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Messages - jimpinder

61
See also a post by mrpeja just down the main page

62
You seem to have an excellent understanding of how to calculate and measure your distances (I am nOT being condecending) so you may be able to figure it out and how it applies to your machine (because I cant - I don't have this floating headI, and don't know how it is setup).

I was reading through the code and as well as the G28.1 command, there is a further one g92 three lines down. I looked it up on my GCode explanation and both codes are to do with offsets. My version of Mach (version 3.041) has a new explanation of GCodes (when you press GCodes) I couldn't make much sense of it, becasue I don't have the relevant machine in fornt of me, but perhaps you can. The G28.1 has Z3 behind it, which might have some relevance to the 1.2mm torch movement, and the (roughly) 1.5mm height problem - if you add them together 2.7 isn't far off your problem.

Is there any explanation in Sheetcam of the offsets it is applying.

63
You can, of course, still use inches or mm. G20 makes the machine move in inches, G21 makes the machine move in millimeters.If you include these two commands in your programs, Mach will move in either. It will take all your settings and convert them to the other unit.

The only thing the set up units means is that ALL you settings, motors, tool offsets, general offsets etc etc must be in your selected unit - i.e. MM.

64
General Mach Discussion / Re: Strange motor speed on reversing....
« on: April 30, 2009, 01:31:58 PM »
You will probably find the "motor banging" (although that sounds a bit harsh) on reversal is the backlash compensation system, which you say you have turned on. There is very little you can do about it. The backlash seems to (as you reverse direction) - start in the reverse direction - suddenly realise this and stop - apply backlash (at whatever speed you have indicated) - stop - start again to complete the move

I have my backlash comp speed set at 50% (although I recently fitted ball screws and got rid of most of the backlash) and I found this reasonable. It's not too bad when you realise what it is - and it certainly works very well. The problem is, of course, on some moves you have to apply backlash on both axis, and these have to be independently applied to each axis. It is quite fun to listen to.

65
General Mach Discussion / Re: Strange motor speed on reversing....
« on: April 29, 2009, 03:18:41 PM »
I will bow to Hood, who knows a bit more than me.

To go back to the microsteps issue. Hobbycnc are quite right, you do not use microsteps to increase accuracy - although you would think it would. It does, infact, but the reason that advice is given is that the distance between microsteps is not even and you cannot guarantee that say 5 microsteps of a 10 micro step driver is exactly in the centre of a motor step. It does, however, give the maths of Mach more to go at when making the divisions necessary to drive complex fractions of measurement. Mach works to a 0. (12 figures) of accuracy - althoug only 4 are shown on your DRO's.

The reason you use microsteps is for smoothness of running, and you will find that 8 is a good smooth run with most motors and drivers.

66
Have you any backlash compensation on this axis?

I was only thnking that when you are setting the parameters for your torch height, you are going down, and down again.

I assume that you have home switches fitted, and would bet on a Z axis, these would be in the "up" direction. If you then use an offset to come down again to the torch height, you will have backlash to take into account, becasue you did not start with zero in the the same place (or direction).

I would add the 1.2 mm to the backlash and try that.

67
General Mach Discussion / Re: Strange motor speed on reversing....
« on: April 29, 2009, 12:14:04 PM »
I have looked at the video and - yes - it does seem odd.

Reading your text, I wonder why you only have the system on 1.2 step ( which I assume means 2 microsteps) . It will work more smoothly if you work on 8 microsteps, or - for example - my Ghecko drivers work on 10)

I would increase the number of microsteps, then go to motor tuning, and make the appropriate adjustment to your steps per unit.  Your motors will be 200 step, if you use 8 microstep that will be 1600, you appear to have about a 2 to 1 reduction, so that will be 3200, then what ever your leadscrew is. Mine on the lathe was 10 turns per inch so this would be in the order of 32,000 per inch - do not worry, Mach can take it.

My lathe was 60,000 turns per inch - and Mach coped very well. I have now gone metric, with a 5mm ball screw, so I am down to 1200 per mm - but it is, in effect the same motor speed.

As regards you motors, if they are eight wire, they will be much faster if wired in parrallel. I wired mine in series at first, with disappointing results - only 4 ins per min.I wired mine in parrallel, and I shot up to 10 times that figure. I have eased it back to 24 ins per min to keep accuracy. My next move is to increase the voltage.My Ghecko drivers will take it, but my Z drive is limited to 24 volts so I am stuck at the moment.



68
General Mach Discussion / Re: Steps (chugging) around radius.
« on: April 29, 2009, 11:46:12 AM »
Have you tried to do anything manually - e.g. a G2 or a G3 move. This is an arc (or circle) generated by Mach, and is a recognised CNC move. I think your will find your machine will do that properly.

Most CAD/Cam programs  do not generate arcs or curves at all, they are all straight lines - short straight lines - and this is probably what is causing the marks on your  workpiece.

Also check that the backlash on your machine is non-existant, or is at least compenstated, becasue every time the axis changes direction, backlash occurs, and again, marks your work.

Lastly try to ensure that your machine is on constant velocity, not absolute stop. In constant velocity Mach computes the acceleration into the next line as it is slowing down the present line, and strikes a level between the two. In absolute stop, Mach completes one line, i.e. slows to a stop, before accelerating into the next line. This will make the short straight lines all the more apparent.

69
General Mach Discussion / Re: button code
« on: April 29, 2009, 11:25:42 AM »
The leds are either true or false, not 0 and 1. The "0" is 0, but the "1" is "non-zero" not necessarily 1.

Just try If GetUserLED(****) Then  - or - If NOT GetUserLED(****) Then for the "on" or "off"

70
General Mach Discussion / Re: Help with Mach3 config.
« on: April 27, 2009, 03:26:33 AM »
The tool display does not show the workpiece. It shows the outline of your program. We must assume you will put the workpiece in the correct place.

This may be the time to explain the difference between Machine and Program Co-ordinates, if you are fitting limit and home switches.

Mach 3 keeps track of your machine in Machine Co-ordinates. You can look at the Machine Co-ord DROs by pressing the Machine Co-ords button on the screen. The led surround will light. You cannot alter these co-ordinates, and you have no control over them. The only way to affect them is to "home" your machine. The machine will move to the home switches, one by one, and then stop. The DROs will set to zero (if you have the auto zero ticked). This is the only way to alter the Machine Co-ordinates.

Mach now knows exactly where the machine is.

It is not likely that the position of the "home" switches will be in a convenient position to work from, and will certainly not bear any relationship to the program you are running.For this, you use program co-ordinates. Program co-ordinates are determined by the program, either one you have written, or one a Cad/Cam program has written. This will have a 0.0.0 position for the three axis. For different programs, the 0.0.0 position may be different, depending on size, layout, thickness etc. and you must look at your machine and table, and work out the best place for your workpiece, and where the 0.0.0 position is on it. It may be a small piece, in which case you may decide to use the centre of the table, or one corner. It may be a large piece which overhangs the table.

The general start point for programs is X0 Y0 to be the bottom left hand corner, with Z0 as the cutting tool just touches the top of the workpiece. This is a general thing, but not necessarily so, and your 0.0.0 position can be any where.

If you are doing a large number of the same piece, you will probably have so jig attached to the table, so that each work piece will be in exactly the same position.

How do you marry up the Machine Co-ordinates that the machine knows, with the program co-ordinates ? The answer is offsets.

If you "home" your machine, and then press the Machine Co-ordinates button, the led will go out. The DROs are now displaying Program Co-ordinates. When you first start the day, these may, or may not be the same as the Machine Co-ordinates. If they are not already at zero, you now press the zero X zero Y and zero Z buttons, the Program Co-ordinates will go to zero. If you check with the Machine Co-ordinates, these should also be zero. If you now check Config/Fixtures you will see a table which sets out offsets. When you are first starting they should all be zero. You will fill the table gradually.

If you now jog your table to Program Co-ordinate 0.0.0 position and press the zero X zeroY and zero Z buttons again, the program co-ordinates will zero. If you check the Machine Co-ordinates they will not have, and the display shows the offset for that program. If you check Config/Fixtures you will see that G54 has altered, to reflect the offset. You can use G54, but this is the default offset, and if you are wanting to use the offset in a program, you will be better to copy the figures to a different offset (g55 to g59 - and 250 sub sets of g59 - so there are plenty to go at.

If you choose shall we say G55, then you enter this is your G Code program as a line, near the begining of the program. Many programs include G54 (the default) so you can instead alter this to your program offset.

How does this work?.

"Home" your machine. Run the program into Mach 3. Lay your workpiece in the jig. Press the Cycle Start button.  The machine knows where it is, becasue you homed it. It knows the offset to the program and picks up the offset value from the table, and then moves to the new "start" position and gets on with the job. You sit back and have a cup of coffee. When the machine has finished, put another workpiece in the jig, and press cycle start again. Have another cup of coffee.

You need not "home the machine" before every cut, only at the start of the day (things may have moved slightly when the machine was turned off) or if you think somethings has gone wrong, i.e. a tool broke or the cat got stuck in the machine or something. If you suspect the machine has slipped, then you "home" it to put it back on track.

Each program can have a different offset - there are 255 to choose from, or if you use a jig to locate the work, then you can use the same offset all the time.

Hope all this makes a bit of sense.