

Not quite so easy Rod, as the mass of the tools act from different points due to their differing shapes, which is why I went on to consider the 'analogue' approach using a mocked up disk.
Andrew Mawson
East Sussex

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #757 on: February 12, 2019, 03:08:30 AM »
Proof of the pudding will be tomorrow morning when it's cold again I suppose

I'm pleased to report that it's passed the 'cold test' this morning, behaving right from the get go  :thumbup:

However last night I went through the various circuit diagrams and worked out the anomalies in the numbering scheme for the 'offset' adjustment, how to disable the servo brake (not mentioned in the book procedure!), and to the disable the X & Z axis so they cannot move. So if I get time this afternoon I'll see if I can perform the procedure.
Andrew Mawson
East Sussex

Offline hermetic

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #758 on: February 12, 2019, 04:43:02 AM »
I agree, that little extra move to get final alignment doesnt look right, partly as you say, because the movement is unequal in the different rotations, from my simplistic, completely non cnc point of view, could there be some small amount of slop in the servo drive system, like a slightly loose pulley, or a partially sheared key, caused by the machine crashing, which the alignment system is compensating for, I suggest this because many times in my life, looking for a complex answer to a relatively simple problem has always come back to bite me in the arse, especially if I have assumed that the fault always lies in the most complex part of the system, ie, the damned electronics!
Phil

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #759 on: February 12, 2019, 04:55:52 AM »
Now I've roughly tweaked the 'offset' the Curvic Coupling seats nicely each time, so although I agree it could easily have been something 'a bit loose' it almost certainly was that the offset was wrong.

If you watch the last short video "Turret Exerciser Better Angle" you'll see that the servo hunts either side of set point then when on station fires the lock solenoid pushing the two parts of the curvic into mesh, and at that point there is very little (if any) relative movement implying that not only was  it at set point, but that the set point is correct.
Andrew Mawson
East Sussex

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #760 on: February 13, 2019, 07:53:51 AM »
Getting so far with the Curvic Coupling seating nicely, I thought I'd push my luck, and re-install the 90 degree powered tool, which weighs literally twice the weight of the other tools.

Well, the answer is, yes, my turret exercise program still runs ok, but you can see the previous symptom of a bit of movement as the coupling goes home. What would you do with an unbalanced car wheel - you'd fix lead weights to balance it - so why not?

First need to work out how much by weighing the tools
« Last Edit: February 13, 2019, 09:02:34 AM by awemawson »
Andrew Mawson
East Sussex

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #761 on: February 13, 2019, 07:58:26 AM »
Then we need a wooden mould to pour the lead in. The lead I had lying about had been flashing from a roof, so it had some pitch on it, and the melting was a bit messy producing lots of dross, but we got there, poured the mould and it worked out bang on the right weight :thumbup:

Trying the machine with the turret now balanced, bingo the curvic coupling is again seating nicely, so a successful experiment
Andrew Mawson
East Sussex

Offline WeldingRod

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #762 on: February 13, 2019, 09:55:57 PM »
That must be one heck of a pocket for that scale!

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Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #763 on: February 14, 2019, 07:09:00 AM »
We don't do 'small' round here  :lol:
Andrew Mawson
East Sussex

Online cnc-it

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #764 on: February 14, 2019, 11:06:44 PM »
It looks like the servo is overshooting?..I've had this on the older Siemens dC drives..it looked just like this symptom. I increased the gain with the proportional gain pot until it settled down.

If I'm correct it's pot R125 (x axis) , R225 (Yaxis) , R325 (ZAxis)  Kp (n) on the AC drives. The manual says turn the gain up if you have inaccurate positioning.



 

 
« Last Edit: Today at 11:28:06 AM by cnc-it »

Online cnc-it

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #765 on: Today at 11:39:19 AM »
Here is a picture from the Siemens DC drive manual. Not sure if it's relevant here but worth a try  :med:


https://drive.google.com/file/d/1_fheJGFmyK5layWUKvz-G2y88A2-c6_o/view?usp=sharing

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #766 on: Today at 11:47:28 AM »
Thanks old chap, but if you look 'up thread' I've already fixed this issue - it was the servo 'offset' adjustment.
Andrew Mawson
East Sussex

Online cnc-it

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #767 on: Today at 12:34:17 PM »
No problem Andrew. It's just that I had an Hitachi Seiki lathe that used a proximity sensor to position the turret like the Beaver here but it didn't back off and re position on the notch like yours does, it just stopped when it reached a tool position so that got me confused for a while :doh: