Messages

721

General Mach Discussion / Re: Toolpath Displays incorrectly when using Work(fixture) Offsets-is it me?

« on: April 07, 2008, 01:16:45 PM »

To carry on from that, therefore - if you want to see the correct tool path display, then press the Machine Co-ordinates button. If this is lit the display you are seeing is machine co-ordinates - the actual path the machine is cutting. It shows you all the table - that may or may not be a disadvantage - it depends how big your table is.

The DRO's however also change to machine co-ordinates - which will bear little resemblance to what you have written, because they also include all the offsets - and make it difficult to check where you are.

The system works fine if you only have one offset, but if you have multiple offsets in the program this will happen.

722

General Mach Discussion / Re: Toolpath Displays incorrectly when using Work(fixture) Offsets-is it me?

« on: April 07, 2008, 01:06:08 PM »

No - I understand exactly what you are saying - look at the tutorial video on Co-ordinate systems.

You machine runs ALL THE TIME in machine co-ordinates.

Machine Co-ordinates X0 Y0 and Z0 might be at odd places - usually at the bottom left hand corner of table movement - with the Z at rest at 0. This might be a **** position from which to start any work. Your table might be 10" by 10"

When you write a program, it is normal to start the tool at X0 Y0 (with Z0 touching the top of the workpiece). This is easy to imagine, and you write the program. The whole program area might be 5" by 5". AND TO MAKE IT EASY YOU MOUNT THE WORKPIECE IN THE MIDDLE OF THE TABLE.

To reconcile the position of the mill, with the position of the workpiece, you the EITHER jog the mill to the bottom left hand corner of the workpiece, or you use an offset say G54 which takes your mill to the point at which your program starts and you zero the axis. The axis will not zero on machine co-ordinates because they are tied to the home switches, but if you press the machine co-ordinates button and the light goes out you are then on program co-ordinates - and you zero the axis.

If you then look at the toolpath display it will show the crosshairs at X0Y0 at the bottom left hand corner of the workpiece (the centre area round which you wrote your program). The DRO's conveniently show you at 0,0,0 because it knows that we humans are less intelligent, and we like to see what we expect to see. You start the program and the display conveniently follows the toolpath you have written.

THE COMPUTER HOWEVER knows this is a sham !! it knows it's actual position, according to the MACHINE CO-ORDINATES, is 0.0.0. plus the offsets. It displays the toolpath you want to see, but carries on itself on its own (the true) toolpath.

When you come along and put in another offset, it cancels the first and puts in the second, zeros the display and shows you at position 0.0.0.  THE COMPUTER KNOWS THIS IS A SHAM AS WELL - it has just moved to a different location, but for you poor humans, so not to get you upset, it shows that you are at position 0.0.0. because thats what your program says - and it gaily starts to cut, showing you the display it thinks you want to see.

To your eyes, of course, you are seeing two tool displays, one on top of the other - because they both were written starting at the same place - but the COMPUTER IS NOT BOTHERED - it started at the right place according to it's MACHINE CO-ORDINATES and cuts the right path.

I don't know whether that explains it - but if you watch the Co-ordinates video tutorial, I'm sure the two will explain it.



 

723

General Mach Discussion / Re: Mach3 Turn... Pro?

« on: April 07, 2008, 12:36:53 PM »

I don't know - what features do you mean.

I am using the downloaded version of Mach3 Turn and it seems to have everything I want

724

General Mach Discussion / Re: Help with Toolpath display

« on: April 07, 2008, 12:33:54 PM »

Yes Ken - I was going to say that -

In your machine - does the head move X and Y or is it the table that moves -X and -Y.

I had the same difficulty.

725

General Mach Discussion / Re: Why do large files cause lost steps?

« on: April 07, 2008, 12:05:46 PM »

How have you got the A axis set up. You say it is a rotary axis. In that case your number of steps per unit should, I would have thought, be in degrees. The speed then translates to degrees per minute - not ins or mm's as shown on the screen.

If you say the computer has no problem with xy or yz or whatever, why don't you set up the a axis as a linear axis. Compute whatever the distance is you want to move at the circumference, think of this as a distance unit and enter in the appropriate nuber of pulses to turn your A axis far enough to give that distance at the circumference ( a bit of pi will be involved) but to Mach it makes no difference - all it wants to know is the number of pulses it has to output to move your axis whatever distance you decide upon - it could be measured in finger widths for all the computer knows.

You may be right - the computer might have difficulty doing CV on a rotary axis (I can't see why, but it might)

I am assuming this pattern is described on wood of a given diameter, and therefore it does not matter if you are in rotary or linear settings.

726

General Mach Discussion / Re: Hello 1st post, need advice on controller, board, drivers

« on: April 07, 2008, 10:23:03 AM »

Scott - The clique that is testing the "smooth stepper" is keeping everything close to the chest.

As far as I understand it, all it is is a USB version of the LPT1 printer port.

When Mach3 started, the system to connect the computer to the machine was a printer port cable. This was satisfactory, it had the necessary speed and all computers had one. To be fair, it's cheap and it works well - I am still using mine - because my system is simple.

The big problem with it is the lack of pins (outputs and inputs). There are 8 outputs (mainly to drive the axis - 2 wires per axis), another 4 outputs (mainly for coolant, spindle motor on off and reverse) and 5 inputs. The inputs are a problem. If you want limit switches, home switches, spindle speed reader, and feedback from any measuring device you have on your machine (like servo motors) then there is just not enough input via the LPT1 port.

You could get additional printer ports, but modern computers are now coming out without the old 25 pin printer ports and doing everything via USB.

I understand the "smooth stepper" is just that - a collectionof input and output ports to connect to your machine - and all you do is plug in a USB lead. I understand there is also some sort of driver chip (s) on it, so whereas before your computer generated all the pulses necessary to drive your machine, now the smooth stepper does a lot of the work. This means that the type of computer is less demanding - many of us like laptops in the workshop (but some of these had problems). Smooth stepper will apparently work with any computer that can run USB ( I assume USB 2")

Thats my bit - no doubt I will get shot down in flames if the info is wrong - but as yet I've got to see a spec - come on guys - let us into the secret.

727

General Mach Discussion / Re: Toolpath Displays incorrectly when using Work(fixture) Offsets-is it me?

« on: April 07, 2008, 10:03:22 AM »

The only way to do it, I think, is having set it going revert to a machine co-ordinates view and regen the toolpath. This should then regen everything from machine co-ords 0.0.0. and then put it on the screen with the offsets.

It should then show the difference between the two different offsets.

728

General Mach Discussion / Re: Using_MM_Ballscrews_with_Inches

« on: April 07, 2008, 09:50:34 AM »

It doesn't honestly matter if you set up in mm - as long as you do it all in mm - i.e. tool offsets etc as well as your motors.

I am changing my leadscrew and crossslide to ball screws - and they are metric, so I will probably set up in mm's

if you are running your code in inches, Mach3 just converts it anyway, and vica versa. I don't know which country you are in but in the UK there is more metric stuff about here, and really metric is the one to set up in.

So - if you buy your parts in metric - maybe your tools are metric diameters as well - set up your machine in metric.

When you use G20 in the code, Mach 3 changes all the DRO's etc to inches, and also brings out all offsets from tool tables etc in inches. It is then, to all intents and purposes an imperial machine.

729

General Mach Discussion / Re: Toolpath Displays incorrectly when using Work(fixture) Offsets-is it me?

« on: April 06, 2008, 03:31:02 PM »

In answer to the question in the heading - yes it is!!!

I don't know how you set up your machine at the beginning of a job, but offsets are calculated from the homing positions of the machine. When you put in G55, Mach3 adds this to 0.0.0. in machine co-ordinates and then calculates everything from there.

Your display - if it is not in machine co-ordinates - displays your program co-ordinates. So if you have written your program starting at X0 Y0 that is shown on the screen as the bottom left hand corner of your program area ( the area of space the program takes up) BUT  you are not actually at X0 Y0 you are at X10 Y10.

On the second half of your program you put in a second offset (G56). Mach3 takes off the old offset and adds the new offset, and runs from X10 Y5 BUT if your program again starts at say X0 Y0,  on the toolpath display it will overwrite the first one.

Although the displays overwrite, the machine working on machine co-ordinates actually cuts at the right place.

As far as I can see, do not regen the toolpath between the halves of the program. It might however do this automatically when it encounters a new offset.  You can use the machine co-ordinates display - but then the co-ordinates will not be the same as those your program is running.

See the Video Tutorial on Co-ordinate systems.

730

General Mach Discussion / Re: Hello 1st post, need advice on controller, board, drivers

« on: April 06, 2008, 02:36:28 PM »

I dont think they are steppers either.

Whatever type of motor you have, basically Mach3 puts out two signals for each axis. One is a step pulse, and the other is a dir pulse. Both - coming from the computer either via LPT1 printer port output, or the new smooth stepper USB output, are at 5 volts.

If, in the end, you decide to replace your motors, then, if you pick stepper motors, you will find that the drives will operate directly from the computer signals. You merely put in a drive voltage from your power supply, and connect up your motors. If you then input the two signal wires (three with the signal return line) to the step and dir inputs, the motors will drive, It is that simple.

I might be preaching to the converted here if you are used to CNC.

Although you can use feedback from measuring instruments to confirm Mach3's position, it does not need any. Mach3 keeps a record of it's own position through the program by counting the number of step pulses it puts out - the only problem is if (for some reason) your motors miss steps. This is usually caused by trying to get too much speed or acceleration on G0 moves - but all in all it is accurate, and if you run well within the limits of your machine, it will be accurate.