Messages

841

General Mach Discussion / Re: Cutting Circle / Hole

« on: March 08, 2008, 03:17:45 AM »

I started to reply to this last night but got my ********* in a twist trying to work it out. This is what I think happens.

This, I think is due to cutter width compensation.

The tool will start at X0 Y0 (which we will take as the centre of the circle). G42 is applied (which for a straight line effectively puts a - minus distance on the X and Y if required). The tool then moves to X2 Y0 to start the circle - it will actually move to X1.875 Y0 (allowing say 1/8 inch for a 1/4 inch cutter)

When describing a circle, GCode has to effectively errect a complete 1/8 barrier round the tool, because, unless it knows exactly which part of the tool is in contact (which takes some really serious maths (sorry Art if you have done it)) there is no other way of applying the offset.

We start to cut the circle, and the offset correctly applies the 1/8 barrier on the outside of the tool.
Unfortunately, as we get to X2 Y0 again, it is still applying it. It correctly stops at X1.875 but also applies it to the Y axis and stops at X1.875 Y-0.125.
Depending on how your GCode is written for each pass depends on whether the "shortage" gets over cut.
If the Code carries on and does another pass, it will be over cut, but say it retracts and goes to X0Y0, then comes out for another cut, the same "mistake" will apply.

842

General Mach Discussion / Re: Mach 3 limit switch overide

« on: March 07, 2008, 03:00:59 PM »

Look on the Mach 3 Settings page. You can set what you like there.

I suggest you have a look at the instructional videos which gives you details on how to set them. They have generally been enhanced on Mach3.

I do not know if you have doubled homing switches with limit switches.  You can do. However make sure the correct pin number is shown on BOTH the limit and the home switch. Mach 3 (if it knows it is going home) turns off the appropriate limit switch, and uses it as a home switch. What you are getting is a failure to do that - it is still acting as a limit.

As far as debounce is concerned, start with a fairly large setting say 200 and see what happens - it connot hurt anything. If everything works at that setting you could try reducing it, which might help with homing accuracy.

 

843

General Mach Discussion / Re: Testing LPT Port

« on: March 06, 2008, 02:39:23 PM »

As a matter of course, it is no good trying to test your LPT1 socket using the motor driver outputs. Since the outputs are pulsed, depending on speed, the voltage you see on the output pins will vary.

It is better to configure Mach 3 to put out M3, M4, M7 or M8 signals  to pins. These are constant signals, either on or off, and are much easier and more reliable to test.

844

General Mach Discussion / Re: Missing steps at 10 ipm? Taig, Mach3, Xylotex

« on: March 06, 2008, 02:27:41 PM »

I think some of the suggestions on here are superb, that's why it is such a good forum.

I'm going to throw my hat in the ring.

The problem is the computer !! I don't know what you mean when you say the machine is over running etc etc.

Any chance of borrowing another computer, loading Mach3 and plugging in the LPT! socket !!. You might as well start eliminating something, because all you are doing at the moment is altering things and getting nowhere.

Change the computer. If the problem is still with us, at least then, we know where to look.

845

General Mach Discussion / Re: usb to parallel

« on: March 06, 2008, 09:41:51 AM »

Yes - Mach 3 is simple, because it uses the parrallel port. I think that was what attracted me to it.

I have read your post again - and in the last two lines you are saying "The only SPEED issue is that if you use a USB and the associated and required external hardware then the USB must be able to send data fast enough that the SERIAL data can be parallelized in the same time as a parallel port could have sent it."

Perhaps we are coming from different angles - but that is what I was saying.
The PC collects date for the LPT1 port in three addresses. It amalgamates that into 17 lines of data and puts it out on the parrallel port. It is hard to know the internal workings of the CPU, but somewhere between 4 and no more than 8 moves would be required. For serial work, the same data has to be amalgamated, then moved to a buffer for one bit at a time for transmission. The transmitters I am familiar with only go at CPU clock speed. It follows, therefore that in simple terms the CPU will take at least 25 moves more to put out the data.

I must admit - and I know nothing of USB systems - if the CPU can put the parrallel data into a buffer, and then a seperate system moves the data serially at an enhanced rate - the the time difference may be small.

With the dissapearance of LPT1 ports, it would be a great benefit if someone could produce a USB2 to Parrallel output that could guarantee the speed and reliability of the LPT1. Even better if it had reversible pins. The plug and play type of connection could be a great enhancement.

846

General Mach Discussion / Re: 360 deg A Axis homing using an encoder

« on: March 06, 2008, 08:52:59 AM »

Why do you need positional feedback. If you set the Mach DRO to zero, it will keep track of where the axis is - if you are using stepper motors it simply counts and says I have moved so far and puts it up on the DRO.

If the A axis is rotating I don't know how many steps per unit you have it set on, or even what your units are, but that is easy enough, and if that is 360 degrees, then Mach 3 can put out the correct number of pulses to turn the wheel a known amount. Since it is rotary, you can have it set at anything - 10, 36, 100, 180, 360 etc. Mach 3 will keep track of this position on the A axis DRO in the units of your choosing.

The only thing you need to know is a zero position. You can either set this manually, before you start machining, which I find adequate for most of my machining, and providing you don't force the axis and loose steps, it is absolutely accurate,

I have no idea what a pizza wheel is - do you mean a rotary table - if so, you could use a reflective optical sensor on the side of the table. I used one on my spindle, the reflective part being a small "mirror" from my grand-daughters box of "stickies". It works perfectly and can be connected by a single wire to Mach 3.

847

General Mach Discussion / Re: BACKLASH COMPENSATION - FUNCTIONALITY - SUGGESTION

« on: March 06, 2008, 08:18:32 AM »

I agree with Graham that all possible backlash should be taken out of the mechanics of the machine, and with modern equipment zero backlash is nearly achievable.

There must always, however, in any mechanical system, be some space between the "bits" otherwise the whole thing would seize up although they can be so small as to be ignored.

As far as the two suggestions go, I agree with Brett - what can possibly have given rise to the idea backlash can be spread over the length of travel of the table. Backlash is not about movement. It is about the non - movement of the various parts as they settle in to begin to pull the pther way. This is why surely, in Mach 3, there is a quite distinctive difference in sound at the beginning of a move, as the backlash is applied - and you should certainly NOT see any movement in the table while this is happening.

848

General Mach Discussion / Re: Question around operation and parameters

« on: March 05, 2008, 01:23:09 PM »

I think it is a Wiki attached to this forum -
it is at

849

General Mach Discussion / Re: limit switch trouble

« on: March 05, 2008, 01:17:25 PM »

To put a stop to the argument -

All limit and home swtiches do, is send a signal to the computer. It makes absolutely no difference if they send a 5 volt signal or a 0v signal. The system will stiill work. Mach 3 can be configured in either way.

Neither does it make any difference if you wire all switches seperately, or in series to save pins, Mach 3 can accomodate them all.

However you do it, all you want is your table to stop when it hits a limit, or home to the same place every time when you hit home.

The only reason for saying  switches should be normally connected to 0v - and then pushed open to send the signal - i.e. using the internal pull up resistor to raise the line voltage to 5 volts is for safety. Should any of the wires break, or come loose, or the switches fail, then the system will signal a limit switch open, and stop, before any other damage is caused. I don't think, in my case it would cause much bother at the speeds I travel, but some of these big fast rigs could cause a bit of damage if they didn't stop when they were supposed to.

I looked through this earlier, and couldn't understand the diagram - have you seperate switches for limit and home - it would appear so from your description. This is not necessary since one switch can double up as a limit and a home switch - the computer knows what to do, and it saves you inputs - but if it is working, don't touch it - the main thing is it is working.

You should not, now, need to touch your limits again. You can set your soft limits just inboard of your physical switches, and your table shouldn't go anywhere near them.

I must admit I found my home switches (allied with the limit switches) in a most inconvenient place, so I am now working on a laser homing device to put my table somewhere useful.

850

General Mach Discussion / Re: Question around operation and parameters

« on: March 04, 2008, 02:30:20 PM »

My list shows that  "SetCurrentTool"(Tool  as byte) is a subroutine, not a function.