Messages

911

General Mach Discussion / Re: VERY IMPORTANT INFO FOR THOSE USING Z HEIGHT SETTING MACROS

« on: February 07, 2008, 02:23:01 PM »

I am an amateur at writing G-Code. The stuff I see written by professionals seems to have a block of what I would call "standard intro" stuff and most of this seems to be aimed at cancelling offsets, tool settings and other things - so the program starts at ZERO, I suppose.

I don't know if Graham Waterworth or somebody using G Code professionally woud like to comment - and give us a hint how to start so that the machines are set up correctly for a program.

912

General Mach Discussion / Re: setting up a reflective object sensor for dummy's

« on: February 05, 2008, 07:57:27 AM »

If my maths is right, each debounce is 40 _usec, so 500 would give you 2/100 of a sec. Anybody confirm that, I only did it on the back of an envelope.

Seeing you are trying a load of things, I would leave the slot as it is for the time being. The debounce will nullify it anyway.

Next thing for you to try - I am just fitting a laser with some sensors on my table to get more accurate positioning - I don't know how well that will work. Always something to keep you busy!!!

Jim

913

General Mach Discussion / Re: Mach software to label printer?

« on: February 05, 2008, 07:40:05 AM »

Do you mean engrave a label on each part - which I have seen done at my local CNC shop, or merely print a label on a printer.

Funnily enough - the engraving will be the easiest - becasue my printer port runs my CNC

914

General Mach Discussion / Re: setting up a reflective object sensor for dummy's

« on: February 05, 2008, 03:54:09 AM »

As far as debounce is concerned - if the spindle is rotating at 3000 rpm (which is above the speeds you mention) then the slot only comes round every 2/100 ths of a second - so to get rid of any spurious count - set the debounce at that - the switch only needs to be live as the slot is coming round again.

As far as noise is concerned - make sure your lead from the optics is shielded to stop it picking up noise from your driver boards and spindle driver if you have one.

You have chosen to go with a 12 volt system. This seems to me unescessarily complex, in that you are introducing additional chips and a voltage change for no reason, but all of which can contribute to delay. You could drive this lot from one of the 5 volt supplies, and feed the input signal direct to the computer, therefore cutting out a lot of ****

Paint your disc MATT black with a good quality paint, not with sticky tape - mine with the Fairchild sensor - is painted matt black - with a reflective piece of self adhesive mirror on - and works well.

You do not need a 1 inch gap in your disc. Your problem is not GETTING a reading, your problem is your are getting too many. A 1/8 or 1/16 slot will be enough - if you look at the rise time of your optical sensor. - work out at 3000 rpm how long the gap will be above the sensor. If it exceeds the rise time then you are OK.

In a simple system like this you will always get spurious readings. Mine occur near the bottom of the readings - say 100 rpm. Between that and full speed it seems to be fine.

Since I do not know what system you are then employing to drive the spindle, I cannot comment on the calibration - however if it is the PWM system put out by Mach3, calibration is relatively simple and fully automatic - but save the calibration then restart your computer. It seems to work better when it has digested the information.

915

General Mach Discussion / Re: upside down help

« on: February 02, 2008, 03:33:31 PM »

Andrew - are the setups for your machines(s) the same on both computers.

i.e. the active highs and the active lows.  To regenerate the cut pattern, Mach 3 literally runs through the  program quickly and writes the picture to the screen as per the signals it puts out to the motors - so if you don't have both set up identically they will appear differently.

I had this problem - because I write most of my programs on this computer - in my office - and then take what I need through to the workshop.  Particularly on mill, the picture appeared correct as I wrote it on this computer - in the workshop the machine promptly cut in reverse.

This is particularly apparent if you move the head of your miller, or move the table - the table has to move in the opposite direction to keep the cut moving as planned.

Jim.

916

General Mach Discussion / Re: Spindle RPM

« on: February 02, 2008, 03:21:45 PM »

Arthur - I seem to have this problem.  I take it you have done the spindle calibration on the automatic mode. This on my lathe then set the spindle moving at an increasing rate. It then came up satisfactory - save data  (or something similar) which I did. But the spindle speed still seemed to be about 10% up in my case. This I reckoned to be because my feed to my Omron Inverter scaled 0 - 12v instead of the asked for 0 - 10.

That seemed to be the case all the last session with the lathe, and although I was using G96, Constant surface speed mode, the actual speed seemed to be up on the asked for speed.  Today, when turning some little thing up, I set the speed using the speed DRO on the screen. I had reset the lathe with a G97 - The recorded speed was exact (within 2 rpm either way ) of the asked for speed of 800.

I don't know if the programming gang can comment on the apparent problem

917

General Mach Discussion / Re: Hooking up limits!

« on: February 01, 2008, 09:39:50 AM »

Yes - I'm sorry - and I assume since it does each axis seperately, it doesn't need to differentiate between the switches.

I had a bit of difficulty with mine, and needed to press reset after homing. They weren't in a good position anyway, so I've abandoned them for the time being. I particularly need something on the cross slide if I am going to use it for drilling, to get the drill(s) properly centered. I was thinking of some optical sensor with a slotted plate so I can stop at a choice of positions.

918

General Mach Discussion / Re: Initial Loading of g21 and Z axis absolute versus machine cordinates

« on: February 01, 2008, 09:21:40 AM »

Steve - there are some video tutorials covering the different types of co-ordinate systems.

To cover your points -
I do not see the difficulty in setting up your  machine for metric. The only important entry is the "steps per unit" since it is the only one that affects accuracy. If your leadscrew is imperial, then calculate the "steps per inch" say 48000 in my case, and simply divide by 25.4 to give you step per "mm". For the rest of the setting up (apart from backlash) a divider of 25 should do.

The machine keeps track of it's position in machine co-ordinates and when you home the machine, "ref all home" the machine moves to each home in turn - and zero's the machine co-ordinate. You can then move the machine to a better position for working either by jogging or using one of the g54 etc offsets.

If you have pre programmed the g54 etc offsets, then entering g54 as a command will add the offset to 0.0.0. (the home position) and the D.R.O.'s now show the offset position, so a move to 0.0.0 will move the table away from home to it's work position and all G Code commands will use the offset position as  a reference for 0.0.0, not the machine co-ordinates.

If you wish to move the table to a particular position - say for a tool change - regardless of where or what offset is in force, then you use a G53 command in front of G0. This instructs the machine to move to the machine co-ordinates position specified - this is also known as moving in absolute co-ordinates so as far as I know, machine and absolute co-ordinates are the same.

As far as you Z co-ordinates altering - check the entries in the fixtures table and see there are no stray entries in it. There is one intriguing box in the General Config - copy g59p253 to g54 on start-up - whatever that means.

To avoid changing to metric units, you might want to include G21 on initialization string on General Config before you swap - and see if it has the desired effect - although if you are working in metric, it would be better to have your machine set up in metric.

Yes - you set your limits up as per "machine co-ordinates"

What you seem to be saying, however is that you do not want "home" switches. You want to pick a position and call that home, zero the machine co-ordinates, and then set up all your other limits and offsets around this imaginary position. Yes Mach 3 does keep track of its position as it moves around, but unfortunately things conspire to put it off track. May be a stepper motor misses, a tool jams, etc etc. If this happens - you have no known reference to return the machine to, to pick up your correct position again, because - even if the tool is jammed and the stepper stops, the DROs will carry on counting becasue the computer is still putting out the necessary pulses.

All CNC machines must know where they are. They must start from some pre-determined place. One way is to have home switches. These, as you know, are physical switches that do not move - therefore if the machine references on these, it knows where it is.

On my lathe, however, my home switches are so far away, and speed of travel is so slow, this is not practical. So what I do is take a passing cut off the end of the work, and this position is Z0. I then measure the thickness of the bar and touch the tool up to this thickness - this is X (whatever thickness). The machine now knows where it is in relation to the work. If I am making several of the same part, I do not need to repeat this, because the machine knows where it is, but in case of accident, I can repeat the positioning accurately.

On the miller if I am machining a slab of metal, I touch the tool on the botton side and left hand side - and transfer these positions to the DRO's and again the machine knows where it is.

With any of these methods, if a tool jam, or a stepper misses or a bolt of lightening hits the machine, you can go back to a known position to start again.

I think this is enough diatribe so I will post and let you digest that first.

919

General Mach Discussion / Re: Hooking up limits!

« on: February 01, 2008, 07:51:57 AM »

Catch - yes you have the idea -

At the moment, all your limit switches are "off" - their contacts are open.(+5v to computer) Along comes the carriage - hits the limit and closes the switch.(0v to computer)

What you need to do is swap the terminals so that the limit switches are in fact "on" all the time (0v to computer) - along comes the carriage - hits the switch and opens it - 5v to computer. YOU NEEDN'T WORRY ABOUT THE 5 V - THE WIRING IS INTERNAL - THE LACK OF 0V READS AS 5V. Change the Active Low box to a cross and away you go.

It is fail safe, in that, if any wires come loose, the internal pull ups pull the signal to 5v and signal a limit is hit - you know it hasn't hit a limit - but it gives you a clue where to look.

The other advantage is, you can connect all the limit switches in series, and just use one wire as input to the computer - saving inputs (although this doesn't work if you are also using the limits as homing switches)

920

General Mach Discussion / Re: frustrated new guy

« on: January 31, 2008, 10:35:37 AM »

Re-reading this, you may be well ahead of me - (I don't have a scope) - but I remeber a post from a guy who was also using hobby CNC boards. The problem seemed to be with the earth, or more correctly 0volt line - and there were also some common lines that could be tied to either 0v or 5v.

The thing to ensure is that your computer has a good connection on the signal ground side, to your breakout board - i.e. one of pins 18 to 25 is tied to the 0v of your breakout board. There may be a jumper to do this if the pins are not readily available.

Best of luck - Jim