Messages

1181

General Mach Discussion / Re: Spindle relay

« on: August 04, 2007, 05:20:35 AM »

Getting the parrallel port to drive relays is fairly easy. 
The books I have are fairly old hat now, but more modern transistors can be used. I am looking at the design now - which is a BC 549 transistor, fastened to ground, with a relay up to a 12 volt line.  It is driven by the 5 volt signal ( or in actual fact the 0v signal ) from the parrallel port via a 2K2 resistor There is a diode across the relay pins (to protect against voltage spikes etc and a 3K9 resistor base to ground. Only four components.
I had suitable values in my bits box to knock up two similar circuits for the spindle motor pins. I have a resistor to cut the 24 volt power supply for my stepper circuits to 12 volt of these relays - and since only one of these is on at once, one resistor is enough for that.The relay outputs go to my Omron inverter.
I can repeat this for the coolant relays - with the advantage that the seperate circuits are completely isolated from one another - via the relays.

1182

General Mach Discussion / Re: spindle encoder?/

« on: August 04, 2007, 04:57:11 AM »

I looked as well and couldn't find the number quoted - can anybody enlighten us

1183

General Mach Discussion / Re: Z axis design and Mach3 control

« on: August 04, 2007, 04:44:24 AM »

If you look at the video tutorials, there is a section on scripting, where you can write your own logic and scripts to activate or do various things in response to input buttons being pressed. You do not need to use the coolant or spindle relay outsputs, in fact these are just output pins that have been configured by Mach 3 to be coolant and spindle pins.

As far as I understand the tutorials, you can configure the pins and write your own logic to make any pin do what you want.

1184

General Mach Discussion / Re: Lathe Threading With Backlash

« on: August 03, 2007, 04:43:55 AM »

Whilst I don't fully understand which chamfer it is you want to cut, surely this must be a problem for CNC machines. On a manual lathe, where movement of the tool is mechanically tied to the spindle, the practice was to stop the spindle (which stopped the tool in the right proportional position) and then withdraw the tool. Cutting should always take place in the same direction, because of backlash.

On a CNC lathe where normally the spindle fires up before the tool is in position, or the tool is withdrawn with the spindle still turning, you will get a circular cut, unless you float the tool off the thread and loose the depth of the cut. I would have thought, therefore, you must start the lathe off the workpiece to allow both spindle and tool to get to the corrct speeds and then come into the workpiece on the move, so to speak, but then when you copme to withdraw the tool at the other end of the thread, either float off or suffer a circular cut. Which ever you use, you must always cut in the same direction.

1185

General Mach Discussion / Re: spindle encoder?/

« on: August 03, 2007, 04:21:34 AM »

If you look at the video tutorials, Artsoft say that a one pulse per rev encoder is sufficiently accurate and recommend something similar to the Omron SD 5B.

1186

General Mach Discussion / Re: Scary depth

« on: August 03, 2007, 04:18:08 AM »

Can you read the G code and find out if the program as written is dong this or not. I assume this is your Z axis, and you should be able to decipher where it is told to move down to. Then you know where to start looking.

If it is not your program, then it must either be that your start position ( i.e. the starting height of your tool is incorrectly set or not zeroed, whatever, to match your program start position) or as you say, it is the tool offsets.

The tool offsets you can cancel and try again without them and see if there is any difference. Most of my difficulties have been - either the workpiece is not where the machine thinks it is, or my machine was not zeroed in before the start.

1187

General Mach Discussion / Re: USB output board instead of printer board

« on: August 03, 2007, 03:59:16 AM »

As far as I understand Artsofts reasoning, only the 25 pin PARRALLEL printer port is fast enough to provide the control signals to your machine, particularly when moving several axis simultaneously, to maintain the accuracy of what you are cutting. If you imagine a circle (or a sphere even moreso) all axis are continually moving but also continously changing speed, and a parrallel port is capable of doing this.

USB and other serial connectors have to convert the many bits of data into a stream of information, which all has to run at the same speed (by definition) and may miss the subtle timings of signals to your stepper drivers. Serial connections are OK I woud imagine for switches for limits, motor, coolant etc but not for the business end.

It may be that there is available a serial connection working at such a fast speed that these difficulties can be overcome, but I haven't seen any sign of it yet from Artsoft.

The printer port is only three addresses (suitably buffered) on the internal parrallel bus of the computer &H278,279,27A  or &H378,379,37A the first address handling the 8 main data pins, the second address handling the 5 input pins and the third one the 4 other output pins, so as we know, you can get parrallel port cards to fit into your computer - yes - they are called second printer ports at the moment - maybe they will become just a parrallel port card in future, with perhaps say 16 inputs, 16 outputs - all addressable.

I dont know whether Artsoft will comment on this, but, yes, it would be nice to know, or obtain advice on which way to go.

1188

General Mach Discussion / Re: Help with acceleration and speed settings

« on: August 02, 2007, 04:34:24 AM »

I don't know what the current reduction does on your 201's

On my boards I can reduce the current to STATIC motors to reduce current on the system generally when the motors are just stood, but this does not apply when they are moving.

1189

General Mach Discussion / Re: Step losses in specific displacement

« on: August 02, 2007, 04:30:16 AM »

I don't know a lot about power supplies, but the reason I use batteries is that the voltage stays constant, both when the motors are on ( and if all three are on together they could pull 7.5 amps) but also when they are off, the voltage does not rise above24 volts ( as I have found with a lot of transformer based power supplies, unless properly regulated).

My stepper motor boards  by Stepmaster says specifically that supply voltage should not rise above 30 volts (against a working voltage of 24)

1190

General Mach Discussion / Re: Spindle relay

« on: August 02, 2007, 04:23:00 AM »

Brian - I don't know whether that was aimed at me - I don't have one. I got an old printer lead and identified all the wires in it with the pin numbers and soldered them, in order, on a small piece of copper clad stripboard.

The wires to the stepper motor drives go directly to those boards. The other functions I make the circuit up as required. At the moment it is just the two spindle relays for M3 and M4 commands. I have to do the coolant relays next.

I don't know how to stick a picture on this forum, or I could put one up.