Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: cliveastro on March 06, 2009, 05:33:39 AM
-
Whilst machining under mach3 control my mill just wanders off, this just happens on odd occasions. I have checked the wiring etc and I am at a bit of a loss.
Can anyone help please?
Clive
-
Clive - does this just "happen" or have you done something just before like "start from here" or similar.
It sounds like Mach 3 looses it's memory, which it can do if you "start from here" without backing up enough for Mach to have full details of it's position
-
It seems to happen at the start of a sequence, it happened twice today once while cutting a 25 way d type hole it started to ramp in then carried on down the ramp line. and the same with a circle.
-
So this 'wander away' is happening during a circular interpolation? Are you programming in incremental or absolute?
You may be attempting to run an incremental I&J program with Mach set for absolute. That can certainly 'wander off' for sure!
Bill C.
-
Yes it is wandering after/during a circular interpolation.
I am using a D2NC generated program and I dont know whether it is absolute or incremental.
But I will have a look at my settings. I think my machine is running as incremental as I reset the zero position.
Although I have made a few things I am still a bit green.
-
When you regenerate your tool path, what do you see in the toolpath screen? You ought to see the part....
If Mach is not set to interpret I&J according to the program you should see that effect in that screen as very enlarged circles - that is if the program is in incremental and Mach is set for absolute. Try a known bad (wandering off) program again but go to general settings and check theincremental box for the I&J circular interpolation and see what happens.... slow her down in feed and go for it! Absolute is the default setting.
Bill C.
backwards again.....but corrected! A mind is a terrible thing!
-
The program appears to run correctly ie. after it wandered off I unloaded the program and reloaded it with no changes and it ran correctly.
So it doesnt appear to be program related and that was the same for the hole. However I had previously changed the zero position as each of the features had been set at 0,0 in autocad/dxf/D2NC, which relates to the absolute and incremental theory.
Have I just cheated?
Thanks Bill
-
Mach is smart but dumb about cheating...it then thinks you're smart!
Bill C.
-
I was going to answer this earlier today, but my server went down.
You must be sure, when you start, that your machine is properly zeroed. This means the machine co-ordinates, and the program co-ordinates. If you do not, any offsets introduced will not necessarily result in the right position.
The machine keeps position by using machine co-ordinates - displayed on the DROs when the Machine Co-ordinates button is pressed and the surround is illuminted. If you have home switches fitted, then the only way to alter these is to "home" the machine. If you do not have them fitted, or have them disabled, then pressing "RefAllHome" with zero the DROs.
So - the way to start (if you have no home switches) is to jog to the X0Y0Z0 position of the program. Press the Machine Co-ords button, and the "RefAllHome" the DRO's will all zero. If you then press the Machine Co-ords button so the led surround goes out, you can now zero the DRO's (if they are not zero) by pressing the zeroX zeroY and zeroZ buttons. This zeros the program co-ordinates. If you check the Config/Fixtures table you will see that G54 (the default offset) is now zero.
If G54 is not zero, then some other offset is selected, and you should select G54 and repeat the procedure. Unless you use offsets, all the table should be zero, and you can clear any figures that show in there.
Your machine-co-ords and your program co-ords now coincide with each other, and you can run your program, without any stray offsets value interfering. The problem is that Mach3 alters its Machine-Co-ordinates to reflect the actual machine position, with all the offset values added to it, whereas the program co-ords reflect the value of X,Y and Z in the program. The two are often miles apart.
-
Thanks Jim
I had guessed it might be finger trouble.
Trouble is only using the machine occasionally doesnt help, I did read the manual but that was a while ago.
I will probably get back up to steam again as I am converting my lathe to CNC at present.
Doing the lathe seems to be more daunting than the mill from the mach 3 point of view.
From a mechanical point of view the lathe is far easier to modify than the mill and an awful lot cheaper.
Clive
-
I suppose I have the best of both worlds, in that I have a Warco lathe with a milling head attached. The lathe can turn 9 inches, although at that size you get problems with the spindle motor power since the VFD cuts down the power when running at under 50% speed. I have fitted a set of six pulleys, so I can get down to 200 rpm at full motor speed.
The other drawback is that the milling head isn't really rigid enough for big milling jobs, but thanks to cnc, I can keep the cuts down to about 0.5mm (20thou) and it seems happy with that. If you are cnc, it doesn't matter how many cuts the machine takes. I had it chewing through 10 mm plate last week making some suspension parts for a train I am building. Each part took about 45 minutes - but I went off and had a cup of coffee. I had 16 to make, but I had them finished inside a week.
The lathe is simpler to set up. since it is not likely you will bother with homing switches. I do have one on the cross slide, because I have a centre drilling attachment on the cross-slide to take the place of the normal centre drill. I home the cross slide, and then put in the appropriate offset, and the drill comes across and centre drills the workpiece.
Other that that, work tends to be zeroed in the chuck. X is zeroed by taking a small cut off the workpiece and measuring the diameter of the bar . This is typed into the X DRO (or 1/2 the value if you are on radius). The Z is zero'd by takeing a facing cut across the workpiece and setting the DRO to 0. It is as simple as that.
In other words x0 is the centreline of the lathe, and z0 is the workpiece face.
Get going and get cutting - great fun.
-
I had the same problem with my mill . It would run fine then for no reason it would just take off in a wrong direction. I fixed the problem I had to isolate my control boards power supply . You can disconect the ground wire , use a ups power supply or a isolation transformer. I used a isolation transfromer .
-
Hi Mintz
I have thought about your suggestions and I favour the isolation transformer most, but it did lead me to the thought that it could be a grounding issue.