Messages

391

General Mach Discussion / Re: Problems with Parallel Port inputs on Motherboard

« on: July 29, 2008, 04:13:50 AM »

The LPT port addresses, LPT1 and LPT2 are, in actual fact, three addresses each in the PC.

LPT1 is &H378, &H379 and &H37A, LPT2 is &H2278,279 and 27A

378 and 278 are the OUTPUTS for lines 2 - 9 on the 25 pin port (the old printer data pins). 379 and 279 bits  3 - 7 are the 5 input lines( pins 15,13,12,10 and 11 - note the order)(see later) and 37A and 27A, bits 0 - 3 are the other output pins, 1,14,16 and 17. Pins 18 to 25 on the port are signal return (0v) connections to the computer.

The LPT1 port was normally in built in the motherboard of the computer and therefore the input/output capabilities are fixed, whereas a second port if added as a plug in COULD have bi-directional capabilities, depending on the board.

If your LPT1 port is buit in, there is no point testing it - you cannot change it - but you seem to be saying that you can changes the input/output capabilities - so are you using two plug in ports, or is your first one fixed and the second one a plug in.

I have never seen the need to muck about with my computers BIOS. If your computer is working properly (and I like the touch screen, I have one on my organ simulator) then the basic operating system - to be compatible with the IBM PC format - should already have at least the LPT1 port properly addressed and formatted.

If the port is an add on, and you have the axis and spindle working, then it would seem to me that your port card is switchable, and you have the input pins designated as outputs, so although the card is seeing the inputs, in is not passing them to the computer.

I think that is all I can say at the moment till you have another "fiddle" with it.

In Mach 3 set your port one address at 378. If your switches are live, then go to the Mach 3 diagnostics screen and see what the led.s show for activity on the port. They light up if an active signal is detected so toggle the switches and see what happens.

If you use your port test program and that is telling you that the inputs are being detected when you switch them manually, and the led,s on Mach are not showing then your configuration file on Config/Ports and Pins/ Input Signals needs  attention. The favorite thing  on that page that I kept missing was the port number !!!

392

General Mach Discussion / Re: Progressive Move Error with X and Y

« on: July 28, 2008, 02:02:56 PM »

I agree with Overloaded that it is a good idea to reference reasonably often - Mach 3 has no feedback, and therefore if an error occurs it will continue to show.

The only thing I can think of is that there is a difference between drivers that require a positiove voltage and those that require a negative voltage. I dont know how they work, but if they fire when they see a positive or negative going voltage, then there will be a difference whether you have selected "active low" or "active high". If you have a pulse figure between 1 and 5 ms then fine, the difference is not going to be great - but is the Sheerline a 50 50 pulse - in which case there would be a timing difference. I don't see a great difference if your steps per unit are high, but if they are low then this could show.

Does anybody know how stepper motors react to microsteps. I know that manufacturers will not guarantee these positions - but say a motor is called to halt at a position the is 3 or 4 microsteps from its full step position - can we guarantee they will hold that psotion until the next time they move. I don't know - but I would like to

393

General Mach Discussion / Re: Limiting motor acceleration

« on: July 28, 2008, 01:27:11 PM »

We are getting a bit off the post here - Yes - I think Mach 3 is the best thing since sliced bread ( to coin a phrase). It let me convert a lathe/mill into a CNC machine for a very small price. It is, as far as I can see, complete in evey way, and opened up a whole new approach to my machining. I was getting a lot of my stuff done professionally - in steel and in plastic - and I am capable of doing this at home now (if my machine is good enough). At least I can understand what the CNC guys are on about.

I haven't run up against a limit with the download version - and being from Yorkshire is like being a Scotsman with no arms, we don't like spending money if it is not necessary.

Now another short coming is threading - I think - and I want to have a go at that sometime - at the moment I have a good range of taps and dies - .

Yes - you are right - when the shortcomings start limiting my work I will gladly pay my money for what I consider to be a superb product.

In a post reply to Ftec -
Yes - Mach 3 can be set to any acceleration - and the ones you are quoting are at the bottom end of the scale.

394

General Mach Discussion / Re: Simulating around subroutines

« on: July 28, 2008, 01:14:28 PM »

What might be a logical place to you to start the program, is not necessarily a logical place for the computer to start the program.

It is all to do with whether or not the computer can properly work out the precise position (in machine co-ordinates) in the line.
It may be that using a subroutine necessarily denies it that function, unless it goes through the sub-routine to work out the final position.

In such circumstances I have often included a "positioning" line which doesn't mean much, because the computer is probably already there (and so ignores it), but when doing a run from here it is a place where the computer can get a finite position.

This is fairly important when you are using longs lines of GCode which only have one reference position, or have no command code (because it is global) and the computer has to back track to find the finite place it can tell what it was it was supposed to be doing.

395

General Mach Discussion / Re: Limiting motor acceleration

« on: July 28, 2008, 12:52:00 PM »

O.K. - I'm sorry - 

396

General Mach Discussion / Re: input diagnostics

« on: July 27, 2008, 01:55:39 PM »

Can you just expain what you have connected to this system.

Are your home and limit switches connected and wired. What is this kit that you have bought to wire the three switches.

Quite simply you do not need all this **** to get started, so I think you are getting too complcated without any reason.

What are you trying to do.

As far as I can see it is just to zero your axis, and then run a program.

If this is the case, just say so and we can tell you what to do - indeed it is so simple, I will tell you what to do now.

Make sure you machine is in "program co-ordinates" - see my previous post - press the "Machine Co-ordinates button until the surround led goes out. Then jog the machine to the place where you want your program 0.0.0 and reset all the DRO's to zero.
Providing your program does not zoom off to some silly co-ordinate to start with, if you press cycle start, then the program should run.

You must make sure your parameters in the program do not run off the table extremeties - but other than that it should cut.

If you have used some sort of kit for your limit and home switches it may take a bit of time to get them sorted, but for now disable all the pins for them - you can run without them. You can get them going "when you feel the need for them"

397

General Mach Discussion / Re: Hardware suggestions?

« on: July 27, 2008, 01:13:33 PM »

And - where are you based.

It is supposed to be a global market, but some things are easier to get in some places than others.

398

General Mach Discussion / Re: Limiting motor acceleration

« on: July 27, 2008, 01:10:14 PM »

I keep saying I will get shot for this - but you do not need to buy Mach 3 .

The free downlaod version will get you 95 % of features of the purchased one - certanly enough to get you going and  try - for nothing.

I am still using the free downlaod version. The only major difference between the two is that the free version is limited to 500 lines of code - and I have never come up against that barrier.

399

General Mach Discussion / Re: UK CNC Convention.

« on: July 27, 2008, 12:57:15 PM »

The picture I use is one of my Great Northern electric engine (circa 1904) - but it is after I sold it to the chap driving it, hence the caption.

As far as the convention is concerned - where are all the lads staying. Are they in Hotels or being put up by other people.

I am coming down for the Monday and Tuesday - I have a two day pass from the wife - and we run the railway at the week end so that is out. I have a two day ticket so thought I would come down on Sunday evening. I have no idea of hotels in the area, so if anybody can tell me where everybody else is, I would be happy to know.

400

General Mach Discussion / Re: Taig Mill not that precise Please Help

« on: July 27, 2008, 04:15:01 AM »

Are you saying that some of your moves are 20 thou of an inch out, which is how I am reading it. We have jet engines over on this side of the pond, a local firm in Barnsley (of all places) markets them - and they are looking for accuracy down to 1 thou.

I think - instead of messing about with bit and pieces, if you are to get down to the accuracy required, you will have to set out a plan and stick to it, otherwise you will do one bit, and it will upset another.

The first thing, as has been said, is to check the gibs on your table. Depending on where the table is pushed or pulled, if the gibs are slack then the table will "lurch" as it changes direction. On my lathe, it lurched on the Zaxis, and affected the X axis diameter it was cutting. If you have not done gibs before, by all means read up on them, but they are relatively simple - a series of screws pushes a metal plate in, against the running surface of the table, taking up the slack. Unfasten the locknuts, and (mine have an allen key) gently tighten the inner screw up - not tight, just take up the slack and a fraction more. Tighten the locking nut again (without allowing the inner screw to move).

It is a bit difficult to measure the effect of this, but if all is nicely "gibbed up" movement of one axis should not alter the setting of the other, particularly on a change of direction, but you should still retain smooth, even movement. Be careful on the table extremeties, where there is less wear, becasue it is easy to overtighten these and cause the table to stick or at least loose steps.

The next thing is to set your steps per unit correctly. This does not mean measuring anything - it means calculating (sorry BobShop - I do not use the Mach 3 function - it is open to inaccuracy). The calculation is simple - (motor steps per rev) multiplied by (microsteps - see drive) multiplied by (gearing - direct drive = 1) multiplied by (pitch of leadscrew). This should round off at a simple number (unless your leadscrew is something you picked up on a second hand stall) - mine is 60,000 - 200(motor) x 10(Gecko microsteps) x 3(gearing) x 10 (leadscrew 10 turns per inch), You can see from this I have 60 steps to 1 thou of movement - which is good for accuracy. You may not have the gearing so you might be down to 20,000 - still 20 per thou, (although you cannot guarantee the accuracy of microsteps)

Once you have done this you can test your movement. With a digital caliper, you can test the movement of you table over say 6 ins, using the MDI. move to the right, zero your DRO's, then with the MDI go in 1 inch steps to the right and check each distance. They should be accurate to within say 2 thou. The purists will say this is not good enough - but, quite frankly, I defy them to measure any more accurately with a caliper. The "error" if any should be consistant (+ - 2 thou)  throughout the length. If it is consistantly accruing  or loosing thous as it goes along - then there is a fault - and this is probably in your leadscew - all other things being simple numbers.
If this is the case, then (and only then) can you try making small adjustments to your steps per inch to correct the matter. This is extremly rare, and really I do not like even mentioning it, becasue it confuses the issue.

The above measurements can be taken with the "backlash compensation" on or off, but to adjust for backlash you need the compensation OFF.
It is very simple. Starting at 0.0 - on the MDI go to X1 (to get rid of backlash). Set up your caliper and zero the DRO's. Do a G1 on a low Feed Rate say 4 inch per min and go X2 then X1. In theory the table will move right then move left and be at the starting point. It will not be and you can read the distance on your calipers. The missing distance is the number of steps that the gearing and leadscrew took to get their shoulders ready to push the table the other way. You can, if you wish repeat this and take an average - since you are measuring - but if you are careful one will do. This is the backlash compensation and should be entered in the backlash table and compensation switched on. If you do averages - do not forget the initial move to get rid of backlash each time.
The only things about backlash is that it will not be consistant over the length of the table because of mechanical wear. If you job entails you using one particular part of the table, then measure the backlash over that part for better accuracy for that job.

You should find now that you can move your table up, down, in and out to a good accuracy - and it is worth taking the time to do this, becasue you can sit down and machine something with a bit of confidence.

This has nearly taken longer to write than to do it - except maybe for the gibs. My table is accurate to a thou (and you want to see my backlash) and I regularly machine steel to within a thousanth of size - i.e. fitting a wheel on an axle requires a two thou gap for the glue.

The other "trick" when machining parts to a fine accuracy is to, as we used to do manually before a computer did it for us, always do the cutting move in the same direction - i,e, run back a little over, then come in again from the same direction every time, not just run back to the spot and start machining. This makes sure that any innacuracies still in the system always happen (or dont happen) on every cut. It dosen't matter which, as long as you are consistant.

Somebody also put in another post that mills are not as accurate as lathes - and I do not know the Taig machine so you may have to be especially considerate to good machining practise to get the accuracy you seek, but good luck.If you already know most of this I apologise - once I get typing I don't know when to stop.

If the household authorities were more forthcoming then I would love to have a go at a little 7 H.P. turbo prop engine - coupled to a 175 amp 24 volt generator - which would make a fine basis for a gas turbine locomotive - and be totally authentic. I have the generator - now..............................