Messages

601

General Mach Discussion / Re: Setting Z Axis Origin height from the Mill table

« on: May 13, 2008, 02:20:41 AM »

Simple - flip the "dir" pin on your Z axis to "active low" (or if it on active low, then "unflip" it)

The Z axis should be negative going down and positive going up.

I have no doubt the vendor made the correct connections etc for your mill, but Mach 3 has a lot of configuration still for you to do. You should also check - althougn it appears you have - that your other axis are going it the right direction. This is one of the fundamentals, and a lot of other stuff follows on - i.e. jogging, homing, etc.

Look in Config/Port and Pins.

602

General Mach Discussion / Re: Hot stepper Motor

« on: May 12, 2008, 03:52:29 AM »

That is faster than Eurostar!!!

Now I appreciate your problems -

Unfortunately you will not get rid of the jerky movement using exact stop - because that is what it is - all axis simultaneously stop, and then start again on their new path. Quite clearly it will get worse with fast speed and quick acceleration.This - coupled with the speed (and therefore the acceleration) might be the reason for your loss of steps on the cutter. I think you are saying the BED is made from some material to stop the cutter blunting too quickly. Is it soft - does the cutter dig into it slightly. I was wondering if this was the problem. Although only lightly loaded when cutting ( and I have no idea what shape this is ), the strain of trying to turn shall we say "left" when the two axis are pulling you and accelerating to the left must be quite high. The force on the knife is to the right.

There are probably limitations to the Mach3 tangential control - I have no idea about it at all - and maybe someone might tell us. However, it seems to me that the turn of the knife should be BEFORE you then accelerate the other axis, so the knife is correctly lined up at the start of movement. This would mean the A command is on a seperate line before the XY command (otherwise all three happen simultaneously). It may be that tangential control does that - I don't know.

Are you limited to that type of knife - at those speeds a pizza wheel type cutter comes to my mind, -  and if this were mounted slightly behind the Z axis (with the pivot on the Z axis) then it would have a "following" action instead of having to steer itself (rather like a castor action) . Mounting the knife behind the Z axis would, on reflection work for all types of knife and reduce the negative turning force on the blade.

The alternative to Absolute stop is Constant Velocity - but here the next line is read into Mach and the deceleration of the last line is blended into the acceleration of the next line (which is quite easy actually becasue the resultant change of direction is merely an alteration in the speeds of the axis).

How many lines of code are we looking at to produce this shape - are there complex curves in it . I was thinking of how to incorporate the A axis command in the GCode.

603

General Mach Discussion / Re: limit switch response

« on: May 12, 2008, 03:00:45 AM »

Moving that at 20 inches per second - phew I can imagine the crash at the end.

Hood gave you the idea of soft limits which can be set inboard of the limit switches. My limit switches are small laser (pen type pointers) shining onto photo-detectors and therefore do not come into contact with the table - they are very reliable and accurate - and on your table would be easiliy fitted. The beauty about them is they do not get wiped out if the table over-runs for any reason.

I would tend to do the soft limits, laser type switches, and then either solid rubber buffers, or a small hydraulic piston (railway buffer stops) right at the physical limit of the run. I wouldn't want that lot dropping on the floor.

604

General Mach Discussion / Re: Accuracy of DRO's

« on: May 11, 2008, 03:18:28 PM »

DRO's are simply counters, they have nothing to do with accuracy, or speed or anything else.

The thing that decides on accuracy is the number of "steps" or pulses per inch or mm.
If your machine has 1000 steps per inch, then the best accuracy you can get is 1 thou. Any less than this and clearly accuracy suffers accordingley. Speed is set by the inches per minute setting on your motor tuning.

If you are moving two axis together then the relationship between those two axis is tangential. Mach 3 will move the furthest moving axis at the speed set in motor tuning. The other axis will move more slowly, but in time with the first axis, in the ratio of the tangent of the angle between the start and finish points. It sounds a bit more complicated than it is.

We know one or two of the angles from our schooldays - a 3,4,5 triangle for example, one axis would move 4 units whilst the other moves 3 (5 being the hypotenuse) and a 45 degreen triangle when the two sides are equal.

There may be others, but the vast majority are not simple numbers, and the short moving axis will have to be truncated. Even more complicated in a circular movement. It then might have to be truncated again, dependent on your "steps per unit figure"

Machs maths are done to 12 decimal places and then rounded up or down, and therefore the actual error is less than the error you see on the DRO.

In the end Mach 3 decides how many pulses to put out to your "stepper" - and the DRO merely counts the number of pulses and then
 translates this into a figure you can understand.

I must agree with Hood though. On a properly set up machine with realistic figures for step per inch, I have never seen "errors" more than 1 or maybe 2 tenths of a thou.

605

General Mach Discussion / Re: Help needed Connecting NPN Proximity sensors to BB`s

« on: May 11, 2008, 02:45:46 PM »

Sorry - I didn't  have any details of the Brealout Board.

I would go back to one of my earlier posts - I would think a different sensor, preferably 5 volt PNP, would make life a lot easier, especially when you are all up and running - and all of a sudden, one of your sensors fails. The fewer parts, the easier is life.

Having said that - the BOB is a bit of a *****. The vast majority of sensors pull the signal to 0v. This is what the computer port is looking for. Why invert it.

606

General Mach Discussion / Re: Lathe spindle index quit working

« on: May 11, 2008, 02:28:20 PM »

This sounds like debounce is set way over the top. Everything is alright at slow speed - debounce doesn't really come into it. As soon as the sensor starts flashing faster, the debounce period is that long that Mach3 is only seeing the detector intermittantly - and in a completely pseudo random manner dependent on the speed of rotation.

607

General Mach Discussion / Re: Spindle Index problem.

« on: May 11, 2008, 05:04:18 AM »

You will have to ask someone who has more experience of threading ( Hood might be able to answer) - but the answer MUST be YES.

Quite clearly the speed of the Z axis must be varied with the speed of the spindle.

When you say the Z travel does not seem to vary when you alter the spindle speed - are you doing this on the "fly". If so, the only thing I can think of is Mach looks at the "line" of Code and says  - I am going from A to B, pitch is X, spindle speed is Y therefore my Z speed is whatever. It then puts out that information until the move is finished - and does not vary the speed whilst moving.

This is why I am saying that the machine should be working well within its parameters, so there is little likelyhood of anything altering.
The best way is perhaps a set of gears connecting the spindle to the lead-screw (now where's my spares box - I have some somewhere)

608

General Mach Discussion / Re: Few questions about configuring Mach 3, one problem

« on: May 11, 2008, 04:48:23 AM »

The backlash is odd.

It starts, stops, starts, stops and then finally starts again. The second start is controlled by the backlash speed or % input and as far as I can see the other starts must be dependent on the speed your want the axis to travel (G0 or G1 F**).

I think the logic is - start the axis - which way is it going -
Then it is either the same way that it was going, in which case it continues uninterrupted, or the machine finds the axis travel is reversed, in which case it stops the axis,(perhaps both axis) applies however much backlash travel, at whatever  % or speed, then stops again, then carries on with the move.

I have mine simply set at 50% - with the idea that all the acceleration and deceleration could cause it to miss steps.

Having said that - although it sounds a bit rough, it is accurate, and turning some ball shapes on rods - I couldn't see the join where the backlash had been applied

609

General Mach Discussion / Re: Help needed Connecting NPN Proximity sensors to BB`s

« on: May 11, 2008, 04:31:43 AM »

Kenny - I think I've missed something in your explanation - I've drawn out your diagram and have got the input to the Bob pulled to 5 volts. The problem is the proximity switch activates - i.e. pulls low, when the chunk of metal goes near it. Not the other way round - so while I agree that electrically this would work as you say, mechanically it will not - becasue I assume you are detecting the fact that something has come within 2mm of the switch - not that it has gone away.

Attached is a diagram of my thinkings about it. As I say the output is normally high and goes low when activated. Try connecting to an input. The pull up resistor shown may be strong enough to pull your Bob to 5 volts as it is. If that is the case it should work OK.

610

General Mach Discussion / Re: Tool Offset

« on: May 10, 2008, 03:59:01 PM »

I do not use Lazy Cam so I cannot say for sure.

Does Lazy Cam compensate for Tool Diameter, or is it just drawing the shape that it sees. The simple way to check is to draw a 2 ins radius circle (4 ins diameter) (100mm diameter) using LCam and then print the G Code.

See if the tool is being lined up exactly on the circumference line or not - it should be easy to see if the numbers are simple. eg assuming you are starting at 0,0 the command will be  G2 (or G3) X0 Y4 R2 or something similar using I and J  The other thing to check - does LCam ask you for the details of the tool you are using.

Tool offsets (diameters and lengths) are normally entered in the tool table on your Mach 3 mill, and are called in GCode - allowance is not made in the CAM program. The Tool change is therefore ask for at the beginning of the program so you can enter the tool number into it and then the machine knows what allowance to make.Check your code and see if there is a G41 or G42 call - which means that the allowance is being made by your machine and not by LCam

You should enter your tools in the tool table. When the machine stops for the Tool Change command, enter the tool number in the tool window and press cycle start - the machine should now cut your shape, making allowance for your tool diameter.