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Author Topic: 4th Axis move after feed hold  (Read 4354 times)

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Offline Doorn

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4th Axis move after feed hold
« on: October 21, 2010, 05:19:40 AM »
Has anyone encountered the same problem and know how to solve it?
I have a mill with a 4th axis. Normally i do not use this A-axis so normally "A" does not appear in my programs.
However, when I'm running a program and press the feed hold button, the A axis starts rotating as soon as i press cycle start.

I did a small test in which the i made a program flattening program with only a G01 command and the X and Y coord.
As soon as i pressed feed hold the axis stop moving as they should, but after cycle start the A-axis revolves 180°.
After every feed hold it rotates 180° further. The speed of the programmed X and Y movement is at that moment reduced to match the speed of the A-axis,
so the X,Y move that was being performed when feed hold was pressed are finished at the same moment as the A-axis completes this 180° move.
After that the X,Y moves continue on normal speed again and the A-axis stops as if nothing happened, until i press feedhold again.
It does not happen after stop start jog or what so ever, only after a feed hold.

Problem is that i now want to start using this 4th axis and that i sometimes need to place a workpeace next to the 4th axis even when i don't use it.
This means i can not use the feed hold button or the part will become scrap metal or the axis will hit the workpeace.

If anyone has an idea what causes this problem....

Regards
David




 

Online Tweakie.CNC

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Re: 4th Axis move after feed hold
« Reply #1 on: October 22, 2010, 03:01:02 AM »
Hi David,

This is a weird one.

I think the correct sequence after 'feedhold' is to press 'stop' before continuing again by pressing 'start'. Have you tried this and does it still rotate your 4th axis ?

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

Offline Doorn

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Re: 4th Axis move after feed hold
« Reply #2 on: November 13, 2010, 03:44:48 PM »
Hi Tweakie,

Was milling a lot so I wasn't around a while.
When you need to press stop after a feedhold, why press feedhold in the first place and not stop directly (that's how i do it now, no A-axis does not turn)
Stopping in stead of feedhold has however a disadvantage. Mach3 forgets certain words in a code line.
When you start again it reruns the current line, If this is a complete line with all coord present its ok.
However, if you are doing circles with IJK left out because they didn't change or you leave out the G code it often doesn't work anymore.
It often happens that i just have X or Y and (the last G code was G1) After restarting it says it misses IJK when it needs to do a straight line, but it just forgot.
Then i need to find the previous z move at clearance level or move to a safe place before starting again.
Feedhold does not stop the program it just delays the output until start is pressed. therefor i would like to use Feedhold if this A-axis problem would not occur

David
 

Offline Hood

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Re: 4th Axis move after feed hold
« Reply #3 on: November 13, 2010, 05:02:45 PM »
Afraid I have never used a 4th axis so dont really know what to suggest but feedhold should work just fine as you are doing. Stop after the feedhold should only be needed if you want to actually halt the code and go and do something else such as load different code, go back or forward a bi and use RFH or just stop the machine all together.

If you want to attach your xml and the code you used for the simple test I will see if I can simulate it and hopefully find the problem.

Hood
Re: 4th Axis move after feed hold
« Reply #4 on: November 14, 2010, 09:55:13 AM »
Hello David,

I have a 4th Axis on my mill.
It is always connected and powered up even when it is not bolted to the machine table.

I use feed hold - more like a pause, when I press feed hold and then start to resume cuting.
I have never seen  the 4th axis move after FH.
I only press stop after a feed hold if I want to abort the run.

So its strange you 4th axis moves on a feed hold.

Maybe Hood can shed some light after checking your XML.

ATB
Derek
You can "chop it off" but can't "chop it on"

Offline ger21

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Re: 4th Axis move after feed hold
« Reply #5 on: November 14, 2010, 10:33:26 AM »
What does your code look like?
Gerry

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Offline Doorn

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Re: 4th Axis move after feed hold
« Reply #6 on: November 15, 2010, 04:16:43 PM »
Hello Hood / Ger21 Find the documents attached,
My test code can't be any simpler it's just zigzagging with a G01 the words i used is an F at the start and an M30 at the end the rest is just G01 X Y.

Hello Derek,
For me exactly the same, always connected, always powered.

I had never noticed it moving before, but didn't use it either until i mounted it recently.
I made an bridge between the Axis clutch and a bracket with a bearring so i can bolt my workpeace to this bridge.
Directly beside this bridge i bolted a temporary bracket to mount parts upright but it stands in the way of the bridge when rotating , so i have to remove this bracket first.
My Axis is never homing (no sensor) and was constantly at the same angle to stay clear from the the bracket but suddenly i found it moved against this bracket.
and i found scratch marks on the shaft of the bridge in the clutch so it had been slipping.
First i thought i had accidentally pushed a jog button, but a while later i witnessed the axis moving after restarting a feedhold.
I did some testing and found out it did happen constantly after every restart of a feedhold.
Since then i did milling with and without the Axis in use without a problem as long as i don't use feedhold.
but being able to use feedhold would be a lot easier.

Regards

Offline Hood

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Re: 4th Axis move after feed hold
« Reply #7 on: November 15, 2010, 04:52:10 PM »
Do you see the A Axis DRO move in Mach when the axis moves?
I see you have a load of OEM Triggers so presume you are either using a macropump or Brain, can you disable them and see if it still happens, also if you can disable any plugins you are using and see.
Hood

Offline Doorn

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Re: 4th Axis move after feed hold
« Reply #8 on: November 16, 2010, 04:04:55 PM »
Hi Hood,

I do have a macropump running, it controls my pedant for jogging an the fro. There is a plugin for a pokey55 also used for the pedant.
The axis control itself runs via LPT and a BOB without plugins.
As far as i can remember the DRO was changing during this move after the feedrate. i currently can't check it, i have a part mounted to the A-axis and the program has to run about 20 hours.
I can only let it run a few hour in the evening after work and because i have no reference on the A-axis and I'm afraid to lose the product home when i go experimenting before it is finished.
As described before, it always moves 180° and reduces the speed of the other axis so it finishes at the same moment at which the programmed move, that was paused by the feedhold button, finishes.

Regards,
David

Offline Hood

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Re: 4th Axis move after feed hold
« Reply #9 on: November 16, 2010, 05:07:28 PM »
I tried with your xml and first just simulating on the workshop computer and there was no A Axis DRO movement, so that was why I asked. When I got home though I hooked up the scope to the  A Axis step pin and again no movement so that is why I am thinking it is a plugin, macropump or Brain problem, something is telling the axis to move..

Hood