View Full Version : NEW MEMBER: mach3 mill

05-06-2010, 10:02 PM
Hi All
I am a newby at mechanical engineering so forgive the stupid question. I have just converted my old Tom Senior Milling machine to CNC, (well seemed a good idea when I started).

I have 5mm pitch ball screws and 200 (1.8o) steppers. I have set the micro stepping drivers to 4 (800).

Upon test I find 1 unit or x, y, or z = 5mm or one complete turn of the motor. I would have thought having set the units in Mach3 software to mm, that 1 unit of x,y,z should be 1mm ?

I tried out the miller using the TEXT wizard setting the height to 3 units and sure enough the writing came out at 15mm high.

Now I have not got as far a drawing anything and importing it into Mach3.

Can anyone advise if my thinking is askew ?

Many thanks for any help


John S
05-06-2010, 10:23 PM
The maths is 200 x 4 /5 so you want to set steps per to 160

05-06-2010, 10:31 PM
Are you sure John?

1 rev of motor = 5mm = 200 full steps so one full step = .025mm, microstepping by 4 means one microstep = .025/4mm = 0.00625mm or steps/mm = 1/0.00625 = 160 steps/mm

Done your way = 200 x 4 / 5 = 160

And Joe, there is no such thing as a stupid question... the only stupid thing is not knowing when to ask it... (or so I tell my team)

05-06-2010, 10:47 PM
Hi John
thanks for the help. I just tried 320 in the steps per box and that gave me 2mm per unit of X. 160 gives me 1mm per unit of X.
the stepper driver is def set to 800 and the ball screw is 5mm, direct drive from a 1.8o stepper.

The motion at 160 is rough but I will tune it tomorrow, but would be interested in your thoughts as to why the math did not work out.

05-06-2010, 10:48 PM
Hi Irving
also thanks, by the time I had put the reply together and posted it, you had appeard.
many thanks

John S
05-06-2010, 11:43 PM
We both have the same answer ?
200 steps per motor rev times how many micro steps divided by the pitch.

Anyway 160 is the correct answer.

You gave this advise to Kamo the other day

"8mm threaded rod is 1.25mm pitch so one rev of the motor = 1.25mm movement. The motor has 200steps/rev so 1 full step = 1.25/200 = .00625mm and if it 1/8 microstepping 1 microstep = .00625/8 = .00078125mm which is 1280 steps/mm"

So try 200 x 8 /1.25 it equals 1280 which is what you got, just easier maths.

06-06-2010, 12:06 AM

either Joe and I are both going mad or something's weird ... your post definitely said:

The maths is 200 x 800 /5 so you want to set steps per to 320 but now it says the correct answer and doesnt show you edited it :confused::confused::confused:

btw, i agree the maths is easier expressed as s x m / p, but I was showing how to get to that from first principles in stages...

(my equivalent of 'give a man a sack of grain and you'll feed him for a month; give him some seeds and show him how to harvest, you'll feed him for ever')

John S
06-06-2010, 12:18 AM
Sorry, both of you were quick off the mark.
I did edit the post as i put the total micro steps in [ 800] instead of the number [4]

I did it pretty quick so that's probably why it didn't show

btw, i agree the maths is easier expressed as s x m / p, but I was showing how to get to that from first principles in stages...

So how do you express Ohms law in first principles ?

06-06-2010, 02:05 PM
Thank you for your reply. I had another half hour this morning and made some dial measurements. The back lash in the new H screw is 0.08mm and in the Y screw 0.05mm.

In order to finish the miller off, I need a plate to mount the Z drive and this plate has a hole of 32 mm . So I thought I would use the Hole Wizard. Having set units to mm and entered the data for X and Y centres plus hole diamter, I did a test run.

No good, circle was far too big-- recheck data still too big. Change diamter data and re-run but the same size appears. The X and Y centres are spot on, the no mater what diameter I enter into the wizard (and save) the G code always describes the big circle. I realise that the wizards are not supported, so need to ask if there is a known problem? or is it me?. many thanks // Joe
Ohms law states that the current through a conductor between two points is directly proportional to the potential difference (PD) or voltage across the two points, and inversely proportional to the resistance between them .

06-06-2010, 03:27 PM
Hi All, forget the last post re circle cutter, a PC restart and it now does what it says on the tin.