Messages

1111

General Mach Discussion / Re: Mach3 and Boxford Duet

« on: September 05, 2007, 07:53:26 AM »

If they are stepper motor driven, just change the stepper driver boards for a modern version.

Mine are Stepmaster - got them on Ebay - they came from the States. The run up to 2.5 amps at 30 volts, they are fully adjustable and wire directly to the printer port of your P.C. to be controlled from Mach3. They worked straight from the box with comprehensive instructions and  wiring diagrams for different motors.

I think Boxford were made in Huddersfield - which is 10 miles from me, but I never had one.

New cards run at about £30 per axis.

You can get moroe powerful boards for 4 or 6 amps - there is a British supplier on Ebay as well.

1112

General Mach Discussion / Re: Mach 3 won't jog with keyboard

« on: September 05, 2007, 07:44:15 AM »

In one of the tutorials Art mentions that jogging is switched off on some of the screens so that  you do not accidently jog the machine out of position once it is set up. This is because ( I think) jogging only affects one set of co-ordinates, and if you have set other co-ords, or are not running in machine co-ords, the two sets will get out of reference with each other.

On my Turn program, jogging works only on the "Manual" page as you are setting your work up. Once you move page, say to input code directly to the machine via the key board, or to enter and run a program, jog will not work.

On my Mill program, as far as I can remember, jogging only works on screen 1

1113

General Mach Discussion / Re: phase drive control

« on: September 05, 2007, 07:30:08 AM »

 I think Art tried to make the interface as easy as possible - and it is all designed to run via a 25 pin printer port. The outputs and inputs to that port are limited - I just forget the actual numbers but there are something like 14 output lines and 5 input lines. The other six are common return wires.

They are arranged in three seperate addresses in the computer, one with 8 lines, one with 6 lines and one with 5 lines.

If you use an external stepper driver board, each motor only requires two wires and a return, so using the eight line address you can drive four motors which are three axis and maybe a rotary table or someother equipment.
You would like to run the spindle motor M3 M4 and M5 (forward, backwards and stop) which takes two wires of the second address, and maybe the coolant which takes another two wires.
On the input side you need limit switches, homing switches and motor speed reading wires.

I don't mean to be unkind to Art, but the programming is also easier if you only have to put out step and direction pulses, and as has been said, step and direction are a standard which can be used by other applications

If you think of it that way, the 25 wires of the printer port are soon taken up.

If you are driving motors direct from the printer port (apart from needing some sort of interface because the port is not powerful enough to do it directly) you need 4, 6 or 8 wires to drive one motor. You run out of wires very quickly - you would need 12 just to drive three axis, which would only leave you 2 to drive all the other things you might want.

Since you need some sort of power amplifier anyway, you might as well get a driver board, which has all the on board electronics in it to control current, shut down if over heated, drive different types of motor etc. It will not cost any more - and only uses two wires per motor !!

1114

General Mach Discussion / Re: online tutorials

« on: September 05, 2007, 07:07:50 AM »

Sorry - I don't have that one saved - and as you know, I can't save the new format - sorry.

1115

General Mach Discussion / Re: Lost Step on complex program

« on: September 04, 2007, 04:00:58 PM »

From that I doubt the first 10 - 15 are the same - it is just that you can't measure it. Also the fault appears to get worse the more repetitions you do - as though the fault compounds itself.

I cannot think of a simple explanation, because I do not know how the maths stacks up. I know Art in the tutorials says Mach3 works to over 12 decimal places.

The only explanation I can come up with is that when rounding up or down you must make an approximation. If you start from a position of X1 Y1, then after the first sequence the final position might be X 1.000086324874 Y1.000000986362. These might be small enough not to move the steppers an extra step.

If we set off again (without resetting the DRO) then all calculations start from the new position (not X1 Y1) and it may be eventually they trigger off extra steps (or a missing step) in the movement.

I do not think Art would have the DRO's go to zero, because as far as the machine knows it is where it should be.

If at the end of each phase of your test piece (when you are back to where you started) you add in a line G0 X1 Y1 this would reset the DRO's to the original reading. The axis would not move because the amount is too small, but calculations would still start from the same position everytime. It might even be better to include this at the start.

Try this and see if it cures the circular problem - I would be interested to find out.

1116

General Mach Discussion / Re: Constant velocity

« on: September 04, 2007, 03:21:52 PM »

Brian - Thanks for that, I was begining to get the old grey matter working on the maths.

Is there any chance of a tutorial?? They do help, especially when you don't necessarily understand it fully without a bit of experimenting.

Jim

1117

General Mach Discussion / Re: Constant velocity

« on: September 04, 2007, 09:50:50 AM »

As far as the puzzle is concerned - surely  Andreas is correct in his findings, but is trying to achieve somethings that cannot be achieved.

Either the machine is in constant velocity or it stops. The problem is that the milling head (at a right angle) must instantaneously change from one direction to another.

 You cannot do that instantaneously

The head must either decelerate to a stop in one direction, and after it has stopped accelerate up to speed in the other - OR -
as it decelerates in one direction it starts to accelerate in the other (in which case you get a rounding of the corner).

If you have set the machine to stop it will ensure it has stopped in every direction before in moves to the next one, or, in constant velocity mode there will be a smooth transition from the speed in one direction to the speed in the other.

I do not see how the software can interpret what you want, unless you tell it, therefore you can make settings for  the norm, for example, constant velocity, but you would then have to tell the machine if you required anything different for a particular corner.

I must admit, now that you have brought it up - it would be nice to have a tutorial on this aspect of how the machine functions. It would appear that it may be possible to set an angle where a change takes place between Cv and exact stop - I do not know. Try setting the "Stop CV on angle" at 91 so that it includes your 90 angle, and it may do what you want.

1118

General Mach Discussion / Re: Constant velocity

« on: September 04, 2007, 08:43:58 AM »

Thanks Hood -
That is what I meant - so, as you say I must be in constant velocity mode, because it certainly doesn't hesitate when it comes to the corners. Having said that, my feed rate is not very high - so maybe it still has planty of time to think !!!

1119

General Mach Discussion / Re: Finally Ready to CNC

« on: September 04, 2007, 08:36:42 AM »

I take it the Mill is as per the pictures, but is just manual at the moment. The write up tells you basically what they have done. It does not give you, however, any specs for the finished mill, such at table speeds etc, so just what the performance is, I wouldn't know.

If you are looking to convert your mill into a CNC machine for as little as possible, I would personally use stepper motors instead of servos. The driver boards can be connected directly to your breakout board (or even directly to your computer port) and give excellent performance. You do not need to bother about feedback.

I am in UK so cannot give you any idea where to buy you motors - but mine ( for a similar sized machine 5" lathe with a large milling head) are 220 Ncm. They have a 12mm through shaft. I have mine connected to the lathe with toothed belts, giving a 3 to 1 reduction as per the photograph. This was the simplest way I could devise to fit them on.

Looking at the photos of your mill, the firm seem to have done something similar with their servos.

The motors are driven by Stepmaster drives. These are American, I got them on Ebay. They cost about £30 each ($60) but I imagine you can get them cheaper over there. They are rated at 2.5amps, fully adjustable and come complete with a comprehensive wiring diagram.
I run them using 24 volts from two leisure batteries that I happened to have

I did not bother with a breakout board. The Stepmasters are run direct from the printer port - (three wires per drive - step, direction and common). I built a small driver board to trip two relays from the printer port to control the spindle and I have control of M3, M4 and M5. Speed I have to control manually from the Omron inverter (which I was given by my brother-in-law) I am working on speed control using a servo run by the pwm output from Mach3.

The relay board I am going to rebuild using a single ic Darlington array to drive 4 relays - two for the motor, but also two for coolant control.

I still have all the input wires to go at and I will probably try to fit some sort of reference device, so that the lathe/mill can reference itself if need be. I do not see the need for Estop limits - you can set the soft limits on Mach3.

The whole thing has cost me £200 ($400) so far, and I am very satisfied. I have turned handrail stanchions on the lath, and cut window spaces (with rounded corners) using the milling head (these are 4 inches by 3 inches) and both these are jobs that I simply could not do manually, without a lot of additional tools.

Not quite the $199 or whatever Art says, but very, very cost effective and satisfying.

1120

General Mach Discussion / Re: online tutorials

« on: September 04, 2007, 07:46:15 AM »

which ones do you want ??