Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: B.E.N. on February 07, 2008, 03:45:11 PM

Title: Feed Rate
Post by: B.E.N. on February 07, 2008, 03:45:11 PM
I put in what I thought would a feedrate for one axis and it messed up every setting I was using. Line was add as follows I think, I took it out and had to fix home positions and it tried to move the z axis which I have bolted down. Also, I could not start the spindle again. I had to exit Mach 3 and reload. Evidently F is a global statement.???

N65 G01 Y-0.225 F001
Title: Re: Feed Rate
Post by: jimpinder on February 08, 2008, 11:21:19 AM
There doesn't seem to be anything wrong with the line as you have put it. I don't use all the 0000 that you do, and I dont use  line nubers, but basically it is telling the computer to G1 - move at cutting rate to position Y-0.225 at feedrate F1.

I assume the machine can do this so I dont see what the problem is - what is the code before and after this line ???
F is a global statement. What units are you in.
Title: Re: Feed Rate
Post by: Graham Waterworth on February 09, 2008, 03:46:10 PM
It also depends on weather this is a mill or a lathe, if its a lathe F1 can be F1 per rev or F1 per minute, mills are normally F1 per minute.


Title: Never the same.
Post by: B.E.N. on March 26, 2008, 03:01:36 PM
Every time I work with Mach 3? it is never the same. This provides me with very little faith that it is making the parts I think it is making. I am running a lathe with no home switches. I have motors on X, Z, and the tailstock is driven as Y. I have watched the homing video several times, he does mention not using home switches but only briefly. The demonstration does not have a home switch on the Z and that seems very straight forward. It seems like the X would not need home switches either because it can only travel till it bottoms in one direction and the screw will come out in the other so I would think you could lock those in. I wish the difference between G28 or G30 and G54 was explained on the video. If G28 and G30 do the same why have both?

I am concerned about accuracy because when I run the program with no part it works just fine. Then I put a part in and as soon as the bit hits the work the dimensions are not the same any more. I have even told it to go back to zero, zero position and I can see it is not in the same place anymore. The part I am working on right now I have run before and it seemed to be OK. Since then I have had to reload the software for your website to get it to run again, now I have no idea what it is doing. Most of what I am doing is very simple, the programs are usually less than 30 lines. I have the MACH 3 Turn Release 1.84 handbook it is not very helpful unless you are just going to turn something. Trying to run the same part again the DRO values are not even close to what I had before. One dimension I was using was 0.75 inches now I have to put in 2.60 to get close to the same result. Would that have to do with the pulses per in motor tuning? Still 0.75 inches in the DRO should be 0.75??? And for the X axis I know the distance between the holes I am working on before I put in 2.82 now I have to put in 3.26 what is going on?

Do get me wrong I am more than willing to work with things but it gets very frustrating when you get a different result every time you do something.

Looking for some help with the basics so I know what the software is going to do.


Title: Re: Feed Rate
Post by: jimpinder on March 26, 2008, 05:42:53 PM
You do not need home switches or any other switch for that matter.

The simplest way to set a lathe up for CNC is


Put the work in the chuck.
Move the tool to the end of the work and take a facing cut across it.
Jog the tool a little way down the work and then touch it onto the work.
Measure the thickness of the work using a caliper and PUT 1/2 THE VALUE IN THE X AXIS DRO (Full value if you are in Diameter mode)
To zero the Y axis (tailstock) you can touch the drill on the end of the workpiece and zero.

The lathe is now set and knows where it is. - i.e. X0 is down the centre of the lathe and Z0 is at the outer end of the workpiece.
Your G Code program should be written from these markers. Include in the code the following at the beginning -
G17 G20(if in inches) or G21(if in mm's) G40 G49 G94. This cancels all offsets and sets the machine so it knows what it is working in.

You can check these settings each time you put in a new piece of work - but as you grow more confident you will find that it is possible to repeat without checking everytime (although bear in mind it is still possible for a motor to miss steps from time to time - you certainly need to keep an ear open)

When finished jog the tool away from the work to a convenient position to remove it.
To do another part, do G0 X0 Z0 which puts the tool back where you started, put in a new piece of stock, pull it out to the tool, tighten the chuck and away you go.

I cannot help you with the rest other than to say -
1. Yes - you must accurately set the number of pulses per unit your computer has to put out to the motor drivers - mine for example is 48,000 per inch. You must do this for each axis.
2. You MUST NOT ramp up the speed too high, because the motors will miss steps. If you have a simple system with no feedback like mine, then this is important. My lathe will only traverse at 4 inches per minute without losing steps. (This is a mechanical thing - I am working on it)
3. You must accurately set the backlash, and enable it.
4,. On your drilling with the tailstock - is the motor powerful enough. Drilling is very heavy work (more that tool turning I think). Your motor must be powerful and the feedrate (as set by the F command - not the motor settings) must be low or you will loose steps again.
If you think about drilling manually - a drill bit takes a lot of pressure and only goes in slowly - it is important to get the spindle speed correct for the size of the drill.
(On my milling head, I put too small a motor - the thing worked very well indeed - it would go up and down - and hold the tool in the same position as I milled - but when it came to drilling - it just stopped! - I have now changed it for one at least three times the power.)

Sorry if you know a lot of this - hope it helps.

Persevere - you will get better all the time. You will not get better software than Mach3 (not without paying a great deal of money, anyway) and this is the best forum in the world.

Title: Re: Feed Rate
Post by: B.E.N. on March 27, 2008, 05:00:45 PM
Thanks for the reply.

I have spent a couple hours going through everything again and seem to have things back in order. You did reply about drilling, I have the drill in the headstock and I am bringing the part to the drill so am am using the Z axis to push the part into the drill I am cutting several holes in one plane.

After I had run a few parts I was panning around on the display and the X axis went goofy and drilled a hole where I didn't want one any idea whats up with that?? I stopped the program told it 0,0 again. I did decrease the velocity some on the X - axis to see if that helps. I also noticed that if the jog button is selected while running a program it is more likely??? an axis will erratic.

Tell me about G90, I would think I would want that in the beginning as well?

Title: Re: Feed Rate
Post by: Graham Waterworth on March 27, 2008, 06:01:48 PM
G90 tells mach3 to take all dimensions from one point eg the face of the part, G91 moves from the current position the said amount.


G90 G00 X10. Z0
G01 Z-90 F100.


G90 G00 X10. Z0
G01 Z-45. F100.

Both bits of code will cut 90mm in the Z axis.

Title: Re: Feed Rate
Post by: jimpinder on March 28, 2008, 05:37:21 AM
I must admit I have never bothered with the difference between G90 and G91 - and therefore I must have assumed that the lathe would be in G90 mode all the time.

Having read Graham's explanation - yes - I must agree, a G90 at the begining would make sure of it. A G91 popping up unexpectedly could cause chaos!!

Tested my new motor yesterday on drilling - yes - it worked. A 6mm drill, spindle speed about 1300 (top speed on this motor til I fit a gearbox) and a conservative feedrate of 0.25mm and it had no problems.I'll try upping the feedrate a bit, and then I'll try some of my bigger drills.
Title: Re: Feed Rate
Post by: Graham Waterworth on March 28, 2008, 12:59:35 PM
Not drilling 316 stainless, I guess  ;D

Title: Re: Feed Rate
Post by: jimpinder on March 28, 2008, 01:41:37 PM
Give me a chance - I'll get there - but not with this machine.

No -  most of my stuff is mild steel 5,6 or 8 mm to drill -  sometimes up to 12mm - as I said, I need to fit a gearbox on the 3 phase motor - it looses a lot of power at lower speeds. I'm designing one now :-\ :-\
Title: Re: Feed Rate
Post by: Hood on March 28, 2008, 07:50:34 PM
Give me a chance - I'll get there - but not with this machine.

No -  most of my stuff is mild steel 5,6 or 8 mm to drill -  sometimes up to 12mm - as I said, I need to fit a gearbox on the 3 phase motor - it looses a lot of power at lower speeds. I'm designing one now :-\ :-\

Get yourself an AC Servo ;) , thats the way I am hoping to do it on my Beaver Mill. Have a 5KW servo which supposedly has 163lbin torque from 0 to 3000RPM. Have a drive that will run it, only thing I am lacking now is an encoder with Hall signals suitable for a 4 pole motor, dont suppose you have one in your back pocket :D

Title: E-Stop
Post by: B.E.N. on April 01, 2008, 05:52:19 PM
General question regarding MACH 3. I would like to stop all motion when I open the safety cover over the spindle of a lathe. The lathe is a Wabeco D2400E that has a cover switch built in. Right now the cover stops the spindle but not the axis motors. Is it possible to use this switch together with a space bar input or something else to stop all movement or send all axis to zero coordinates just by opening the safety cover without causing a reset?

Title: Re: Feed Rate
Post by: Hood on April 01, 2008, 06:02:01 PM
You could possibly use a brain or the macropump to do a feedhold when the switch is activated, that would halt the axis movement, not sure about the spindle, depends how its set up but you could also add an M5 to it to stop the spindle as well.
 Not sure how your lathe is set up but I would think it might be quite dangerous to make the axis move to zeros when the cover opens, X0 on a lathe is usually the spindle centre.
Title: Re: Feed Rate
Post by: Graham Waterworth on April 01, 2008, 07:15:05 PM
I must agree with Hood, the only safe way is to stop the machine, you can not send it to home as you have no idea what the safe path to home is at any given point.

You could make the spindle switch latch a relay that cuts the power to the spindle and the axis drives.