Messages

531

General Mach Discussion / My Fixtures are not "fixing"

« on: June 13, 2008, 01:53:20 PM »

Having taken the plunge, and set up my homing switches, I decided to become more professional , and fill in the offset table to bring various tools etc, into line with my chuck ( I am on the lathe at the moment, but the query applies to Mill as well)

I am missing something !!

I fill in the fixtures table. I click select, I click save.  The trouble is the entries are not constant. Sometimes they are there, other times the table has reverted to 0.0.0
At the moment g59p7 seems to be fairly constant - it is staying on the table, even after I shut down and start up again, but I did what I though was the same for g59p8 today - and after a couple of calls it had zeroed itself.

Can anyone tell me how to "freeze" the offset table - like the tool table (with which I have no trouble)

532

General Mach Discussion / Re: Starting from Zero, need advice

« on: June 13, 2008, 01:44:33 PM »

Don't worry 

You are certainly getting very advanced before you even start.

You don't need home switches, or limit switches to enjoy CNC. If you have your axis working from Mach 3 then that is all there is to it.

You're main job is to get the axis up and running reliably and accurately, which means setting up your motor tuning (see Config/Motor Tuning). Setting your "Steps per Unit" and your sped and accerleration for each axis is the first thing to do. Do backlash next - and you are ready.

You seem to have a grasp of the Ports and Pins, if you are talking about Limit and Home switches, so I will move on quickly.

CNC depends on your machine knowing where it is. There are two ways of doing this, and the easiest is to set up your work on the table, move your cutter to a fixed point, and tell the machine that is where it starts from. This is usually point 0.0.0. which is the bottom left hand corner of the work, with the cutter resting on top of the work. (This is where most G Code programs are written from) This is known as program co-ordinates. The machines says "right" and carries on the program. You can do that many times, as long as you are satisfied that the machine is starting in the same place each time (and therefore knows where it is)

The second way is more professional, and involves "home switches". These are fitted to the machine in a specific place (one on each axis) and if you press the "Ref All Home" strip, then Mach 3 will automatically move the table and cutter in turn, until all switches have been contacted, and it will remain there. (Any axis without a switch is just zeroed, with no further movement).  The table therefore has zeroed itself and knows where it is and this position is called "machine co-ordinates" 0.0.0

It is doubtful whether these switches would be in a place that is any use at all for machining anything, and certainly would not be at a place from where a G Code program would be written (unless you were a mathematical genius). To make use of this is the job of the Offset table (see Config/Fixtures) and here can be entered offsets to move the table to a convenient position to start work. Offsets start at G54 to G58 and G59P* (where * is 7 to 255). If you enter an offset, then tell the table to move to 0.0.0, the table will move to iits new starting position, which can be anywhere for your convenience. The new position is shown in Program Co-ordinates.

That's enough of that, but it gives you the idea.

Fortunately Mach 3 can double up on limit and home switches, so you can designate the same switch to be both a home switch and a limit switch. Mach 3 will change the function of the switch as it needs to. You need to make sure that they are designated on Config/Ports and Pins/Input Signals.

533

General Mach Discussion / Re: Matching Dros

« on: June 13, 2008, 02:18:00 AM »

I take it your mean that you have some sort of independent scale attached to your miller which gives a read out, as well as the computer screen which also shows a readout.

Since they are both independent, more than likely they will both show different readings. This is not important. The main thing is, if the reading on Mach says an axis has moved 1 inch, then the reading on the other scale should say it has moved 1 inch. Neither reading has any influence on the program - it is just for your information.

By that I mean that the DRO's on Mach 3 do not recieve any signal from your machine. If you want to move 1 inch, Mach looks at the steps per unit you have set, and bangs out the appropriate number of pulses to move the axis. Similarly your other scale has no influence on the machine either. You are dependent on keeping your machine operating within reasonable parameters to maintain accuracy. Start trying to go too fast or too much acceleration, or if your machine binds here and there then you will miss steps. You will find that Mach 3 says the machine has gone further that your other scale reads.

If you are fitting "home" switches, then you could "zero" both DRO's when you home, and this would keep them in step - you would soon see if the were different, However - you would be limited to "machine co-ordinates" since your other DRO would have no way of taking on board any offsets that Mach uses. Having said that, it is easy enough to add a set of DRO's to any of the Mach pages (and you can reduce the size) and say fit a small readout under the main one - and show on this the machine co-ordinates - which you can glance at and check if they are still in line.

There is also an add on board you can get which reconciles the two and puts out an alarm if the two readouts get out of kilter. This will stop your machine, but there is no way at the moment to get Mach 3 to then correct the fault.

534

General Mach Discussion / Re: G02 & G03

« on: June 13, 2008, 01:54:04 AM »

There is nothing wrong with Mach 3 - BUT - because the program is so flexible, setting all the "bits and pieces" up together is sometimes quite difficult. I am having "difficulty" (i.e. I need to do a great deal of headscratching) when reconciling the movement of my "milling" head in relation to the toolpath.

1. Are you looking at the table, or at the tool. It is the TOOL that moves - not the table.
2. When you say they move in the wrong "clock" - do they actually complete your program correctly - i.e. join up with straight bits on either side - or just take off into pastures new.
3. You must make sure that your axis are set up correctly, and move in the correct direction. If what you say is happening, then one (not both) axis is set up the wrong way. Put a felt tip pen in the cutter chuck. If you start at 0.0 and tell the machine to draw a semi circle G2 x2 y0 r1 this should draw a hump up and to the right. If it draws up and left, the x axis is wrong, if it draws down and to the right the y axis is wrong

535

General Mach Discussion / Re: Height Following

« on: June 12, 2008, 04:34:48 AM »

What are we talking about here -
Are you asking a simple device to come down, read where the top of the work is, then move z down and cut level -

Or are you asking for a device that comes down, and continuously reads an undulating surface and keeps the cutter a set distance above (or below) it - i.e. cutting a groove of a set depth.

536

General Mach Discussion / Re: Question on homeing

« on: June 12, 2008, 04:20:09 AM »

No wonder the Scots invented golf (and Scotch)

537

General Mach Discussion / Re: Homing all axis Help!!

« on: June 12, 2008, 04:14:00 AM »

I will let Hood confirm it, becasue I am not experienced at reading XML files - but your configuration does not appear correct. You do not appear to have any home or limit switches active.

538

General Mach Discussion / Re: Setup problem

« on: June 12, 2008, 03:44:54 AM »

I think you are missing something -
Mach 3 does not work out of the serial port. It uses the 25 pin LPT1 parrallel printer port.
If you have not got one on your new computer (many new ones do not have a parrallel printer port, especially laptops), then you will have to invest in a Smooth Stepper card. This plugs into a USB socket on your computer and provides all the inputs and outputs necessary to run your machine.

Now I've read your post again - I am not sure which port you are using on your new computer. Give us some more detail - such as - printer port to so and so breakout board to so and so drivers etc.

Mach 3 is very configurable, in that nearly all combinations of pins, directions, speeds etc can be catered for, but until you give us an idea of what exactly your set-up is, we are at a bit of a loss.

I still think however, that Smooth Stepper might be the way for you to go.

539

General Mach Discussion / Re: Home/ Limit switch problem

« on: June 11, 2008, 03:27:32 AM »

Whatever your new board is, it may invert the input signals.

There are many combinations of inputs, all configurable on Mach 3 - you say you are using Mach 2, but this will probably be the same.

The thing Mach needs to know it what signal it will see on the pin when the switch is activated.

Switch on your machine and, without anything running, manually activate the limit/home switches. If you look on the diagnostics page, you should see these switching - if they are active.

On Config/Ports and Pins/Input Signals then ensure that the limit switches you are using are enabled (Column 1), and all are correctly designated to Port 1 pin whatever you are using. Then go through each one and make sure that when you switch the switch, the appropriate led lights up. If they are already lit and they go out, then "Active Low" for that pin needs reversing.

If you get no signal at all then there is a interface problem with your new board. For this you will have to test the signal coming from the switch to your Bob board, voltmeter will do, and ensure it changes when the switch is pushed. If it does - but this is not getting to the computer - then a bit of headscratching is called for.

I think thats enough for now

540

General Mach Discussion / Re: Help! Spindle OFF Intermittently Trip Limit Switch

« on: June 11, 2008, 03:03:36 AM »

Have you just the one limit switch or several. Can you trace which one it is.  Has this problem been with you all the time, or has it just started and is getting worse.

If you can trace the switch, and the problem has just started or is getting worse - then change it. Vibration is the death of these things, and there's plenty of that on a Bridgeport.

If the trouble has always been present, then I go along with Chip - make sure your wire is shielded and avoids any places where it is likely to pick up noise - e.g. to close to axis motor feeds etc.

You will not see the switch on the diagnostics page, since it doesn't persist. I have just thought that a small Brain or something would be ideal to put up a message e.g. "Switch 4" or something when these transients occur.