Messages

851

General Mach Discussion / Re: Feed Rate

« on: March 04, 2008, 02:02:22 PM »

Since you haven't posted your program, it is a bit difficult to know what the problem is.

The tool will move at different speeds.

G0 is the fast traverse so G0 X10 Y1 will move the tool as fast as it can from here to there. The speed is dependent on the axis motor setting on Config. You should spend a bit of time on these and increase the speed as much as you can, consistant with reliable travel. If you try and move too fast, the motor will stall. Try increasing the acceleratio, to make it a bit quicker off the mark.

G1 is what one might call cutting speed. G1 calls are affected by the F command which is feedrate, and you can put any speed in here (although there is no point going above your maximum for G0, because the machine won't do it)

so G1 F2 X1Y4 is move at feedrate of 2 inches per min to X1Y4.

Feedrate is I think, global, so you can set it at the beginning of the program and it will  stay at that til altered. In your intro include the command G94 which is move in units per minute for feedrate.

One problem I have found is if you are set in inches and you move to metric - the feedrate does not alter but stays at the figure set - but unfortunately moves to millimeters instead of inches, so if you do alter your units, you must alter your feedrate to compensate.

852

General Mach Discussion / Re: Tell me where to get ball screws in UK

« on: March 04, 2008, 06:26:57 AM »

Yes - the lead screw is 20mm, and I don't think I want to go below that - I'm trying to get a bit more speed out of it, as well as get rid of backlash.  It would do for the cross slide, however, that is thinner.

Phil H's Motion Control site looked promising. I have an engine to finish for a customer before Easter then I will have a serious look at it.

853

General Mach Discussion / Re: Backlash problem, possible solution?

« on: March 04, 2008, 04:31:56 AM »

You seem to be making heavy weather of this.

Why are you trying to do both axis at once !!

Backlash is a simple problem - put your cross slide, or carriage in it's most used position. and zero all DRO's.
Ensure backlash compensation is turned OFF
Type in G0 X1. Fix your measuring instrument to measure the position of the carriage and zero it. I use digital calipers. Type in G0 X2 and check the carriage has moved 1 inch - it should have if your pulses per unit are correct. Type in G0 X1 - move the carriage back one inch and check the readout.  It should be 0, but will not be - this is the amount of backlash.

Repeat for the other axis.

You can, if you want, do this several times and take an average.

Enter the backlash figure in the table and turn on backlash compensation. Run the test again, and the carriage should return back to zero.If it does not - and say you get a reading of 2 thou - you can add this figure to the backlash compensation, until you find zero.

YOU MUST MOVE THE TABLE TO THE LEFT and then move it right before setting your zero position after each run (to eliminate backlash)
If you are using millimeters then chose a convenient number of milimeters, say 30  - remember, however - the back lash will still read directly, you do not need to divide by 30.

Backlash has nothing to do with the distance the table is travelling. It is only the movement (or NON-movement) of the table, whilst the gears, leadscrew and ball nut settle to the job of pulling the other way.

If you are having trouble because your table is not moving the correct distance, this is all to do with pulses per unit - not backlash.
In measuring distance, you must ensure your table always moves the same way - i.e. to the right - stop - to the right again - stop - measure - until you get pulses per unit and backlash correctly set.

You do not need to move the table great distances to set backlash and pulses per unit. If they move accurately over one inch or, say, 25 mm then they will be accurate over the travel of the table (although this does not rule out the possibility of some other minor fault causing you to loose steps)

854

General Mach Discussion / Re: Tell me where to get ball screws in UK

« on: March 04, 2008, 03:52:50 AM »

Thanks for the replies - plenty to go at there !!!

855

General Mach Discussion / Re: Animatics motors?????????

« on: March 04, 2008, 03:10:41 AM »

I don't think you are a "beginner" then, clearly the engineering side of building the machine is no problem.

I will go along with Hood (having read your post) - if the motors are there gathering dust, use them. As far as I read the Animatics web site, your motors do not need drivers, they are all built in, so it is just a matter of working out which input to use. Do you have any documentation with them that could give you a clue???

856

General Mach Discussion / Re: Can someone review my code adn explain M01

« on: March 04, 2008, 02:55:52 AM »

Learning GCode is a bit like learning mental arithmatic.  If you don't know anything about it, how do you know when the machine has gone wrong.

If you Google GCode there are one or two sites that will give you an idea of the rules of GCode. However - it isn't that difficult to get started. G0 moves you in a straight line from here to your new destination, G1 does the same at cutting speed, G2 and G3 move you in a circle at cutting speed. That is all there is to it and with those four instructions, you can write all the programs you need.

As Hood said, your problem is not with the code but with the settings, and the main problem with all programming is starting at a position that everybody knows. Start the machine at position 0,0 with all offsets cancelled and away you go. Practise writing a few moves your self, or a short program. Leave the cutting tool out and watch the machine trace out what you have written. Another thing I do with some of the complicated bits is to put a piece of soft material - pine or soft plastic - and let my machine chew that up, rather than damage it on steel.

If you study the rest of the GCode list on Mach 3 you will find that the rest of the instructions are mostly to do with offsets and different drilling patterns - but the basic four movements are all you need.

Have a go - you can't hurt the machine - and you can't hurt Mach 3. You can, by the way, write a program and run it in  Mach 3 without the machine attached. This, with the toolpath display, is an excellent feature that lets you see what the machine would cut before you even attach it. I use this feature on my office computer to check programs before going throuh to the workshop.

857

General Mach Discussion / Tell me where to get ball screws in UK

« on: March 03, 2008, 01:48:16 PM »

My lathe was relatively cheap, and suffers from a large amount of backlash on both axis. This was fine when I was only using it manually, but it does suffer now it is CNC.

Can anybody tell me where to get new leadscrews etc - preferably ball screws in the UK.

My lathe is a large Warco.

858

General Mach Discussion / Re: Animatics motors?????????

« on: March 03, 2008, 01:33:56 PM »

I have looked at the web site, and I am afraid it does not say alot. I will bow to Overloaded's view if he has had experience with them.

I am afraid from my point of view that - if you are a beginner - then they are far too complex for you. The traditional system (which I would recommend to a learner) is a computer - and you are having a bit of difficulty with that so far, a set of drivers (which normally come about £30 per axis) and stepper motors. I bought mine for £40 each from Arc Euro Trade.

I cannot remember now whether you were doing a lathe or a miller.

The advantage of these simple units is that, to test them, you can set up one, run it, GCode it etc etc. When you know that is correct, then the second and third axis are only more of the same. There is a three wire connection from your computer to your driver and a four wire connection from your driver to your motor. Nothing could be much simpler and if you can't get it to work, your are wasting your time.

As you advance, you put all your drivers in one box - may be with a 25 pin breakout board, and you do all the wiring in the box - power supplies, fuses etc. All you then have to wire is the 25 pin lead to the box (buy a printer cable) and then wire each motor to its driver - I used flat 10amp loudspeaker cable (four core) and 4 pin din lockable plugs and sockets.

The whole system is easy to see, easy to test, and if any single part goes wrong it is easy to identify and replace. Since all the parts are standard, you can swap them about to fault find quite easily.

The motors you identified listed about 6 different ways of wiring to them - fine, but you will never use them, so why pay for them. They listed in built drivers - fine, but if the motor or the driver goes, then it is all to replace, not just the part that has failed.

I built my system in three days, from receiving the motors and driver cards - including working out some way to drive the axis from the motors and for £200 I had a three axis CNC system (my lathe has a milling head). I later blew the drivers ( I think by connecting the power supply wrongly) but at least only the three drivers needed replacement. The system still works. I am adding limit switches and home switches etc etc  as I feel the need.

Take my tip - keep it simple until you have it up and running. You could do with some sort of breaxout board to test your PCMCIA - printer port adaptor. You can test this without a machine attached, and then go from there bit by bit.

If you already have the motors, fair enough - are they powerful enough to do the work !!








 

859

General Mach Discussion / Re: usb to parallel

« on: March 03, 2008, 01:04:49 PM »

Why use the name of your cat???

From one Jim to another - yes Stirling has the nub of it - you can use a serial connection if it can send the information fast enough - and in this case we are talking about 16 times or more faster that the parrallel port.

I got a pcmcia adaptor the other day for my laptop to try and get a USB 2 output to run a camera - it failed miserably. I hope you have more luck - I take it it is a PPMCIA to parrallel port card. It could work - best of luck.

860

General Mach Discussion / Re: usb to parallel

« on: March 02, 2008, 03:10:39 PM »

You are not giving us much of a clue.

What machine - lathe, mill etc have you got, what drivers and more important - what laptop.

When this project first started, the output to the machine was via the parallel port - LPT1, principally because this port was faster, and could keep up with the fast response needed for a CNC system. The system could support a serial port for some of the slower responses.

I run my system from a laptop - but I am lucky - my Toshiba laptop has a parallel printer port - and runs from a 5 volt system. A lot of modern laptops have no LPT1 and only a 3.5 volt system.

What output have you got from the USB - is it USB2 - how does it fan out. To drive the various stepper motors and switches you need about 16 outputs and maybe 8 inputs - so you need a 24 port card, that is as fast as the old LPT1.